: Northstar 4.0 mods?



Rambo
03-29-04, 12:22 PM
Just got a 98' Aurora and have already decided that once I get my loan paid in full I will begin to modify my car a little. The car has Northstars smaller 4.0 liter V8 engine, thats why i'm asking in here. Can anyone tell me what mods are available to Aurora's? I would lke to do at the very least exhaust and intake to wake things up a little. I am also considering a possiblilty for a new PCM. I don't even know if one is available, but if there is one that I can get to override the speed limiter and other computer controlled things that'd be great. Well, thanks for any information anyone can provide me with.


-Kevin :)

Aurora40
03-29-04, 02:55 PM
Pretty much the same stuff that's available for the 4.6L V8. Which is to say, not a lot. A freer exhaust will help, and there are some easy airbox mods you can do to help it breath a little better. RSM makes a bored throttle-body for the classic.

My suggestion, get a Corsa, a K&N, mod the airbox, and enjoy the car... :)

BeelzeBob
03-29-04, 03:36 PM
Just got a 98' Aurora and have already decided that once I get my loan paid in full I will begin to modify my car a little. The car has Northstars smaller 4.0 liter V8 engine, thats why i'm asking in here. Can anyone tell me what mods are available to Aurora's? I would lke to do at the very least exhaust and intake to wake things up a little. I am also considering a possiblilty for a new PCM. I don't even know if one is available, but if there is one that I can get to override the speed limiter and other computer controlled things that'd be great. Well, thanks for any information anyone can provide me with.


-Kevin :)

Uh...RAMBO would not be caught dead driving a 4.0 Aurora.....unless it had NOS or a supercharger.....LOL....just kidding. Really.

Aurora By Olds
03-29-04, 10:26 PM
Uh...RAMBO would not be caught dead driving a 4.0 Aurora.....unless it had NOS or a supercharger.....LOL....just kidding. Really.
Yeah he wouldn't be caught dead with a 4.0....only cause he couldn't handle it.:lildevil: LOL

Aurora40
03-29-04, 10:30 PM
I thought it was because he's too ugly. An attractive car like the Aurora needs an attractive person to pilot it. :D

Aurora By Olds
03-29-04, 10:54 PM
I thought it was because he's too ugly. An attractive car like the Aurora needs an attractive person to pilot it. :D
Well yeah, that too, obviously... LOL

Rambo
03-29-04, 11:38 PM
Pretty much the same stuff that's available for the 4.6L V8. Which is to say, not a lot. A freer exhaust will help, and there are some easy airbox mods you can do to help it breath a little better. RSM makes a bored throttle-body for the classic.

My suggestion, get a Corsa, a K&N, mod the airbox, and enjoy the car... :)


First: Is the exhuast on a 4.0 the same as on a 4.6? As in Cat, into resonator, into dual mufflers? If so, would I be wise as to replace the cat with a hi-flow unit, ditch the resonator, and get some free flowing mufflers such as the suggested corsa? Does Corsa make a direct bolt on muffler system for Aurora's?

Second: Does K&N make a FIPK cold-air induction system or do you just recommend I do the free air box mod along with a K&N filter?

Third: Will a bored-out throttle body even help at all?

Fourth: Do I have any other options?

Fifth: Why is everyone making fun of Rambo?

Sixth: I need to make a lot more money!

Thanks!

-Kevin

Aurora40
03-30-04, 12:55 PM
I'm not sure if the exhaust is exactly the same, but it is similar. Corsa does not make a direct replacement, but the Seville system can be modded to fit by a local shop. It is a cat-back system, and includes a resonator. You can see right through all of it (mufflers included), so I don't see how replacing the resonator with straight pipe would gain very much. It is almost a straight pipe already except for a small gap for sound waves to enter.

I don't think K&N makes a FIPK. I just meant the panel filter and the free airbox mod. You could try a cone, but I wouldn't unless you built some sort of shield/chamber to keep it away from engine heated air.

The TB, some say yes, some say no. A few people with the Aurora dynoed it for about a 9hp gain at the wheels. Even if the extra size isn't needed, having it ported makes it all much smoother for flow. Otherwise, on the classic, the TB is about 75mm, the spacer behind it is 78mm and the intake manifold entrance is 80mm. So even though it gets bigger, it does not do so in a smooth fashion, which can affect the flow. But you have to decide if you think it will help.

I'm not aware of too many other options. There has been talk of a 4.6 supercharger for years, and domesticperformance.com claims to be taking orders for an Aurora supercharger.

Also, I personally don't see how high-flow cats can actually flow more unless they do a worse job catalyzing stuff. Most people who have replaced theirs have had the MIL light come on. I wouldn't swap mine out just for the possible gain. But again, it's up to you. :)

BeelzeBob
03-30-04, 04:18 PM
One of the guys with a Northstar tried the larger throttle body and it did nothing for performance at the dragstrip even with exhaust and inlet mods...

Based on the sizing of the production throttle body it will support even more power so I can't understand how a bigger one would show more power.

How on earth someone dyno'd a 4.0 and got more power with a larger throttle body is beyond my understanding. The production throttle body is plenty big enough for even a 4.6 much less a 4.0....must be the same shop dynoing the car that sold him the throttle body....LOL....dyno results, especially chassis dyno results, can show many erroneous things depending on what the operator is wanting to see....especially if the runs are on different days....

Dubya
03-30-04, 10:14 PM
first off, you talk of removing the speed limiter. there are 2 versions of aurora's. 1 has a limiter of 112 and 3.48 gears. the other has a limiter of 139 (some places claim 135, but ive seen 139 before i ran out of road) and 3.71 gears. open your drivers side door, check what the oem tires were. if it says they were V rated, you have the higher limiter and better gearing. (it'll say 235/60/16 V instead of 235/60/16 S) or check your spare tire cover for option QQX which stands for the autobahn package (what its called).

for exhaust id get a highflow cat. you can get a carsounds for $50. you'll need a $10 o2 simulator also so your MIL light doesn't go off. i changed out all of my exhaust, then the cat and noticed a improvement, a pretty big one i think. then go 2.5" all the way back, get a strait through racing muffler or glasspack for a resonator. i don't have a resonator and i plan on getting one because of the highway drone i get. then it splits, and get 2 more strait through mufflers. corsa exhaust is awesome, but very very expensive (1,000 plus install, maybe another 250). expect to pay in the area of 600 for a complete exhaust from cat to tips and install. check out caddyinfo.com for instructions on how to mod your airbox.

i personally wouldn't spend the money on the bigger TB, maybe if i had a 4.6, but the 4.0 already has the same 74-75mm TB as the bigger 4.6, and a 4.0 doesn't breath as hard. ive heard of 4.6's seeing little to no improvement, its NOT a cheap mod either. domesticperformance.com should be able to hook you up with a reprogrammed pcm, id do that before a TB

Aurora40
03-31-04, 06:29 PM
Just a few notes...

I'm not endorsing anyone get the bigger TB, but it isn't really that expensive. I believe it's like $200 from RSM. I guess I don't consider that an expensive mod.

Also, Bbob, you mentioned that the 75mm is plenty big for the 4.6, but the RWD 4.6 actually went to an 80mm TB, and it only move the fuel cutoff 50rpm up the scale. Also, even if the larger size isn't warranted, it should flow better than the mismatched size that's there previously. It is 75-78-80mm. I would bet if it were all 75mm and matched up that it would flow better than the expasion does (especially a jagged expansion like that).

And you said someone went to the track to test it and noticed no improvement. While a chasis dyno is not a perfect tool, it is quite a bit more controllable and repeatable than going to the 1/4 mile track... And the tests I'd seen were on the same day, I doubt the same is true of the 1/4 mile guy (as that'd be interesting swapping your TB out at the track). And none were by shops in any way affiliated with the sale of the product. They were on purchasers cars at local dynos, not numbers supplied by the TB maker.

I'm not saying the TB is worth the money or that it does anything, what I'm saying is I think it shouldn't just be dismissed out of hand like that. :)

Also, that's what I meant about the "high-flow" cats. Really, they aren't high-flow, they are just bad at catalyzing. To me, high-flow implies they do the same job but can flow a lot more. In fact, they do a poor job which is why they flow more, and they set off your MIL because of it. It's sort of like calling a piece of straight-pipe a "high flow cat"... If you are gonna do that, why not just gut your cat for free and retain the stock appearance and your money? Just an opinion. ;)

BeelzeBob
03-31-04, 09:57 PM
I wasn't dismissing them out of hand. I have tested larger ones on engine dyno tests and they did nothing for power on a production Northstar engine. If other mods were made to increase air flow then a larger throttle body might be adviseable but not on the production engine as is....


Chassis dynos are good...but only as good as the operator. They can be made to read whatever you or the operator wants.... Besides, the goal is to go faster on the dragstrip, not spin the chassis dyno. Back to back passes at the strip in a short termaround time are a pretty good comparison of the two throttle bodies as it was done. My point was that a reasonable test was done with the larger throttle body and the results in the real world matched the engine dyno results. Sometimes a dragstrip run is actually more repeatitive than a chassis dyno...if the engine heats up or the underhood temps go up the readings can change significantly. Hard to keep a car cool on the chassis dyno for many runs.

This is getting to be a tough crowd....LOL.....You are comparing apples to oranges in a way with the transverse (FWD) and longitundinal (RWD) Northstar throttle bodies. Definitely a valid question though. First, the RWD engine makes 320 HP as is. so it can use a slightly bigger throttle body...and it is the first version of the RWD Northstar engine family....more to come...so why size the throttle body for what we have today....catch my drift??? Second, the throttle body on the RWD engine is a drive by wire electronic throttle body that has to be incorporated into the electrical architecture of the vehicle....so one might size it larger than currently needed since it will be more difficult to change in the future and very expensive if we had to change the size of the throttle body...so , since it was new to the engine for 04 there was a little forward planning going on there.

Rambo
03-31-04, 11:27 PM
first off, you talk of removing the speed limiter. there are 2 versions of aurora's. 1 has a limiter of 112 and 3.48 gears. the other has a limiter of 139 (some places claim 135, but ive seen 139 before i ran out of road) and 3.71 gears. open your drivers side door, check what the oem tires were. if it says they were V rated, you have the higher limiter and better gearing. (it'll say 235/60/16 V instead of 235/60/16 S) or check your spare tire cover for option QQX which stands for the autobahn package (what its called).

domesticperformance.com should be able to hook you up with a reprogrammed pcm, id do that before a TB

Do you think it would be at all possible to get a Autobahn version PCM? Is this even possible? If so, how much would one run, where would I get it, and how hard would it be to install?


Thank you!

-Kevin

Dubya
04-01-04, 12:52 AM
1st, a autobahn pcm would also make the car think you'd have 3.71 gears, and mess all kinds of stuff up

i remember this TB vs highflow cat discussion on edmunds, lol, you are scewing the numbers some there. they're $250, but you need the matched mount plate, $100 more. so $350, plus the cost of a new TB, unless you can have your car down for 1-2 weeks.

highflow cats arn't just cheap cats, there much more expensive to make. we went over this before. there made of better materials. because these better materials catilyze (SP?) better, they are allowed to use less material to get the same effect, which means shorter bricks, more flow. they have very strict rules to apply by, and are CARB legal, no way they can be CARB if there just "bad oem cats". they also have more expensive casings in which all the rough edges and little ridges are gone. this is also a $50 mod vs a $350 mod.

not only this, both the TB and the cat can sorta plug up, droping flow. you can clean the TB, i did and noticed a good improvement in power and response. these dyno's showing all this power increase is a dirty oem vs a clean bored out one. the 5-8hp improvement garnes got would have been less, clean vs clean. you can't clean a cat, so a new one is needed

and serioulsy seriously sersiously saying a VVT RWD 4.6 northstar having a 80mm tb means that a fwd 4.0 northstar would benifit is like saying we should also put a 80mm TB on the 3.5 dohc, why stop there, even the 2.2 cavilier motor. not only is the 4.6 bigger so it breathes harder, it has VVT which contributes to needing more air. i don't understand why you and garnes keep bringing up this point, its not releavant at all. that engine even revs higher than the classic aurora (only years tb could even apply)

Aurora40
04-01-04, 11:06 AM
Wow... Way to make an argument where there wasn't one... At what point did I compare the 80mm 4.6 TB to the 75mm 4.0 TB? I believe I addressed a point where Bbob said the 4.6 doesn't even need a bigger TB. You're right, RSM has it for $250 not $200. I think it used to be $200. :hmm:

I also don't believe I said the TB was a better buy than the cat. Nor did I say the high-flow cat wouldn't free power. These are more arguments you must have dreamed up. What I said is that they don't do as good a job catalyzing. If they do as good or better than an OEM cat, why is it they set your MIL light? Why would you need a fake O2 sensor? I'm also a bit surprised that they can use better materials, better machining, and still sell one for $50. What are these better materials, anyway? The catalyzing agents in an OEM cat are very expensive precious metals. So what's the modern miracle catalyzing agent that is in a Carsounds cat? If you are going by the claims on websites like Random Technologies, they compare their "modern miracle" agents to the old pellet-type cats. In that comparison, the catalyzing agents and honeycomb structure are far superior and flow better. However, your OEM cat has exactly the same advantage over pellet-type cats.

You're right on one thing, though, this argument is tired. You shout out the same "points" no matter what the discussion is about. Again you mention that these "high-flow" cats still pass emissions ergo they must catalyze as well as the OEM cat. But this would only be true if the OEM cat were right on the ragged edge of passing. In fact, with an OEM cat and a car in good running order, you will be way way under the state emissions requirements, even in CA. So just because a replacement cat will also pass the emissions requirement does not mean that it must catalyse as well. And what's wrong with making that point anyway? Just tell the truth, the "high-flow" cat doesn't work as well, but it flows better and works well enough to pass emissions. Isn't that a good enough reason for those who are interested? Why try to bs about how it's some miracle thing made of magic ingredients?

And as far as hollowing out your cat, I'd bet a lot of people here could do it and still pass their state emissions tests. It would be cheaper, look nicer, and using your logic, it would catalyze as well as it did stock. If anyone ever looks in it and wonders why it's empty, you could pull an "emperor's new clothes" and tell them it was some magic catalyzing material that only smart people can see.

BeelzeBob
04-01-04, 12:06 PM
highflow cats arn't just cheap cats, there much more expensive to make. we went over this before. there made of better materials. because these better materials catilyze (SP?) better, they are allowed to use less material to get the same effect, which means shorter bricks, more flow. they have very strict rules to apply by, and are CARB legal, no way they can be CARB if there just "bad oem cats". they also have more expensive casings in which all the rough edges and little ridges are gone. this is also a $50 mod vs a $350 mod.

)

Not to start a flaming argument, here, but this concept is BS.

There are VERY relaxed rules for what has to be done for an aftermarket part to be labled "CARB legal". VERY VERY relaxed rules. Basically, all an aftermarket parts maker has to do to get that label/designation is to emission test a particular car and then install their part and show that the emissions didn't change. Why is this BS??? They bring in a ragged out car with a 100K cat on it, put their brand new cat on the car and run a test real quick before the angle dust in the cat gets burned away. Sure it performs the "same". Is it as good as the factory OEM cat.... NO NO NO NO NO.

Better materials so it catalyzes better...????...that is a hoot. There is no magic here....GM invented catalytic converters and the auto companies use the absoute best materials, designs and processes to make the cats as is available. That is because the autocompanies do not get a "free pass" on the "CARB legal" status. The auto companies are on the hook for the system to pass the emission standards for 100K to 150K depending on the cert process.

Automotive cats use platinum, paladium and rhodium. That is it. There are no "better" materials. Period. Those are THE materials that work. And they are incredibly expensive. The cost of the cat is based almost purely on how much "precious" metal is in the cat. A cat is made of a ceramic or metallic/ceramic monolithic substraight that is coated with precious metals dissolved in a "washcoat". The concentration of the metals in the washcoat is what determines the cost. Period. Nothing to do with the "quality" of the materials or "better" materials. You can be sure of one thing....if one cat costs $300 and another costs $50 then the $50 cat has WAY LESS precious metal in it. WAY LESS. It only meets the "CARB legal" nomenclature in that it performed equivalently to an OEM cat (of unknown mileage/age) for one test when brand new. It will NOT live for as many miles nor will it provide the level of compliance needed for a mass producer of vehicles.

The "high flow" cats just have more open area in the monolith. That means there is, by definition, less surface area and that the cat is less reactive. So it is NOT as good....certainly no better than...as an OEM cat.

If making more power was as simple as putting a $50 cat on instead of a $300 cat then why on earth wouldn't the OEM's do it...???

Dubya
04-02-04, 01:27 AM
well i didn't invent the cat so i cant vouch for whats in there. what i do know is they use shorter bricks (not larger holes) so they flow better. i find it odd that you (aurora40) bring up the point of hollowing out a cat instead, save some money because a highflow doesn't catalize as well, but it is more than enough to pass anystate emissions, not get you a insanely huge fine that will cost much more than a car, and still free up some power, sounds like a good compermise. if i was worried about getting really low emissions i wouldn't have boughten a aurora anyways.

rsm tb is 350, you need the $100 mounting plate they dont list. it was 300+100, at one time, they must have recently dropped the price. i was mearly pointing out the fact that its not $200, its almost double that, 350 to get it done right.

i misread your post aurora40, and it reminded me of other posts in which you wrote not to get highflow cats because they did nothing, and a bigger tb will help.

im to tired to right anything else

Aurora40
04-02-04, 10:54 AM
Um, replacing a catalytic convertor that was not defective will get you that same huge fine...

I don't quite follow on the "if i was worried about getting really low emissions i wouldn't have boughten a aurora anyways." An Aurora is a pollution-mobile? Or a muscle car? I don't see what you are getting at. When I had the Aurora tested for the VA emissions test, the emissions were in some cases 1/300th of that allowed, and were in a few cases so low that the measurment could have a larger margin of error than the magnitude of the actual value.

Also, you say you didn't invent the cat so you can't vouch for what's in there, but didn't you just vouch for what was in there when you said: "highflow cats arn't just cheap cats, there much more expensive to make. we went over this before. there made of better materials. because these better materials catilyze (SP?) better, they are allowed to use less material to get the same effect"

I think if you look back at all of my other posts, you will find the exact same message. And that is that if a cat were to do the same job of catalyzing, it likely would not be able to flow more, or at least significantly more. If you wanted to make a cat that was 10" around so that it had more flow capacity, but with the same quality and length of substrate, it probably wouldn't flow much more than stock because the exhaust coming out of a 2.5" tube will not just expand in flow to 10" and then back again. Most of the exhaust will flow right through that 2.5-3" center of it.

I have made this exact point every time, but you don't seem able to wrap your head around it so you think I just bash high-flow cats. I never said they do nothing. What I said is if they actually do flow more, it is because they do a worse job catalyzing. And every time you argue with that by saying they are full of magic and that they still pass emissions, as if making that point somehow contradicted mine (I never said they can't pass emissions, and passing emissions does not mean they work as well as the OEM cat).

I also don't know why you think I preach about the TB. All I am saying is that it isn't impossible that it improves the flow, and some people have demonstrated that. I don't expect that everyone will take those dyno results as gospel, but the dyno runs did happen. Those folks who did dyno it at least tried to explain all the factors they took into account and such instead of just saying the TB was full of magic flowing ingredients and showing a scan of a dyno sheet supplied by the TB maker as proof (something you in fact did with the Random Tech cat). I think, especially on my car where everything matches up well, that the 80mm TB would not be worthwhile and I have no plan to shell out for it, and little expectation it would help my particular car.

Quit trying to make arguments where there are none...

eldorado1
04-02-04, 03:04 PM
$750 in cams and springs will gain you (up to) 75-100 extra horses... CHRfab has those. They're the same ones as on the 4.6L. You might also gain something by going to 300hp 4.6L cams, but I haven't seen the specs to compare the two.


I should also mention that your car will lope like a warmed over 350... and you're probably going to need an aftermarket controller (unless the aurora code has been hacked, I don't know)

BeelzeBob
04-02-04, 03:14 PM
$750 in cams and springs will gain you (up to) 75-100 extra horses... CHRfab has those. They're the same ones as on the 4.6L. You might also gain something by going to 300hp 4.6L cams, but I haven't seen the specs to compare the two.


I should also mention that your car will lope like a warmed over 350... and you're probably going to need an aftermarket controller (unless the aurora code has been hacked, I don't know)

It will make more power but the car will be slower. This was already tried by one of the members of this forum who put the 300 HP Northstar inlet cams into his 4.0 Aurora. It was so slow off the line and sluggish due to the loss of low end torque that he put the original cams back in and was happy to have them back in. The engine would definitely make a little more power on the top end....but the tradeoff in low end torque loss was overwhelming and caused the vehicle to be slower.

Big cams work at higher RPM. If you cannot rev the engine harder due to gearing, vehicle mass, torque converter stall speed, etc... they will slow you down. They work in light cars where you can change the final drive gearing and/or have a manaul transmission so you can "drive around" the loss in low end torque. You do not want more cam in a 4.0 Aurora engine unless you can make some serious mods to the trans, final drive, controller, torque converter, etc....

Aurora40
04-02-04, 03:23 PM
So when is GM Performance Parts going to come out with the 4.0L to 4.6L kit? I mean, come on, the GXP has it... And where are the GXP brake kits for the Aurora, Seville, LeSabre (it's possible), and regular Bonnie? Actually, I can lock mine up on decent roads at over 80mph, so more brake probably won't help much until I get more rubber (which isn't likely as the car rides and handles very nicely as is).

BeelzeBob
04-02-04, 03:55 PM
So when is GM Performance Parts going to come out with the 4.0L to 4.6L kit? I mean, come on, the GXP has it... And where are the GXP brake kits for the Aurora, Seville, LeSabre (it's possible), and regular Bonnie? Actually, I can lock mine up on decent roads at over 80mph, so more brake probably won't help much until I get more rubber (which isn't likely as the car rides and handles very nicely as is).

The larger brakes can be purchased piece by piece using the GM parts catalogue from other car lines...

BTW...the larger brakes do not necessarily mean shorter stopping distances on that first stop....they have more capacity and heat up less so that the 10th or 20th stop on a race track is the same as the first one.

Doubt that you will see a 4.0 to 4.6 kit.....it would need to include all the parts in the engine....virtually everything is different. The block is a different bore, the pistons, crank, heads, etc....you get the idea. The "kit" is available in a fashion today.....it is called an STS.....or a GXP....or a DTS.....LOL

Aurora40
04-02-04, 04:07 PM
Doubt that you will see a 4.0 to 4.6 kit.....it would need to include all the parts in the engine....virtually everything is different. The block is a different bore, the pistons, crank, heads, etc....you get the idea. The "kit" is available in a fashion today.....it is called an STS.....or a GXP....or a DTS.....LOLWell, I meant a whole engine swap and some PCM calibration and whatever else it takes. And those "upgrade" kits you mentioned come with a downgrade in style!! :bouncy: :hide:

And yeah, I hear you on the brakes. I can't imagine taking the Aurora to a track, though... The stock brakes are more than up to the task of aggressive everyday driving. Plus, those 14's probably wouldn't fit in my 17" wheels, and they'd weigh a lot more. But it's nice to know that just ordering the parts would bolt up to my car.

Dubya
04-02-04, 05:23 PM
wow, in refrence to not getting a aurora if i was worried about emmissions i was reffereing to gas mileage, these aren't the most economical cars around. but im sure you'll respond with a bunch more useless information comparing them to smaller cars so that maybe you'll feel better about yourself

no, replacing your cat will not get you a fine. it will on a newer vehicle, but I and the original poster have over 5 year old cars with over 50,000 miles most likely - i believe thats the law.

no i don't know whats in cats or how there made, neither do you. you go by what other people tell you, or from what you read (i know you'll have some sarcastic comment about this too).

im not going to waste my time looking up your older posts in which you specifically say that, if there putting a 80mm tb in a vvt northstar 4.6, the engineers must have seen the benifit, so it would also be benificial to us, but yes you did say somthing to that effect. in addition to saying you'll see no improvement in a highflow cat, but this was 4-6 months ago. you seem to adjust your "beliefs" everytime new information comes so that you can make it seem like thats what your saying all along, whatever im tired of arguing with you about it. for someone who's supposedly so mature (in refrence to a older post in which you say my immaturaty shows my age) you sure like to make personal attacks - score for you

go to the mirror and pat yourself on the back, maybe itll help you sleep better, wait, im sure you already have........

eldorado1
04-02-04, 05:53 PM
It will make more power but the car will be slower. This was already tried by one of the members of this forum who put the 300 HP Northstar inlet cams into his 4.0 Aurora. It was so slow off the line and sluggish due to the loss of low end torque that he put the original cams back in and was happy to have them back in.
Got a link to this? I'd like to take a look... Assuming the cams aren't that far apart, I don't see how there would be much (if any) measurable difference in torque... I think on the 4.6's, between the two cams, there's 5ftlbs difference, and 400rpm difference at peak. Like I said, I'm not sure how that correlates to the 4.0's cam specs, but assuming the 4.0 is 'similar' to the 275hp 4.6, then it should lose ~2ftlbs and gain 20hp. But then, they may already have the 4.0 pretty cammed out, and you just might be 'stepping backwards' losing HP when you put those two together.

Aurora40
04-02-04, 06:24 PM
Dubya, sorry for passing on facts that I've read. Next time I'll go get a job in a catalytic convertor factory first.

Gas guzzling and pollution really aren't that related. According to the EPA's "Green Vehicle Guide" my 2002 Aurora 4.0 in 48-state trim puts out as much pollution per 15,000 miles as a 2002 1.0L I-3 48-state Honda Insight.* You probably consider this a useless fact too, but I couldn't come up with any useful BS to post instead; no back pat for me today... :(

Also, are you sure I mentioned immaturity and age? That doesn't sound like me. I tend think there are immature people of all ages... I'm only 28. And I do tend to be incredibly sarcastic, but when did I make a personal attack? What did I call you or imply about you? I apologize if I upset you and I didn't mean for you to take it as a personal attack.



* Disclaimer: I read this on the EPA's website. I didn't go get a job at the EPA and retest these cars.

Aurora40
04-02-04, 06:38 PM
Eldo, here's the power graph from gmpowertrain for the L37: http://www.gm.com/automotive/gmpowertrain/engines/northstar/apps/images/l37curve.jpg

They don't seem to have the 275hp graph up anymore, but when overlaying them (though they are just press release stuff, but I guess they should be reasonably accurate) you can see some low-end differences that were a lot bigger than the 5 lb-ft peak difference would suggest.

BeelzeBob
04-02-04, 11:19 PM
Got a link to this? I'd like to take a look... Assuming the cams aren't that far apart, I don't see how there would be much (if any) measurable difference in torque... I think on the 4.6's, between the two cams, there's 5ftlbs difference, and 400rpm difference at peak. Like I said, I'm not sure how that correlates to the 4.0's cam specs, but assuming the 4.0 is 'similar' to the 275hp 4.6, then it should lose ~2ftlbs and gain 20hp. But then, they may already have the 4.0 pretty cammed out, and you just might be 'stepping backwards' losing HP when you put those two together.

You have to look at the area under the torque curve. Plus, the effects of a bigger cam are magnified by less displacement... The L37 cams make 5 ftlb less torque at the torque peak...but...they make substantially less torque than the LD8 cams at lower RPMs and the L37 trails the LD8 in torque up to about 5000 RPM...so for a great deal of time the LD8 is making more power. Without the 3.71 final drive to spin the engine faster the L37 would be slower all else being equal. So...you take a 4.9 Aurora without the 3.71 and take the LD8 cams out and put the L37 cams in and it is behind in torque up to about 5500 or higher due to the lower displacement magnifying the bigger cams effect. Note that the LD8 cams peak for HP at about 5700-5800 RPM in a 4.6 but the 4.0 with the same cams peaks at 6000-6200. That is the smaller displacement magnifying the effect of the cam.

Dubya
04-03-04, 01:13 AM
remember the DTSi, the tim allen DTS, it had close to 400hp i thought, and ran a high 14, barely faster than stock.

check this link out

http://www.caddyinfo.com/northstardyno.htm

basically shows what bb said, the Ld8 is a better engine. though it sounds better (300hp vs 275). im really anxious to see what kind of times the magazines get for the bonneville gxp, its a ld8 with the 3.71 gears, weighs a little less than 3800 (SLS/STS are about 4000) and to top it off, it has 6500 rpm shifts, sounds like a awesome combo. its funny that people are complaining that the gxp got the 275 hp version, but it got the best combination possible. better engine, better gears, better shift points and lighter. i would think low 6's for 0-60, pontiac is only claiming a 6.5 though, should smoke a sts which is 6.8 i think

edit : what i meant to say, the l37 sounds better with 300hp, the ld8 is 275, thats the better one

Dubya
04-03-04, 01:19 AM
also, what i don't get is the current sls is actually at 305 lbs tq, changed somtime around 2000 i guess (so 275hp/305tq vs 300hp/295tq) but the gxp is 275hp/300tq. i wonder if it is EXACTLY the same engine in a 2004 gxp as a 2004 sls, anyone know? i thought i read because of the less restrictive backpressure it allowed them to do 6500rpm shifts vs whatever a sls is (6 or 6.2k?) but that should push the numbers past a sls if its less backpressure, maybe it really is higher, but they de-rate just a little so they don't outshine cadillac?

eldorado1
04-03-04, 12:16 PM
Interesting posts! Looks like the only way the L37 would win is if the redline was stretched out a little, and both shifted there... Anybody see this site: http://www.angelfire.com/stars/mycaddy/dustindyno.htm this guy can't do math... 25% would be 265hp.

Aurora By Olds
04-04-04, 11:59 PM
Got a link to this? I'd like to take a look... Assuming the cams aren't that far apart, I don't see how there would be much (if any) measurable difference in torque... I think on the 4.6's, between the two cams, there's 5ftlbs difference, and 400rpm difference at peak. Like I said, I'm not sure how that correlates to the 4.0's cam specs, but assuming the 4.0 is 'similar' to the 275hp 4.6, then it should lose ~2ftlbs and gain 20hp. But then, they may already have the 4.0 pretty cammed out, and you just might be 'stepping backwards' losing HP when you put those two together.
That certain "individual" was me. I never botherd to have the thing dynoed, cause the torque band was horrible after the cam swap.
I couldn't even get the tires to break loose at a dead stop.
The car makes great power from about 5500 - 6000.....quite a punch at kick down from the old cams, but take it from bbob, the car is MUCH slower overall.
Try to take off quick to change lanes....youre screwed.
Try to pass without totally floor stomping it....youre screwed.
The HP and TQ curves are definilty way better with the stock cams than the so called VIN 9 cams.
It was a good waste of time, thats for sure.

ronbo
09-05-07, 12:23 AM
OK, I was just browsing the old forum, and here's a reason I believe the larger throttle body bore MIGHT help...

Let's say we start looking "outward" from within the intake manifold... which is (reportedly) 80mm diameter... which equates to 7.7911 square inches of circular AREA.

Assuming we bore the spacer plate out to 80mm, that leaves the throttle body bore in question.

Let's grab the largest Northstar throttle body I know of... because I have it in my hands... which is a 2006-2007 electronic throttle "drive by wire" unit - which has a huge 87mm (3.425") diameter bore. This comes out to 9.2132 square inches of circular area.

Seems overly large? Well, consider the fact that there is an obstruction in that bore... the throttle shaft.

On this unit, the throttle shaft diameter is 0.463". Take that times the length of 87mm (3.425") and we have a blockage area of 1.585 square inches... leaving an open Area of (guess what?) - 7.627 square inches... or about 0.1641 square inches SMALLER than the 80mm intake and spacer plate.

Then take into account the fact that intake air flows like fluid, and imagine what that large throttle plate does to airflow... tumble, tumble... more restriction.

This gives good reason to why guys used to machine the throttle shafts down in racing carburetors...


Too bad we don't have center-opening "Iris" diaphragm throttle plates... no shaft to block flow, and a nice center opening aperture which doesn't force low throttle-angle airflow to the outer walls, where surface tension plays even more dirty tricks on us.

Just my $.02 worth.

God-Follower
05-03-08, 08:28 PM
So, is there a place that will custom-create Iris-type throttle plates? That would definately be a unique modification, along with what seems to be a beneficial air-flow upgrade.