: Conversion to LSx Throttle body



fubar569
04-05-07, 11:35 PM
Now this is something that is probably very very far fetched but i know they make 90mm throttle bodies for the LS1/6/2/46546...and i'm wondering if there is anyway possible to convert to that style of throttle body with the northstar and keep things like all sensors communicating with the PCM and your cruise, etc...

it's probably not worth the effort, and definitely isnt the big restriction in the system, but i figured i'd throw the idea out there. i hope to have my spare N* TB and manifold in a week and i'd like to compare the 2 TB units to see if its even possible without too much trouble...

i cant find too many detailed pics of the LS style 90mm TB but maybe all it would take is an adapter plate and perhaps a bit of phenangling with the sensors...the TPS is the same sensor as the 98 LS1 camaro and the IAC's are different part numbers but the signal is likely the same...

just tossing this out there....

CadillacSTS42005
04-06-07, 01:11 AM
doesnt matter
the hole on the intake is only 80 mm anyways... more than that is a waste...

fubar569
04-06-07, 01:18 AM
as i figured...and probably cant go more anyways...
oh well...no loss...
carry on...

eldorado1
04-06-07, 09:11 AM
LS1 = RWD

The throttle cable is on the wrong side.

fubar569
04-06-07, 09:17 AM
LS1 = RWD

The throttle cable is on the wrong side.

that was the other little "issue" i noticed after i posted...but depending on which way it flipped open, it could still be worked out...

i am not going to go any further with this though...it was a late night no sleep brainfart...lol

ronbo
09-08-07, 11:37 PM
OK, I was just browsing for some throttle body discussions, 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... clear and free.

Assuming we can bore the spacer plate out to 80mm (more on this later...), that leaves the throttle body bore in question.

Let's consider 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...

Spacer plate - would need to be taper-bored... TB side at 87mm, intake side at 80mm.

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. (but mechanically complicated... failure-prone)

Electronic throttle can be modified to mechanical... but not easily. That's not really the issue anyway... the more common debate is about 80mm throttle body bore, which would still be restrictive considering the throttle shaft obstruction.

Just my $.02 worth.

airfuel2001
09-27-07, 11:20 PM
the idea crossed my mind as well...I have a ls1 throttle which is also 75mm it will support more power than than our cars have at the flywheel at the ground, more might not be better. the only solution I have, is fabbing a plate to bolt an existing 2001 n* body onto our manifold-the linkage will work as well as the trans...the only drawback would be you will need to relocate your mass air downstream, and upgrade to a powerpipe 3.5 in

Submariner409
09-28-07, 12:00 PM
:yawn:When you finish with all the "bigger is better" speculation, calculate how much air a 281 cu.in. engine needs at 0" vacuum......(theoretical WOT, 6200 rpm redline) Then calculate the airflow available through a 7.5 sq.in. throttlebody........

fubar569
09-29-07, 01:40 AM
:yawn:When you finish with all the "bigger is better" speculation, calculate how much air a 281 cu.in. engine needs at 0" vacuum......(theoretical WOT, 6200 rpm redline) Then calculate the airflow available through a 7.5 sq.in. throttlebody........

if this is the case, then why does eldorado1 have documented dyno gains from going to 80mm TB from stock, and also at least one other independent person reported gains even on the 4.0L Northstar? there seems to be some benefit from it, i just wondered if there could be anymore left on the table from another bore increase...

for what its worth...LS motors going with a modified intake and 90mm TB see some pretty awesome gains when THEORETICALLY the stock TB is enough...so how do we explain that?

eldorado1
09-29-07, 08:17 PM
:yawn:When you finish with all the "bigger is better" speculation, calculate how much air a 281 cu.in. engine needs at 0" vacuum......(theoretical WOT, 6200 rpm redline) Then calculate the airflow available through a 7.5 sq.in. throttlebody........

I have a better idea. Take a scan tool and log MAP vs RPM at wide open throttle, and compare to the barometric MAP readings. If they're the same, then there's no restriction and nothing can be gained by enlarging the intake/TB/induction tubing/airfilter.

Submariner409
09-29-07, 09:56 PM
:thumbsup: Eldo.....That's truly the best (electronic) way. I'm used to calculating carb size and secondary opening rates for various car and boat tunes for Olds 455 and GM 454 engines with either Holley or Quadrajet setups. What a lot of people seem to forget is that too large a carb or throttlebody will almost always result in low rpm power losses and a midrange stumble. Redline is one thing, overall driveability is another.

eldorado1
09-29-07, 11:44 PM
:thumbsup: Eldo.....That's truly the best (electronic) way. I'm used to calculating carb size and secondary opening rates for various car and boat tunes for Olds 455 and GM 454 engines with either Holley or Quadrajet setups. What a lot of people seem to forget is that too large a carb or throttlebody will almost always result in low rpm power losses and a midrange stumble. Redline is one thing, overall driveability is another.

A throttle body can't be compared directly to a carb though. (we might have had this conversation before, I'm having deja vu)

But basically, a throttle only throttles the air flow through the engine. Its purpose is to give a linearly controllable range of power output from the engine. (linear and controllable are key words there) There is nothing to lose, in terms of power or torque, from going to a larger throttle body. There could be additional airflow, power and torque to gain. The only downside to a larger than necessary throttle body, is that "linear controllable range" can become skewed. It becomes less like a throttle, and more like an on/off switch. The reason is, cracking a 3" throttle open 10 degrees allows a lot less air than cracking a 10" throttle open 10 degrees. That 10" dia throttle body @ 10 deg could flow what the 3" throttle does wide open!

That's an extreme example, but that's why you wouldn't want to double the throttle diameter. Usually the streetability limit is ~1.5x the stock diameter for naturally aspirated. That's still more than double the flow capability, so there should be some good mods behind the change.

Carbs are a different matter altogether, because they control the fueling by venturis. Those venturis need sufficient velocity to atomize the gas. Too large of a carb and you get stagnant airflow. Won't make any power until the RPM's and airflow pick up.

That's why they're different animals.

Submariner409
09-30-07, 11:38 AM
So you're saying that Cadillac purposely strangles the N* series ? To what end ? I assumed, from other discussions in the Seville and N* threads, that the engines were tweaked to the max power/driveability for the application.

eldorado1
09-30-07, 12:37 PM
Not at all. Everything is a series of engineering compromises... usually boiling down to cost vs benefit.

The higher up said "give us a 270hp v8 engine to go into our refined cadillac series... something to compete with other high end lines (bmw, mercedes, etc)" Out popped the N*.

Did they purposely strangle the engine? No. Is it living to it's full potential? No. Think about this - it would have been very easy to change the stamping process slightly to create something close to full headers - maybe with 12" long primaries. Short, but there might have been 20hp to gain. Didn't do it. Why? Costs more. Already had the 270hp needed.

Take a look at a stock vette's exhaust manifold:

http://images.carcraft.com/techarticles/116_0501_03_z+ls1_header_test+vette_manifold.jpg