: Higher Octane For Your Fleetwood????



SDCaddyLacky
11-06-10, 12:01 AM
So I decided to put in 91 Chevron Supreme gas in my 94 FWB, and right away I noticed that the car took off a little faster with less effort while running slightly smoother. Can using higher octane gas in high mileage engines, really make a difference in power and MPG's? I realize in newer cars, or low mileage cars, it probably wouldn't matter at all, but with years or carbon build up and tired valves on a 156,000 LT1, can it make a small difference?

csbuckn
11-06-10, 12:44 AM
What is the compression ratio on the LT1? Isn't it around 10?

Stingroo
11-06-10, 01:52 AM
10.4:1 for stock I think.

Maybe 10.5 - but still, around 10. lol

SDCaddyLacky
11-06-10, 08:11 AM
Ah ha, so it would make sense to use 91 or higher because of the high compression. It's not necessary, but will most likely help make a difference right?

turbojimmy
11-06-10, 08:36 AM
Ah ha, so it would make sense to use 91 or higher because of the high compression. It's not necessary, but will most likely help make a difference right?

I noticed a difference in mine right away when I switched between 93 and 87 octane. With the 87 octane, I could hear it knocking. Even when there's knock you can't hear, the PCM is retarding the ignition to prevent it. Retarding ignition = less power.

SDCaddyLacky
11-06-10, 08:51 AM
I really dont know why Cadillac said to use 87 in these heavy ass Fleetwoods, sure it gets the car moving, but with a performance engine like the LT1, you would think the minimum octane to run the engine would be 91. I am going to run 91 for a week or 2, then switch back to 87 to see if there is any reductions in MPG's and power.

ShadowLvr400
11-06-10, 09:47 AM
I run 91 or 93 only. However, I do have a cam, valvesprings, headers, comp tuning, etc. Calculations based on 1/4 mile time and trap speed put me at around 315-320 horsepower. Torque would be estimated in the 375 range. Not a bad climb for a motor that started at 260/330 combo. Still totally driveable too. :) (Cam is 218/224 at 112 LSA.)

I~LUV~Caddys8792
11-06-10, 10:20 AM
I ran 87 octane in my '95 Roadmaster all the time. They recommend 87 octane, I don't know why you'd need to go to anything else...?

The problem with running a higher octane than recommended is that a higher octane burns slower, which leaves more carbon deposits in your combustion chambers, thereby raising the compression ratio, if only for the tiniest bit. So in turn, to get that feeling of "raised power", you'll need to keep continually running a higher octane, unless you can clean all those carbon deposits out with a fuel system cleaning, which will get you all your power back and make it feel like new again.

N0DIH
11-06-10, 12:18 PM
Stock the difference is minimal if any, ILuvCaddys8792 is right, the higher octane burns slower, even can be somewhat harder starting in winter.

The 10:1 comp on the LT1 is reverse cooled, so it isn't like 10:1 comp on a normal cooling system, the heads are much cooler in the LT1.

Tune the LT1 and the engine wakes up some more on 93 octane. I do some PCM tuning and know the LT1 well, I actually run mine on E85 and it runs quite well (high compression really helps).

My Fleetwood on the datalogger showed 15.2 @ 95 with 3.42's and 15.3 @ 93 on 3.08's. I have toyed around with and spanked Hemi Ram pickups (short cab short box) and found the SS Silverado is a close match to the tuned LT1. Mind you, that is a SCSB truck with 4.10's, AWD and a 345hp 6.0L LQ9. And mine is a 3.08 geared Fleetwood with 260hp (adv).

The LT1 is either quite underrated or the Hemi and LQ9 is overrated....


I run 91 or 93 only. However, I do have a cam, valvesprings, headers, comp tuning, etc. Calculations based on 1/4 mile time and trap speed put me at around 315-320 horsepower. Torque would be estimated in the 375 range. Not a bad climb for a motor that started at 260/330 combo. Still totally driveable too. :) (Cam is 218/224 at 112 LSA.)

ShadowLvr400
11-06-10, 09:09 PM
15.2/15.3 aint bad on the 1/4 mile. My Fleetwood's been at a 14.5 with the 3.42's but without the engine tune quite right. Now the engine tune is stronger, but the rear is 2.56 open. I've been able to outrun my buddy's 14.2 Caprice, but it's rather streaky... His Caprice sometimes runs well, sometimes,not so well. Also outdistanced a 350Z on the highway up until 120. Oh, and a Charger SRT8 in the 20-90 range was a dead heat. (I don't know how that happened, but we did it several times.) I think if I can rebuild the rear again, I'll drop to 3.27 gears. 3.42 left me a little too close together and they were the shorter of the 2 sizes I had been considering.

Stingroo
11-06-10, 09:48 PM
Find a 3.23 from a tow package Caprice like mine then.

csbuckn
11-06-10, 10:19 PM
Now yall have me worried. I just got 373s to go in my brougham with a th400. Do yall think ill be okay or should I sell and go lower?

77CDV
11-06-10, 11:21 PM
unless you can clean all those carbon deposits out with a fuel system cleaning, which will get you all your power back and make it feel like new again.

And coincidently, Chad has just the product you need, and very reasonably priced today! :)

N0DIH
11-07-10, 03:31 AM
Gotta love the heavy Fleetwood and the LT1 eh??

Here I was pondering going with 3.90's!


15.2/15.3 aint bad on the 1/4 mile. My Fleetwood's been at a 14.5 with the 3.42's but without the engine tune quite right. Now the engine tune is stronger, but the rear is 2.56 open. I've been able to outrun my buddy's 14.2 Caprice, but it's rather streaky... His Caprice sometimes runs well, sometimes,not so well. Also outdistanced a 350Z on the highway up until 120. Oh, and a Charger SRT8 in the 20-90 range was a dead heat. (I don't know how that happened, but we did it several times.) I think if I can rebuild the rear again, I'll drop to 3.27 gears. 3.42 left me a little too close together and they were the shorter of the 2 sizes I had been considering.

Cadillacboy
11-07-10, 12:43 PM
I do run premium but I should say I have a tuned PCM on my ride

ShadowLvr400
11-07-10, 06:59 PM
Now yall have me worried. I just got 373s to go in my brougham with a th400. Do yall think ill be okay or should I sell and go lower?



Depends honestly. If this is a primary driver, that you enjoy hot rodding with to some degree, and you go on the highway more than 30% of the time, I'd sell the 3.73 and go to either a 3.23 or 3.42 posi. 3.73 is just a bit too short for a DD. If this is more a weekend car and dragster, 3.73 works well.

N0DIH
11-07-10, 07:36 PM
Definately helps, the car is happy with 10:1 comp and 87 octane, so putting in 93 really does almost nothing for it. So having a tune on it will help. But you really can't drop back to 87 when you do it unless you comprimise in the middle somewhere.

The newer PCM's have dual octane tables and will make an adaptive timing map so if you toss in low or high it adapts.

Can mod for a newer PCM, but it isn't for the feint of heart, but it sure brings a lot to the table....


I do run premium but I should say I have a tuned PCM on my ride

csbuckn
11-07-10, 09:49 PM
Depends honestly. If this is a primary driver, that you enjoy hot rodding with to some degree, and you go on the highway more than 30% of the time, I'd sell the 3.73 and go to either a 3.23 or 3.42 posi. 3.73 is just a bit too short for a DD. If this is more a weekend car and dragster, 3.73 works well.

Perfect. I don't drive it everyday, mainly around payday.

turbojimmy
11-07-10, 10:20 PM
Definately helps, the car is happy with 10:1 comp and 87 octane, so putting in 93 really does almost nothing for it. So having a tune on it will help. But you really can't drop back to 87 when you do it unless you comprimise in the middle somewhere.

See mine just isn't happy with 87 octane. It might be the extra weight of the limo, but it knocks like an SOB with anything less than 91 octane. 93 is better (knocks less).

The LS1 in my TA knocks like crazy with 93. Whole 'nother story with that thing, though.

jayoldschool
11-07-10, 11:21 PM
See mine just isn't happy with 87 octane. It might be the extra weight of the limo, but it knocks like an SOB with anything less than 91 octane. 93 is better (knocks less).

Bet you have a bad EGR.

turbojimmy
11-07-10, 11:40 PM
Maybe. But it's going away with the new engine anyway :-)