gchu

I know the manual calls for premium (91 Octane) on my 88 Iroc 305 TPI w/Auto.

With the price of gas lately, was thinking about switching to regular (87 Octane). Has anyone been running their 305 TPI with regular? Any problems (i.e. overheating, pinging, detonation)? I know that the newer cars have the "brains" to adjust for lower octane fuels, but wasn't sure about an 88 Third gen.

Thanks,

George

Larry

After data logging and getting on knock counts with 87 octane on my 91 tip 305 thats all I ever run. Just don't try to advance the timing much above stock.

WaOnFiRe

I tried regular 87 octane fuel once and my 305 TPI GTA wasn't running right... Switched back to 91 octane and no more problems...

The fuel price here is 1.454$ (canadian) for each liter of regular fuel. I don't know how much it does for a gallon, but I know it's not cheap.

92blue

iTrader: (1)

Your car isn't going to develop any problems by running 87 octane. If your car starts pinging or detonating by running 87, then lowering the octane is showing you problems that were always present that you didn't know about (ex: carbon buildup).

Your 88 also has the brains to adjust for low octane fuel. It will pull the timing back if it encounters detonation.

1989GTATransAm

iTrader: (3)

I some people running 87 octane in their 10.5:1 modified cars. Just keep the throttle lite.

87TPI350KID

Mine runs best on the 93 octane we have here, which is 3.30 a gallon btw

GOY

Mine runs best with 87 and 1.5 ounces of acetone per 10 gallons. Some people will complain about acetone eating a fuel system - those are the people that don't use it just saying it will. The people that ACTUALLY USE IT haven't had any problems, that I've come across anyway.

... Then again, if gas comes down to $1.50 a gallon, I may skip acetone all together, but in the mean time I'm making ends meet and enjoying it at the same time....

firebirdjosh

iTrader: (1)

I've always ran 87 octane in my 305tpi and had great performance considering.

3.8TransAM

Stock TPI cars are prone to detonation even when you run 91-93 octane.

Some cars are worse than others due to age tolerance and buildup in the engine.

Simply do a little datalogging on various octane grades and see which one works best for you. If u see excessive knock, I would recommend upgrading the octane rating of your fuel.

Althought be sure to take into account all sensors are ok and your car is properly tuned and the timing set correctly.

And if u datalog, log some knock data now, and then do it again when they blend the even crappier winter fuels :-)

later
Jeremy

92blue

iTrader: (1)

What is it about TPI cars that makes them prone to detonation?

GOY, whats the benefit of blending in a little acetone? I am assuming its knock related by the nature of this thread.

3.8TransAM

Cylinder fillling and the tuned effect from the runners would be my first logical guess, also the fact that most here are no longer new low mileage queens.

Do a lot of testing on datalogging and tuning on my own cars. For best results on the TPI cars, you do need to run premium grade fuels. Most guys on the prom board doing tuning have actually pulled large amounts of timing from their cars and they went faster and knocked less.


The deal with acetone directly has to do with its effects on lessening the surface tension of gasoline. Thereby promoting better atomization. The theory is sound. But after many tests indiividual results still vary.

later
Jeremy

GOY

Absolutely Correct! I am a firm, firm beleiver in the theory, and I was before I tried it. However - in a well built SPFI, with multiple nozzle (6 or more) fuel injectors - the "Benefit" of adding acetone won't be as noticable, because the fuel is being sprayed just as the air is at peak velocity through the port, and on top of it, it better atomized right from the injector tip. In an application like ours, where there is often only one nozzle in each injector, and it is a "Bank" fire system... the theory typically works well.

In my TBI application, which flows through a wet flow manifold (read fuel puddling/falling out of suspension) - the driveability alone was good before, but now it's fantastic! I am amazed at what a difference it has made at low engine speeds; it is night and day. Fuel milleage improvements can't be shown yet (haven't gone through the tank) but I suspect a large savings when done.

There is a thread about it in the general tech section.

KamikazeIroccy

iTrader: (1)

Well I tried to run regular 89 octane fuel in my 89 Iroc and it detonated like hell. Ran like crap, switched back to 92 octane and performance was normal. I would at all by possible buy the premium only. Save yourself a few bucks and run some cleaner through there or go to Jiffu Lube they got a fuel system treater that's awesome and go through the brake booster tube.

92blue

iTrader: (1)

I see where you are coming from, but the problems with poor cylinder filling would be at or above 4600 RPM, and most of the people that are noticing /complaining about detonation problems due to low octane are on daily drivers. How often do they go above 4600?

I agree that most TPI engines have alot of mileage. But you are confusing two separate issues it seems. As any engine picks up mileage, oil consumption increases, and oil has a tendency of causing preignition. Running a higher octane fuel will lessen or hide this problem. That does not mean however that TPI needs higher octane. If you had a carb or TBI on there, it would behave the same way. The induction system is a completely separate matter from mileage induced preignition.

92blue

iTrader: (1)

What exactly does Jiffy Lube do, I'm curious? I'd drive over to one and ask, but I doubt I could find an employee that can tell me more than "it cleans your fuel system".

I don't understand what your talking about with the brake booster tube?

KamikazeIroccy

iTrader: (1)

well that is the quickest way for the cleaner to get to the injectors/
I dont know really. I just work there

3.8TransAM

If it doesnt run thr the fuel rail, its not cleaning a darn thing in the injectors :-)

Thru the brake booster line would just be pulled thru the engine and into the combustion chamber and blown out, much like GM top engine clean or Sea Foam is used.

later
Jeremy

rx7speed

[QUOTE]Originally posted by 92blue
I see where you are coming from, but the problems with poor cylinder filling would be at or above 4600 RPM, and most of the people that are noticing /complaining about detonation problems due to low octane are on daily drivers. How often do they go above 4600?

I agree that most TPI engines have alot of mileage. But you are confusing two separate issues it seems. As any engine picks up mileage, oil consumption increases, and oil has a tendency of causing preignition. Running a higher octane fuel will lessen or hide this problem. That does not mean however that TPI needs higher octane. If you had a carb or TBI on there, it would behave the same way. The induction system is a completely separate matter from mileage induced preignition. [/

QUOTE]

think by cylinder filling he might mean it fills the cylinder more. least that is the only thing I can think of being with the cylinder being fuller should mean higher pressure upon combustion.

92blue

iTrader: (1)

Is that what Jiffy Lube trains you to say?

I would get fired by lunch time if I had to work there.

KamikazeIroccy

iTrader: (1)

well I dont work there any more. Look I may be wrong but dont make jokes. The **** works, you can literally sit there any watch all the gunk come out. It may not be the brake booster but I know it's one of the vacumn lines though. IT WORKS>

GOY

Well, in their defense, when you trump up a product, and are VERY WRONG in what your saying, of course they are going to slam you. The very fact it goes through a vac line and not a fuel line should have indicted something to you as you were typing it...

... ya damn JIFFY LUBE BOY

Zig

I have run 91 in my 5.7 TPI for the last two year. But... I tried 89 today and drove about 60 miles with no noticeable effect. I'll stick with it as long as I don't see any ill effects.

Have heard about the acetone and I think I'm going to try it after I find some. If it work, great. If not, Oh well.

I take my car to jiffy lube for coolant exchange ONLY. I have watched them perform rear end service (don't even remove the cover), trans service (don't even remove the pan) and the fuel injector service (they do connect to the fuel rail) and I am not really inpressed with any of them. True, for the most part, the techs are not properly trained but I'm sure there are exceptions to the rule. Just haven't seen one yet. BTW, the only reason I take it for the coolant exchange is because I live in CA and they are convenient. I never let them work without me watching every step.

Mkos1980

iTrader: (8)

When I had my 350 Bone stock I ran 87 with 0 problems, and also when it was modified and I did a ton of highway driving on the power tour I used 87 still. As long as you dont advance the timing and keep it at 6 you should have no problems.

92blue

iTrader: (1)

I'm dying of curiousity.... where can you see all this gunk come out of?

KamikazeIroccy

iTrader: (1)

The exhaust pipes SMART ASZ!

USMC3782

I guess htis means my oil blow through of a 305 tri is on its way out, my brother put a half tank of regular in and he could barely get it to the next station down the road. As a side note, i know it is ready to be pulled, so heck with it, i have never put over 89 in it. When it is noticably faster than someof these new 4 bangers, I will worry about better gas.
As a side note, the IROC runs great on 87!

92blue

iTrader: (1)

You should be careful. You don't want any of that gunk getting on your muffler bearings. Those are a real pain to get to. You probably know that though, you worked at Jiffy Lube.

rx7speed

come on guys a job is a job. sometims wee need to take things just to make the bills.


also even if he doesn't know that much about cars we all learn. and I bet at one point that you didn't know much either young whipper snapper :-p

KamikazeIroccy

iTrader: (1)

No need to Cuss

92blue

iTrader: (1)

What are you 12?

Sent you a PM.

91blue_fire

so u really only need 2 put in the high octane gas if u need more out of your car? not so much if its just a daily driver? ive been chasing this subject for a wile! i just wanna know if were sopposed 2 use 87 or higher on a stock 305. i didnt get an owners manual with my car. or any of my thirdgens........

high c

i dont understand, why are they prone to detonation with 9.5.1 CR?