I ususally use the 89 or 91 octane gasoline, but I replaced my head gaskets with these ones from TPIS that are .029" and claim to raise the comp ratio by 1/2 a point. That means my normaly 9.3:1 L98 will have 9.8:1 comp? Does that mean I need to get only the93 octane or what??

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission
Borg Warner 7.75" 9 Bolt Rear End

Current Mods: LT4 Hot Cam, Comp Cams 1.52:1 Roller Rocker Arms, Edelbrock TES 1 5/8" Headers, Hooker 3" Aerochamber Cat-Back System, Performance Resource Chip, Accel Ignition Coil, Cap, Rotor, 8.8mm Wires, K&N Filters, JET TPI Air Foil, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET (w/o LT4 cam): 14.32 @ 97.7mph
(corrected for elevation)

7.5" 10 Bolt with 3.42s soon to come!

 

93 would be wise..

i'm still running 87 in mine, which dosen't seem to cause any problems at all, but i realy should use the better stuff..

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My `91 Z28 Convertible

 

yeah 93 sounds good to me and it will help your fuel milage!

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1989 firebird formula

Mods: converted from T.B.I. to a carburator 305 to a 350. Flowmater exhaust,hedman shortie hedders,202 160 (882) heads,.447/.447 lift 222@.050 duration speed pro 327/350hp cam 350 .40 over (356) Edlebrock torker2 and a 600 edlebrock manual choke (1405)

Future mods performer rpm air gap intake (polished) comp roller cam, and way better headsa 400 defintely in the works!

 

It would help your milage out if your engine detects knock. The engine timing is increased and if you run low octane the fuel burns too fast and you get ping. That ping is picked up by the knock sensor and the ECM retards timing a lot to get rid of the pinging. That up and down is a real killer on gas milage. That is why getting a custom chip can sometimes save you money in the long run.

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, Jon (91 RS too many mods to list), getting new engine in summer

 

I believe if you will measure your factory gaskets that you will find them to be much thinner than .029
So is .029 the compressed height? if so then you probably have less compression than before.
What type of headgasket did you just remove from your engine? Most factory gaskets I see are metal shim much thinner than .029

Check your old gaskets just to be safe. I doubt that a gasket change could make .5 point of compression on a smallblock chevy.
I am curious now so please let me know what you find.
thanks,
ODB

 

TPIS... yea
Anyway, with that gasket and typical SBC numbers your compression comes out to... 9.33:1. I think I measured a stock 305 gasket at .020, and I imagine the 350 one is the same. The thickest gasket I have seen is around .040, and the compression ratio would be about 9.1 using that, so 1/2 point is totally wrong.
Dont worry about it, thats not enough change in compression even if there is any change (and I doubt there will be)

Found my old post, got the right stock gasket thickness... You arent going to see any increase in compression.

[This message has been edited by madmax (edited February 10, 2001).]

 

I learn something new everyday on this board

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89 IROC-Z 350 TPI

-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Problems every other day with the car (probably not a mod, but to me it sure makes a difference)

 

TPIS will sell you a dream on the phone.

Anything for a dollar!