BillyB4C

Does anybody know the compression ratio on a 92 305 TPI?
Thanks

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Billy
92 B4C 305TPI T5
Black W/ Purple ghost stripes
Texas Spokes Sports Car Club #63 ESP
14.32@98mph

b4c1le

I believe it is about 9:3:1 or 9:8:1, one of those two. Can you tell me what you've done to get the 14.32@98mph?


Sean
1991 B4C Camaro, 305 5-speed.

1986CamaroIROC-Z

I believe all the TPI engines came with 9.5:1 compression, im sure if i am wrong i will be corrected.

BillyB4C

gutted airbox, K&N filters, air foil, removed EGR walls in plenum, afpr, relocated air temp. sensor, MSD wires and coil, Flowmaster cat-back, smog pump and cats removed, A/C taken out, moved battery to spare tire well, Sphon torque arm, and 3:73 gears with a Torsen posi. I was runnug on an old set of Kumho autocross tires. My 60ft times are in the 2.2-2.3 range. I think thats all. The time has not been corrected for altitude. (if you know how to calculate that let me know). I've got a set of Corvette heads, a ZZ4 cam and headers that I will be installing this winter. Hopefully I can get deep into the 13's with this combo.

BTW...motor has 184,000 miles on it.

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Billy
92 B4C 305TPI T5
Black W/ Purple ghost stripes
Texas Spokes Sports Car Club #63 ESP
14.32@98mph

91 RS

92 service manual says it's 9.1:1 for a 305 and 9.75:1 for a 350

fly89gta

iTrader: (1)

really? i thought the 305 was 9.3:1 and the 350 was 9.5:1..hmmmm....

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*89 Trans Am GTA
*Moderator at www.transamgta.com

To hell with the GM vs Ford war. We must unite, as brothers to fight the plague that is overtaking the world...RICE

Tony

palric

iTrader: (1)

Last time I researched the matter (compression ratio on the 305) I remember reading 10.25 to 1 compression for the '91 and '92 LB9. Now that is a ton more than the others have been saying. Wonder what gives ?

I remember reading that the cam and dual cat setup was the same for the 89 through 92 LB9 motors which were spec'd at 215 or 220 hp depending on the source, and that the late increase to 230hp in '91 was the result of a compression ratio increase.

I can tell you this -- my '91 is tuned to factory setup and if I use anything but 92+ octane I get brutal pinging. Just assumed this was a result of the compression ratio and limitations in the chip to deal with it ?

.02 cents worth,
RP.



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'91 Formula Firebird G92,WS6,5-speed,3.42 a ton of fun to drive.

Grim Reaper

My 1991 GM Shop Manual says 9.3:1 for 305s and 9.75:1 for 350s. I would assume 9.3:1 for 92 305s also.

fly89gta

iTrader: (1)

10.25???? no way man, no way they'd give a 305 more CR than a 350, not with the difference in heads

b4c1le

Thanks for listing your mods, good luck on your quest for 13s. Kick *** on the mileage too! I've got 60k on mine and I'm still trying to break 14s, just replaced the intake gasket. I'm not used to these slow 305s. Usually running an L98 or LT1 in the high 13s, low 14s. LB9 5-speed combo makes for some fun driving though.


1991 B4C, 305/5-speed, loaded, slow, for now

Willie

iTrader: (1)

My reference that has engine specs list the 1986 thru 1992 305 TPI with a 9.3 CR. This was verified on my 1987 305 and Tim Burgess' 1992 305 TPI by measuring combustion chamber volume when both our engines were apart. The Manufacturers Motor Vehicle Report for 1987 lists the 305 and 350 TPI with 9.3 CR's.

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Willie

Supercharged 1987 305 IROC-Z, Daily-Driver, Emissions-Legal.
Former Paxton (6-psig) with 50-hp nitrous: 12.043 @ 112.86 mph.
ATI D1SC (10-psig): 12.056 @ 116.62 mph.
All stats are altitude corrected for 3,100 feet using NHRA's Altitude Correction Table.

http://willie.camaro-firebird.org/

1987 "20th Anniversary Commemorative Edition" Z28 Convertible -- Super Chevy Show Class Winner, 1998.

BillyB4C

Thanks for all the help!

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Billy
92 B4C 305TPI T5
Black W/ Purple ghost stripes
Texas Spokes Sports Car Club #63 ESP
14.32@98mph