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Discussion Starter · #1 ·
What is the compression ratio for a stock 87gn? Also, what sort of CFM does the stock TB flow?
 

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It was listed at 8.0-1

Probably was below that as tolerances stack up.

TB a/f, I have seen various numbers presented from tests but don't recall. The mailing list archives may hold that info. I believe stock is 58 mm in diameter but I may be thinking of something else. Jay, who advertises in the vendor section will mod it to 62 mm and rework the plenum to match for a very nominal fee.

Guys go into the tens on the stock diameter so the engine is not exactly starving for flow ability as delivered once the air filter log jam is rectified.



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Steve Wood

Growing old is mandatory; growing up is optional.


86 GN bought new, 87 T-type-81 El Camino with GN drive train-basically stock 86, 94 Caprice 9C1, 69 SS396 Camaro Convertible
 

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Discussion Starter · #3 ·
Thanks Steve. I have a carb guy at work wanting to comopare his 750 carb to my engine and I have no clue what to tell him.

As for the compression ratio 8:1 is ok. One thing I never understood about turbo engines is why they have lower compression ratios to begin with just to strap on a turbo and raise the pressure in the cylinders.

My Daytona has 7.5:1 but the non turbo version is like 8.8:1. Just doesn't make sense to me. Wouldn't you get better performance out of leaving the compression ratio where it is and then adding a turbo? Oh well....just ramblling.
 

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Renthorin - yeah, you'd have better performance with the 8.8:1 Daytona (2.2L or 2.5L?) motor and a turbo.. Thing is the factory stuff is designed with the average person who knows squat about octane and knock retard in mind.. So this turbo motor has to be able to (at times dpending on owner) pull up to the pump, add in some 87 octane.. pay for the gas.. leave and merge on to the freeway and then pass that Semi truck at WOT and 7-10 PSI of boost... all with the school girl who added the 87 octane


As for your buddy, tell him that at around 14 PSI of boost (I think 14.7 or something close PSI boost is adding 1 atmosphere??) is like almost doubling the 231 cubic inch displacement of our engines, and making it equivalent to a mild 462 c.i. motor..

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Steve Ruston
1987 Turbo Limited
 

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Discussion Starter · #5 ·
That makes sense. BTW, my Daytona is a 2.5 turbo. Used to be quick....now it is just a daily driver but is very good at that ;-)
 

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In theory, established I believe mback in the thirties, more power may be made with lower compression rations and more boost.

Modern cars have used 7.5 to 8.0-1 crs traditionally. Using lower ratios takes all the throttle response away from cars when not under boost It also tends to make spool doggy.

Some think that confusing peak horsepower with overall torque "under the curve" might not be optimum for street cars.

There are lots of Regals, including mine. that run more than stock compression with good results. Lawrence Conley, Ken Duttweiller and others routinely add compression. As one exceeds 9-1, one may have problem tuning for 93 octane, however, and a good chip man is required.

Remember that compression ratio is just one of many components or attributes that affect final performance. A longer duration cam will reduce low rpm cylinder pressures and will make higher compressions more tolerable.

A swirl combustion chamber as was used on the Stage II heads will tolerate more compression....etc, etc, etc.

It is not a simple subject and definitive statements can get one into trouble. Everyone has a theory on engine combination and they may ALL be right.

The Stage II Grand National (Nascar) engines made more hp per cubic inch than did the v8s of the time. They had monstrous ports yet had good low rpm torque. Go figure! Apparently the Buick Engineers had their own bible.

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Steve Wood

Growing old is mandatory; growing up is optional.


86 GN bought new, 87 T-type-81 El Camino with GN drive train-basically stock 86, 94 Caprice 9C1, 69 SS396 Camaro Convertible
 
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