Compression test on 383 results..

[SRT-440]

First those that have read my other posts about my 383 I don't know much about it..I don't know what cam it has or pistons...I do know that it was built for drag racing and is a high compression engine 12.5:1.

This test was done with the engine cold...I know that readings are better when it's warmed up but that wasn't possible right now..but maybe I can still get an idea on the condition of the engine.

During test the carb wide open, with all 8 plugs out and the ignition disabled. Intake manifold is a Torker 383, headers.. plugs look old but ok.

Cylinder:
#1: 220 psi
#2: 230 psi
#3: 240 psi
#4: 230 psi
#5: 240 psi
#6: 220 psi
#7: 240 psi
#8: 220 psi


are these high numbers normal/average for a high compression engine and does these numbers indicate relatively good compression/life left in the engine? Thoughts?

[SRT-440]

..after looking closer and wondering why this motor idled so rough (along with other issues) I start looking at the plug wires and up on the distributer at least two of the wires have split boots exposing bare metal/wire. I'm not engine expert but that would be a bad thing..LOL. Hopefully new wires (firecore) will help my idle and hesitation problems.
Also, I need to replace the plugs but with it being 12.5:1 I'm not sure which plugs to get..suggestions? 

[71bee]

I run NGK's. i've had great results with that plug in particular.

[mhinders]

Compared to my 383 those compression numbers are high.
If I remember correctly I had something like 145 psi with an engine that was very cold (2 below freezing), wide open throttle and cranking a few seconds per cylinder.
In my engine has a "big" cam giving very low vacuum at idle, I guess that could make my numbers look less good.
Cheers,

[SRT-440]

Compared to my 383 those compression numbers are high.
If I remember correctly I had something like 145 psi with an engine that was very cold (2 below freezing), wide open throttle and cranking a few seconds per cylinder.
In my engine has a "big" cam giving very low vacuum at idle, I guess that could make my numbers look less good.
Cheers,

Yea I think 140-170ish is average...I read somewhere that someone had a 270psi on a high compression race motor..anything above 200 seems very high.

[firefighter3931]

That engine is in great shape mechanically....nice even compression numbers ! 

There is no chance it will run on pump gas though....the cylinder pressure is too high. It should run fine on 110 octane fuel. An NGK 7 series plug would be the correct heat range for that build, inmo. 

What heads are on this engine ? What carb ?


Ron

[SRT-440]

That engine is in great shape mechanically....nice even compression numbers ! 

There is no chance it will run on pump gas though....the cylinder pressure is too high. It should run fine on 110 octane fuel. An NGK 7 series plug would be the correct heat range for that build, inmo. 

What heads are on this engine ? What carb ?


Ron

It's got ported 906 heads milled down to help reach 12.5:1..it's only got a Holley 750 DP (which I'm told might be a bit small), 383 Torker intake, crane roller rockers (1.5). It was built for racing back in '96 and from what I'm told a LOT of time and effort was put into it to make it race worthy. So far, it seems to run ok with 50/50 110 race gas and 93 octane..but I can tell it prefers only the expensive stuff. LOL.

[Cooter]

Strong Comp numbers, but IMO, with all the stroker stuff out there today and being that they can make HUGE HP and torque numbers with 93 pump gas, it is crazy to put 12.5:1 pistons in any engine.....Even a race car.... My .02

[SRT-440]

Strong Comp numbers, but IMO, with all the stroker stuff out there today and being that they can make HUGE HP and torque numbers with 93 pump gas, it is crazy to put 12.5:1 pistons in any engine.....Even a race car.... My .02

I agree... This engine was built back in '96...I'm eventually gonna go with a 440 > 512 stroker. 

[firefighter3931]

That engine is in great shape mechanically....nice even compression numbers ! 

There is no chance it will run on pump gas though....the cylinder pressure is too high. It should run fine on 110 octane fuel. An NGK 7 series plug would be the correct heat range for that build, inmo. 

What heads are on this engine ? What carb ?


Ron

It's got ported 906 heads milled down to help reach 12.5:1..it's only got a Holley 750 DP (which I'm told might be a bit small), 383 Torker intake, crane roller rockers (1.5). It was built for racing back in '96 and from what I'm told a LOT of time and effort was put into it to make it race worthy. So far, it seems to run ok with 50/50 110 race gas and 93 octane..but I can tell it prefers only the expensive stuff. LOL.

A 750 DP carb is fine on that combo, especially with a single plane intake manifold. 

It takes a lot of fuel $$ to make up the difference a Stroker will cost to build. I would tune it and run it for now so you can enjoy the car.  As long as it doesn't detonate you're in no danger of hurting the engine.


Ron