Compression Test Results

[Dean85GT]

Today I decided to give my stang a nice compression test. I had done one when I first got the car but I never did it properly cause I was more caught up in just driving it. Since the day I bought it the car has ran very strong but I planned on building up a fresh motor for it this winter. Long story short, I did a compression test (wide open throttle, engine warm) and got the following results.

1 ----- 145
2 ----- 135
3 ----- 145
4 ----- 145
5 ----- 140
6 ----- 148
7 ----- 147
8 ----- 140

I think those are pretty damn good numbers, especially since the engine has 216000 km on it without a rebuild! Keep in mind that this is an 85 which came with less compression from the factory. As for piston 2, I think if I was to test it again it would be right with the other numbers cause it was the last piston I did and I was kinda rushing it...

Anyways....New Intake, carb, and hopefully heads here I COME!!!!!!!!!!

 

[Daggar]

Well... shop manual calls for a max of a 25% difference between cylinders. Your best and worst is well within 10%. I'd say you're in excellent shape!

 

[Mavrick]

I got basically the same results on my 89 motor. All cylinders were within 15lbs of eachother, lowest being 135 and highest being 150.

I forgot to have the throttle body open though, not sure whate difference that makes.

 

[Daggar]

I got basically the same results on my 89 motor. All cylinders were within 15lbs of eachother, lowest being 135 and highest being 150.

I forgot to have the throttle body open though, not sure whate difference that makes.

Not much so long as you tested all the cylinders under the same conditions.

 

[HISSIN50]

And as everyone knows, doing a wet test thereafter can help one to get a feel for how rings are doing (even if numbers are good, as yours are).

Leakdown is further revealing yet.

 

[Dean85GT]

I think the motor is ready for all boltons but if I was to go with forced induction I would obviously get a rebuild. Do you guys think my car will be ok to handle a 75 shot? I was actually looking at a Sneaky Pete system in particular.

 

[VibrantRedGT]

Those are damn good numbers. I'd say your good to go with future plans. As mentioned the throttle body wide open is recommended as well as a strong charging system to get accurate numbers. I normally do it with a battery charger on during the test with 10 minute intervals. It's also recommended to have the motor warm (not hot).

 

[Dean85GT]

Those are damn good numbers. I'd say your good to go with future plans. As mentioned the throttle body wide open is recommended as well as a strong charging system to get accurate numbers. I normally do it with a battery charger on during the test with 10 minute intervals. It's also recommended to have the motor warm (not hot).

Ya I had the motor warm and all...I'm pretty pumped now too that the motor is in this good of shape. My friends have a dyno day booked this saturday. Maybe I'll throw my car on for ****s and giggles and to get a baseline. What do you guys think it would put down with just flowmasters and upgraded ignition? My guess is probably around 170. The dyno is a mustang dyno and my car is a 5 speed.

 

[HISSIN50]

Having a warm motor is a must with forged slugs IMHO. It is still pretty important with hypereutectic slugs, but with their tighter fitment and lack of expansion (silicon content, etc), it is not as huge a deal.

 

[vristang]

Having a warm motor is a must with forged slugs IMHO. It is still pretty important with hypereutectic slugs, but with their tighter fitment and lack of expansion (silicone content, etc), it is not as huge a deal.

Forged Al pistons have to be hot. I am learning this first hand right now. hyper pistons will not be as touchy.

I would also suggest the leakdown and wet compression test as mentioned above, but it sounds like you are good to go.

Happy Modding,
jason