compression through the intake manifold *HELP*

[thedsmguy]

So, I have never seen this. A good friend whom seems to know what he is doing is having this issue. He is getting great compression numbers and no noticeable leaks via a leakdown tester. But, we are turning this motor over, the car is literally spitting compression back through the intake, through the tb, throuh the intercooler, turbo, and the maf! Is there any way to mess up so badly on the timing yet still pull 170psi compression numbers? I'm completely dumbfounded, it might be because I'm late and have tried many things.... Any help is appreciated.

 

[Barnes]

It's late for me too, but I'm 99% sure you simply have the cams timed 180 degrees off.

 

[cheekychimp]

That does actually make sense.

 

[vr4play]

I just had a race car in the shop with the same problem. It was a Doran Sports 2000 car with the pinto engine. He crashed it and we got all the suspension on and finished and decided to start it and would puff out the carburetor. Ended up being a broken rocker on the exhaust. The exhaust stroke was pushing compression out the intake.

 

[holeshotmoe]

Assuming you're talking about our motors...
If the intake cam is 180 deg off, the intake valves will be closed on the compression strokes and you'll get your 170 psi reading. As the piston approaches TDC, the mixture is ignited. Just after TDC, the intake valve opens (remember, it's beginning its intake cycle). So instead of the blast forcing the piston down the bore, it blows out the intake side. Simultaneously, the intake cam has positioned the CAS to signal the ECU to fire the injector. /ubbthreads/images/graemlins/ooo.gif

 

[cheekychimp]

Flamethrower anyone?

 

[thedsmguy]

Both the cam dowel pins are in the correct position... Any chance that the HKS 264 cams in it could be an issue?

 

[Wizardawd]

I've seen the dowel pins shear off and the cam is no longer indexed by the cam gear.

Wiz

 

[holeshotmoe]

Quoting thedsmguy:
Both the cam dowel pins are in the correct position... Any chance that the HKS 264 cams in it could be an issue?


Have those in my eclipse. I'll look tonight to see if there is any difference how they mount and align at tdc...but I'm almost certain it's the same as stock.

 

[galant651]

id agree with vr4play. seen it alot and its usually the exhaust valve wont open because something is broken so exhaust pushes out the intake. and it will show great compression. pull valve cover and see what you have.