Need Compression, lots of it

[BillS]

You aren't using very high boost but I'd sure shy away from raising compression past about 8.5:1, and away from cutting anything off your pistons. Buy pistons that give you what you want. I use Ross Racing, but Wiseco makes an excellent product too.

I run 10 psi on 8.5 compression and have had no problems over many years.

[caffeine]

I don't get why you'd shy away from 8.5+ with only 10 psi. Plenty of people are running 10 psi+ with stock 3x00 compression which I think is 9.5-9.8:1.

[3400-95-Modified]

I know it's not the same motor, but a stock legacy with cast pistons is 8.9 CR with 13.5PSI from the factory... many run WELL over that too on stock type pistons.

[BillS]

I know it's not the same motor, but a stock legacy with cast pistons is 8.9 CR with 13.5PSI from the factory... many run WELL over that too on stock type pistons.

There are lots of motors that run higher pressures on higher compression ratios. My street driver runs 25 psi into an engine with 9.2 CR. It all depends on how the engine is set up, and what other bits you use (in that case direct injection and a huge IC). With a stockish compression 2.8 and not running an intercooler, 10 is the point of diminishing returns, and you'd better have a knock sensor. My cut out is set at 13.5 and I only hit it on long straights with wide open acceleration.

Installing an IC in a Fiero without chopping it up is a challenge.

[yeyo_racing]

Installing an IC in a Fiero without chopping it up is a challenge.

Go AWIC, that's what I did. Just two holes in the trunk for the hoses.

[yeyo_racing]

Does anyone knows what psi should I be getting during a compression check?

I got high to mid 90 psi dry, and about 10 psi more oil squirted. This is on all cylinders

[BillS]

Does anyone knows what psi should I be getting during a compression check?

I got high to mid 90 psi dry, and about 10 psi more oil squirted. This is on all cylinders

Sounds way low to me. Going from distant memory but 140 rings a vague bell (sure someone that has checked a stock engine will chime in)

[caffeine]

I'm pretty sure anything below 100 psi is too low, according to service manuals. You are supposed to warm up the engine before doing a compression test though. That may change your results.

[3400-95-Modified]

It's going to really depend on his cam overlap... Service manual specs are thrown out when you have an aftermarket cam because the cranking compression is greatly reduced if valves are open much longer than stock.

How many compression strokes did you let it complete? I'll usually let it pump till the gauge stops climbing... and I also do it with all the plugs out and the TB open.

[BillS]

And don't forget to hold the throttle wide open so you aren't working against the closed throttle.

[trotterlg]

I think you are OK there, it is just your cam that is showing low compression. This why all hot cams list a recommended static compression ratio, to make up for the cam overlap. What is your calculated CR for this engine? Larry

[yeyo_racing]

Ok, let me answer the questions in order:

- Engine was fully warmed (195 deg)
- Cranked til needle stopped climbing with TB fully open and no plugs on any cylinder
- Calculated CR is 9.0:1

[trotterlg]

Considering the cam you have I would say things are normal. Just start it up and see what you get. Larry