whats the question? are you asking if the engine is damaged? Do a leak down test.Or are you thinking the cam timing is bleeding off CR?

 

You don't have enough static compression for the camshaft in your engine. That will cause low cylinder pressure. Either get your SCR up to around 11:1 or your camshaft duration down to around 208-216 deg @.050"

Read this

http://www.crankshaftcoalition.com/wiki/Cam_and_compression_ratio_compatibility



Duke

 

I have now checked compression and there all at 100 except for 5 and 7 they are at 95. I didn't check the compression when I first got the engine I kick myself in the but now. But to me these numbers sound low I was thinking I should be up in the 150s+? the motor is built to be a 9:1 compression motor.

Bullet cam Chs 278/286-064f at .50 in 248 exh 256
1.5 rocker ratio exh 532 lift in 353 cam is in at 102

I'm uncertain as to how you circle track guys build a motor, but what I hear you saying is that you have taken a camshaft that should have been screwed into a 11.00:1 to 12.50:1 static compression ratio motor according to the 248/256 @0.050" tappet lift figures you listed, but you have, instead, screwed it into a motor that has only 9.0:1 static compression ratio. Is that correct? And you're wondering why the cranking compression is low?

If you install a camshaft that is compatible with the static compression ratio, you can expect the cranking compression to be in the 150 range. If you install a camshaft that is incompatible, as you have done, then you can expect 100 cranking compression.

I figured your Dynamic Compression Ratio at 7.4:1 and I'd be surprised if you can get out of your own way on the track.

Duke was posting while I was typing, but both of us think alike.

 

Yes my question is does the compression sound too low?

So what you guys are saying is that I should probably be seeing low compression numbers because of the cam being to big for the motor? I was afraid I had hurt the motor running it while the timing was retarding and the engine was popping and shooting flames out the exhaust maybe rings or something because the motor does have a fair amount of blow by but it has always had some. I am no engine builder these are the specs I was given on the engine and the engine was supposedly built by a reputable race shop. And the motor when it was running right It was one of the fastest cars at the track.

 

Yes my question is does the compression sound too low?

If the specs on the engine that you quoted in your original post are correct, you have a fundamental problem, a mismatch with your SCR and your camshaft selection.
Read my first post, did you check the link?



Duke

 

how long since it was built?

 

It has maybe 10 races on it. At an average of 30 laps a race on a 1/2 mile track.

 

If the performance has dropped then the engine is hurt.read my first post

 

With my setup could the cam timing bleed off compression test?

I need a good quality leak down tester the one I have is one of those low pressure ones I think it only uses 15 psi. Although with that I do notice the air coming from the valve cover breathers.

 

most race car crews use a leak down tester both on new engines and after every race.If competition is not that toug then just freshen the engine when the driver whines about not enough power.

 

What RPM are you turning? You can likely drop 10-20 degrees off that can and pick up speed depending on the rpm you're turning.

Buzzing an engine high with crappy heads does require more duration but you're likely way over that.

 

A common cheap cam for a circle track engine like yours is the prc 108 cam, still a little big but getting better. The 108 cam is good for a max rpm of 6500 or so, lower redline would mean lower duration.

 

I'm running 6500 rpm. When the car was running with the retarded timing the car seemed to blubber or really hesitate in the high rpms. I would assume because it wasn't burning properly in the cylinders and the combustion was happening as the piston was on the down stroke.

 

Running the timing way retarded will cause the engine to run HOT. have you done a leak down test yet?Not looking for you to make more power before you establish the engines health

 

The thing that baffles me is I have even compression across within 5lbs of each other.

 

widgeon smacker,are you even reading my posts?

 

Yes I am reading your posts.

I have checked leak down with a crappy leak down tester that only uses like 15lbs. I need to borrow a better one. The car did have some blow by through the valve cover breathers and the guage read 40%. Once again I think it was a harbor freight leak down gauge. Could the cheap gauge with low pressure contribute to a high percentage

 

It's always a crap shoot when you buy a used engine unless you know the seller real well. You might not even end up with the engine you think your buying. The first things you need to due are get a know good leak down compression tester or see what pressure yours runs. If it puts out at least 80 psi it will work. The next thing is to pull the timing cover and see if you can confirm what cam is in it. If you can't figure out what cam is in it by the numbers on the end of the cam you're going to need a degree wheel and a dial indicator set up to find out what cam you have.
Unless dictated by rules I don't see how you can run competively with flat top pistons and 76 cc heads. If you are require flat top pistons you need to run the smaller chamber heads. If you're required both flat tops and 76 cc heads you need a camshaft designed just for limited compression.

 

Remove the guage and put 60# direct into cylinders,and listen,make an educated guess by what you hear

 

Ok I did another leak down test I think my gauge is messed up. I warmed the car up to 180 degrees and did the test. When I connect air ti my gauge I set the right gauge by turning the regulator until it says set which is about 15lbs on the left gauge. When I click the regulator back so it can't be turned the set gauge slowly will climb up. So I hooked it to my cylinder at tdc and it showed a leak down of 35% with a noticeable are leak from the valve covers. I realize an engine won't seal completely.

I think my % leakdown gauge (right guage) is screwed up. So I then decided to try it by using the reading only on the left psi gauge. I set the gauge to 100psi with 120 psi constant pressure to the inlet and hooked it up the psi dropped to 90 psi so I am assuming that means 10% leak down correct????

Any in site on doing the leak down this way? I'm looking for another leak down gauge to test with

 

you are guessing 10% blow by?
it takes an hour to remove most race engines or less? gaskets cost?
do you have measuring tools?The engine has a problem,it should already be apart and waiting for repair pieces,,,,
measure your cam
check deck height
fix all problems
race next week end

If you can buy parts tonight,,,
buy everything,take it apart,
replace whats needed,assemble by midnight
install and run by 3AM
race!!!
return un used parts Monday

 

If you can buy parts tonight,,,
buy everything,take it apart,
replace whats needed,assemble by midnight
install and run by 3AM
race!!!
return un used parts Monday

My youngest son and I ran on that schedule for a few years.....:thumbup:

 

Exactly what I'm doing this week.

 

Don't expect any higher cranking pressure unless you address the camshaft/static compression relationship.



Duke