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Old 05-24-2013, 08:54 AM
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The thing that baffles me is I have even compression across within 5lbs of each other.

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Old 05-24-2013, 09:01 AM
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widgeon smacker,are you even reading my posts?
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Old 05-24-2013, 09:02 AM
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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.
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Old 05-24-2013, 09:11 AM
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Originally Posted by vinniekq2 View Post
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
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Old 05-24-2013, 09:14 AM
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Remove the guage and put 60# direct into cylinders,and listen,make an educated guess by what you hear
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Old 05-24-2013, 09:37 AM
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Quote:
Originally Posted by Duckhnter83 View Post
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
Deadhead your leak down tester and see what you get. If it shows that it's holding anything near 100% you have answered the main question. Even at 15 psi you have a big problem. I'm not sure if you mean it's holding 40% or leaking 40% either way. the motor is done.
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Old 05-24-2013, 10:15 AM
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Quote:
Originally Posted by Duckhnter83 View Post
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
This test sounds valid. Leakdown testing doesn't use much pressure 10-15 pounds is right. 40% is the bottom value of acceptable. I consider anything higher than 20% to be refresh time.

Running retarded is hard on the valves because the fire of the chemical reaction is still going on and the maximum cylinder pressure point for maximum effort on the piston has been missed all of which means the gases in the cylinder are extremely hot because the burn isn't finished and the energy (temperature) of the burn hasn't been reduced by doing work against the piston. At least the blue falmes out the exhaust are telling you the mixture ratio is correct.

Cylinders with common pressures next to each other can be an indicator of a blown head gasket. But I'd expect that more with 2 and 4 or 3 and 5 rather than 5 and 7. But you never know till you look. The difference between the the 100 pound and the 95 pound cylinders while low overall the difference is close enough not to be a concern.

Overall the compression is quite low but that's not considering whether or not this is a rules limited engine. Different associations and tracks have some of what I consider to be strange rules when it comes to cams and compression. You'd need to discuss the rules this engine is built under for me to be specific. I will say this in assumption you're not rules restricted on compression and that is something that's already been mentioned which is the Dynamic Compression Ratio (DCR), you shouldn't let that fall under 8 to 1, more would be better but there are physical limits that the shape of the combustion chamber and the material of the head dictate. For example fast burn chambers like those of the L31 Vortec head will accept a higher ratio, aluminum will accept a high ratio where Vortec type chambers and an aluminum head come together the DCR can be pushed to 9 with a light vehicle and stiff gears. Within the confines of the head and cam, which may be rules limited, try to keep the compression up or the cam milder in order to meet a minimum of 8 to1? Dynamic Compression Ratio is an adjustment made to the Static Compression Ratio (SCR) for the apparent loss of stroke that occurs by keeping the intake valve open while the crankshaft is pushing the piston upward on the compression stroke. The cutoff point is where in crankshaft degrees the intake seats. Keith Black has a good calculator <<< United Engine & Machine Co. Incorporated >>>, however, it makes an assumption about valve closing from .050 inch measured timing that is valid for a fast ramp cam like the Voodoo or the Xtreme Energy but is not enough for longer ramp cams that predominate dirt track, and other places, so I recommend that you add 5 more degrees to the KB .050 timing adjustment for your cam.

I'm guessing about your track but if it's a short track you really need to bump up the compression to get the torque to pull the car off the turns and get it up to speed quickly for short straights, I'd say you need to be looking at cranking pressures in the range of 180 to 200 psi certainly not 100 psi.

Bogie

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Old 05-25-2013, 11:31 AM
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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
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Old 05-25-2013, 08:10 PM
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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
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Old 05-25-2013, 10:43 PM
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Quote:
Originally Posted by vinniekq2 View Post
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.....
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Old 05-27-2013, 03:38 PM
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Quote:
Originally Posted by vinniekq2 View Post
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

awesome attitude, just what I have done , comp test low on 5 and 6 and oil on plugs . 4 hrs . shes out , being rebuilt this week . engine dyno weekend after next , then back in.

duckhnter83. get this engine on a bench , 2 or 3 evenings ( in-between work if have to ) gaskets are cheap . engine parts and machining aren't . confidence is everything when flooring it
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Old 05-27-2013, 04:39 PM
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Exactly what I'm doing this week.
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  #28 (permalink)  
Old 05-27-2013, 05:35 PM
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Quote:
Originally Posted by Duckhnter83 View Post
Exactly what I'm doing this week.
Don't expect any higher cranking pressure unless you address the camshaft/static compression relationship.



Duke
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