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440 500 build

IMHO combination is the key. Actual CR is based on measured dimensions, not printed guestimates. Some builders know what they are doing, some not so much so. 10.5 with an aluminum head, fairly small cam is safe w 92. A little more CR gets into the danger zone, unless the cam has fairly big overlap. My opinion.
 
Let's try again. What exactly does the "big overlap" do?
 
In my opinion a "big overlap" decreases cylinder pressure for a portion of the stroke. As a professional, you may have more knowledge than I do.
 
Two more questions then.

(1) How does overlap decrease cylinder pressure.

(2) Why do they use intake valve closing points and not camshaft overlap duration to calculate dynamic compression and cylinder pressure.

Let us also dispel any notion of me being a professional. I'm just a backyard hack that was lucky enough to have a Dad that built a few engines in his garage for NASCAR, and that later I could afford to buy a used dyno so I could waste tens of thousands of dollars experimenting.

I'm having more fun on https://sparmountainsos.com/ than I ever did building engines.
 
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eric383 said:
See if this helps.....
http://www.crankshaftcoalition.com/wiki/Cam_and_compression_ratio_compatibility
Click to expand...

No. That does not help explain how overlap allows more CR.

To the OP - Lots of good info here. You do need to discuss with the engine builder what he sees as the build plan, and ask him to explain it to you - face to face. Was your initial encounter a sit down with him discussing the engine in detail, or a phone call kicking around ideas about a hypothetical motor?

Personally, I do like the TF 240 and 17cc piston. But as others have stated, above 10.5:1 and at your elevation, you are getting close to the edge. Cam timing will matter, and 92-93 octane will be required, more than likely. The details will matter. If you go with 10:1, you might leave a little on the table, but will likely be safe no matter what your other choices are.
 
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Stubby said:
Hey everyone I am looking for some info on a 500 stroker engine build. I called 440 source and asked them about a street motor set up for pump gas. They said to go with 27 dish pistons with stealth heads for a cr of 9.6 to 1. My engine builder is telling me to stick with flat top pistons and 78 cc 240 trick flows. 440 sources website says that set up will get 11.5 to 1. Im stuck on witch way to go. I have worked with my builder for years. He is a mopar drag racer for 40 plus years and has ran strokers for years. Any info would be great. Im going to call 440 source tomorrow and pick their brain..
Click to expand...
Stubby, first get a copy of andy f.s book, max performance mopar big blocks, then chuck senatores big block mopar performance, sift thru all the info contained therein and build your engine the way you want it, once you decide what you want, DO NOT deviate from plan, no matter what your engine man says. check the big block recipes in andy f.s book. talk to 440 source, talk to dave hughes @ hughes engines. glean all the info and do it your way!!! (andys book was a super help). I made a few with my build but overall I am happy, the car scares the **** outta me, which means its just right!!!! Dave.
 
IQ52 said:
Two more questions then.

(1) How does overlap decrease cylinder pressure.

(2) Why do they use intake valve closing points and not camshaft overlap duration to calculate dynamic compression and cylinder pressure.

Let us also dispel any notion of me being a professional. I'm just a backyard hack that was lucky enough to have a Dad that built a few engines in his garage for NASCAR, and that later I could afford to buy a used dyno so I could waste tens of thousands of dollars experimenting.

I'm having more fun on https://sparmountainsos.com/ than I ever did building engines.
Click to expand...
Glad you're having fun, involves your son, antlers, the outdoors, creativity...great combo.
As far as your skills in engine building, you have no equal, IMHO. I honestly can't even think of anyone close for Mopar engines, but trusting the builder is a huge factor in perceived capabilities, although the results of your builds truly speak for themselves.
Can you spell out some of "the answer" to CR, piston top shape (dish, flat) etc.? (If you have time)
The numbers you have achieved with low compression motors is epic.
I wish I knew half of what you do about how to maximize Mopar engine performance.
 
IQ52 said:
Two more questions then.

(1) How does overlap decrease cylinder pressure.

(2) Why do they use intake valve closing points and not camshaft overlap duration to calculate dynamic compression and cylinder pressure.

Let us also dispel any notion of me being a professional. I'm just a backyard hack that was lucky enough to have a Dad that built a few engines in his garage for NASCAR, and that later I could afford to buy a used dyno so I could waste tens of thousands of dollars experimenting.

I'm having more fun on https://sparmountainsos.com/ than I ever did building engines.
Click to expand...

To my way of thinking, overlap is the period in the cycle when both valves are open, bleeding down compression being built by the piston on the compression stroke. Your point about using the intake closing point is certainly valid as a reference point.The point at which the intake valve is closed is when maximum compression is starting to be achieved. It is a good reference point, my overlap comment probably relates to my age, that is what we talked about "back in the day". BTW, I am a backyard hack, that used quality engine builders to get the performance I achieved. You posts indicate a high level of expertise.
 
Unless I'm mistaken, overlap occurs at the end of the exhaust stroke as the piston is going up to expel the exhaust and the beginning of the intake stroke (piston going down) to take in the fresh air charge. No compression of the fuel/air charge there.

The piston is drawing air in on it's way down during the intake stroke and doesn't start to compress anything until it begins to travel up, 180 degrees after the beginning of the piston intake stroke and well after the overlap period. Then it really begins to compress the fuel/air after the intake valve closes as the piston heads back up.

If I do nothing but go for 5 degrees more overlap by just narrowing the lobe separation, say going from 110 to 105. I will actually increase the cranking compression because I advance the intake valve and close it sooner during the compression stroke.

Cams with more overlap don't reduce cranking compression because of the overlap. It's because they generally have longer intake duration and close the intake valve later in the compression stroke.

I could have reduced the whole thing to the previous two sentences. But I'm sick of hearing that overlap "bleeds off compression". Kind of like reading "prolly" instead of probably and "dizzy" instead of distributor.
 
Thanks for enshrining that in the digital archives Jim.
I had to stop myself from rereading the various Amsoil/HRM articles so I wouldn't be late to work this morning.
 
IQ52 said:
Unless I'm mistaken, overlap occurs at the end of the exhaust stroke as the piston is going up to expel the exhaust and the beginning of the intake stroke (piston going down) to take in the fresh air charge. No compression of the fuel/air charge there.

The piston is drawing air in on it's way down during the intake stroke and doesn't start to compress anything until it begins to travel up, 180 degrees after the beginning of the piston intake stroke and well after the overlap period. Then it really begins to compress the fuel/air after the intake valve closes as the piston heads back up.

If I do nothing but go for 5 degrees more overlap by just narrowing the lobe separation, say going from 110 to 105. I will actually increase the cranking compression because I advance the intake valve and close it sooner during the compression stroke.

Cams with more overlap don't reduce cranking compression because of the overlap. It's because they generally have longer intake duration and close the intake valve later in the compression stroke.

I could have reduced the whole thing to the previous two sentences. But I'm sick of hearing that overlap "bleeds off compression". Kind of like reading "prolly" instead of probably and "dizzy" instead of distributor.
Click to expand...

IQ, I stand corrected, overlap is at the end of exhaust stroke. Your point of lobe separation seems straight on point. Intake closure point is the mechanical factor. Overlap is very "old school".
 
Usually a cam with lots of overlap will have a ruff idle.
I’d prolly just dial in a little more initial timing by turning the dizzy to smooth it out a bit .
 
PRHeads said:
Usually a cam with lots of overlap will have a ruff idle.
I’d prolly just dial in a little more initial timing by turning the dizzy to smooth it out a bit .
Click to expand...
Ha ha ha, now that’s funny!
 
Me, the rookie, thinks that overlap is to allow scavenging of the exhaust pulse to assist in pulling the intake charge in, right?
 
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