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Old 11-09-2002, 05:33 PM   #3
jim_howard_pdx
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Join Date: Apr 2002
Location: Portland Oregon
Posts: 247
Cool

They have s h i t for brains.......

Sorry, but many speed shops do not know what intake dilution is, how to minimize it, or how to build power around it. Most do not know what exhaust ringing means. Most can not explain why an X pipe flows more than an H pipe.

So you have some nicely ported heads. So I should NOT run a split duration camshaft??????

I plan to run my car only to 6,000 rpm and I should NOT run a split duration camshaft?

My engine has 8 primary header tubes bending and snaking into collectors dumping into exhaust tubes that are bent, possibly modified for H or X flow, welded to real CATS or Mufflers or BOTH, and then have tube exiting the car and I should NOT run a split duration camshaft?

You have 8 cylinders feeding high pressure exhaust into a tuned exhaust system that is overcome with backpressure as rpm increases, and you should not run a split duration camshaft?

They have s h i t for brains. And that is all I have to say about that. Decide if you are at the right shop.

Thanks for the message. I really needed to vent, my wife is giving me a pain in my a s s.

Better yet, go to your town's best dyno shop. They will have kept every dyno run on every engine they ever worked on IF THEY ARE WORTH A D A M N. Then give them your engine specs and have them show you the horsepower and torque curve of an engine similar to yours with small primary tube full length headers, then with large primary tube full length headers.

The split cam will provide the horsepower of the large primary tube header, but with the broader and more useable torque curve of the small primary tube header. This is my most simplified explanation of what reducing intake dilution reads like when you test ANY engine on a dyno.....

The split duration just holds off the intake dilution volume and ratio to a higher rpm point which will improve the ets on your car. If you don't believe me, and you don't believe them, then buy both and run each for one month. Then keep the one that produces the best times with the best overall usable torque curve for the driving you do. I am betting that cam will be a split duration cam EVERY TIME.

You just cannot take a flow bench result, and say this is what the engine flows at high rpm with an engine running.

Even a wet flow bench, where they use water and a carb to simulate gasoline CANNOT show you dilution effect because there is still NO BACKPRESSURE, NO EXHAUST RINGING, and No PREIGNITION or FLAME PROPOGATION that might be ruined by the contamination caused by the dilution.

Do you see where I am coming from? YOU TEST AN ENGINE AT A TRACK not on the dyno. The dyno helps you get to the best combinations so the track testing gives you meaningful ways to improve your combination.

Hope this helps explain some of your questions.

By the way I LOVE Crane hi lift, low duration, with split duration camshafts. Other than the racing cam profiles I use from Comp Cams, Crane does the best on the street cam profiles. I will probably catch some grief on this, but if you pick a well engineered brand like crane or comp cams, and test their series of cam steps on a given combo it makes development time much faster than trying 8 brands of cam. So YES there are a lot of really great cams out there. I have just picked the poison that tastes best in my opinion.

And by the way, I have not run a standard grind camshaft since split duration camshafts were first made available on a custom grind basis.

And finally, When you are running 9,000 to 15,000 rpm engines, this is where split duration cams show the least effect. This is because even the spit duration cannot overcome the exhaust pressure and ringing. So dillution must be overcome with more and more intake event. That means more and more overlap. You cannot increase overlap without increasing dilution.

Hope you see the light now. Your shop has things back a s s ward.
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