Ok I know this could open can of worms.

Using desktop dyno,which you may or may not believe is fairly good tool.

Every cam I run thru it shows that running more intake duration than exhaust makes best power.Usually some where around 8* less exhaust.Where as most BBC engine show that little more exhaust makes best power.
This is on my Hemi engine with BAE fuel heads, I know not norm around here and maybe out of realm of working knowledge. I figure some will have thoughts that may be helpful. For what its worth Chad Speirs Had similar results using his calculations a while back.

Opinion as to why?

I have my own thoughts,but figure other opinions are worth listening to.

Maybe helpful:Intake flow .100 85
.200 152
.300 214
.400 293
.500 364
.600 440
.700 494
.800 518
.900 526
exhaust flow.100 73
.200 138
.300 203
.400 270
.500 335
.600 387
.700 390
.800 398
.900 401

is there a free desktop dyno to play around with?

don't know of any free. The basic is about 60 bucks at jegs. IMO its well worth it. I have taken info from actual dyno runs and if head flows are correct,cam numbers,induction flows and exhaust it will normally be less than 2% difference. Not be techno geek I was freaking amazed at how close program could be considering all of the things that can make difference in a engine.

Here's part of what Darin Morgan had to say, for what it's worth:

"Recently a racer questioned me about all of the components in one of our Super Series bracket racing engines. I gave him the information he requested, and he modeled the engine with a simulation program. His results were fairly accurate, with an error of about 2.5 percent (20 horsepower), which I thought was reasonable. But the software stated that if the exhaust duration were increased 10 degrees, the engine would gain 25 additional horsepower. I just wish it were that easy!

We’ve built and dyno tested dozens of these engines. They’ve logged thousands of runs on drag strips. Now a customer tells us that we left 25 horsepower on the table. But what the simulation software didn’t allow him to do was input the discharge coefficient of the exhaust port. In other words, the program didn’t “know” the design specifics of the exhaust system. It based its calculations on simple airflow, and therefore didn’t have enough information to generate a realistic answer."

Maybe I stated question wrong. I am not questioning software so much,mainly because cpl other have got same answer using different means to get there.

My question is why does Hemi with heads I have seem to want less exhaust,while almost all BBC calculations seem to show little more exhaust is better?

My thinking is the intake port to exhaust port flow number ratio with Hemi is closer. Like I said I just looking for opinion,but hey if have proven answer.Lets have it.

quote:

My thinking is the intake port to exhaust port flow number ratio with Hemi is closer.

I would say that's a valid assumption. Also, which BBC intake port configuration is being used, siamesed or spread port? That could have an impact.

quote:

Originally posted by wideopen231:
don't know of any free. The basic is about 60 bucks at jegs. IMO its well worth it. I have taken info from actual dyno runs and if head flows are correct,cam numbers,induction flows and exhaust it will normally be less than 2% difference. Not be techno geek I was freaking amazed at how close program could be considering all of the things that can make difference in a engine.

Thanks! sounds like something fun to play around with

i used to play on one of those things and found that if i just kept adding lift more and more power just kept going up.i think cams though have to stay in certain ranges of lift and duration in relation to each other to keep the valve train in harmony.

yea but stands to reason if you are putting in bigger opening to feed more air program will see more air to chamber and calculate more power.

Cam and valve train in general do have limits for many reasons. Just like you can not actually open intake and/or exhaust at any point you want because of piston or other valve being in the way,especially true on Hemi with valves crossing paths. I found this out on Harley when not letting lifter settle after adjustment.A cheap $250 lesson.

The cam numbers I use are existing cams with a tweak one way or other of open and close points.Maybe 5 to 6 degree +/-.
I did miss making statement that if you enter correct info.

quote:

Originally posted by Canted Valve:

quote:

My thinking is the intake port to exhaust port flow number ratio with Hemi is closer.

I would say that's a valid assumption. Also, which BBC intake port configuration is being used, siamesed or spread port? That could have an impact.

Don't think I ever tried spread port numbers. Mostly get BBC numbers from Stan Wiess site. Even then have to pick out what closest to head used and hope numbers are close.

http://www.virtualengine2000.com/

I've been using this one for years.

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