I know how there's a lot of formulas to figure out things with an engine.

Is there any way or any formula that can tell you how much cfm (air flow) each cylinder needs to flow to its max potential?

Like say someone used an ITB intake and each runner supplied 293cfm to each cylinder (2,344 cfm total being delivered to the heads), how would you know if thats sufficient, and you're not leaving any HP on the table.

Someone once said there's no such thing as a dumb question, so.........

Thanks,

 

Self-bump.

Well tell me this than.

Lets say a given head flows 400 cfm at .650. Shouldn't the runner, from whatever intake you use, be able to flow 400 cfm of air flow into each individual head port?

 

Its more complicated than that bro because you have to factor in helmholz resonance effect and the way it creates one type of venturi effect try this out its not the best at expaining what occurs in an intake but it will help explain those to LAWs its all fluid mechanics gets a lil techinical but its how +100% VE happens
heres the link http://en.wikipedia.org/wiki/Manifol...ve_engineering)
read the intake manifold part basically u dont need runners that flow as well or better than your heads

 

Thanks, that explains things pretty good.

 

Say WHAT?

LS6427, be careful of what you choose to believe.

I'm being nice.

 

remember to subtract the axle area from the itb bore area when comparing cross sections to your cylinder head. We have a lot of Honda N/A racers running itb's that were too small and they were knocking down the heads...they called Kinsler to get properly sized ones and WHAMMO...11% horsepower gains. You can never have to much cfm as long as you're willing to use increased displacement/rpm to soak it up...power is the result.

 

old ss i didnt say that was the best explanation just a "simple" one most people never took any fluid dynamic or mechanics classes i thought it would give a lil bit of basic background or explanation if youd like to explain the thoery behind Intake Manifold tuning be my guess i was just trying to help sincest I dont think there is any EQUATION to to help.

 

No offense intended, but you are almost impossible to read. Complete sentences and some punctuation would help a heck of a lot. it'salmostlike tryingtoreadthisextralongwordandmakesomesenseofit.

I reread and reread your original post and I still can't make much sense of it. I guess it's my problem. I'm getting old.

And I thought Prof. Blair was a challenging read!


Jon

 

I didn;t say my prayers were answered, it was just a good basic read about intakes.

 

well, "briannutter", I just got in contact with a guy who built a 454ci LSX and used the Harrop Hurricane with the 58mm ITB's. I have a video of it and it idles and revs smooth *** silk. He says its very nice to drive and it was easy to tune, he did the tuning by himself. I'm waiting to hear what kind of numbers it put down and some other things I asked.

My question is: Is there a way to figure out through any type of formula what the PERFECT size ITB would be for a given head and cubic inch combo?

Can an example engine combo be given and the correct size ITB's figured out from there?

 

My question is: Is there a way to figure out through any type of formula what the PERFECT size ITB would be for a given head and cubic inch combo?

Can an example engine combo be given and the correct size ITB's figured out from there?[/QUOTE]

There's a couple things to do to know if you're too small or not. If you're buddy is curious about the flow ability of the Harrop versus what his engine wants, have him run the engine at wot at Max rpm and check for vacuum between the head and the throttle blade (map sensor numbers work too)...If you see some vacuum that's not good. The problem is too small itb's can CAUSE the engine to run at less rpm than it wants too. With carbs, it can be argued that a bit of vacuum is good for booster signal, but I don't see that with injection. Measure the axle diameter of the 58mm Harrops and I'll send a pm with "theoretical" flow. If it looks like they are a restriction, I'd suggest he flows the heads with the intake attached to verify whether they are being knocked down or not.

for the first timer, Taper numbers are hard to come by. Length numbers are easy....but often only a starting point. The most important thing to itb's and tb's is the cross section of the barrel (with an increase in o.d. to offset the decrease of the axle area). A rule is to make it larger than the smallest cross-section of the intake runner. The tight point of the runner is usually the limitation of the port flow (not accounting for lost "virtual venturi" restrictions caused by incorrect short turns and laminar flow problems resulting). If this is done, and the taper/length takes advantage of wave tuning, you're off to a good start. Flow versus venturi diameter numbers aren't easily found on the internet, but the top head porters know them. What is also of interest is Where they put the restriction in the runner...lately it has been down in the venturi area below the valve.

I'm not a professional head porter or intake manifold designer, so the guys at Kinsler would probably be the best at answering the issue...their experience is far beyond anyone here....I'll take experience over theory any day. Choosing theory over experience is what costs racers from making horsepower gains.

 

For some odd reason, I can read stuff like that just fine! Thanks to the internet, I guess!

 

LOL. I just noticed that I couldn't even type it without inserting a space.

 

Sweet, thanks for the info. My conclusion, more research is needed.

Its gonna be the Harrop or a dual TB sheet metal.

 

man old ss all you ever seem to do in theses threads in add useless info and knock people down. Instead of always being a wisea$$ why don't you help out or get out of the thread.

As far as the topic I agree with "brainnutter" experience over theory is the best way to go.

 

I think what you are looking for is the MAX amount of air a particular cylinder can pull in right? If so:

((Max Engine Speed X Max Volumetric Efficiency X Total Engine Displacement)/(3456))/(Number of Cylinders)

Engine speed in RPMs, VE in decimal form, displacement in cubic inches. 3456 is really 1728 X 2. 1728 converts cubic inches to cubic feet (12^3.) The 2 accounts for the fact that the engine pulls in a complete engine displacement every 2 rotations, not every 1 like a 2 stroke.

The final answer is in CFM. If you want to get really technical you can find mass flow from temperature based on pv=nrt. Let me know if you want that also. But I don't think that is very useful for sizing a TB, CFM is a more common way of rating them.

A couple notes too- You can use a VE of .85 for the lower end of performance and a VE of 1 if this is a hardcore build. The formula is not actual airflow, only a relatively close approximation.

-Wes

 

1) Please put me on your "ignore list". It will dramatically lower your stress level.

2) Brian is one smart guy. We have talked in the past. My only tiny disagreement with what he said was that "theory" can get you into the right ballpark before you start experimenting and either save you lots of time and money finding the optimum solution, or even getting you out of the box to perhaps find a solution most others have not tried. Sometimes playing in a new "ballpark" is not only fun, but profitable.

Brian is quite correct that much of the information you need is not found on the net, and for good reason. I strongly support his advice to contact the experts.

As far as answering the OP's question, Brian's answer was the only one that I think was very useful. OP was correct that there is no such thing as a dumb question, but the correct answer might be way more complex than you expect. This is a good example of that.

Jon

 

The more I learn, the more I find this to be true. And similarly to you the more difficult I find it to answer, what the person asking considers, a very simple question.

I also agree that experience holds much value, but the theory will tell you why.

I find it much more useful to figure something out on my own by thinking it through. I'm sure with a small nudge in the right direction, there are people lurking here that would be willing to do the real legwork, and therefore relieve the burden of total explanation from those who have the answers.

Plus we know you love to ask questions and assign homework.

 

See post 16?