VetteRacer282

Anyone have anything that can explain air flow to me?
The ammount needed per engine size.
As far as head flow to engine size (and relations of lift)... Intake manifold flow to Head flow... Runner flow to manifold flow... And throttle body to the whole thing.

I am trying to get an idea of whats going on here... The specs I can find, the manifolds dont flow what the heads can, the runners dont flow what the intake can, and the throttle body is just there it seems..
Anyone?

Matt

LD85

Hope this helps http://temp.corvetteforum.net/c4/ld85//airflow.pdf
http://www.grapeaperacing.com/GrapeA...ntaketerms.cfm
http://iroc.fbody.com/intake.html

69stingray

Here are some more web site on airflow for your reading enjoyment:

http://www.centriprecleaner.com/cfm.htm
http://www.streetandstripmotorsports...harts_carb.htm
http://www.fordmuscle.com/archives/2...s/index2.shtml

Also, here are three sites (one of them is mine that I haven't finished yet) on the airflow of various cylinder heads:

http://www.chevyhiperformance.com/te...598/index.html
http://users.erols.com/srweiss/tablehdc.htm#Chevy
http://temp.corvetteforum.net/c3/69stingray/head.html

I am looking for one more piece of info for you........

69stingray

VetteRacer282, first, I suggest picking a copy of John Lingenfelter on Modifying Small-Block Chevy Engines, excellent book. Easy to read and understand.

Lets start with cylinder heads. Most cylinder head mfg. post their flow numbers. You need to ensure they are all measured the same. Usually everyone measures at 28 inches of water test pressure. You can check out mfg. websites in addition to the websites I posted earlier.

Typically, the more cfm an cylinder flows, the more power it will make. BUT, it you are looking for an street engine where low speed torque is more important, the velocity of the air through the intake port is more important. Higher port velocity allows the cylinder to be filled better at lower engine RPM. This is usually accomplished with smaller intake port sizes, 160-180 cc. If you are looking for higher RPM power, then you want the cylinder to be able to breath when your engine RPM gets high, the cylinder head shouldn't restrict the engine from breathing, this is usually accomplished by larger intake ports, 200-215 cc.

The same applies to intake manifolds. Smaller port intake manifold allow for higher port velocity (Performer). Larger port manifold have less port velocity but don't restrict the engine at higher rpm (Victor Jr.)

Happy reading! Here are some other posts that talk about cylinder head airflow:


http://<a href="http://forums.corvet...?id=469304</a>
http://forums.corvetteforum.com/zerothread?id=507305

HeaderDesign.com

Cylinder head port flow and size are directly related to horsepower, not displacement. The cross-sectional area of the intake port, especially at the port choke above the valve, must be matched to your horsepower goal. The best head choice is the one with best flow numbers and minimized port dimensions.

Picking the best intake and exhaust ports for an application is something I do with an advanced engine simulation program that can model all the critical dimensions. It is very difficult to just look at head data and guess how good the head will do with the engine combination and design goals. This makes alot of people oversize their heads because they like the flow numbers, not realizing that the next smaller head may very well make more power across the board while reaching their power goals.

Intake runner dimensions are designed to produce correctly timed wave action, not to maximize flow. But you need to know how the head flows with the intake runners installed for an accurate simulation. Keep the losses and directional effects through the throttle body out of this measurement.

The low-lift, mid-lift and high-lift flow numbers are all very important in the intake and exhaust ports. They have great influence on the cam design since they determine what high-lift is, how well the flow bias is matched to the engine, and strongly influence the best open/close events. Cam design is very difficult since it must make use of, or compensate for, all the strengths and weaknesses of the heads, intake, and headers. I design cams all the time and I still can't guess the correct solution at the beginning of the project. The advanced simulation I do uses actual valve lift at every 2 crank degrees, so there isn't much left to guesswork at the end of the design process. The cam designs for older versus newest heads tend to be much different from each other. Also, cam designs for long-runner vs short runner intakes are much different from each other, even though the same heads might be used in each case.

This might help explain something about flow bias http://www.headerdesign.com/extras/engine.asp

VetteRacer282

I have abit of reading to do from all those links, but in scanning, I dont see one thing covered, which is alot of my question. (Header designs link is long and I didnt go through it much, answer might be in there)
Manifold (and even runner) to head relation.
If a head flows say 260cfm at 550 lift, which say is max lift of cam to make things easy. Wouldnt the manifold and runner need to be capable of flowing 260cfm? The specs I can find on the heads and the intake I want dont match up like I would assume they should. The manifold with runners only flows 240cfm (according to specs I can find so far), which to me seems like at .400 lift, on that head, the intake will limit the engine from getting any more air.

I hope I am missing something :confused:
Matt

HeaderDesign.com

If the intake runner is the size and length you need to produce the best torque curve for your application, then 240CFM is all you get. There is usually some loss due to the intake runner. You still need to use a cam lobe that gets the valve open and flowing near 240CFM for considerable duration. You need to look at the CFM vs. valve lift measured with the intake manifold installed to find the lift where the valve flows near maximum.