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Intake Runner Volume VS: CID, VS: RPM

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Intake Runner Volume VS: CID, VS: RPM

Postby W8Dart421 » Sun Sep 07, 2003 7:12 pm

Hey Don, I'm back for more info LOL.

Alright I want to know if there is any kind of mathematical formula for determining optium intake runner size in terms of both VOLUME and CROSS SECTIONAL area with a given CID and RPM window.

Let's look at two different engine Combo's:

First a 422" Small Block Chrysler with a 4.10" bore, 4.0" Stroke, 6.300" Rod. Max RPM will be 7200-7400


The Other Motor would be a 342" Small Block Chrysler, 3.94" bore, 3.51" Stroke, 6.125" Rod. Max RPM 7800

And let's assume both are going to be 13:1 on Gasoline, and both will have very similar Solid Roller cams, ~274 @ .050" .675" lift on a 108 LSA.

Now, Am I wrong here in thinking that the 422" motor will NEED a lot more runner volume and possibly a little more cross section to work effectively compared to the smaller motor? ie. The 342" motor actually exists, I have seen it with a set of 215 CC intake runner, 2.95" Cross Section W5 heads.....It REALLY works well. Made ~625 HP on the Dyno.

Now IMO bolting those same heads on the 422" short block, will not gain me as much as possible, because I'm thinking they may be too small.

I've been looking at what Chapman Racing Heads has been putting on some of the older Mopar Sprint car motors. at 410", 8000 RPM on ALKY they are using a 269 CC intake runner in a W7 head and making ~795 HP. On the same flowbench, those 269 Runner CNC'd 2.18" heads really are'nt blowing away the 2.08" 215 CC runner W5 in terms of airflow. They are ~15 cfm better at .500" and ~18-20 better at peak of .700". Not a huge gain considering the 54 CC larger runner, larger valve and taller short turn. But I know there is more to making power than damn flow #'s. That's why I want to know if that Large Runner CC was done on purpose.

I'm thinking for the 422" motor I will raise the runner and widen it. Epoxy the floor, increase the Cross Section to ~3.0" and Runner volume to ~ 245 CC's.

Thoughts?
W8Dart421
 

CROSS SECTION?

Postby speedtalk » Sat Sep 13, 2003 9:43 am

When you speak CROSS SECTION, where are you measuring it at?
Thanks, Don
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Postby W8Dart421 » Mon Sep 15, 2003 11:38 am

Measured at the runner entrance, but most of these heads, like the W5 and W7 have relatively flat floors, and maintain their cross sec throughout the port......I'm more concerned with Runner VOLUME than the minimum Cross sec.
W8Dart421
 

Runner Volume

Postby speedtalk » Mon Sep 15, 2003 3:11 pm

I'll be honest, the only time I check runner volume is when the rules force me to (Stock, Super Stock). I focus on the cross sections. As for a formula, I don't know of one - wish i did. As for the two engines you noted, the 422" may only need a slightly large runner given it's running 400-600 less rpm. The combinations you gave look like what would happen if you had the same head on both. Turn the 422" 7800 and yes, it's going to need a lot more.
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Postby W8Dart421 » Tue Sep 16, 2003 10:07 am

OK good info..... I just laid out the head in layout dye.......looks I'll do a 2.18" Tall 1.40" Wide port that is 1.10" off the deck. I should be able to increase airflow 20-30 cfm in the .500" and up lifts and only increase runner volume by ~15cc's The Cross section will increase from 2.95" to 3.05" not taking the corners into account in the equation...... I think the 422" motor will benefit........
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Runner volume

Postby DynoDon » Sun Oct 05, 2003 2:05 pm

Only trial will really tell. If the runners are bigger than what the smaller engine needs, then there's the odd chance that the larger engine would run quite well with the intake off the smaller engine, no?
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Re: Runner volume

Postby W8Dart421 » Sun Oct 05, 2003 2:36 pm

DynoDon wrote:Only trial will really tell. If the runners are bigger than what the smaller engine needs, then there's the odd chance that the larger engine would run quite well with the intake off the smaller engine, no?


That's just the point. the W5 mopar head was never designed for a 422" motor. Back when the heads was designed, crankshafts to easily build a 400+ inch Chryler SB did not exist. The W5 was designed for 355-358" Dirt track engines...... And from the past 10 yeas of use, the W5 has proven to be a VERY effective head for 340-375 CID Drag engines. I just worry about the larger engines, since the recent release of an affordable 4" stroke crank.

Anyhow, what I ended up doing was the layout mentioned above. I increased MINIMUM cross section from 2.06" to 2.34" Flow increased from 294 @ .500" to 313 @ .500" Peak is now up to 346 @ .700" with the same 2.08 valve. Runner volume ended up being smaller than I expectd. It's now 223 cc Vs 218 in true W5 form.
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Postby maxracesoftware » Tue Feb 17, 2004 2:02 pm

I'll be honest, the only time I check runner volume is when the rules force me to (Stock, Super Stock). I focus on the cross sections
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port volume is the "By-product" of the "Correct" cross-sectional area
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