The Road to Drag Week 2014 - June 2

[cobracammer]

There is actually a guy now re-popping the alternator brackets for 427 SOHC motors out of Georgia.  I picked one up last week.  He is selling on eBay, but I don't believe anywhere else.  Its a pretty solid quality piece.

[TomP]

I like plenum volume small. I think it makes for better throttle response. A dual plane intake works without a shoebox sized plenum so will single planes.

[machoneman]

More on plenum volume, this time from Darin Morgan back in '05, currently Ford's Pro Stock engine designer:

Re: Plenum Volume

Postby Darin Morgan » Sat Mar 05, 2005 11:37 am

BRENT FAY wrote:
Plenum volume- what would be a good starting point as to know if you have enough? Measure volume of intake tract and divide the plenum by 4 (single 4 single plane intake or even tunnel ram) to end up with at least the volume of one cyl. or more if VE is say 110%? Or would you want a certain distance to the center opening of intake tract to throttle plates to keep fuel hitting plenum floor? Or you just keep adding carb spacers until carb loses it signal strength. Has anyone put a window in the side of plenum or int. tract near the opening to observe the A/F flow (Bill Jones?) on a running engine. On the intakes Jean Dittmer did for me he said to add a 1/2 in. spacer to make up for volume after reworking plenum floor. Or should one take a bunch spacers to track and do A B A B B C B C test. I dont have a dyno.... Just wondering, Brent

Plenum volume is interrelated to so many other variables such as, Engine size and rpm. Engines indented use such as Drag Racing, oval track, truck tractor pulling, boat racing, off shore boat racing and does it have an automatic transmission or five speed. These are all questions that need to be asked before deciding on how large the carbs and plenum should be. Its also the questions I ask when designing the manifold itself. If your asking for a magic number or formulas for any given engine, it does not exist. Its one of the last tuning factors we explore on the dyno. Its also very easy to get the plenum to large when chasing power numbers on the dyno! You can get a plenum way to big if you just look at power numbers on the dyno. Then, when you take it to the track the engine wont recover on the shifts and wont accelerate very well. An AED competition eliminator engine is good example. They have a sheet metal single four barrel manifold. On the dyno you can just keep stacking vertical spacers under the carb and the engine will continue to make more power. I have seen 7 one inch spacers make a lot of power on the dyno but the engine would lay on the converter and not recover. The farther you get the carbs from the runners, the more the signal suffers. There is a magic spot on every manifold as far as carb height goes. The track has the final word on that.
Darin Morgan
-Induction Research and Development
-EFI Calibration and Tuning
Reher Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
Phone 817-467-7171
Cell 682-559-0321
http://www.rehermorrison.com
Darin Morgan Show Guest
Show Guest Posts: 1088Joined: Tue Nov 02, 2004 10:56 amLocation: Arlington Texas


 

[jayb]

That's interesting information, Bob, but it relates to carbs, not EFI.  I think an EFI sheet metal intake like mine is a whole different animal, since you don't have to worry about a vacuum signal to the carbs to ensure proper fuel delivery.

[machoneman]

Quite true!

I thought Darin's statement though that "no magic formula exists" was on the mark. Experimentation (and having the time, $$$ and discipline to do so) is seemingly the key. 

[cdmbill2]

When the Wilson guys did my manifold, we talked about volume and their CNC program for the cast Trick Flow tunnel ram was created with my heads and and the flow numbers we had from the devlopment process. As is it's about 112% of CID. We had to guess a bit at operating RPM as that version had never been together before. The big deal according to them was the runner inlet shape which in turn was dictated by the casting thickness.

I like the 'hump' idea for adding volume. Good luck this weekend!

[My427stang]

That's interesting information, Bob, but it relates to carbs, not EFI.  I think an EFI sheet metal intake like mine is a whole different animal, since you don't have to worry about a vacuum signal to the carbs to ensure proper fuel delivery.

EFI and carbs certainly display the effects differently, but port length, plenum size, and intake design certainly makes a difference.  A couple examples are Dodge small blocks in the 90s and SBFs, they had long runners if varying design to keep torque and velocity up in all throttle positions.

Look at the Ford manifolds, they certainly could come up with a cheaper design for mass production than this. 



However, those long runners with a big plenum allowed a stable fast cylinder fill.  Less runner, more plenum, drive the peaks up just like a carbed car, longer runner, less plenum, response goes up.

I agree through, less worry about carb signal but the air is still doing the same thing, especially important on road course cars.  Also, no doubt packaging is important, so if yours flows the number it needs and has a decent plenum (which it does) and fits the car, runner length is less critical for a drag car IMHO

[cdmbill2]

Runner length is critical on a drag race motor, but, 98% of us don't get to play with runner length and shape as well as plenum volume except at the most coarse manifold swap level. That said I know of three, now four EFI Drag Week style engines that have picked up across the board with a tunnel ram. Narrow band, high RPM WOT only makes for a different set of choices.

[cdmbill2]

But, the question today is cam phasing, do you know where yours is?

[jayb]

LOL Bill, after today I know where mine is!  I think...   

[My427stang]

But, the question today is cam phasing, do you know where yours is?

I am just a knuckle dragging wedge owner...one cam, and I know exactly where it sits   If I could find a set of heads that flowed like those SOHCs...

[cdmbill2]

Me too, on the wedge front, but sometimes we have to test our assumptions about those things we take for granted. In a months time I'll have my 598 on the pump and we will be looking at cam phasing even though it it just a conventional single cam, push rod antique.

I'd never really worried about it and today we learned that stuff moves around move than we knew.