Club Cobra GasN Exhaust  

Go Back   Club Cobra > Engine Building, Tuning, and Induction > Weber Tuning

Keith Craft Racing
Nevada Classics
Main Menu
Module Jump:
Nevada Classics
Nevada Classics
MMG Superformance
MMG Superformance
Advertise at CC
Banner Ad Rates
Keith Craft Racing
Keith Craft Racing
March 2024
S M T W T F S
          1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
31            
  #1 (permalink)  
Old 12-06-2009, 03:18 PM
bobcowan's Avatar
CC Member
Visit my Photo Gallery

 
Join Date: Feb 2007
Location: Colorado Springs, CO
Cobra Make, Engine: Backdraft, supercharged Coyote
Posts: 2,430
Not Ranked     
Default Runner Length

If you put a spacer underneath Weber IDA's, what will happen to the power curve? Making a longer runner would (I think) make more torque and less top end power. Or the other way around?
Reply With Quote
  #2 (permalink)  
Old 12-06-2009, 05:01 PM
CC Member
Visit my Photo Gallery

 
Join Date: Oct 2003
Posts: 4,078
Not Ranked     
Default

I agree Bob but how do you handle the taller carbs and the FFR hood? Taller scoop in mind?
__________________
Chas.
Reply With Quote
  #3 (permalink)  
Old 12-06-2009, 05:12 PM
SoTxButler's Avatar
Senior Club Cobra Member
Visit my Photo Gallery

 
Join Date: Jan 2008
Location: McAllen, TX
Cobra Make, Engine: Butler...488" hi-rise, dry-sump FE s/o w/stacks
Posts: 543
Not Ranked     
Default

The longer runner will produce more torque at a particular RPM depending on the length of the runner. The science of pressure waves bouncing back and forth in the runners is complicated. With the pressure wave moving at the speed of sound, figuring out the valve openings at a particular RPM and then figuring out the length of the runner to achieve the exact moment that the pressure wave bounces into an opening valve is difficult at best. If you could, you would see an improvement in performance at that RPM and a small RPM range. The effect would be like a mini supercharger, but when the RPM changes, the benefit is gone....the waves are bouncing back and forth again. If the wave is headed into the manifold when the valve opens, there will be no effect. IMO, you will probably not be able to notice any difference by adding a spacer even if you could figure out at what at RPM the pressure wave is headed into the open valve.
__________________
Russ

Last edited by SoTxButler; 12-06-2009 at 06:22 PM..
Reply With Quote
  #4 (permalink)  
Old 12-06-2009, 07:02 PM
Rick Parker's Avatar
CC Member
Visit my Photo Gallery

 
Join Date: May 2001
Location: California, Ca
Cobra Make, Engine: NAF 289 Slabside Early Comp Car with 289 Webers and all the goodies. Cancelling the efforts of several Priuses
Posts: 6,592
Not Ranked     
Default

Along this same theme, were the shorter Stacks that I have seen on the Daytona coupes necessary for hood clearance or were they operating in a narrower (higher) RPM band due to track design, making the short stack more efficient for High RPM? It would have also necesitated shortening the Auxillary venturies a like amount thereby reducing the signal to the main well??? Am I overlooking something?
__________________
Rick

As you slide down the Banister of Life, may the splinters never be pointing the wrong way

Last edited by Rick Parker; 12-06-2009 at 07:06 PM..
Reply With Quote
  #5 (permalink)  
Old 12-06-2009, 07:08 PM
bobcowan's Avatar
CC Member
Visit my Photo Gallery

 
Join Date: Feb 2007
Location: Colorado Springs, CO
Cobra Make, Engine: Backdraft, supercharged Coyote
Posts: 2,430
Not Ranked     
Default

Actually, I'm thinking of removing the spacer. Initially, I had to space them up to get everything to fit right. I get a slight bit of rubbing on the right front corner of the air cleaner. The stacks have plenty of room.

But, I'v changed things around since then. If I want to, I can remove these 1" spacers. I could stand a lose a little bit of torque, I'v got plenty to spare. Especially if I'll gain some top end.

Reply With Quote
  #6 (permalink)  
Old 12-06-2009, 07:56 PM
SoTxButler's Avatar
Senior Club Cobra Member
Visit my Photo Gallery

 
Join Date: Jan 2008
Location: McAllen, TX
Cobra Make, Engine: Butler...488" hi-rise, dry-sump FE s/o w/stacks
Posts: 543
Not Ranked     
Default

Rick, you are probably on to something. Higher horsepower was probably the goal and they had to spin them tighter. Based on that line of reasoning, the shorter stacks would be helpful.

Bob, take off the spacer, 1" should not make any noticeable change since you have way plenty torque and since it helps things fit better, so much the better.
__________________
Russ

Last edited by SoTxButler; 12-06-2009 at 08:02 PM..
Reply With Quote
  #7 (permalink)  
Old 12-06-2009, 08:28 PM
CC Member
Visit my Photo Gallery

 
Join Date: Apr 1999
Location: cleveland, OH
Cobra Make, Engine: CSX4000, 427
Posts: 1,999
Not Ranked     
Default

I wouldn't remove the spacer if you were having fitting problems. If you want to make the runners longer or shorter, like what was stated before, concentrate on the air horn stack lengths, as, when at full throttle, the throttle plates are wide open, and the plenum is really the atmosphere at the entrance of the stacks.
__________________
"After jumping into an early lead, Miles pitted for no reason. He let the entire field go by before re-entering the race. The crowd was jumping up and down as he stunned the Chevrolet drivers by easily passing the entire field to finish second behind MacDonald's other team Cobra. The Corvette people were completely demoralized."
Reply With Quote
  #8 (permalink)  
Old 12-06-2009, 08:49 PM
bobcowan's Avatar
CC Member
Visit my Photo Gallery

 
Join Date: Feb 2007
Location: Colorado Springs, CO
Cobra Make, Engine: Backdraft, supercharged Coyote
Posts: 2,430
Not Ranked     
Default

Quote:
Originally Posted by Anthony View Post
I wouldn't remove the spacer if you were having fitting problems.
.
I was having fitment problems with the original set up. But that has changed dramatically, and I think it would now fit correctly. And, it would help me get the linkage to operate better.


Quote:
Originally Posted by Anthony View Post
If you want to make the runners longer or shorter, like what was stated before, concentrate on the air horn stack lengths, as, when at full throttle, the throttle plates are wide open, and the plenum is really the atmosphere at the entrance of the stacks.

Hmmmm. I could then use a stack that's 1" taller; almost a 50% increase. Now that might actually net me a little more power at the top end. I think you're on to something there. More power at the top end is always usefull.
Reply With Quote
  #9 (permalink)  
Old 12-07-2009, 05:55 AM
CC Member
Visit my Photo Gallery

 
Join Date: Dec 2004
Location: Kansas City, KS
Cobra Make, Engine: jbl
Posts: 2,291
Not Ranked     
Default

here is an example of tuned length runners from a pipemax program just to give an idea of the differences in runner lengths used. this is off a 9.5 deck windsor with mild solid roller cam and afr205's. the plenum would fit on top of the runners.

- Induction System Tuned Lengths - ( Cylinder Head Port + Manifold Runner )
1st Harmonic= 32.201 (usually this Length is never used)
2nd Harmonic= 18.276 (some Sprint Engines and Factory OEM's w/Injectors)
3rd Harmonic= 12.759 (ProStock or Comp SheetMetal Intake)
4th Harmonic= 10.042 (Single-plane Intakes , less Torque)
5th Harmonic= 8.148 (Torque is reduced, even though Tuned Length)
6th Harmonic= 6.855 (Torque is reduced, even though Tuned Length)
7th Harmonic= 5.916 (Torque is greatly reduced, even though Tuned Length)
8th Harmonic= 5.204 (Torque is greatly reduced, even though Tuned Length)
Note> 2nd and 3rd Harmonics typically create the most Peak Torque
4th Harmonic is used to package Induction System underneath Hood
Reply With Quote
  #10 (permalink)  
Old 12-07-2009, 09:40 AM
bobcowan's Avatar
CC Member
Visit my Photo Gallery

 
Join Date: Feb 2007
Location: Colorado Springs, CO
Cobra Make, Engine: Backdraft, supercharged Coyote
Posts: 2,430
Not Ranked     
Default

That's pretty interetsing. The shorter the runner, the less torque you make. What happens to the HP? Is the runner length measured from the intake valve to the top of the stack?
Reply With Quote
  #11 (permalink)  
Old 12-07-2009, 10:25 AM
CC Member
Visit my Photo Gallery

 
Join Date: Dec 2004
Location: Kansas City, KS
Cobra Make, Engine: jbl
Posts: 2,291
Not Ranked     
Default

post your engine specs or send them via pm and what are the dia. of the webers in inches and i'll put them in and tell you what the different lengths will do, or try. i can specify different lengths anyway and see what it does to the curves, it uses fuel injection though for delivery.

length would be from the valve face to atmosphere across the top of the stacks. if you put a breather on top i believe i can find what the area of it should be, which would be the plenum size, if you leave it open, atmosphere is the plenum.
Reply With Quote
  #12 (permalink)  
Old 12-07-2009, 11:32 AM
bobcowan's Avatar
CC Member
Visit my Photo Gallery

 
Join Date: Feb 2007
Location: Colorado Springs, CO
Cobra Make, Engine: Backdraft, supercharged Coyote
Posts: 2,430
Not Ranked     
Default

427W, dart block, 4.125 bore x 4.0 stroke. 10.7 staic compression.

Heads are Dart Pro-1's 2.02/1.60 valves, heavily ported.

Cam is Comp Cams XFI248HR. 248/258* @ .050, .608/.608. 114*LSA

Throttle body throats are 52mm. Stack height is 2.25"

Thanx for your help on this. I really do appreciate it.
Reply With Quote
  #13 (permalink)  
Old 12-07-2009, 01:05 PM
CC Member
Visit my Photo Gallery

 
Join Date: Dec 2004
Location: Kansas City, KS
Cobra Make, Engine: jbl
Posts: 2,291
Not Ranked     
Default

no problem, probably be tomorrow evening. do you have a dyno of this, any bsfc,ve #'s, etc for comparison?
Reply With Quote
  #14 (permalink)  
Old 12-07-2009, 01:09 PM
CC Member
Visit my Photo Gallery

 
Join Date: Oct 2003
Posts: 4,078
Not Ranked     
Default

Quote:
Originally Posted by bobcowan View Post
427W, dart block, 4.125 bore x 4.0 stroke. 10.7 staic compression.

Heads are Dart Pro-1's 2.02/1.60 valves, heavily ported.

Cam is Comp Cams XFI248HR. 248/258* @ .050, .608/.608. 114*LSA

Throttle body throats are 52mm. Stack height is 2.25"

Thanx for your help on this. I really do appreciate it.
Bob,

Is there such a thing as chokes for your system? I would think 52mm is a lot, even with that good sized cam and good heads.
__________________
Chas.
Reply With Quote
  #15 (permalink)  
Old 12-07-2009, 01:16 PM
bobcowan's Avatar
CC Member
Visit my Photo Gallery

 
Join Date: Feb 2007
Location: Colorado Springs, CO
Cobra Make, Engine: Backdraft, supercharged Coyote
Posts: 2,430
Not Ranked     
Default

Quote:
Originally Posted by vector1 View Post
no problem, probably be tomorrow evening. do you have a dyno of this, any bsfc,ve #'s, etc for comparison?
I have dyno charts. But probably won't have what you want on it. Just power curves and O2 sensor readings.

Quote:
Originally Posted by ERA Chas View Post
Bob,

Is there such a thing as chokes for your system? I would think 52mm is a lot, even with that good sized cam and good heads.
No chokes, don't need them. If it's really cold, it might take a couple tries to get it running. Once it's running, it stays that way. This is EFI, the computer handles all that.
Reply With Quote
  #16 (permalink)  
Old 12-07-2009, 02:04 PM
CC Member
Visit my Photo Gallery

 
Join Date: Oct 2003
Posts: 4,078
Not Ranked     
Default

Quote:
Originally Posted by bobcowan View Post
No chokes, don't need them. If it's really cold, it might take a couple tries to get it running. Once it's running, it stays that way. This is EFI, the computer handles all that.
Sorry, I didn't make myself clear. I meant the chokes that Webers employ to go from 48mm IDA's to smaller like 44, 42 or 37mm for example. It's a tuning aid for them.

So I take it your computer adjusts the pulse and duty cycle of the injectors so as to not over carburate?

Using Webers, I always read that 52mm was too large for a displacement of 427 and 48mm or smaller was more beneficial.
__________________
Chas.
Reply With Quote
  #17 (permalink)  
Old 12-07-2009, 02:27 PM
CC Member
Visit my Photo Gallery

 
Join Date: Apr 1999
Location: cleveland, OH
Cobra Make, Engine: CSX4000, 427
Posts: 1,999
Not Ranked     
Default

Quote:
Originally Posted by vector1 View Post
here is an example of tuned length runners from a pipemax program just to give an idea of the differences in runner lengths used. this is off a 9.5 deck windsor with mild solid roller cam and afr205's. the plenum would fit on top of the runners.

- Induction System Tuned Lengths - ( Cylinder Head Port + Manifold Runner )
1st Harmonic= 32.201 (usually this Length is never used)
2nd Harmonic= 18.276 (some Sprint Engines and Factory OEM's w/Injectors)
3rd Harmonic= 12.759 (ProStock or Comp SheetMetal Intake)
4th Harmonic= 10.042 (Single-plane Intakes , less Torque)
5th Harmonic= 8.148 (Torque is reduced, even though Tuned Length)
6th Harmonic= 6.855 (Torque is reduced, even though Tuned Length)
7th Harmonic= 5.916 (Torque is greatly reduced, even though Tuned Length)
8th Harmonic= 5.204 (Torque is greatly reduced, even though Tuned Length)
Note> 2nd and 3rd Harmonics typically create the most Peak Torque
4th Harmonic is used to package Induction System underneath Hood

All of those numbres are for a specific rpm, not listed.

Whenever you calculate an optimal runner length, you need to pick a rpm where you want the maximum increase in power, and calculate runner length based on that particular rpm range. There is a formula, based upon the speed of sound, the speed of the pressure waves.

the early Chyrsler 300 413's had those long cross ram tubes, tuned for 3000 rpm or something like that. Racers, cut the tubes, rewelded them with shorter runner lengths to raise the rpm of the maximum power boost to 5000 rpms or something like that.
__________________
"After jumping into an early lead, Miles pitted for no reason. He let the entire field go by before re-entering the race. The crowd was jumping up and down as he stunned the Chevrolet drivers by easily passing the entire field to finish second behind MacDonald's other team Cobra. The Corvette people were completely demoralized."
Reply With Quote
  #18 (permalink)  
Old 12-07-2009, 04:26 PM
bobcowan's Avatar
CC Member
Visit my Photo Gallery

 
Join Date: Feb 2007
Location: Colorado Springs, CO
Cobra Make, Engine: Backdraft, supercharged Coyote
Posts: 2,430
Not Ranked     
Default

Quote:
Originally Posted by ERA Chas View Post
Sorry, I didn't make myself clear. I meant the chokes that Webers employ to go from 48mm IDA's to smaller like 44, 42 or 37mm for example. It's a tuning aid for them.

So I take it your computer adjusts the pulse and duty cycle of the injectors so as to not over carburate?

Using Webers, I always read that 52mm was too large for a displacement of 427 and 48mm or smaller was more beneficial.
Yeah, in a carb application, thoat size and intake charge speed are pretty critical. Too big and it won't idle or perform like it should at low rpm's. EFI changes all that. You can use really big throats to make power at top end, and still perform well in traffic.

But, since these are individual runners, you have to be very carefull about intake port and valve size. I used a set of Brodix heads with huge ports and valves. On a 4 barrel carb it would have made gobs of power. But I lost all low end torque.
Reply With Quote
  #19 (permalink)  
Old 12-07-2009, 04:45 PM
CC Member
Visit my Photo Gallery

 
Join Date: Oct 2003
Posts: 4,078
Not Ranked     
Default

Quote:
Originally Posted by bobcowan View Post
But, since these are individual runners, you have to be very carefull about intake port and valve size. I used a set of Brodix heads with huge ports and valves.
Would the valves be 2.08" x 1.60" with about a 220 intake runner?
__________________
Chas.
Reply With Quote
  #20 (permalink)  
Old 12-07-2009, 05:05 PM
bobcowan's Avatar
CC Member
Visit my Photo Gallery

 
Join Date: Feb 2007
Location: Colorado Springs, CO
Cobra Make, Engine: Backdraft, supercharged Coyote
Posts: 2,430
Not Ranked     
Default

The valves were 2.10 x 1.90, with a 225 runner. Yes, they were custom made, from Gordon Levy.

I could probably make a little more top end power by using a 2.05" valve. But I'm not after every last bit of power. It's for fun, not for money.
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -7. The time now is 08:46 AM.


Powered by vBulletin® Version 3.8.0
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.6.0
The representations expressed are the representations and opinions of the clubcobra.com forum members and do not necessarily reflect the opinions and viewpoints of the site owners, moderators, Shelby American, any other replica manufacturer, Ford Motor Company. This website has been planned and developed by clubcobra.com and its forum members and should not be construed as being endorsed by Ford Motor Company, or Shelby American or any other manufacturer unless expressly noted by that entity. "Cobra" and the Cobra logo are registered trademarks for Ford Motor Co., Inc. clubcobra.com forum members agree not to post any copyrighted material unless the copyrighted material is owned by you. Although we do not and cannot review the messages posted and are not responsible for the content of any of these messages, we reserve the right to delete any message for any reason whatsoever. You remain solely responsible for the content of your messages, and you agree to indemnify and hold us harmless with respect to any claim based upon transmission of your message(s). Thank you for visiting clubcobra.com. For full policy documentation refer to the following link: CC Policy
Links monetized by VigLink