Weber carbs - reversion plate

Cliff:

Which God fearing power hungry GT 40 owners want their engine to idle like a sewing machine? Surely not on this forum.
Ha! Yeah, you're right, not on this forum..... Was meaning the general consuming public rather than this forum.

I took a gal pal for a ride in my GT40 earlier in the year and her first reaction was "it's kind of loud...does it need a tune up or new exhaust or something?" I then stomped on the loud pedal and said "no".....
 

Randy V

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Frank, at 7,000 RPM, there is very little reversion effect...

Tom, I am home now and will find the cam card or find a link to the same cam I have..

With 108 LSA, a small displacement engine l like a 289 or 302 would barely be able to get out of it's own way below 3,000 RPM. If the compression was lower than 11:1, it would be far worse and not at all something that would work on the street. Think about what the dynamic compression ratio would be with that cam!

Back in a bit...
 

Randy V

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Found the info that I had posted here on another thread:

Description
Ford Sml Blk 289/302 FO - Inglese Cam Hydraulic Roller Series by COMP Cams®

Inglese™ Weber carburetors offer outstanding performance and throttle response, as well as an incredible underhood appearance. But until now no manufacturer had created camshafts designed specifically to optimize this classic high performance induction system. The new Inglese™ Weber Performance Camshafts by COMP Cams® are designed to enhance the power and drivability of these systems; Inglese™ having worked closely with the COMP Cams® engineering staff to create the most advanced camshaft designs possible. As a result, Inglese™ announces the creation of 16 hydraulic roller cams for Ford, Chevrolet and Chrysler engines.

The secret behind these camshafts is the strong vacuum and signal they create; key ingredients to delivering peak uncompromised Weber performance. While most camshafts are designed for plenum-type 4-barrel carbs or electronic fuel injection, the Inglese™ Weber Performance Camshafts by COMP Cams® were designed from a “clean sheet of paper” for the best performance and drivability possible. The new Inglese™ Weber Performance Camshafts by COMP Cams® are offered in two performance levels for each engine platform, including four popular Ford engines, Small and Big Block Chevrolet, as well as Small Block Chrysler engines.

SBF
----------------------- Dur @050 Lift w/1.6:1 Lobe Sep
31-490-8 272EHR15.... 216 218.... 0.566 0.555 115°
31-491-8 272EHR15.... 222 224.... 0.571 0.565 115°
 
Here's an interesting little vid clip showing a good dose of reversion on a 351C. Imagine all that gas getting soaked up by a paper filter of some kind. Yikes.

[ame=http://www.youtube.com/watch?v=JRdwWgSGqvc]Pantera 351 Cleveland engine on dyno 2 - YouTube[/ame]
 

Chuck

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Randy:

Interesting information. I was not familiar with those cams when we built our engine.

I know you are aware, but for those that are not, Jim Inglese has no connection with Inglese, per se. He is not connected with that company presently although they use his name. He has his own separate company at Home. When we built our engine, his primary cam recommendation was lobe separation between 110 and 114 being ideal. The other parameters were of lesser concern to the Webers, per se. Ours ended up at 110, and thus far it has been ideal.

I suspect that the amount of lobe separation on those Inglese / Comp cams accounts for the absence of spitting and reversion. Good information.
 

Chuck

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Here's an interesting little vid clip showing a good dose of reversion on a 351C. Imagine all that gas getting soaked up by a paper filter of some kind. Yikes.

Needs a reversion plate!

If there had been a reversion plate, I wonder what the distance would be from the top of the velocity stacks to the bottom of the plate? Just curious.
 

Brian Stewart
Here's a screen-grab from some footage of an original car Cliff. Looks to me like the gap is slightly less than half the diameter of the velocity stack.
 

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Ian Anderson

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A few years ago a set of fluid dynamics articles were written on this site By Adam Christian

a search will show his work.

Perhaps an e mail or pm to him will get the correct answer


Ian
 

Mike

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Sorry guys to revive an old thread but I have a couple questions. 302 11:1

I'm considering 48 IDAs and am willing to make lots of compromises on drivability. I really am going for that old school GT40 growl. Anything result that ends up not producing that would be a failure.

Question for you guys running Webers with wider LCAs? How do your cars sound? I don't really care for the big lumpy cam big block Chevelle sound but I also don't want the 1978 Granada exhaust note either.

The only thing stopping me from just going with a narrow LCA cam is the danger of fire. I don't care if it pops and spits but burning the car down would not be something I'd want in the back of my head constantly.

The conclusion I think I'm reaching is that to get the old school sound you need a narrow LCA. With a narrow LCA then reversion and fire potential comes into play. I'm starting to lose sleep over the paradox.

I also feel like that once your start covering up Webers with a plenum or reversion plate, then what is the point? Might as well run a carb under an air cleaner at that point.

So, you guys running wide LCAs, do any of you have video of your car that would shed light on the sound? Thanks
 

Randy V

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Mike, you've done your homework and have highlighted a couple of key reasons to steer clear of narrow lobe centers with an IR manifold and Webers...
If I was really bent on having the top-fueler at an idle sound, I would look into some of the Weber Clone stack injection systems as their injectors should be below the throttle plates and hence, less reversion.
 

Mike

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Are you saying the original GT40 sound is a top fueler at idle sound? If you are, then I am bent on that. Webers would be nice from an originality and visual appearance perspective but that is secondary to the sound I'm after. I'd like to hear a 289/302 Weber setup with a wide LCA. Do you have any of your car?
 

Randy V

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My engine has a relatively wide lobe center angle as it is a roller cam designed by Jim Inglese specifically for Webers. It is a 115 LCA cam and idles relatively smoothly and has off idle throttle response that is far more "crisp" than any engine I've ever built before. My engine is only a 331 stroker with 10.2:1 compression.
I will find the dyno video, but it sounds like any other engine on the dyno.
Most of the GT40 sound is produced by 180 degree headers with minimal silencers if any. The rest of it is the exhaustion of strong power pulses from a higher compression engine.
You'll find that the strength of the bark increases with two things -
1) Displacement (bigger engine = bigger bark)
2) Compression - a 12:1 engine has a much stronger power pulse than does a 9:1 engine.

Look back at posts 22 and 23 on this thread..

Here is my engine on the dyno..

http://youtu.be/HBqWB_4ZZuI

Produces 415 HP / 430 TQ
 
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Two things in particular "make" the GT40 sound - a cam with the correct (1-5-4-2-6-3-7-8 I think) firing order and a cross-over exhaust. Webers will add some induction noise but a lot of this will be drowned out by the exhaust sound.

If you don't have the cross-over exhaust and the firing order you will never get that sound.

Regards,
 

Mike

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Guys, first thanks for the input. I'm aware of all of these things for the most part. I also believe that sound and tone is more nuanced than just cross over, firing order, and compression. I have been wondering how much induction noise plays in if exhaust noise would for the most part drown that out? I would like to ask how firing order would play any part as long as you were crossing the right cylinders? I'm aware of the firing order differences between the 289/302 and later Windsors. Are you suggesting that the 289 firing order produces a different tone than the 351 order? I question that but am interested in understanding more. Cam timing and lobe shape are a key ingredient as well. It's hard for me to hear your engine idling Randy. It did look like power was dropping off at 5500rpm which would make since with 115 LCA. I would guess it idles very smoothly at 800rpm? Any video of that? Thanks!
 
Two things in particular "make" the GT40 sound - a cam with the correct (1-5-4-2-6-3-7-8 I think) firing order and a cross-over exhaust. Webers will add some induction noise but a lot of this will be drowned out by the exhaust sound.

If you don't have the cross-over exhaust and the firing order you will never get that sound.

Regards,
Not technically correct, if you look at the attached dwg the primary pipes can be arranged in the collectors so that either firing order will have a rotational sequence in each collector. However if you check original 289 MK1 exhausts you will notice ford did not bother with this, so perhaps the 'non-sequence' pipe order of the factory exhaust plays a small part in what mike is looking for also.

Ray-sneaking pics of FE's in to a SBF discussion is a likeable form of thread drift!:)
 

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If you think that the sound is more nuanced than just cross-over etc. then have a listen to a 289 Shelby Mustang or Cobra - same engine, different exhaust, TOTALLY different sound. Ditto the Mk.III GT40, different exhaust layout, different sound.

Regards,
 

Randy V

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I won't say that it idled perfectly smoothly at 800, but it did idle at about 900 with a very slight lope to it.. That cam has a bunch of lift and that will also make a difference in idle quality as the valves are slammed open then shut again quite quickly.. As a matter of fact it was dropping off power wise, but the engine would start to develop a slight miss at that RPM. From the AF ratio and sound, it appeared to be floating the valves. As I recall, the springs that came from Comp Cams were 330# and it was suggested by Comp that we step that up to 350# open.. I may do that and dyno it again afterward and see if it makes any more power. Still, it does quite well and seems (again dyno only) to be quite responsive and docile..

I had taken a couple of other videos and may still have them on another computer...
 
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