webers cost me HP?

[dlampe]

I am building an engine for my new GT 40 that will be based on a 8.7 deck hieght (between an 351 and a 302 block) that I was planning rev past 7500 rpm. This is a race motor that will spend 90% of its time on the track. This is my delima. I want an original looking car and I really like the webers. However the cam that I have to run with the webers must have a shorter duration to control the overlap. Webers don't like overlap. Is it true that the webers will sufficate a high reving motor? Will the old holley/victor intake combo outperform the webers? My car runs awesome with the webers right now but it is a HD roller that is all done at 6500.

[Cracker]

I've had both IDA's and a single 4 with the overall, all out performance edge in power going to the single. In the "looks" comparison we all know there is no comparison.

Another option is to go with the IR FI route which would allow you to run much more radical cams with Weber kind-a-look induction.

Bottom line - pure performance = single four. IMHO

[Brian Paul]

Go with the Webers. If your are going to use this mostly on the track, tune it with big chokes. Lots of torque for coming out of corners and high RPM.

As far the "Looks" department goes, great.

I built the 428 with Web's that Cracker mentioned. It was a good looking engine and a torqure monster to boot. Have fun.

Brian Paul

[BERNIE]

Originally Posted by dlampe

I am building an engine for my new GT 40 that will be based on a 8.7 deck hieght (between an 351 and a 302 block) that I was planning rev past 7500 rpm. This is a race motor that will spend 90% of its time on the track. This is my delima. I want an original looking car and I really like the webers. However the cam that I have to run with the webers must have a shorter duration to control the overlap. Webers don't like overlap. Is it true that the webers will sufficate a high reving motor? Will the old holley/victor intake combo outperform the webers? My car runs awesome with the webers right now but it is a HD roller that is all done at 6500.

Tested back to back 331cu
Weber outdid holley through midrange but overtake by holley at top
Results Holley left column:

--------------------------------------------------------------------------------
Engine specs:
stroke 3.250,5.400 rod lenght,crower ultralight crank 11.0 CR
Head:Victor JR 301.5/200.5 @.600,Victor Jr manifold
Buddy Rawls flat tappet cam:.592/.544,262/264 @.50
Holley Weber carbs
Tq Hp Tq Hp
4000 338 257 382 291
4400 371 311 400 335
4800 398 364 449 411
5200 411 407 441 436
5600 413 440 438 467
6000 412 470 434 496
6400 400 488 422 515
6800 401 519 399 517
7000 390 534 386 514

[Rick Parker]

I like the idea of Webers on an engine too, they look great. I think you have to evaluate (as you have done) where and how the engine will be used and what your end result is to be. On a race track the flexability and increased torque production of the Webers will produce better results and faster lap times, that is where they shine (Torque). Yes the camshafts cannot be as radiacal as with a single plane and large CFM Holley, but trade offs are to be expected. There has also been vast steps forward in manifolding for 4BBl carbs through the years, adding to that the changes in camshaft theory and technology and you can see why at WOT Holleys can be tuned to out do Webers, (refer to Bernies dyno #'s) and will require less maintenance and tuning and are certainly less$$. But.....we are all attempting to make these cars appear "like they were originally". Consequently we revert to things like Webers. But don't forget, there has been a lot of engine development especially in cylinder heads since the 60's and opens up many different ways to build your engine and achieve similar results.

[dlampe]

Thanks Bernie, that is EXACTLY what I wanted to see. It looks like the webers will win up to 6800. I looks like the webers were done at 6800 and went south while the holley was still climbing. It also looks like you are running more cam than most weber guys recommend. What is your overlap and LSA? I thought about 240 @ .050 was about the max. Are you happy with the way it runs? What chokes are in your webers? I could live with the webers if I had your numbers. Lastly, what effect will more cubic inches have on the performance difference between the carbs? This info is a huge help to me.

[Jeff Bridges]

dlampe,
Just bear in mind, the entire engine specs are completely different for a Weber set up over that of a single 4 bbl. spec setup. Do you have the research and support for maintaining and keeping a system like that in "sync" over a Holley AAA carb, that is hard enough to keep in proper tune, especially for track conditions.
Shelby American abandoned them in favor of 4 bbls. at LeMans and on thru the later decades for a reason. I understand that later EFI and the related electronic controls came into play, but those were tunable very easily thru the "old black boxes" aka early laptops, that the engineers used in racing.
Yes, they look like a million bucks!, but might require that type of budget to be competitive also.
Jeff

[RICK LAKE]

Hi Dean Without chokes in the webers you should be able to turn 7800 with a small motor. If you want more a set of 52-58 mm TWM will take you to about 9,500 rpm, about the same time the bottom end comes out the bottom. Change the gear ratio first. It's got to be cheaper in the long run. I will call Rick L I will talk to you about cams latter

[Woodz428]

It looks like the Holley out torqued it through most of the range also. That should be expected with the extra venturi area. I ran Webers on a 3.8 E-type in the early 70's and set up several Fiats, Datsuns Alfas and VW's with Webers in the late 70's,early 80's and never had any synch problems once they were set.

[dlampe]

Woodz428, I think you might be looking at the numbers wrong. The webers have much better tq numbers than the holley all the way up to 6800.

Jeff, I run the webers now in the Kirkham and I find the extremely easy to tune. I have most of the weber tools. I have never had a serious problem with them. The definately have more throttle response than the holley and I think they will out run the holley untill about 6500 to 7000 rpms based on my personal experience and the numbers posted above in this thread.

I think I might be worrying to much about top end. As Rick said you could change out the chokes and dramatically effect the upper end. All that being said, I will probably get them because they look cool!

[BERNIE]

Originally Posted by dlampe

Thanks Bernie, that is EXACTLY what I wanted to see. It looks like the webers will win up to 6800. I looks like the webers were done at 6800 and went south while the holley was still climbing. It also looks like you are running more cam than most weber guys recommend. What is your overlap and LSA? I thought about 240 @ .050 was about the max. Are you happy with the way it runs? What chokes are in your webers? I could live with the webers if I had your numbers. Lastly, what effect will more cubic inches have on the performance difference between the carbs? This info is a huge help to me.

42mm choke,107.0 lobe deparation,cam installed@105.0 centerline
F 16 ,160 M, 130 A
I think over 400 CU Holley are better.Weber are too testrictive on the choke size (maxi 45 mm) interesting to test with enlarged the bore from 48 to 51.5mm or BERG expensive solution up to 58mm choke

[Rick Parker]

This chart may be of interest:
http://www.gt40s.com/forum/tech-engi...turi-size.html

[Zoom This]

I read the posts with interest. I thought long and hard about setting up my 418W with Webers, but the Weber guys were telling me I had too much cam. Baloney! At the time I wasn't about to pull the motor from the car, change the cam for this. I wound up using a Victor Jr intake and Mighty Demon. One of our club members just built the exact same motor as mine. 418W, 6.2" rod length, polished and ported Edelbrock Victor Jr heads, 11:1 CR, .576 intake lift, 242 duration at .050" with 110 lobe separation. Only trouble in setting up the carbs was getting them jetted correctly for idle mix, primary, secondary jets. After many hours of jet and emulsion tubes to get rid of his transition gurgle, sputter and pop we settled on an F-11 emulsion tube. This wound up being the key to perfectly running Webers for street and track using 44MM chokes.

[01yelrt]

Real world performance? Are you looking for a track/drag set up or are you looking for something that you can use on the street and track. Horsepower at very high RPM is not too desireable on the street. Low RPM torque and early HP in the poweband is the way to go. You get power and torque earlier with the Webber setup. PEAK HP and Torque were also higher in the Webber setup that Bernie shows. I don't see any advantage to 10 or 20 more HP at 7000RPM when the Webber setup produced many more than that much earlier in the curve. Looking at the powerband it is longer and flatter in the Webber setup. Tuning is a PAIN though I have been messing with mine for about 6 mos. Nothing is terrible but it always seems like you can make an improvement somewhere. I'm waiting till I can say I have my setup perfected. Hopefully it will be soon! Good luck and have fun with the build. Aron

[Woodz428]

Dean, You are absolutely correct. I was viewing them on my head, I guess, and maybe sideways.

[KevinM]

What is the displacement of your engine? That makes a difference.

Weber's don't like overlap because they have reversion issues. If you only use it for the track, and don't mind blowing a fair amount of fuel back out the tops of the carbs, they can take more cam.

Here is the formula for calculating optimum port (and venturi) size for any engine:

Cross Sectional Area of a Port (venturi):

Area = Volume of One Cylinder (Cubic Inches) x Peak Torque RPM / 88200

Once you have the Area (in Sq. Inches) you divide it by 3.14 then take the square root of the resulting number and multiply that by 2 to get the diameter of a round port in inches. Then multiply that by 25.4 to get millimeters.

There is another formula (actually a “Rule of thumb”) that was developed by Alfa Romeo for sizing webers. This is not as accurate as the other formula and only gives you a ballpark approximation. It is:

Size (mm) = CC’s (of 1 cylinder) x Peak HP RPM x Square Root / 50 (for Venturi size)

48 Webers will probably be too small. 44mm venturis are about the biggest you can go for street use. For track only, where you don't care how they carburate at low RPMs, you can use 46's.

If you need larger than that, look at Gene Berg's line of weber look-alikes that go to 58 mm.

When all is said and done, the Webers will probably give you better midrange and the 4-bl better top end.

Kevin

[ChipBeck]

One big factor to consider is running without an air cleaner. Here in Arizona where the ground is always dry and dirt and sand are the norm, not using a filter is a tough way to go. The single 4bbl with an air filter will perform much better at any rpm than the Webers with air filters. I have both induction systems and have used both on my Kieth Craft built 482ci FE. The car has a better hit at any rpm with the Webers(4x48 IDA's) than the 750cfm vacuum secondary Holly. When I put ANY kind of filter on the Webers however (and I've tried several) the performance suffers drastically. The Holly runs great with or without an air filter. My car is much more drivable and smoother with the 4bbl. Overall I prefer the superior drivability with the slight performance penalty of the 4bbl with an air cleaner to the open Webers. At the Pavillions on a Saturday night with the hood open however, people go nuts over the Webers. Do you want to drive or do you want to show??

Chip

[edmonds007]

What is involved with switching back and forth betwen a traditional carbeurator and manifold and the webers (assuming the webers are tuned and set)once the webers are tuned and set)?

I understand this is an expensive proposition but for someone who already has one or the other that's considering switching they'll already have the hardware for both.

Thanks for any ideas you may offer. By the way, I've uploaded pictures of my old weber setup.

Bryan

[RICK LAKE]

ChipBeck Chip have you looked at dirttrack filter kits? I think the one that Ed Pink company sells would be something you might want to look at. How much hood clearance is there? He makes custom filters. ITG looks nice but they might be oil filters or the foam jobs that let large pieces through. Jay Brown made a nice trick setup for his blower motor, that also may give you some ideas Rick Lake. Carbs are nice but a set webers is pricless.

[Rick Parker]

This might be able to be tweeked to work on Webers:

[IMG][/IMG]