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Weber/Holbay manifold modification using standard Zenith downdraft manifold

jdoclogan

Platinum Level Sponsor
Here is what my cognitive fermentation came up with for the Weber/Holbay manifold to Weber/Alpine modification.

Left standard Zenith downdraft manifold Right Weber/Holbay manifold ---- Top - Bottom respectively
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The runner length measurements (67mm) are exactly the same as are the thickness (7mm) of the manifold to block faces.

Weber/Holbay ---------------------------------------------- Standard downdraft Zenith
upload_2020-5-9_12-45-4.png upload_2020-5-9_12-45-43.png

This is what I originally thought may be the case. Thus, I plan to cut each at the 67 mm line and Tig weld back together with a 5 degree upward direction. This should provide clearance for the Webers in relation to the inner fender surfaces. What also appears to be an advantage, the 33mm inside continuous orifice diameter of the standard Zenith manifold will be replicated to the Weber/Alpine setup. My manifold port and polish process has the head intake orifice at 30mm from the standard 28mm. I could make it 33mm. Any thoughts are welcomed.
 

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bernd_st

Bronze Level Sponsor
Looks an interesting idea. Just my concern would be how the Zenith runners will meet the wider apart Weber flange holes. Think there will rather big gaps to be bridged with TIG welding. Anyway might be worth a try. Another approach would be to make a one off manifold out of flat water cutted steel flanges & tubings ...
 

alpine_64

Donation Time
Jerry,

When i mentioned this in the other thread ghe aim is to use the flange at the head side of the zenith manifold and cut the flange off the head side of the holbay side with a 10deg angle.

If you do it the way you are showing you have to also cut the Weber mounting side betweem the 2 carbs to make them individual so you cam bring them closer.

The constant is the head side not the carb side.. So you should modify at the head mounting flange
 

jdoclogan

Platinum Level Sponsor
It has always amazed me that I could get an "A" in Euclidean Geometry and yet my brain has difficulty processing mirror images. It is good to have friends in all the right places.

I went ahead and put my best fabrication effort forward with your inputs at the forefront. Cut Weber/Holbay intake at a 10 degree correction compensating for the angled Holbay engine compared to the straight-up Alpine engine. I also cut the twin Zenith intake manifold to engine mount to accommodate the Holbay/Weber "Weber mount."


From left to right - Holbay/Weber "Weber mount" with runners (A) - Zenith intake to engine mount (B) - Holbay/Weber to engine mount(C)
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Refitting "C" to "A" with 10 degree wedge removed. A fairly decent fit. Still needs a bit of porting to 28mm or a lot to get 33mm (out to circle line)
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Fitting "A" to "B" shows some offset. The good news I can weld and port to 33mm. This may very well be the way to go.

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Note: Both configurations ended with runner lengths of 82mm. I'm not certain that 1 0r 2 millimeters difference in runner length would affect performance. I don't see the need for the vacuum orifices in the Holbay/Weber intake so I will weld them shut. The distributor will need to be re-calibrated for a Weber setup anyhow.
 

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bernd_st

Bronze Level Sponsor
Interesting. Welding "A" to "B" looks feasible despite the slight shifts, but think it can be corrected by some grinding on the Zenith flange remains. Would also not expect a big performance difference from 1-2mm runner length. The vacuum orifices can be welded closed unless you intend to race with a brake servo.

P.S. Would not start to weld up anything w/o checking the installation in the car with both carbs on :rolleyes:
 

puff4

Platinum Level Sponsor
I hate to say this, but one thing to consider is runner length and cylinder pulsing. Depending on the runner’s length, the intake pulsing can significantly inhibit or enhance gas flow to the cylinders, and it takes some fairly sophisticated research and tools to work that out.

Just a thought. Carry on.
 

jdoclogan

Platinum Level Sponsor
I appreciate your response Bernd. Once the weld is done the Zenith flange can easily be shaped (Note: the bottom internal mating points of Zenith flange to Holbay/Weber runner in the lower/center photo). The opposite side (top where the gap exists) will be fill welded and thus can be shaped to provide a 33mm inside diameter runner.

Kevin, I appreciate the input. Now to research any experimental results I can find regarding intake runner lengths vs torque through rpm ranges. Also Weber trumpet lengths vs torque through rpm ranges. Maybe a deduction can be made without expensive pulse tuning equipment. Oh boy, this is getting very interesting.
 

puff4

Platinum Level Sponsor
As to the trumpets, I've always thought that generally the longer ones are better for lower-rpm and torque, versus shorter which are better for high rpm and hp.
 

jdoclogan

Platinum Level Sponsor
Why not bite the bullet and order the correct intake for your application?

I already have a setup, but, engaging in the physics and applying my skills is the fun part. Probably has something to do with a formidable brew of having multiple college degrees and 55 years of restoring/building cars. What a maniacal combination, egghead and jughead all in one.

Will it clear the steering box - or is this for the RHD car?

Dick this is for the #41 Sebring Alpine RHD, thus, no steering box issue. The runner length limit is the inner fender.

As to the trumpets, I've always thought that generally the longer ones are better for lower-rpm and torque, versus shorter which are better for high rpm and hp.

Kevin, great memory from past experiences I assume. I will provide the link to a rather lengthy and involved article: http://www.emeraldm3d.com/articles/emr-adj-length-intake/. Here is the short version:

Conclusions.
Based on the testing we have done to date we can draw certain conclusions:

1. The tapered trumpets work no better than the parallel ones.

2. It is the overall length of the induction that is the single most important feature of any throttle body system.

3. A change of just 4mm in overall length gives a measurable change in the torque curve. Note: longer for low rpm/high torque - shorter for high rpm/low torque

4. You only need to re-map the wider throttle settings of the fuel and ignition maps when you change the induction length. Note: Clearly this was written for computerized system. The same physics apply however I assume one needs to apply "maps" for the cam or change the timing.

Understand this was an engine on an engine stand not going down the road. There would be additional molecular air forces at work in the engine compartment that may give slight variations to the outcome (#3). Commonsense and body restrictions can be applied or you could insert 330mm (13 inch) trumpets and get the performance of a tractor.

The interesting concept that came from this article was the notion of changing the throttle body intake length based on the vehicles purpose, for example, Hill climb vs road race vs autocross vs street. In other words, one could easily change out the trumpets depending on the application needed and get optimum performance from the fuel delivery system.

One comment in another site's thread on the topic reflected back to the old Chevy inline sixes, "fastest style 6 inlines used sidedraft Webers straight on the head."

The research continues on the best configuration.
 

alpine_64

Donation Time
Its not just intakes but the tuned length of the exhausts.

There is an. 1600 Alpine racer that was built in Melbourne in the early 90s that was very trick and fast. When it was sold to sydney the new owner took it out of class so he could do other mods.. Switching to 2 x DCOE and some other internal mods. He spent a long time on the dyno playing with trumpet lengths and exhausts to get his desired balance for HP and torque curve.
 

puff4

Platinum Level Sponsor
.....

Kevin, great memory from past experiences I assume.

.....

3. A change of just 4mm in overall length gives a measurable change in the torque curve. Note: longer for low rpm/high torque - shorter for high rpm/low torque.

......

The interesting concept that came from this article was the notion of changing the throttle body intake length based on the vehicles purpose, for example, Hill climb vs road race vs autocross vs street. In other words, one could easily change out the trumpets depending on the application needed and get optimum performance from the fuel delivery system.

Ha! Indeed. As remembered, longer = low end torque and shorter = high end revs/hp.

Yeah, when I was racing I always kept a selection of different length trumpets (I still have them in my stocks), and I’d fit different ones depending on the track and conditions. Of course it was all just my seat-of-the pants judgement (i.e. my “sphincter dynamometer”) but it seemed to help a bit.
 

jdoclogan

Platinum Level Sponsor
Currently my Harrington Le Mans has twin Webers with a total (from trumpet inlet to head) runner length of 210mm. My seat of the pants dyno suggests a torque increase around 3200-3400 rpm. This calculator (http://www.wallaceracing.com/runnertorquecalc.php) shows my butt has still got the functioning nerve endings because optimum should be at 3600 rpm. It begins fading at around 5500 rpm.
For my #41 engine build I'm applying a non-original Weber installation option along with the original downdraft 150 Zeniths. For the Weber application the calculator determined my runner length (distance from valve head to common cylinder atmospheric intake point) should be 7.3 inches to match the advance cam duration (265 for Delta grind) with a 1.13 square inch port (30mm diameter) and 5 induction waves (to my understanding this is the most common number of pulses). Thus, I should cut and weld the altered Holbay/Weber manifold such that the head face and Weber mount face are close. This will give me optimum torque at 4050 rpm with 15mm trumpets. It also allows me some tuning options with different length trumpets.

I did a calculation on the comment referred to above about "fastest Chevy style 6 inlines used side draft Webers straight on the head." and found that they were probably dirt track racing. That configuration would have given some serious high rpm torque if the trumpets were short.

Kevin, thanks for pointing me into this exploration.

Its not just intakes but the tuned length of the exhausts.

That will be on the agenda at a later date Michael. Maybe you or someone else has ideas for the best exhaust configuration. All I know at this time is that Jerry Titus and Doane Spencer tried (1962 Sports Car Graphic article) a larger exhaust (2") and found the original (1 3/4") worked best.
 

Alpine 1789

SAOCA President
Diamond Level Sponsor
I have followed this discussion with interest, although not necessarily understanding. But, I do have one question: what is the advantage - or hoped for advantage - of combining the two inlets compared to just cutting the wedge out of the original Holbay manifold and re-welding it?
 

alpine_64

Donation Time
@jerry, think you meant the 36WIP downdraft Zeniths as opposed to 150CD zenith-strombergs.

@Jim, i gather the only real advantage to using the zenith manifold face is it had the larger ports.. The holbay one has smaller and if you cut a wedge per the UK "alpine guide" there is a step in the runners that must be ground out due to the constantly tapering runner...
 

jdoclogan

Platinum Level Sponsor
You are right on the downdraft Zeniths Michael. The HLM and #41 both had 150 jets, but sport the 36WIPs.

Jim, and Michael, what I am doing today is welding the Holbay/Weber faces together. Head face almost flush to Weber mount side (photos to follow). I will not just cut the wedge out and weld as many others before me have done for a street application. I first wanted to know if there was any greater advantage to shortening the runner (Holbay/Weber manifold tube). After research on the physics of molecular fuel/mixture flow and engine performance I concluded there is a great advantage for a race car. By mating the two Holbay/Weber faces together (essentially eliminating the tube) I can achieve a peak torque at 4050 rpm. Otherwise peak torque would be attained at around 3500-3600 rpm. I believe following the logic of Jerry Titus and Doane Spencer in 1962 a racing rpm range of 4000 to 6000 rpm is ideal for the Alpine 1592 to sustain longevity. Somewhat the approach (staying between 4000 and 6000 rpm) taken by the great Rootes driving team Peter Harper and Peter Proctor in the 1961 24 hour Le Mans Thermal Index Efficiency winning Harrington Alpine and my #41 Factory Works Alpine (third in class) at Sebring in 1962. The configuration I am incorporating allows for longer trumpets if I want to change the peak torque rpm. As Kevin noted above, "As to the trumpets, I've always thought that generally the longer ones are better for lower-rpm and torque, versus shorter which are better for high rpm and hp." Whereas, at the end of his quote I would replace "hp" with the word "torque." It is just simple physics right? This also overrides any currently produced ("off the shelf just go and buy it option") Alpine Weber manifolds out there -Pierce, Lynx, etc for the optimum racing application. My configuration provides, again as Kevin remembers, the option to change the length of the trumpets for different driving situations. Like maybe longer trumpets for hill climbing at Prescott in the UK. Are you reading this Glen?
 
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alpine_64

Donation Time
Jerry the guy that used to own peirce setup a company called " the weber man" TWM .. He took some of the patterns and peice got the rest.

You can see the old link via the part number 0077.. The peirce curved one uses the same but with addtional code.. Assume 0077 is reference to upright rootes alloy head in their codes.

index.php

index.php

index.php
 

jdoclogan

Platinum Level Sponsor
Great historical information Michael.

Below are photos of the welding process. This takes a very high level of skill (well above my pay-grade) so I brought in my good friend, Ken, who taught me how to Tig weld aluminum.

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upload_2020-5-14_9-48-54.png Note: Ken was able to get inside to smooth out the joint. I will now spend considerable time sculpting the manifold. There will be a clean and polished 30mm passageway to the head orifice.

All of this and I still purchase a used modified Holbay/Weber manifold/40DOCE Webers setup from the UK ebay this morning. Thanks for the tip Bernd!
 
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