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PATMAX
Well-Known Member
This has been done since the mid eighties right after the Max came out. It works. That is about all that can be said. No great leaps in performance. Saw one on a drag bike. Sure is a whole lot of work for just something a little different. Don't waste your time.:bang head:
the bad part of this type of conversion is that the carb can be setup for low end or high end. They simply won't work with the full range of rpm's the vmax sees.
Sean
Sean
kevman
Well-Known Member
And the carb isn't made for motorbikes so I heard you can run out of fuel going around long sweeping curves.Might be an urban myth but you just don't know.Give mythbusters a call.Kevman
KJShover
Proud Vmax lover
It was a carburator consideration on Vmax drag bikes that some ppl used, there was a 4bbl manifold w/a holley that sold on eBay a few months back. I put a bid on it mainly cause I wanted to try out a small throttle body fuel injection unit on it, But was outbid. I think it went for around $500. Oh well, it dosn't look too hard to fab a sheet metal tunnel ram style manifold for the project.
The supercharger setups utilize a holley 390 4bbl.
I don't have any pictures of it but a Vmax owner named Rich Scharf (sp?) has a custom manifold and he's running a 2bbl carb on it.
here is a pic of the 4bbl manifold and the TBI unit I wanted to mess with.
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Rusty McNeil
Well-Known Member
I think Novack, the guy with all the supercharger run videos on the web, used that setup at one time with the holey "pro-jection" which is basically a TBI unit, it offers some tuneability ease.
spyder13
Well-Known Member
I think Dale Walker sold this set option at one point and time. Contact him for more info.
lankeeyankee
Well-Known Member
Yes, but they always go the same direction. I've got a number of increased capacity oil pans if you want to do nothing but go in one direction in a circle. might have to make a custom header too and they may not even clear the frame rails.
Sean
Sean
lankeeyankee
Well-Known Member
There are those that think....
A) It doesnt have a part number for my application cant be done.
B) I can make it work with some time.
A) It doesnt have a part number for my application cant be done.
B) I can make it work with some time.
the carb really doesn't have too many issues with being mounted on a motorcycle engine other then even the smallest 4 barrel is too large. Even many 2 barrels are pusing the size issue. The holley (and quadrajunk) simply don't have the operating range needed to be a good streetable carb.
Sean
Sean
Rusty McNeil
Well-Known Member
I am not saying this because I think I already know the answer, OK?
The Holley 4150 Spread bore, which is a quadrajet replacement, with really small primaries and larger vaccum secondaries. would seem like it would work for this if one could be found small enough. but I don't think there is one that small.
To my way of thinking you could tune to your hearts content and if the airflow/cfm is too big your gonna end up with a low end compromise consisting of a soggy bottom end at best.
It looks like none of thier EFI tbi units are small enough either.
Not do they have any 2 barrell carbs smaller than 300 CFM, the 300CFM being made for marine use usually consisting of more "steady state" throttle conditions and perhaps not useable for the street?
I still like the idea and think it would be cool though, maybe a mechanical secondary carb, perhaps treat it like a flatslide and learn some throttle control,, tuned right, with throttle opening stops to keep it from being opened up too far and bogging out????????
A big velocitity stack sticking through the top cover sure would be cool....
The Holley 4150 Spread bore, which is a quadrajet replacement, with really small primaries and larger vaccum secondaries. would seem like it would work for this if one could be found small enough. but I don't think there is one that small.
To my way of thinking you could tune to your hearts content and if the airflow/cfm is too big your gonna end up with a low end compromise consisting of a soggy bottom end at best.
It looks like none of thier EFI tbi units are small enough either.
Not do they have any 2 barrell carbs smaller than 300 CFM, the 300CFM being made for marine use usually consisting of more "steady state" throttle conditions and perhaps not useable for the street?
I still like the idea and think it would be cool though, maybe a mechanical secondary carb, perhaps treat it like a flatslide and learn some throttle control,, tuned right, with throttle opening stops to keep it from being opened up too far and bogging out????????
A big velocitity stack sticking through the top cover sure would be cool....
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KJShover
Proud Vmax lover
It does sound like a good tinkerer's project.
Figure that the formula for determining the air required by a 4-stroke engine is:
CFM = (engine size in cubic inches) x (maximum RPM) / 3456
assuming that the engine is a, 73.1 ci, Vmax motor that is going to run at a maximum of 9200 RPM.
With 100% volumetric efficiency, we will theoretically need 194.5 CFM, since there are pressure drops in the induction system, we will only need about 145.8 CFM with a VE of 75% and 165.3 CFM at 85%.
2 bbl carbs are rated at 3.0 inches of mercury (3.0" Hg) pressure drop while four barrel carbs are rated at 1.5 inches.
The relationship between the air flow rating in CFM between the two pressure drops is: (Flow @ 3.0" Hg) = 1.414 x (Flow @ 1.5" Hg)
The Carter BBS 1bbl carb was rated around 200 CFM (~ 141 CFM @ 1.5" Hg). The two barrel BBD carb that came with some of the slant 6's was rated around 285 CFM (~ 202 CFM @ 1.5" Hg).
In theory, I think it can be done better with a small 2bbl or a single barrel carb, I would question the performance of it, but it would be fun to play with :biglaugh:
It would be interesting to pick through Rich Scharf and Dale Walker's data when they were running with the setup.
Figure that the formula for determining the air required by a 4-stroke engine is:
CFM = (engine size in cubic inches) x (maximum RPM) / 3456
assuming that the engine is a, 73.1 ci, Vmax motor that is going to run at a maximum of 9200 RPM.
With 100% volumetric efficiency, we will theoretically need 194.5 CFM, since there are pressure drops in the induction system, we will only need about 145.8 CFM with a VE of 75% and 165.3 CFM at 85%.
2 bbl carbs are rated at 3.0 inches of mercury (3.0" Hg) pressure drop while four barrel carbs are rated at 1.5 inches.
The relationship between the air flow rating in CFM between the two pressure drops is: (Flow @ 3.0" Hg) = 1.414 x (Flow @ 1.5" Hg)
The Carter BBS 1bbl carb was rated around 200 CFM (~ 141 CFM @ 1.5" Hg). The two barrel BBD carb that came with some of the slant 6's was rated around 285 CFM (~ 202 CFM @ 1.5" Hg).
In theory, I think it can be done better with a small 2bbl or a single barrel carb, I would question the performance of it, but it would be fun to play with :biglaugh:
It would be interesting to pick through Rich Scharf and Dale Walker's data when they were running with the setup.
kevman
Well-Known Member
Those who say it can't be done should get out of the road of those who are doing it.By the way I looked at the Holley and decided it could be feasible on a bike if you fitted a fuel injection system but the cost was way to high so I am still doing my efi project .Very bargain basement.Cheers Kevman........and before I forget wtf is nascar?
It has been done numerous times and i've seen a few in person. They all work well at max throttle and rpm. Sorry if i've got a bit more practical experience and not just theory. The one set that I liked was on a lawn tractor puller. He got tired of blowing up vmax engines so he went with venture engines. For whatever reason they tended to hold up better.
Sean
Sean
NASCAR....National Assoc. of Stock Car Auto Racing...
Marcos Ambrose, from 'down under' is representing you guys, and doing a pretty decent job too. He was V8 Supercar champ in Austrailia before moving to NASCAR
KJShover
Proud Vmax lover
For street use, do you think a single bbl carb would perform better? There was a racer up here, who was always tinkering with his stuff, he had a similar 4bbl setup he made from a modified sheet metal manifold setup for his Goldwing but like the dragbikes it was best at WOT and up in the R's. So I was thinking a 1 bbl might dial it in a little better.
hmm side draft webber's would look pretty trick :biglaugh:
I've looked at a few IDF carbs for the max and I do think they would work well. Again, it's important not to get too large otherwise you will have nothing but top end power and no low and midrange.
Sean
Sean
lankeeyankee
Well-Known Member
Redbone
Well-Known Member
Nascar = 3 hours of talking heads before the race, caution flags for hot dog wrappers and run for the covers when it rains. :rofl_200:Hell, even motorcycles run in the rain. :worthy:
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