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Re: Mikuni TM's and velocity stacks [Re: Hillbilly bike] #539344 04/22/14 12:29 pm
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Allan Gill Offline
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Originally Posted by Hillbilly bike
Production classes must look like a stock bike but anything goes for engine modifications so long as the stock airbox, if equipped, and stock muffler outlet size.


So a A65 engine in an A10 frame with Alu forks won't cut the mustard then, even if it has the other bits?


beerchug
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Re: Mikuni TM's and velocity stacks [Re: Allan Gill] #539358 04/22/14 2:15 pm
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Hillbilly bike Offline OP
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Originally Posted by Allan Gill
Originally Posted by Hillbilly bike
Production classes must look like a stock bike but anything goes for engine modifications so long as the stock airbox, if equipped, and stock muffler outlet size.


So a A65 engine in an A10 frame with Alu forks won't cut the mustard then, even if it has the other bits?


No,it would be classified as Modified Production ...Engine and frame from same manufacturer but otherwise never came that way from the factory. The rest of the cycle parts can be any brand or home built. The engine cradle has to be stock but the rest of the frame can be modified within the rules.1955 and earlier parts can be run as Vintage. Vintage engines are not supposed to use electronic ignitions or electronic injection... Send for a SCTA rule book to see all the rules...
The ECTA track relies on the honor system, there are no protests, no trophies. If you want a pretty trophy girl to kiss ,bring your own....


79 T140D, 96 900M Ducati ....On a bike you can out run the demons..
Re: Mikuni TM's and velocity stacks [Re: Hillbilly bike] #539382 04/22/14 5:10 pm
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Allan Gill Offline
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Originally Posted by Hillbilly bike
If you want a pretty trophy girl to kiss ,bring your own....


laughing

Thanks for that HB, suppose it makes sense but it was worth clearing it up. I'm guessing the completion gets even harder when you start entering modified frames, when you go to that, you may as well get something lighter still.


beerchug
Re: Mikuni TM's and velocity stacks [Re: Hillbilly bike] #539694 04/24/14 11:58 am
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Ron - in California R.I.P. Offline
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Quick update, as I am headed to the race track.. time to see what we can do..! Did a quick dyno check after going over everything and making a carb needle change.. Aha..! found a bad spark plug cap. You can not easily find stuff like that any other way.. note I said easily.. (with a twin plug head it won't misfire, just lose power). Once I removed the cap, there were the carbon tracks.. all the power is there and a bit more..! Geesh.. that was almost too easy..! I will be short on gearing, as my one transmission sprocket got ruined last week.. but I suspect we will make do OK.

We are going to have some great competition this weekend.. two G50's. two Goldies, a BMW, and one sneaky fellow on an Aermacchi.. could be more, but those are the preregisterd bikes. A couple of those guys are good pals... should be a lot of fun..!

Ron

Re: Mikuni TM's and velocity stacks [Re: Hillbilly bike] #542869 05/13/14 9:24 am
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dommie90 Offline
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If you get hold of "MIKUNI carburetor tuning by victory libary" i has all the information on mikis.
including velosity stacks and jetting its a very detailed book excellent reading
baz

Re: Mikuni TM's and velocity stacks [Re: Hillbilly bike] #598726 05/10/15 4:36 am
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Originally Posted by Hillbilly bike
Using available formulas and plugging in my engine specification comes up with different results.

Engine Pro - Intake Port Length is 14.02 inches
Gordon Blair Formula - Intake Length is 10.69 inches
Simplified Chrysler Formula - Intake Length is 11.67 inches
Simplified Chrysler Formula (with bigger cam) - Intake Length is 11.15 inches
Simplified Formula - Intake Length is 11.00 inches
Simplified Formula 2 - Intake Length is 13.60 inches
Simplified Formula 3 - Intake Length is 12.83 inches

Obviously a formula is only a quess and time spent on a dyno and at the track is the only way to know for sure.
There appears to be two things happening at once from intake and or velocity stack length.
Longer length appears to move peak HP to a higher rpm and moves the torque lower and flatter at the same time.
Shorter length does just the opposite.
but I'll get it done...


with the pro program what dia did it suggest
and what cam ex lengths did you run Hb?

Re: Mikuni TM's and velocity stacks [Re: ken sak] #598735 05/10/15 6:40 am
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Hillbilly bike Offline OP
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Originally Posted by ken sak


with the pro program what dia did it suggest
and what cam ex lengths did you run Hb?


Shorty after this discussion last year I spend hours tuning the bike on a chassis dyno. None of the formulas mentioned produced worthwhile results....
Highest peak power with the broadest torque spread was made with no velocity stacks, the carbs as close as practical to the head (about one inch longer intake manifold than stock).The exhaust was two 1-1/2 x 38 inch exhaust pipes.
The combination made record breaking speed at the track....What works best on my 650 Triumph with Sifton #390 cams might not be best on another engine.


79 T140D, 96 900M Ducati ....On a bike you can out run the demons..
Re: Mikuni TM's and velocity stacks [Re: Hillbilly bike] #598756 05/10/15 8:41 am
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ken sak Offline
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thanks for the info Hb. congratz on your record too, i was thinking of just running the stock 78 750 manifolds with flatside mikuni's and 2 750 inlet cams, only a couple of degrees here and there and much the same lift as the sifton #390
i'm oldish and have looked up the t100 tuning kit to get an idea of lengths of pipes-finish at the back of primary , short megas to about 4" finish about the back axle.
what's your low end power like, with the 390, another site says it's not streetable but I've put radical cams
in cars and put up with it
cheers, Ken

Last edited by ken sak; 05/10/15 9:08 am. Reason: time
Re: Mikuni TM's and velocity stacks [Re: ken sak] #599030 05/11/15 7:16 pm
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Hillbilly bike Offline OP
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Originally Posted by ken sak
thanks for the info Hb. congratz on your record too, i was thinking of just running the stock 78 750 manifolds with flatside mikuni's and 2 750 inlet cams, only a couple of degrees here and there and much the same lift as the sifton #390
i'm oldish and have looked up the t100 tuning kit to get an idea of lengths of pipes-finish at the back of primary , short megas to about 4" finish about the back axle.
what's your low end power like, with the 390, another site says it's not streetable but I've put radical cams
in cars and put up with it
cheers, Ken


My 650 with 34 MM flat slides ans Sifton 390 cams idles reliably at 1000 rpm on the electric tach. Off idle is ok at part throttle but use full throttle and there's a bit of reversion at around 4000 rpm. Once past that the throttle response is fantastic....I think in a 750 the #390's would be ok with the proper gearing in a light bike. Perhaps messing with part throttle jetting, intakes and pipes might get rid of the reversion for limited street use..
Cams for vintage bikes like Triumphs are mostly older grinds and lack the sophisticated profiles of modern car cams.Triumph guys jockey the cam timing around to find power, but on something like a Chevy V8 if you need to alter timing by more than two degrees, it's better to select another cam from the endless list of grinds available.


79 T140D, 96 900M Ducati ....On a bike you can out run the demons..
Re: Mikuni TM's and velocity stacks [Re: Hillbilly bike] #599079 05/12/15 3:51 am
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Originally Posted by Hillbilly bike
Using available formulas and plugging in my engine specification comes up with different results.

Engine Pro - Intake Port Length is 14.02 inches
Gordon Blair Formula - Intake Length is 10.69 inches
Simplified Chrysler Formula - Intake Length is 11.67 inches
Simplified Chrysler Formula (with bigger cam) - Intake Length is 11.15 inches
Simplified Formula - Intake Length is 11.00 inches
Simplified Formula 2 - Intake Length is 13.60 inches
Simplified Formula 3 - Intake Length is 12.83 inches

Obviously a formula is only a quess and time spent on a dyno and at the track is the only way to know for sure.
There appears to be two things happening at once from intake and or velocity stack length.
Longer length appears to move peak HP to a higher rpm and moves the torque lower and flatter at the same time.
Shorter length does just the opposite.
For my racing I need both torque and HP at higher rpm...

Here's what I have as the Gordon Blair formula, and it offers 4 alternative lengths for any given ambient air temperature.

Gordon Blair gives the following empirical formula for induction lengths (see: “Design and Simulation of Four-stroke Engines”). He maintains that it is accurate to about 3%.
The induction wave is reflected up to five times, and the equation for the length is:
L = (aC /N)
Where L = Induction length from valve head to end of bellmouth in mm.
a = reference speed of sound at 340 at 15 degrees C, 346 at 25 degrees C
C = Dimensionless intake ramming factor
* for first ramming peak C = 8900, second C= 6600, third C= 5150, fourth C= 4150.
N = rpm at which you want the torque improvement.

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