Subject: [Fot] Carb spacers & velocity stack lengths

From: [email-masked]
Date: Tue, 26 Aug 2014 19:42:56 +0000 (UTC)

Greetings Fot 
I was wondering if anyone has done any experimentation with carb spacers and/or different lengths of velocity stacks. 
I'm planning some dyno time in the future and want to make the best of it. 
Thanks as always, 
jim g 
_______________________________________________
[email-masked]

http://www.fot-racing.com

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From: "Jim Gray" <[email-masked]>
Date: Wed, 27 Aug 2014 18:24:49 -0600

I'm trying to get a better understanding of " tuned runner length". Some of
the newer cars have variable runner length because as you say Mike
conventional wisdom says shorter stacks are better on the top and longer
stacks better for low & mid range. My rev limit is 6500 and my shift points
are at 6K. I'm looking into carb spacers to see what affect I may have on
the plenum area of the manifold. One could say I've done a little work on my
manifold. Specifically welded the snott out of it and created the proper
taper to the runners. Stock TR4 manifolds actually have reverse taper.
David Vizard has a runner length calc that goes like this... The general
rule is that you should begin with a runner length of 17.8 cm for a 10,000
rpm peak torque location, from the intake opening to the plenum chamber. You
add 4.3 cm to the runner length for every 1000 rpm that you want the peak
torque to occur before the 10,000 rpm. So if I want my peak torque at 5K for
example my ideal runner length would be 15.47" The stock TR4 runner is only
3-13/16 to the partition.
The rest is considered plenum, I think. At the moment I'm just trying to
plan for some engine dyno time in the near future and deciding what I want
to try next.
jim

-----Original Message-----
From: Mike Munson [mailto:[email-masked]] 
Sent: Wednesday, August 27, 2014 8:35 AM
To: [email-masked]
Subject: Re: [Fot] Carb spacers & velocity stack lengths

I have found a general rule of thumb on webers that short VSs give you more
top end HP and longer ones give you better torque. Full radius horns are
better for both.
Keep in mind the old saying; Horsepower is for bragging but torque wins
races. (Or something like that)

Mike Munson 
#28 EP TR6

> On Aug 26, 2014, at 2:42 PM, [email-masked] wrote:
> 
> Greetings Fot 
> I was wondering if anyone has done any experimentation with carb spacers
and/or different lengths of velocity stacks.

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From: "Jim Gray" <[email-masked]>
Date: Wed, 27 Aug 2014 18:24:55 -0600

-----Original Message-----
From: Mike Munson [mailto:[email-masked]] 
Sent: Wednesday, August 27, 2014 8:35 AM
To: [email-masked]
Subject: Re: [Fot] Carb spacers & velocity stack lengths

Mike Munson 
#28 EP TR6

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From: [email-masked]
Date: Thu, 28 Aug 2014 16:48:37 -0400 (EDT)

In a message dated 08/28/2014 3:29:19 PM Central Daylight Time, 
[email-masked] writes:

> What clubs are allowing this sort of mods?  Around here (Nor Cal) the 
> clubs
> adhere to the old SCCA rules...isn't that sort of the definition of 
> vintage?
> 
Yeah, sort of.  Around here (midwest and points further east) that is sort 
of the basis.  The VSCDA embraces the work of our own Jack Woehrle, who put 
in a ton of work in  and set up some highly respected standards for what is 
legal and what is not in vintage racing.  Some modifications from original 
manufacture are allowed based on those old SCCA rules and what was allowed 
back in the day and some mods are allowed for safety reasons.  The VSCDA 
awards an 'era correct' sticker to race cars that follow those guide lines to the 
letter.  Bob Wismer's TR4 was an 'era correct' TR4.  VSCDA then also allows 
for some further modification(s).  You might be assigned a Mod-1 or a Mod-2 
sticker depending upon how radical the modifications are.  For example, 
Tony Drews car gets a Mod-2 sticker designation for the upgrades past what 
would be 'era correct'.  

Last fall I got passed by a vintage TRIUMPH.  It went by so fast I could 
not read the sticker, but I'm gonna guess it was a Mod-16.

Bill Dentinger