DeTomaso Mailing List: May 1997, Message #103
     



From: MikeLDrew@aol.com

Subject: Re: Holley carbs

Date: Sun, 4 May 1997 00:18:45 -0400 (EDT)



Capt Mike Drew

150 Westgate Dr.

San Francisco, CA  94127



Home:   (415) 334-7860



E-mail:  MikeLDrew@aol.com



Hello all,



Chris Bupp wrote to me:



Mike;



I saw your comments about the custom tuned Holleys that Larry has, and I have

a few questions.   Can you custom tune a carb without knowing the specifics

of the engine it is or will be used on?  I know very little about Holleys,

even though I got one (650 double pumper/merchanical secondaries) on my

Pantera.   I would think that the breathing characteristics of the engine,

such as the manifold, cam grind, and exhaust system might affect the carb

settings.  Or are those factors not significant?  Are the custom Holleys

different in parts or features, or just careful, detailed calibration?



How would I make a guess as to whether my car would benefit from the custom

Holley vs my own.  I have no symptoms, as the car runs fine.  I could assume

the previous owner (before I bought it in '93) had somebody do a good jetting

job, but I don't know.  All I have done to the carb is rebuild it due to

leaks from dried out gaskets, etc from I assume lack of use by previous

owner, and adjust idle mixture screws.



>>>Good questions, probably better answered by others more technically adept

than I (there are many, many of those people by the way.)  I'll give it a

stab, though.



This is basically what Larry told me about his carbs:  He spent several years

experimenting with different sized carbs, initially trying a 650 and finding

it too small, then a 750 and finding it too big, and finally settled on a 700

as the best match.  He spent many hours on the phone with the tech guys at

Holley also.  Realize that when they build a carburetor, it goes out the door

ready to bolt on to virtually anything with the correct flange size, from a

289 to a 460.  They use the TLAR method (That Looks About Right) to come up

with jetting, figuring that 90% of the time they'll be within 75% of where

they want to be.



But Larry spoke to them specifically about Clevelands.  Whether you're

running a big cam or a small cam, big intake or small intake, the differences

between a mild and wild Cleveland are smaller than, say, a 289 to a 427.  So

the envelope is narrowed considerably.  In conference with the Holley guys,

and based on several years of testing (using a chassis dyno, but also a

Valentine g-meter which measures linear acceleration and can point out

hiccups and stumbles in a carburetor that a dyno can't see), he came up with

what he thinks is the optimal jetting for MOST Clevelands.  If you've got a

monster motor, or are running around at 8,000 feet, you might need to go up

or down a few jet sizes, but out of the box you'll be close, certainly closer

than you can expect from an off-the-shelf carburetor.



Too, he has them custom-built by the Holley race shop with much better-grade

components than they originally come with.  Holley has a fairly large

optional equipment list, and he ticks off virtually every box.  For example,

the stock carbs come with plastic float bowls; he goes for the all-metal

ones.  The stock carbs, you have to take the bowls off to change the jets,

but he has quick-change jets installed that can be changed with the bowls in

place.  The stock carbs have a brass screw for the float level adjustment;

you turn up the float level until gas pours all out the side, then you're

done.  He has clear plastic caps that allow you to sight the level of the gas

inside and not make a mess.  Stainless steel fuel lines, and so on and so

forth...



When he first told me he was planning on selling Holleys for over $800, I

asked him what he had been smoking, and showed him a Jegs catalog where

nominally the same carb could be had for less than $300.  But he then showed

me the retail price of all the options he adds to the carbs, and by the time

all was said and done, if you bought a Jegs carb and optioned it out like

Larry's you'd be up to $800.



Essentially, you're paying for the hardware and getting the R&D for free.

That's what he says, anyway.  He seems pretty confident in them; he's sold a

bunch (20-30 maybe) with a full money back guarantee-if it doesn't perform as

advertised, he'll just refund your money, no questions asked.  NOBODY takes

returns on carbs.  But so far he's never had one come back.



At a club dyno day several years ago, he was tickled pink when he bounced one

of his carbs from one car to the next, and every one saw a measurable

increase, one car saw a 17 hp jump over a stock 750 double-pumper, with no

additional jetting to optimize it to that particular motor.



As for me, well, considering my car is still in pieces (although it's close,

real close) I haven't bothered to replace the out-of-the-box 650

double-pumper I'm running.  I figure I'll drive the car for awhile before

sampling one of his 700 double-pumper wonders and see if it makes enough

difference to justify the expense.  I maintain a small dose of skepticism,

since my existing carb was dialed in and jetted on an engine dyno (and, I'm a

cheap bastard too.)



In your case, I'd simply urge you to call him and ask him if you can try one

out.  I know he's got one out of the box that the Nor-Cal club ran on Michael

Harper's car for a few months on the Nor-Cal club motor, but is otherwise

new.  You like it, you keep it and pay for it.  If not, just send it back.



Howzat?  Anybody else care to elaborate or refute anything I've said?  I can

blather on all night with no fears, because I'm just parroting what Larry

told me.  I could no more tune or jet a carburetor than I could flap my arms

and fly to the moon, so I'm not offering any personal opinions here.



Mike