SBC tunnel ram carb change , READ... MORE CFM

General engine tech -- Drag Racing to Circle Track

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NormS
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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby NormS » Mon Sep 11, 2017 8:10 am

The key to dyno tuning is to duplicate everything on the dyno that the engine will see in the car...fuel system, exhaust system. and ignition system. When you do this, power gains found on the dyno usually show up at the track. I have found that when power gains do not show up at the track, in most cases, it's because there were some differences in one or more of these 3 major systems, or the effects of G forces on the fuel system were not addressed at the track.
Competition Fuel Systems Vassar, MI.

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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby F-BIRD'88 » Mon Sep 11, 2017 8:17 am

8800 rpm... That$ a- LOT-A boat out a' da water

Good tales ..

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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby randy331 » Mon Sep 11, 2017 6:10 pm

Before spending the money on new carbs you may want to contact Mark Whitener to see if he'd take a look at them. I had a 850 holley that someone machined the venturi way out and it didn't work well. I sent it to him and he replaced boosters and other mods. When I put it on an engine on the dyno it had a very flat fuel curve all the way through the RPM range. After I took a couple jets out of it, It put a little power on my 383 VS my Braswell.
Tried it on my son's pulling truck engine and the fuel curve was flat on it too.

Be worth checking on, cause unless there is something wrong with the fuel curve on the 660s, it's in likely 750s will add much power.

Randy

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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby randy331 » Mon Sep 11, 2017 6:11 pm

Double post.

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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby joespanova » Tue Sep 12, 2017 5:11 am

I've decided not to get the carbs. Car runs so well with the 660's I have no faith in new carbs making enough difference............read that 2 tenths.
Frankly I'm surprised Sherman didn't have more to say since I'm sure he's tried every conceivable combination with the Victor Ram...............right Joe?
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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby cjperformance » Tue Sep 12, 2017 6:33 am

Anyone so positively confident of a REAL good gain would happily loan OR give you a money back guarantee or that swap. Well set up 660's are not that bad !
Craig.

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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby F-BIRD'88 » Tue Sep 12, 2017 7:58 am

You did not provide any information of the car to make any kind of analysis of whether a different carbs set would help.
What is needed? answer: everything....Everything matters.

But here is something...What is the 1/8th mile ET and MPH compared to the 1/4 mile data from time slips?
This is a place to start.
is the top end keeping up with the performance of the first 1/8th mile of the trip? Or is the top end power being snipped off.
Does not tell you what the cause is, but ID's a issue.

I'd rather recommend improvements in other area that don't cost a lot to improve the ET.
EG: How (well) the air enters the carbs. (this matters)
Car areo dynamics.

Fuel used...The racing fuel used matters more than most think. There is power and car performance in that.

TIRES....tires make a big difference. Stuff like that.

Converter change or tune up.

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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby F-BIRD'88 » Tue Sep 12, 2017 8:21 am

If you wanted to measure the intake manifold vacuum , you'd want to measure that during the last 300 feet
of the 1/4 mile. A high (relative) vacuum reading may not be carb cfm size restriction. it can also be
poor air flow quality going into the carbs at high car speed. You could see this when comparing
manifold vacuum measured during a drag pass VS during a run on a chassis dyno.
Making the 140 MPH air flow better into the carbs is as good as sticking a bigger carb on.
And probabily a lot cheaper.
You could "datalog" using a go pro camera on a manometer. or a BIG vacuum gauge with fine movement.

Do you see a different pressure differential when at 140 MPH VS at rest 0 MPH on a chassis dyno, at and near max WOT engine rpm. You want to (at least) eliminate any negative supercharging effect of bad air flow, if not create a small "ram air" pressure gain effect at 140 MPH.

Can you get/borrow another set of carbs to try. Even if it slows the car, it tells you something.

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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby F-BIRD'88 » Tue Sep 12, 2017 8:53 am

A HVAC technicians Digital 2 port manometer with USB connectivity for data logging is not big bucks.
This may reveal some truths. Probably lots of used ones for sale.

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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby statsystems » Tue Sep 12, 2017 9:42 am

joespanova wrote:I've decided not to get the carbs. Car runs so well with the 660's I have no faith in new carbs making enough difference............read that 2 tenths.
Frankly I'm surprised Sherman didn't have more to say since I'm sure he's tried every conceivable combination with the Victor Ram...............right Joe?



Several on here have told you those carbs are obsolete. To make them not obsolete would require more money than buying two new carbs.

It isn't 1975 anymore. Even in 1975 those carbs were too small. These carbs run so great that you start a thread because they car isn't what you want it to be.

Don't be motivated by fear. You are afraid it can't make 2 tenths. I can and will. You can live in the 1970's or move up. Even a pair of BLP B4X carbs would be miles ahead of what you have.

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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby bigjoe1 » Tue Sep 12, 2017 9:44 am

I have seen small gain from bigger carbs on the dyno, BUT--- in the car is a whole nother story. About one out of ten will make the car run quicker with the bigger carbs-- The rest run the same ,OR SLOWER !




JOE SHERMAN RACING

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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby F-BIRD'88 » Tue Sep 12, 2017 10:16 am

Have you considered trying changes to the intake plenum volume/ shape and carb top height?

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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby joespanova » Tue Sep 12, 2017 10:30 am

statsystems wrote:
joespanova wrote:I've decided not to get the carbs. Car runs so well with the 660's I have no faith in new carbs making enough difference............read that 2 tenths.
Frankly I'm surprised Sherman didn't have more to say since I'm sure he's tried every conceivable combination with the Victor Ram...............right Joe?



Several on here have told you those carbs are obsolete. To make them not obsolete would require more money than buying two new carbs.

It isn't 1975 anymore. Even in 1975 those carbs were too small. These carbs run so great that you start a thread because they car isn't what you want it to be.


I DIDNT SAY ANYWHERE , THAT IT ISN'T WHERE I WANT IT TO BE...............LOL
I believe , IIRC from my own brain..........I asked whether larger carbs could offer x amount of performance potential....as in ex. , if I / they pick up about .2 , I can run the 9.25 indexes securely. I'm happy staying right where I am. 9.50 indexes. Its just for the fun of it..........I mean geezus c. , that's the only reason I do any of this..........its not that important that I pick up additional E.T. With the old clutch assisted Nash I run , driving is plenty fun as it is. If any carb guy / shop hands me 2 carbs and it picks the car up .2 , I'll buy then...... right on the spot.
The incrementals from the ET slips don't indicate a strength or weakness anywhere. They do seem to indicate a proportionate / appropriate relationship.
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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby F-BIRD'88 » Tue Sep 12, 2017 1:36 pm

What is the estimated cost (all in) of switching to larger carbs?
Including linkage /mounting changes.

Is this a factor? (budget)

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Re: SBC tunnel ram carb change , READ... MORE CFM

Postby cjperformance » Tue Sep 12, 2017 6:58 pm

bigjoe1 wrote:I have seen small gain from bigger carbs on the dyno, BUT--- in the car is a whole nother story. About one out of ten will make the car run quicker with the bigger carbs-- The rest run the same ,OR SLOWER !




JOE SHERMAN RACING


Could not agree more Joe !
Craig.


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