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Old 05-16-2009, 05:11 AM
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CFM question

Hello everybody,
My question is, what kind of carb. should I buy for my dirt track car?
Here are some engine specs,

chevy 305 small block
XE 274H-10 camshaft
RP1412-16 roller rockers
812-16 lifters
742-16 retainers
7812-16 pushrods
981-16 valve springs
stock intake/exhaust valves
edelbrock performer intake
stock exhaust manifolds

wich is better, edelbrock, holley, rochester??
When I am driving it, it is almost constantly at WOT. ( I only brake for the BIG jumps...)

And does it make a big difference when I degree the cam versus installing it the normal way?

Thanks in advance for your replies, and the best regards from holland!

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Old 05-16-2009, 05:19 AM
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Stick a Quadrajet on it, tune it and forget it. Degreeing the cam won`t likely give you any noticible power gains.
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Old 05-16-2009, 07:09 PM
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Dirt track in Europe must be different than dirt circle track in the US. Did you say jumps?
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Old 05-18-2009, 12:05 AM
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Yes, sometimes the jumps are a bit too much...

you can look at www.dollweekend.nl and watch the u-tube movie on the main page.
then you get an idea of what we do..

greetings,

Ad.
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Old 05-18-2009, 12:54 AM
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Hahahaha that's some good stuff there oilburner...I liked the monkeemobile, and the car with the giraffe head on it...The Unimog with a little pink house was kicking a s s on the sikorskycar....
Looked like a viking version of the Wacky Races.

Later, mikey
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BE different....ACT normal.

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Old 05-18-2009, 05:12 AM
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Some of those cars look like ones you`d see on the Road Warrior lol. The only thing missing is lord humungous lol.
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Old 05-18-2009, 08:16 AM
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I build my firebird like the holden from mad max 2
with the 2 gasoline tanks in the trunk and a home made blower on the hood

I can't seem to put the pictures in this thread
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Old 05-18-2009, 08:21 AM
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Quote:
Originally Posted by oilburner
Hello everybody,
My question is, what kind of carb. should I buy for my dirt track car?
What would benefit you, is a Holley carb like shown HERE.

You can also modify a side-hung float-type carb to behave well in the jumps and extreme lean angles you face in your type of racing. A Holley 1850, 600 cfm carb will feed the 305, and can be bought used for pennies on the dollar compared to new.

If you use a Holley "Trick Kit" kit w/the jet and vent extensions, along w/a piece of fuel tubing that connects the external vent tubes (needs a hole underside of the tube to allow venting), you can approximate the performance of the truck Holley linked above.

But (and a big one)- you will not get the annular boosters of the Truck Avenger carb. They really help more than some realize, but if you're tuned well enough, the standard boosters of the 1850 Holley will work OK as well, especially if you have it WFO for most of the time.
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Old 05-18-2009, 08:28 AM
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Quote:
Originally Posted by DoubleVision
Stick a Quadrajet on it, tune it and forget it. Degreeing the cam won`t likely give you any noticible power gains.
And how much CFM should I go for?
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Old 05-18-2009, 08:54 AM
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Quote:
Originally Posted by cobalt327
What would benefit you, is a Holley carb like shown HERE.

You can also modify a side-hung float-type carb to behave well in the jumps and extreme lean angles you face in your type of racing. A Holley 1850, 600 cfm carb will feed the 305, and can be bought used for pennies on the dollar compared to new.

If you use a Holley "Trick Kit" kit w/the jet and vent extensions, along w/a piece of fuel tubing that connects the external vent tubes (needs a hole underside of the tube to allow venting), you can approximate the performance of the truck Holley linked above.

But (and a big one)- you will not get the annular boosters of the Truck Avenger carb. They really help more than some realize, but if you're tuned well enough, the standard boosters of the 1850 Holley will work OK as well, especially if you have it WFO for most of the time.
Tanks for this reply also, I will look into this also!
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Old 05-18-2009, 09:54 AM
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howdy there!

see these
Q-jet carbs.


http://home.earthlink.net/~quadrajet...ow_ratings.htm


FYI:

all Q-jet carbs were 750 and 800 cfm

some were 800cfm on some of the bigger oldsmobile engines for example, among some other applications. you can tell which is is by loooking down the primary venturii and if there is a pretty noticably tall casting ring(annular ring)around the venturi and is not almost smooth then its the 750.

i recommend one because they always seem to run fine at extreme vehicle angles without stumbling/losing fuel in the bowl, etc.

not to mention they are vacuum secondaries and very reliable, also common and cheap and easy to find parts for should they need any in which is very rare though.

plus they have all the connections available and easy, for power brakes and so on

and theres no real tuning to them, other than the older ones have idle fuel mixture you can adjust,


just make sure the Q jet you use has tight and not sloppy throttle shaft bushings. because if they are sloppy and the shafts' seals/bushings are not good then the idle can be not perfect or good.

also do a test by filling the bowl full of gas; and before mounting the carb to the engine; let it sit over a coffee can or something like that and see if it leaks any gas slowly,
let it sit a long time when doing this,
this will test to see if the main well plugs are leaking.
if they are then simply unscrew the base plate assembly from the carb and get metal epoxy/filler like JB weld for example and seal over the two main well plugs. if they leak then they will allow the bowl to drain when sitting not running and so will make for extra cranking to start up again because the bowl needs re-filled.


very easy fix

these two things are really the biggest flaws of the Q jet carbs, but not a big deal though.

You can add capacity to the bowl by removing some of the material from the bottom areas of the black plastic spacer block that sits over the float in the carb there.
I've done this in a few q jets in the past, especially in later years' ones with a larger block.


interesting racing over there, in your England, wow.

so different and out of the box hmm,,

have fun!!

Last edited by fast68; 05-18-2009 at 11:39 AM.
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Old 05-18-2009, 10:28 AM
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Great stuff oilburner. Great music also. Cole
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Old 05-18-2009, 11:22 AM
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Even so I stick to Quadrajets because in the many many cases I`ve delt with Holley`s I`ve found quality is far from outstanding.
Anyways, since I didn`t realize as it wasn`t mentioned in the first thread that jumps were made in this case I`m going to agree with Cobalt. Annular boosters are something I keep on a closed lip, they are far the best of all booster designs. Downleg boosters are sluggish and just about worthless. Straight leg boosters work okay. Quadrajets have a triple booster design that is just about as good as Annular boosters. Why I like Quadrajets is because the primaries are small and give fuel injection like throttle response, real sensitive. The massive secondaries provide maximum flow for max performance at wide open throttle. The down side to the Quadrajet is the float bowl is on the small side so it has to be compensated for by doing modifications as well as making sure the fuel system can keep a 5 psi fuel pressure and plenty of volume. Quadrajets on a race car is for someone who don`t mind tweeking with them as they are slightly harder to tune than a Holley. So in this case the easier tunability and larger float bowls as well as working with steep angles will be your best bet.
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Old 05-18-2009, 12:00 PM
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according to all specs info i have ever seen from GM directly, its always 7-13 psi with the stock factory pumps. i like tp keep my pressure more towards the 13 when running a q jet. i also do not keep a filter in the carb inlet. solely to keep fuel flow resistance down.
and yeah you can do a few mods to increase fuel bowl volume yep
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Old 05-18-2009, 12:29 PM
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thank you, thank you, for all these replies

I'm going to look for a Q-jet overhere, I have some lying ( correct spelling?)around in my shop, but most of them are very old or/and incomplete.

can anyone tell me how to put a picture on this site?

greetings, Ad from holland.
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