circle track 390 carb motor opions

[SLPRACINGENGINES]

i have a class that runs a very hard compound tire on a 1/4 mile bullring..most cars are running there usual 650 to750 cfm carbs on 600 to 650 h/p motor..there cooking the right rear tire out of the corners..my ideal is to build a motor around 475 to 500 hp.i want to use like a 390 four barrell carb ..use maybe like a sportsman 2 head thats a 200 cc runner ..they flow around 255 to 260 straight out of the box..run a 358 flat top motor ..zero decked ..6.00 rod ..midweight crank around 45 pounds.looking to run a solid roller somewhere around the 610 to 620 lift with a 250 to 252 int dur.and somewhere around a 246 to 248 on exh side.my ideal is small runner head keep the air speed up as much as i can with this carb..havent decided on angle milling the head to bring the compression up some..all input welcome..thanks for everyone input on anything ive every posted in this forum..great group of people here..thanks steve looney slp racing engines

[wyrmrider]

http://www.circletrack.com/techarticles ... z2mZiV3t3e

Another interesting problem Jones is helping many racers combat is spec tire rules. "I recently worked with a guy who was racing a dirt car that was having problems breaking the tires loose coming out of the turns," Jones explains. "His track limited the tire size, and the engine was simply overpowering the tires when he put his foot on the gas. Then, to make things worse, on the straights, when he could use the power, the engine was laying down.

"We didn't want to get rid of the torque the engine was making, but we did want to move it to a place in the rpm range where it would be more useable," he continues.
"The engine was making peak horsepower at 6,500 rpm and peak torque at 4,200 rpm. We estimated at the rpm the driver was coming out of the corners, it was making around 500 ft-lb of torque! So I put the numbers into my program and started playing with them.
I designed a cam with a wider lobe separation that moved the peak torque out to 5,000 rpm. The goal was to give the driver more manageable torque coming out of the turns, and then gain as he went down the stretch.
Again, we gave up a little bit on the peak torque, but in this situation it's OK because the car couldn't handle it anyway."

[pamotorman]

i have found that a vacuum secondary carb works well for these conditions. you can play with the secondary opening to get what you are looking for

[SLPRACINGENGINES]

yeah we tried the sec.holley route.just didnt work out.yeah sort of the same problem im running into here..but were on asphalt.the tracks for years limited us on carbs..350 and 500 ..so we figured out ways around that..so now they are doing the tire deal..running hardier compounded tires.yes i can see where the cam will be a very important part of this.thanks for the input man

[StanJ]

The vacuum secondary approach can work well in these types of situations...we've built and sold probably 50 of them over the years. It does take a little more control over the secondary opening profile than Holley gives you. In addition to secondary spring rate, you also have to control the rate of pressure transfer in the vacuum pod, as well as the secondary "tip in" point (by way of a restriction in the vacuum cross-bleed channel over to the secondary venturi).

[CamKing]

The problem with your idea of running the 390 carb is, at the RPM you're coming off the corner, the 390 carb hasn't become a restriction yet, so you'll still have too much power to hook it up.

[Krooser]

My experience has been that increased compression, with no other changes, will help a car 'jump' out of the corner. Since these cars already are blowing off the tires in that situation maybe you should rethink that option. Back in the 80's when the local pavement guys started running 9-1 motors you could hear and see who was fudging on the compression rule… the high compression cars pulled everyone off the corners.

Without sounding like a suck-up, talk to Cam King about a bump stick. My kid's b-mod had several problems on his initial run last Saturday night but the engine wasn't one of them. While he has a relatively low-buck motor in his car compared to most other guys the HP was certainly there and the Jones cam pulled like two mules on steroids from the corner all the way down the straightaway. The only other cam I can remember doing that was a couple that Chet Herbert hisself ground for me years ago.

[pamotorman]

The vacuum secondary approach can work well in these types of situations...we've built and sold probably 50 of them over the years. It does take a little more control over the secondary opening profile than Holley gives you. In addition to secondary spring rate, you also have to control the rate of pressure transfer in the vacuum pod, as well as the secondary "tip in" point (by way of a restriction in the vacuum cross-bleed channel over to the secondary venturi).

I put a screw in restrictor (allen set screw) in the secondary bleed hole and by changing the size of the hole in the restrictor you can tune the opening

[SLPRACINGENGINES]

mike do you have something we can do with a cam to help cure this...ive got to get with you on grinding me a cam for my big 1/2 to 3/4 mile motor..big cubic inch motor.434 ..ive still got the number wrote down over here than you gave me..when we talked about it a while back.just havent had time to work on my own stuff .. thanks everyone again..yall are always a big help!!!!!!1

[CamKing]

I can help you, no problem.
Email me the rules, the RPM you want to turn it, and what parts you have to work with.

There's no reason you can't build a 650ho engine that doesn't burn the tires off the car.

[wyrmrider]

I dug up the Circle Track article as it's passed its 10th anniversary
trying to help from having one years of experience 10 times
instead of 10 years experience
or history having to repeat itself
drag race motors do not make good circle track motors
nor do those that overpower coming out of the corners and lay down mid track

[SLPRACINGENGINES]

very well said.but i have seen a few circle track motors do fair on the drag strip.no the greatest but fair.but never seen a drag motor do good or fair on a circle track.yeah im going to get with maike and see if we can work out a cam for this.its a weird track..most passing has to be done right out of the corner to the flagstand.very tight corners.probaly one of the worst one groove in the corner tracks ive every raced on..then on top of that they go in a dump sealer on it this year and just makes it worst.but like ive said..i always enjoy everys input on problems..ive always looked at it this away nobody knows everything ..but run it thur enough people and youll usually come up with a answer..thanks everyone as always for your help!!!!!!!!

[ParDeus]

You just need a good tire soak that doesn't affect the duro and can't be caught on the sniffer...

I wonder who has something like that???
(I'm only partially kidding)