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Author Topic:   high rpm question
DirtFreak08
Dirt Forum Racer

Total posts: 77
posted May 24, 2004 07:36 PM  
Here's my deal guys, This past weekend my car sounded good once it warmed up. When it's first started it sounded like it had a little stutter to it. During the race, it accelerated great, but once I hit the 5200-5500 range it sounded like the stutter came back, but still accelerated great. I'm also not at the rpm range I want to be at. I have been hitting 5900 every night this year, but I would like to be at 6200-6500. I changed my distributor cap, coil, rotor button and plug wires last week. It got more power for me but the miss came. Where should I check? I'm going to readjust my valves and timing, and check my plugs to see if I need to change my jets. Should these be the places to look first or is there something I may be overlooking?? Thanks in advance for any help.

racer17j
Dirt Forum Champ
Total posts: 5390
posted May 24, 2004 08:26 PM  
your car needs to warm up first. don't judge it when it's cold. when it's not yet up to temp, the fuel entering the intake manifold and going into the combustion chamber does not atomize/vaporize correctly.

it's like putting water on a cold grill. you will see a bunch of water droplets.
put water on a warm/hot grill and it vaporizes.

you want a vaporized fuel mixture going down the intake, into the combustion chamber; not a bunch of fuel droplets.

if the stutter is more like a hesitation, it's probably a fuel starvation or not enough air problem; if it's more like an miss, it's probably an ignition problem. since you made an ignition change and the stutter is still their, i'd look into the carb.

at the 5200 rpm range, you are well out of the idle circut range and well out of the primary circut range. most like a secondary circut issue.

possible change secondary metering rods or could be secondary air valves opening too quickly and/or slamming shut too soon.

DirtFreak08
Dirt Forum Racer

Total posts: 77
posted May 25, 2004 05:53 PM  
Thanks for the replys! Hey racer17, what gear do you think would get me where I want to be. I'm running a 350, bored .060. Very strong motor if I can get these bugs worked out. 1/4 track, banked pretty good in the corners. 620 gear in a ford 9". I know of a couple guys I run with that have 567's and 600's. What do you think?

Scoot
Dirt Forum Champ
Total posts: 517
posted May 25, 2004 07:05 PM  
For a 1/4 mile track I'd run a 7.00 gear. I know some guys that run that low of a gear on a 3/8 mile. I run a 6.50 on the 3/8 and turn 6-6200, I've thought about going lower myself.

------------------
Scoot
Smith Racing Team
870-365-5989

M1
Dirt Freak

Total posts: 257
posted May 26, 2004 07:06 AM  
I just had the same problem. What it was for me, my fuel filter had come apart internally and all the paper element was plugging the carb up. We took it all apart and cleaned it, flushed the lines out really good and put it all together again. Runs like a champ now!

Since you have the ignition part deemed as NOT the problem, I would bet its just starving for fuel.

If your head have been redone reciently, there is no reason why you couldnt go that high. Old heads with wore out springs will float valves very easy.

20bmw
Dirt Full Roller

Total posts: 74
posted June 06, 2004 07:20 PM  
quote:
Originally posted by Scoot:
For a 1/4 mile track I'd run a 7.00 gear. I know some guys that run that low of a gear on a 3/8 mile. I run a 6.50 on the 3/8 and turn 6-6200, I've thought about going lower myself.


I run a 406 a glide in drive with 5.83 gear and turn 6500-6800 on a high bank 3/8 mile.
Man if i ran a 6.50 i would leave parts all over the track.. I heard other guys on here running your r`s and gear on the 3/8 mile but can`t figure out why the r`s are that low with that gear.. can someone help me out with this???

racer17j
Dirt Forum Champ
Total posts: 5390
posted June 06, 2004 08:07 PM  
Bingo racer! For a long time we have messed with tire size when changing to a different yet similar track. Working at a tire factory we could almost always get tires fairly cheap. And it's less work than changing a gear. A lot of guys never believed what we were running, but they all saw us win. Most were too concerned with stagger, but with an oped rear-end rule stagger didn't matter much. They all wanted big tires to get leg down the straight. We went for little tires for torque in the corners. I still set up my car with the small tires on the rear. I might change a gear now and then too, but I like the little tires a lot.

carolinafast
Dirt Full Roller

Total posts: 72
posted June 07, 2004 04:06 PM  
anybody have the formula for figuring tire
roll out....how much does it change for example if you go up or down 1 inch???

racer17j
Dirt Forum Champ
Total posts: 5390
posted June 07, 2004 04:39 PM  
out here in Ca, we runfrom 715 to 760 I have a 741 right now and 87roll and don,t turn more then 6200 rpm Steve

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