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Old 06-13-2004, 06:09 PM
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rpm's too low

Need some MAJOR help guys. I run a dirt track in FL, roundy round. My car bogs coming off the turns. My final gear is 6:52 at the moment, made through the tranny. I previously had a final of 6:26, again through the tranny. My problem is, I would like to turn the engine up to around 6200 to 6400 rpms, and can't seem to get it to turn more than 5800, no matter the gear. My engines a 350 Chevy, with a stock lift cam (Lunati). It has 232 duration, and a 106 degree separation. Have a stock Q Jet carb, with minor mods. Have 100lb valve springs, w/SS 194/160 valves. The head chamber is 75cc. Have a curve kit in the stock HEI distributor, with the lightest springs installed. Hypertectic flattops, bored 0.30. Everything else in the engine is stock. I'm missing some piece of the puzzle, and can't seem to get it to turn any harder. I need some advice, as I can't stand running 6th or 7th any longer. By the way, the class is a stock class, and restricted to mostly stock parts. ANY help you can give is greatly appreciated.........TY

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Old 06-14-2004, 07:02 PM
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C'mon guys, you mean to tell me, none of you have any answers or suggestions? Please gimme some help............
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Old 06-14-2004, 10:04 PM
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Without being there most anybody in the know could write a book about what could be wrong and still never pin it down. Here's a few guesses. You went to a lower gear but still turn the same rpm sounds like a valve spring problem. Just becuase you have a lot of seat pressure doesn't mean that the springs will be free of surge. Do your springs have an inner dampner. There has been many cheapy valves springs sold as so called Z-28 springs that turn out to be crap. Some of them work ok you're just never sure what you're going to get.
With stock unported heads your horses power is going to max out around 5000-5500 so if you're already turning it 5800 there's nothing more to gain by turning it faster. If you must run stock lift cams you need to know how your track will check this. If they check it at the valve then stock lift is all you're going to get. If they measure it by lobe lift you better have 1.6 to 1 rockers be cuase everyone else will.
Since you having problems getting off the corner your ether pushing real bad or you're needing to make more bottom end torque. Make sure that your dead on on the jets. Make sure that the secondary air valve is not set too loose if so it will kill your bottom end.
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Old 06-15-2004, 12:51 AM
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first, thanx for replying..........I do have dampers on my valve springs, and the track checks the lift of the cam at the valve, so not much more than the stock .390 lift can be gotten. I'm not real good on the carb, usually have someone else put it together, and I put it on the car. The Lunati cam I have makes power from 2600 to 6400 rpms, and I thought I could turn just a little more before the valves float. I'm considering changing the heads to a 58cc chamber 305 set. They are currently at the machinists, having 194/160 valves installed. I also just learned from the tech guy, I can run the lighter Z28 flywheel, 10.4", and have one just resurfaced. I agree I need more torque on the bottom, the cars about as good as it can get on the cornering setup, no push, and only slightly loose off. It just seems other cars, near same make and models are coming off a lot faster. Once mine has built some rpm's, I run with them, and actually gain ground through the entry part of the turns, only to bog coming off.....again, thanx for the reply.......
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Old 06-15-2004, 07:02 AM
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You could well be running out of fuel in the turns. G forces pools the fuel in the float bowl and one or both jets may not getting fuel. Try setting your float a little higher. You are correct you should be getting more revs with the gears you have and the mods on the motor. If the float change does not help, I would tackle the secondaries on the Q jet. My simple mind would tell me to wire it closed and look for not much change in performance. Then I would start working to make it open up properly. I'll get out my book on Q Jets and look for the proper terms for each of the controllers.

Trees
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Old 06-15-2004, 07:45 AM
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Stock Q- jet's are notorious for shallow fuel bowls.

I should think I would start with looking at ignition. Stock type HEI module I presume? They don't work over 5000 very well. Lock out the dist., you don't need these parts and they will break on you sooner or later. After getting the ignition worked out, it's time to work on the carburetor. You need to eliminate the possibility of ignition problems first. After you get squared there, you can tune the high speed air bleeds for power. Those 305 heads will raise compression enough to make the cam work better but you are going to run out of the power range sooner. If our engine is all up to snuff you need to work on carrying the speed through the center and off. If your car feels like it's running on rails, then you are going too slow.
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Old 06-15-2004, 05:40 PM
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What is your RPM coming off the corner? You might be getting below your torque band of the cam. Are you sure that the other cars aren't lifting sooner than you so that they can get back on the gas sooner? You're correct in thinking that you're going to need every bit of compression that you can find.
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Old 06-15-2004, 06:27 PM
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johnsongrass1, you are correct, the distributor is stock. I was kinda thinkin it was in the distributor, but needed further advice. You say to lock out the distributor. What do you mean by this? Lock out the vacuum advance? Could you be a little more specific. As you can probably tell, I'm not up to your speed on all the technical info. Can build the engine, to the basics, but am not versed in all of the tricks of tuning......I appreciate any help you can give. Believe me, I'll try 'bout anything to make it GO.
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