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Old 04-10-2008, 09:46 PM
BMM BMM is offline
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Lazy top end

Hello all. My motor doesn't seem to want to move the car when its above 4500rpm...It screams like its revving, but it doesn't rev up. For example, a 3-1 downshift will put me in the high 4's, but doesn't do anything.

Current setup is :350 Chevrolet, Edelbrock Performer RPM intake, Edelbrock 600cfm mechanical secondary carb (less the 6 months old), Headers with true duals, attached to a built 2004-r with a 2200 stall. Rear end in about 2.80:1.

Could it be the lazy factory camshaft? Maybe my timing isnt setup correctly, although it was done along with a recent tuneup. Any help is appreciated.

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Old 04-10-2008, 10:33 PM
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This problem could be as easy as a wrong kick-down cable adjustment, or not enough fluid in the transmission.

If you have a way to take transmission pressures, put it in 1st gear, or reverse gear and post the pressure you come up with.
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Old 04-10-2008, 11:21 PM
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I installed the BTO tranny in january, and verified the pressures then, but Ill definetly re-check. Fluid level is good. If it were a tranny problem, wouldn't the motor still rev in gear? Thank you.
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Old 04-11-2008, 12:46 AM
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valve springs
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Old 04-11-2008, 12:57 AM
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It could be valve springs... but I suspect either a bad cap and rotor or a bad coil... Valve springs tend to last for damn near forever on a stock camshaft, although maybe that engine has been ran forever...
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Old 04-11-2008, 10:35 AM
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Is the motor otherwise "stock" with a stock gm cam and low compression crap heads? If so, its all done by 4800rpm. Quite beating on it!. Its not a high rpm engine.
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Old 04-11-2008, 03:49 PM
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To the best of knowledge, stock internals and heads.
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Old 04-11-2008, 04:20 PM
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Lazy Top End

Hmmm, stock cam, low compression, most likely smogger heads and tall gears.
F-Bird 88 is most likely right.

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Old 04-11-2008, 11:41 PM
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Quote:
To the best of knowledge, stock internals and heads.
There is your problem, stock heads die out at 4500-5000 rpm, and the cam isn't designed for high rpm power at all. Valve srings may bump it up a bit, but not much, as the crappy port design is suffocating your engine.

Look at it like this: you're going for a walk, but with a drinking straw in your mouth that you need to breath through. Walking, you have no problems. A quick walk, still ok. Now a big *** dog starts to chase you, and you have to run. How fast do you think you can run, while sucking your air though a 1/4" straw? Stock heads are like that straw. They are adequate for stock expectations (walking), but try to make power in the upper rpm (running), and that dog is going to get a taste of your backside.
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Old 04-12-2008, 12:13 AM
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Quote:
Originally Posted by sbchevfreak
There is your problem, stock heads die out at 4500-5000 rpm, and the cam isn't designed for high rpm power at all. Valve srings may bump it up a bit, but not much, as the crappy port design is suffocating your engine.

Look at it like this: you're going for a walk, but with a drinking straw in your mouth that you need to breath through. Walking, you have no problems. A quick walk, still ok. Now a big *** dog starts to chase you, and you have to run. How fast do you think you can run, while sucking your air though a 1/4" straw? Stock heads are like that straw. They are adequate for stock expectations (walking), but try to make power in the upper rpm (running), and that dog is going to get a taste of your backside.
Good one. I really like the straw example.
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Old 04-12-2008, 09:27 PM
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Alright thanks fellas. So, would I be better off to invest in some new heads and stick factory cam for now? Or do I need to do both to see a decent gain? I cant afford both (or either for now).
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Old 04-13-2008, 05:58 AM
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Save some cash until you can do both. You will not get the advantage of better flowing heads with a stock cam.
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Old 04-13-2008, 08:22 AM
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sbchevfreak...that is a good one!

BMM,
if/when you do change to better heads and cam you must also change the rear gears to lower to work with the higher rpms HP peak...and depending on which cam possibly a higher stall convertor...(your RPM intake choice wants a 6500rpms HP peak parts combo "aka" Edelbrock Power Package)

do the gears first...that's the major "fun on the street" improvement for a street car cam...with a stock intake or Performer intake and 3.73 gears it will be a very fun car...a way much "quicker" motor rpms wind up

with a correct intake for the stock cam and gears:
340ft/lbs at only 3200rpms x your present 2.80 gears =952 ft/lbs of force twisting the hides...
340ft/lbs @ 3200 x 3.73 gears = 1,268ft/lbs of force twisting the hides!!!!

that's about 29% more acceleration "power" to move the 3400lbs your sitting in...and still will burn 87 octane with full best timing...

for reference, my 320ft/lbs, 3.55 gears, 3400lb Mustang is 0-60mph in just a hair over 5 seconds on 87 octane...if I did strip about 2-300 lbs off the car it would be 5 seconds "if" I could get the tires to hook up....but for safe in the rain (daily) and traffic it's just right as it is....

"there ain't no such thing as a free lunch"
3.73 gears= about 3400+ rpms at 70mph versus 2800rpms(?) with the 2.80 so choose your gears ratio biased toward how you plan to use the car most...in town or hwy

do some reading in the "Knowledge Base" link at the top of this page...here's just one article example from the tranny-rear section about gears ratio's

http://www.pontiacpower.org/reargear.htm

Last edited by red65mustang; 04-13-2008 at 08:40 AM.
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Old 04-13-2008, 10:03 PM
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+1 on the gear note

Think of an induction system, not just a cam heads intake and carb. You can take the same bottom end of any motor and swap out the induction system with numerous results depending on parts used. In any case, look at the 'system' as a whole, with system parts complimenting each other in order to attain your sought after performance. JMO
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