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Car doesn't pull after 4500

 
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355firebird
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Joined: 07 Oct 2003
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PostPosted: Tue Oct 21, 2003 3:34 pm    Post subject: Car doesn't pull after 4500 Reply with quote

My car doesn't feel like it pulls topend at all. It just revs and doesn't break up. The power range of the cam is from 2200-6000. I'm running a 355 with a 3500 stall and 3.73 gears. I put a 140 GPH fuel pump in this year, new tranny, and MSD box. It only ran more cosistant, not faster. I was told it could be the valve springs, but this is only the second season. I'm wondering if I need a new carb. It's a 750 Edelbrock vacuum secondary. I know it's shitty, but would it cause the car not to pull.
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SMOKEmUP
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1979 Chevrolet Camaro

PostPosted: Tue Oct 21, 2003 4:15 pm    Post subject: Reply with quote

Tough to say. Your trap speed in the 1/8 looks pretty good. If the car weighed 3600 lbs the calculator on the site comes up with 289.8 HP at the wheels which is pretty good. How much does the car weigh?

What about the rest of the combo? What are the cam specs? Based on the rpm range I'd say you should see max power at around 5500 rpm. Have you tried a chassis dyno? That way you can see if the power curve is going flat.

Have you checked all the usual stuff, can you monitor the fuel pressure the whole way down the track? what about the distributor timing? how do the plugs look after a run? are they all the same color?

Why do you think it's the valve springs?
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osmiumfoot
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PostPosted: Tue Oct 21, 2003 6:29 pm    Post subject: Reply with quote

First thing I'd peek at would be the inner springs. They bust up but you can't see it because of the outer spring. You have to pull the spring off and take it apart. This has happened to me once and to one of my friends once, and both times the engine got lazy on top and started to lay down, and both times it was an inner spring breakup. If you've spun the engine up past the happy place for your springs even once, I would be very suspicious about their condition.
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jeep_406
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Location: Tewksbury, Mass 01876
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1972 Chevrolet Nova

PostPosted: Tue Oct 21, 2003 8:24 pm    Post subject: Reply with quote

As osmiumfoot wrote overrevving is a killer to valve springs.
Just for giggles I'd check the vacuum secondary diaphram just to make sure it works right. If the diaphram doesn't hold vacuum the secondaries won't work. I don't know which 3310 you have. If you have one with a metering plate convert it over to a block that you can change the jets in. I've run a 3310 for years. I also tried a few double pumpers but found I got a better 60 foot time with the 3310 and about the same MPH.
And also the stuff SMOKE talked about.

Jeep
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Smokin71RSSS
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1971

PostPosted: Tue Oct 21, 2003 9:02 pm    Post subject: Reply with quote

Have you by any chance checked your fuel pressure when your driving? It could be dropping off in the mid-upper rpm's. Also what size line are you running from the tank to the pump? Sometimes the tiny stock line will cause fuel pressure problems.
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355firebird
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PostPosted: Wed Oct 22, 2003 12:13 am    Post subject: Reply with quote

Could too much converter slippage cause it not to pull. When I had a 2800 stall it was trapping at 87MPH on street tires. Now that I got the 3500 stall and drag radials it's an animal out of the hole. It cuts 1.7's all day.
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2x4
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PostPosted: Wed Oct 22, 2003 9:05 pm    Post subject: Reply with quote

Check out what YEAR F-body this carbed 355 is in! I give ya bonus points just for pulling it off! Shocked


Just a thought on the broken spring idea, wouldnt it break up & act a little bit like valve float if it was a bad spring? He has no "break up" troubles, its just nosediving.

I would check the fuel system & ignition real close.

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free_jax
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PostPosted: Thu Oct 23, 2003 7:22 pm    Post subject: Just a thought Reply with quote

Does your car have a catalytic converter on it? When clogged, high rpm's aren't available(max flow). Just checkin cause i don't know what your car has.
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osmiumfoot
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PostPosted: Thu Oct 23, 2003 9:10 pm    Post subject: Reply with quote

2x4 - I have experienced valve float before but I don't remember it resulting in "breakup", which I am interpreting as a high rpm miss. My combo and my friends combo both had similar symptoms; the engine just layed down early, and in both cases it was caused by broken inner springs. I know that two cases don't prove anything, I just thought it would be worth checking since its happened before.
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jeep_406
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1972 Chevrolet Nova

PostPosted: Fri Oct 24, 2003 12:14 am    Post subject: Reply with quote

Springs don't have to be broken to lose pressure. They could go if you overreved the engine or got them real hot.
I'd still make sure the secondaries are opening on the carb.
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2x4
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PostPosted: Fri Oct 24, 2003 4:51 pm    Post subject: Reply with quote

Your making me feel guilty, I have to change the springs on mine but I've been putting it off Embarassed I'm getting float at 6800-7000rpm (where I shift). It just kinda feels like youve "topped out" when you know theres more.
Now that I think about it, I may be jumping on the "valvespring bandwagon." 355Firebird-what rpm is it falling off at?
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355firebird
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PostPosted: Wed Oct 29, 2003 1:16 am    Post subject: Reply with quote

The car doesn't seem to pull after 4200. I shift at 6000, but last Sunday I left it in D shifting at 4200 and the MPH was 80, but when I shifted it at 6k or 5500 the MPH didn't change nor did the E.T. I was told by Edelbrock that the 1411 carb (750 vacuum secondery) is not for racing. It's an economy carb and the venturies are too small to draw fuel for racing. I was told a guy who runs a 396 in his truck that the screens for the needle and seat might be plugged, because his truck wouldn't pull past 4k until he unplugged them. The car doesn't break up at all. I make no horsepower topend it just revs. I'm thinking its the carb. I here nothing good about Edelbrocks from people. I'm putting the 850 Ray Murray Competition carb on the car next year. It should make a huge difference.
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