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Old 05-08-2011, 11:21 PM
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Got a 91 firebird 305 recently put a cam in it 203 209 450 461. Lt1 equivalent.well I have driven it a few times and it is just as slow now as it was before.my thought is with the stock exhaust and air intake as well as chip putting the cam in before anything else I'm eating time because it is to constricted for the cam. Yay, nay? I was just hoping for more. Please nix the 305 comments I get it

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Old 05-09-2011, 12:03 AM
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Well, yes. Choked intake, choked exhaust, crap heads and small cubes added to a programmed ECM = wasted money on a cam change.

A set of full length headers, full duals, intake upgrade and a program chip would have netted a lot more.
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Old 05-09-2011, 12:11 AM
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Somone is buying the car this week but I just wanted some knowledge
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Old 05-09-2011, 06:10 AM
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Why put a new cam in a car you are selling?
Engines are designed as a package and just changing one component like a cam, can often have the results you got, an engine that runs worse
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Old 05-09-2011, 06:20 AM
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Quote:
Originally Posted by badknuckles
Got a 91 firebird 305 recently put a cam in it 203 209 450 461. Lt1 equivalent.well I have driven it a few times and it is just as slow now as it was before.my thought is with the stock exhaust and air intake as well as chip putting the cam in before anything else I'm eating time because it is to constricted for the cam. Yay, nay? I was just hoping for more. Please nix the 305 comments I get it
If it is a stick shift car, the cam that was in it wasn't too far from what you swapped in:

Lift- .413" int/.428" exh
Duration @ 0.050"- 202 int/207 exh
LSA- 114.5

If the vacuum is significantly less than before, the chip will not allow the engine to run like it could, and opening up the exhaust system always helps matters- but not w/o the chip.
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Old 05-09-2011, 06:28 AM
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Selling it because I just bought another project,i started the cam first. The original cam was the peanut cam, something like 380 lift
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Old 05-09-2011, 07:11 AM
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Quote:
Originally Posted by badknuckles
Selling it because I just bought another project,i started the cam first. The original cam was the peanut cam, something like 380 lift
Could be .350" int/.384" exh 179/194 109 LSA, didn't bother to double check the specs- but it's puny, that's for sure.
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Old 05-09-2011, 07:36 AM
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That's why I'm surprised it feels the same to me before and after, I'm going to take it to have it tuned before it goes. I'm not a tuning man, double check timing etc....
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Old 05-09-2011, 08:05 AM
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I wouldn't doubt the timing could be off, if the distributor was installed by eye, or if the wire wasn't disconnected first, then timing set to TDC, then wire reattached. That alone could make a huge difference. It's not throwing codes, is it?
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Old 05-09-2011, 08:57 AM
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Timing was set at a shop,i think it may be set at 0 I was going to have it advanced maybe 6deg.
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Old 05-09-2011, 10:31 AM
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Maybe someone here can chime in, but advancing the ignition timing doesn't work quite the same way as a non computer controlled ignition, IIRC. I seem to recall someone saying that if the timing was set to something other than "0" or TDC, the computer would misbehave- but I may be mistaken.
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Old 05-09-2011, 10:42 AM
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If it is the 305 TPI, it needs 6 degrees base timing, not 0 like the TBI.
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Old 05-09-2011, 10:47 AM
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Tbi unfortunately
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Old 05-09-2011, 12:00 PM
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Quote:
Originally Posted by badknuckles
Got a 91 firebird 305 recently put a cam in it 203 209 450 461. Lt1 equivalent.well I have driven it a few times and it is just as slow now as it was before.my thought is with the stock exhaust and air intake as well as chip putting the cam in before anything else I'm eating time because it is to constricted for the cam. Yay, nay? I was just hoping for more. Please nix the 305 comments I get it
Not enough compression, changing to a hotter cam closes the intake later, this reduces the effective stroke which cuts the compression ratio. This is the essence of computing the Dynamic Compression Ratio (DCR). See this URL for computing: http://www.kb-silvolite.com/calc.php

You can add; not having enough base ignition as well. Though how much of that will depend upon the DCR. The root issue is one of mixture density; that is molecules to volume not fuel to air. Late closing intakes reduce the cylinder mixture density till a critical RPM is reached and intake inertia ram of the mixture takes effect super filling the cylinder. Until then you need more compression and advance to recover the lost energy from the weaker mixture density.

More gears, later closing intakes moves the power band up the RPM range. To recover driveability stiffer gearing is used to spin the motor up where it's making power. Not good for ecomony.

TBI uses Manifold Absolute Pressure (MAP) to compute the mixture and running ignition advance. This is a complex ratio of throttle position and RPMs to manifold vacuum. A hotter cam reduces manifold vacuum throwing the ratios off. The only solution is a new chip with programming that understands this. Go to this URL: http://www.tbichips.com/

Bogie
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Old 05-09-2011, 03:56 PM
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as long as you set it correctly timing does change like it does on a non computer car (the computer if you pull the ESC plug the computer doesn't know what the base timing is set at and it maps assuming that the base was set correctly, so advancing/retarding the base timing advances/retards the whole timing map). That said, from experience advancing the timing on that setup doesn't make a big difference in overall performance. I tested this at the track on one a couple of years earlier than that and actually ran the same times everywhere from 0-6* base timing.

Biggest problem with those engines- the stock exhaust is junk, the stock manifolds are tiny, the crossover sucks, the cat isn't great and the cat back is only OK, you're not going to see any improvement from those things till you either put the larger HO/TPI manifolds (some would argue that you could just cut >2" outlet on the stock manifolds to the 2.25" outlet on the HO ones, the rest is similar), or much better, put some headers on it.

Donno what you have on the intake side, but if it's the stock manifold/TBI, there's quite a bit of improvement to be had there also before it will actually start responding to engine changes. If it's still TBI it's likely that even that cam is too big for it to know how to run correctly anyway, and TBI cars tend to be hard to tune for more power at stock fuel pressures, typically they're much happier even stock at 13-15psi.
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