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  #31 (permalink)  
Old 01-19-2013, 10:29 AM
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Confused about carbs, need help!

Here is a summits description of the sum-1108 cam. Basic Operating RPM Range: 3,400-7,000. Rough idle, excellent high-end horsepower. Needs 10.5:1 and higher compression, 3,500+ stall, and gearing. 350+ c.i.d., bracket race cam. With that cam you'll want a 3500 or 4000 stall converter. Holley 750 DP and use the single plane intake since you already have it.

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  #32 (permalink)  
Old 01-19-2013, 12:12 PM
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I would get the gears changed as soon as possible. They 3500 stall isnt going to help much with the 308 gears.
I agree with Cobalt on the carb. Use the one you know is good at least to start.
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  #33 (permalink)  
Old 01-19-2013, 12:32 PM
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CHEVILLAC, in case I wasn't clear on my recommending you use the small Edelbrock carb, this is to get the engine up and running. If the carb is in good shape, you can basically bolt it on and w/a possible/probable change to the step up springs, you'll be able to at least drive it to see what else is needed.

I always advise guys to first set the distributor up w/a performance timing curve, before tuning the carb beyond adjusting the idle mixture screws and the curb idle speed.

A performance timing curve for a stock GM HEI consists of lighter mechanical advance weight springs (the weights are usually OK as-is) and limiting the mechanical advance to about 10-15 degrees. The rest of the timing (about 20-25 degrees) will come from the initial timing. Details are at the link I added several posts ago.

I seldom recommend locking the mechanical advance out so it doesn't work, but in this case- w/the cam as big as it is- you can do this to get it up and running. Then later on you can go back and set it up w/a curve if you want to. This is easy to do but it may require an ignition interrupter switch be installed so the engine doesn't kick back against the starter when you start the engine (locking the mechanical advance and the interrupter switch are also covered in the link). I'd use about 32 degrees timing to begin with- not optimal, but enough to see what you have. This isn't what you want w/a high rear gear, but as long as you don't mat the throttle from a too-low rpm you should be OK. If you hear detonation though, you'll need to back off the timing, back off the throttle/load on the engine, or add the curve I talked about above.
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  #34 (permalink)  
Old 01-19-2013, 01:18 PM
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Originally Posted by T-bucket23 View Post
I would get the gears changed as soon as possible. They 3500 stall isnt going to help much with the 308 gears.
I agree with Cobalt on the carb. Use the one you know is good at least to start.
I would love to improve the gears immediately but unfortunately that's the most expensive part. The 3500 stall I can get for about $150. I think I want to use a vac sec 750 holley for ease of driving, I don't want to have to drive the truck like it's a manual all the time, a good used one can be had for $100 or so, but I'll get the motor going with the eddie for now. The gears gears and everything that go's with changing them will run me almost as much as I paid for the motor. I'm on a fairly limited budget right now but I need to get this thing going.
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  #35 (permalink)  
Old 01-19-2013, 01:32 PM
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Quote:
Originally Posted by cobalt327 View Post
CHEVILLAC, in case I wasn't clear on my recommending you use the small Edelbrock carb, this is to get the engine up and running. If the carb is in good shape, you can basically bolt it on and w/a possible/probable change to the step up springs, you'll be able to at least drive it to see what else is needed.

I always advise guys to first set the distributor up w/a performance timing curve, before tuning the carb beyond adjusting the idle mixture screws and the curb idle speed.

A performance timing curve for a stock GM HEI consists of lighter mechanical advance weight springs (the weights are usually OK as-is) and limiting the mechanical advance to about 10-15 degrees. The rest of the timing (about 20-25 degrees) will come from the initial timing. Details are at the link I added several posts ago.

I seldom recommend locking the mechanical advance out so it doesn't work, but in this case- w/the cam as big as it is- you can do this to get it up and running. Then later on you can go back and set it up w/a curve if you want to. This is easy to do but it may require an ignition interrupter switch be installed so the engine doesn't kick back against the starter when you start the engine (locking the mechanical advance and the interrupter switch are also covered in the link). I'd use about 32 degrees timing to begin with- not optimal, but enough to see what you have. This isn't what you want w/a high rear gear, but as long as you don't mat the throttle from a too-low rpm you should be OK. If you hear detonation though, you'll need to back off the timing, back off the throttle/load on the engine, or add the curve I talked about above.
The previous owner says it's setup to be all in (initial + centrifugal) with 36 or 38 at 3500rpm and no vac adv. The motor was setup and tuned on the dyno and the only thing he did since was pull the motor from the car and remove the fuel injection. I know it ran like a scalded dog at that point so I just want to leave it as is, get it carb'd with the proper stall and go from there. I read the link on performance dizzy setup and bookmarked it for later in case I decide to go that route. I'm just reluctant to try to fix something that isn't broke, I just want to adapt it to carb.
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  #36 (permalink)  
Old 01-19-2013, 04:53 PM
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That's good that the distributor is dialed in already. Just give it a check w/a dial back timing light (or whip up a temporary timing tape) to double check it. If the damper is a stock part, it's a good idea to double check TDC to be sure the outer ring hasn't moved. You can mark it w/a line to keep an eye on it.



One thing more- you can use a vacuum advance, and I recommend you do so. The caveat on this is twofold:

• Use ported vacuum
• Use a Crane p/n 99619-1 limiter plate to keep the added advance to about 10-12 degrees (or make one)
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  #37 (permalink)  
Old 01-19-2013, 10:17 PM
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Quote:
Originally Posted by cobalt327 View Post
That's good that the distributor is dialed in already. Just give it a check w/a dial back timing light (or whip up a temporary timing tape) to double check it. If the damper is a stock part, it's a good idea to double check TDC to be sure the outer ring hasn't moved. You can mark it w/a line to keep an eye on it.



One thing more- you can use a vacuum advance, and I recommend you do so. The caveat on this is twofold:

Use ported vacuum
Use a Crane p/n 99619-1 limiter plate to keep the added advance to about 10-12 degrees (or make one)
Ok, I know ported vacuum for the vacuum advance is hooked to the carb so I'm guessing it is operated in a similar way as the vacuum secondaries, otherwise a motor that has very little manifold vacuum wouldn't be able to operate the advance. If the motor runs well as it is, what would be the advantage of adding the vacuum advance back into the equation? Will it be better for for driving conditions between idle and WOT?
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  #38 (permalink)  
Old 01-19-2013, 11:35 PM
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I would change the camshaft to a new summit cam that will run fine the the stock torque converter and gears
you got. A new summit k1104 camshaft and lifter set is $99 and solves all your expensive problems.

Plenty of performance and a good match to everything else and the purpose. The price is right too.

The camshaft mismatch is the problem that needs a fix. Any carb will work with this cam.

You will like this cam in your truck.

Another good cam choice for you is Summit cam #SUM-1788. Either one of these cams fixes your (I got the wrong cam in my motor for my truck) problem, correctly, for a small cost.

Last edited by F-BIRD'88; 01-19-2013 at 11:44 PM.
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  #39 (permalink)  
Old 01-20-2013, 07:05 AM
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Quote:
Originally Posted by CHEVILLAC View Post
Ok, I know ported vacuum for the vacuum advance is hooked to the carb so I'm guessing it is operated in a similar way as the vacuum secondaries, otherwise a motor that has very little manifold vacuum wouldn't be able to operate the advance. If the motor runs well as it is, what would be the advantage of adding the vacuum advance back into the equation? Will it be better for for driving conditions between idle and WOT?
Ported vacuum (passenger side vacuum port on the Edelbrock carb) is only there when the throttle blades are opened. When closed, no vacuum. What that means when applied to a vacuum advance is there will be no added advance at idle. You already have a high enough amount of initial advance (or you should have, like 20 degrees-plus) for the engine to idle well w/that cam, so no additional advance is needed, or wanted.

The vacuum advance will only add advance to your engine at light throttle/light load conditions. This helps the engine to run smoother, maybe a tick cooler, and will use less fuel. There are no downsides to using it- as long as it's done as I've outlined.

Once you get it running, check the initial and total advance to be sure it's what it should be.
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  #40 (permalink)  
Old 01-25-2013, 01:06 PM
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Pulled the valve covers today and found out these are no mystery heads, they are 3947041's which should be 64cc chambers if the weren't resurfaced but I'd lay odds they were so maybe 63cc's? I'm guessing the CR is somewhere around 10.5:1 because from what I've read you have to run 91 octane or higher fuel at that ratio to avoid detination and I asked the previous owner about what fuel he ran and he said premium because the engine would sputter and ping on anything less. I bought a 3500 stall converter and I'm looking for a used 3 series posi carrier with 3.73's in descent condition for my 10 bolt. In the meantime I'll have to run this motor with my open 3.08 12 bolt because I don't think the motor that's in my truck now is going to last much longer. I'll get the new motor in and going next weekend with my 600 edelbrock and post an update. Hopefully I won't have any more carb questions. Thanks again for all your help and suggestions.
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