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Old 01-11-2017, 04:07 PM   #51
BrianG
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Re: Lets talk Small Block

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Originally Posted by storm9c1 View Post
I still think you might be able to gain 1-2" using full manifold vacuum on the distributor and retuning the carb for that. But every engine is different. It'd be more of an experiment than a promise. Keep in mind a few things if you switch this. 1) You have to make the switch with the engine warmed up to see correct results. 2) You will have to lower the idle at the carb with the stop screw. 3) You should retune the carb with a vacuum gauge after making these changes. Otherwise it will seem like you have no gain and perhaps even develop a stumble without that type of retune. It does change the vacuum profile of the engine. Screw the debates about which is better (ported or vacuum), the engine profile tells you this. Stock profiles might like one type. Radical profiles might like another. It's a trial and error process. Nobody can tell you which is right or wrong (which is why this is so heavily debated). But your engine can tell you if you listen.

I'd also be tempted to try a vacuum canister next. Not uncommon to need one with a radical cam. Or last resort, as discussed, change the cam.
I have tried the vacuum advance each of three ways (ported, full vac, and disconnected). I've re-tuned using a vacuum gauge after each change. It seems to like ported best. None have really helped though. I could try a vacuum canister and that would maybe net me a few extra brake pedal pushes. But in the end, it would only solve some of my issues. I still would have a rough idling 350 that just seems to be underpowered until it starts to really wind up.

I've had at least one person respond saying that they had a 350 in a 4x4 that made decent enough power. A few suggestions for putting on Vortec heads and a new cam, but less than I expected responses about feeling that I'd be best off going for the 383.

Honestly, I'm leaning toward pulling the motor and changing the heads, cam and intake to something that have been proven to work well together. I'm not quite sure what that will be though. I've got to figure out if my block is set up for a roller cam. It does have the one piece rear main seal, but I'm not sure if the machine work was done for the roller cam.

I don't think my current stock replacement heads are bad, I'm just not sure what their potential is. Also, I'm on the fence about spending a couple thousand for a top end kit, or maybe 4 thousand for a 383 crate engine. One thing goes wrong if I go with the top end kit and I've got to pull it and start over, and I'd been maybe better off to go with a crate engine. I tend to have bad luck with such things.
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Old 01-11-2017, 11:21 PM   #52
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Re: Lets talk Small Block

Well since you are going to go with a crate deal you should advertise your engine while it's in the truck so potential buyers can hear it run and you should get more out of it. I bet somebody with a drag strip toy or stop light bandit might like to have your engine.
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Old 01-12-2017, 01:16 AM   #53
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Re: Lets talk Small Block

If you do have 64cc chamber heads now and 10.5 compression - your next set of heads needs to be aluminum. Then you'll have alot more leeway with the dynamic compression, (you can use an even smaller cam and gain more low-end torque).

Vortec heads are nice if you've planned your build including them, but will cost you when changing over to them.

I'm betting your setup can be made to work with a cam better suited to you. You need to know more about this setup before changes can be made to it tho'.

A fresh rebuild one pc seal shortblock with flattops is a great start, if that's what you have !?
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Old 01-12-2017, 11:47 AM   #54
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Re: Lets talk Small Block

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If you do have 64cc chamber heads now and 10.5 compression - your next set of heads needs to be aluminum. Then you'll have alot more leeway with the dynamic compression, (you can use an even smaller cam and gain more low-end torque).

Vortec heads are nice if you've planned your build including them, but will cost you when changing over to them.

I'm betting your setup can be made to work with a cam better suited to you. You need to know more about this setup before changes can be made to it tho'.

A fresh rebuild one pc seal shortblock with flattops is a great start, if that's what you have !?
It would be nice to be able to use my stock heads and just find a cam that works better with them. Here are a few concerns with that though. First I am starting to think that the compression really isn't 10.5-1. It cranks easy, has never had any pinging that I've ever heard either while running on 93 octane. I've been reading a lot and to get 10.5 to 1 don't you need domed pistons and a pretty low piston to deck height? I thought he told me that they were Flat top pistons, but I could be wrong. I know that he told me that they had trouble getting them because they didn't bore it out any. It was harder to get a flat top (or higher compression) piston in the stock bore. Not only harder to get, but they cost more I guess. He figured that they didn't save much by not boring it, but also, they had it checked and it was good.

That leads me to ... what do I really have under there. If I knew for sure, it would be much easier for someone on here or a cam company, or Summit, or whatever to recommend the correct cam. But I don't know. The only way I'm really going to find out would be to pull the heads right? I sort of need to know the head chamber size as well as the piston design (top of piston to deck would be nice but maybe isn't as critical). Also, any new cam I choose, assuming it is less aggressive should probably have new valve springs put in correct.

Without knowing, I could make some guesses that I have Flat tops, 64cc chambered heads and probably really something closer to 9.5 to 1 compression. Then find a cam based on that guess. However, if I've guessed wrong, then I'm throwing money away.

I'm nervous of the uncertainty of what I'm starting with. So I probably should pull it out and pull the heads and find out what I'm starting with. From there, I guess it is how much money do I want to spend.

Cam
Roller Cam
Cam and heads
Roller Cam and Heads
new 383 base
new 383 High Performance

anywhere from a few hundred to 7 or 8 thousand.
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Old 01-12-2017, 06:34 PM   #55
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Re: Lets talk Small Block

For all we know it probably has a Thumper cam in it. It will always be doggy and hard to tune. The "racing" pistons are probably run of the mill flat tops. It sounds like you already have a sound engine with new heads. I'll bet if you put a good moderate cam in it, it will run like it is supposed to. I actually took some aluminum heads off of my truck (350) because I figured the extra power wasn't being used with the light hauling and slow driving that I do. If you live near mountains and haul big trailers then maybe big power is more important to you. Everybody here likes VooDoo cams or Comp Cams 268. I'm sure any of them will really really wake up your engine. If you're set up for roller lifters then there is another option.
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Old 01-12-2017, 06:47 PM   #56
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Re: Lets talk Small Block

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For all we know it probably has a Thumper cam in it. It will always be doggy and hard to tune. The "racing" pistons are probably run of the mill flat tops. It sounds like you already have a sound engine with new heads. I'll bet if you put a good moderate cam in it, it will run like it is supposed to. I actually took some aluminum heads off of my truck (350) because I figured the extra power wasn't being used with the light hauling and slow driving that I do. If you live near mountains and haul big trailers then maybe big power is more important to you. Everybody here likes VooDoo cams or Comp Cams 268. I'm sure any of them will really really wake up your engine. If you're set up for roller lifters then there is another option.
No mountains here, but perhaps some dune hills in the future and all the power you can get is helpful there. Other than that, it is sort of a weekend hot rod fun truck. I thought about the Comp Cams 268 but wasn't sure how that would work with the stock replacement type of heads that I have.
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Old 01-12-2017, 09:08 PM   #57
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Re: Lets talk Small Block

Not that you need another opinion, and you have more engine building experience than I do. But I've read the whole thread, and it does seem to be worthwhile to pull your head's and see what you got. Couldn't you add a thicker head gasket if you felt like you were dealing with too much compression? One thing that hasn't been mentioned much is the intake manifold. I didn't see whether you said it was single plane or dual plane. But the previous owner sounds like somebody who might be running single plane. I'll bet with a new cam and possibly a new intake, that you'll be ready to go.
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Old 01-12-2017, 10:17 PM   #58
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Re: Lets talk Small Block

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Not that you need another opinion, and you have more engine building experience than I do. But I've read the whole thread, and it does seem to be worthwhile to pull your head's and see what you got. Couldn't you add a thicker head gasket if you felt like you were dealing with too much compression? One thing that hasn't been mentioned much is the intake manifold. I didn't see whether you said it was single plane or dual plane. But the previous owner sounds like somebody who might be running single plane. I'll bet with a new cam and possibly a new intake, that you'll be ready to go.
You do bring up a good point about the intake. I didn't mention it but it is a dual plane so probably not the issue. Guess that's why I didn't mention it. It is a Holley Dominator dual plane. I think there is better options out there but that was on it and I didn't change it. Just took the 750 double pumper off and put on a 670 street avenger. I think pulling the heads is a smart place to start.
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Old 01-13-2017, 03:31 AM   #59
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Re: Lets talk Small Block

Cool. Yeah it seems that if the cam is pretty aggressive, that a 670 carb may be restrictive. I'll bet that a mild cam could work pretty well with the 670 carb and the dual plane intake, even if you have flat topped pistons. If you experience some detonation, maybe you can back the timing off some? IIRC it's set fairly advanced currently, right? I don't think that will solve the problem if the compression is too high, but it will keep from making it worse. What does it idle like now?
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Old 01-13-2017, 11:28 AM   #60
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Re: Lets talk Small Block

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Cool. Yeah it seems that if the cam is pretty aggressive, that a 670 carb may be restrictive. I'll bet that a mild cam could work pretty well with the 670 carb and the dual plane intake, even if you have flat topped pistons. If you experience some detonation, maybe you can back the timing off some? IIRC it's set fairly advanced currently, right? I don't think that will solve the problem if the compression is too high, but it will keep from making it worse. What does it idle like now?
It has a pretty decent lope to the idle now. One big issue with the idle is how many rpms I loose when I put it in drive. I do have a stall converter, but I guess they still grab to some degree until the real power is applied. If I set the park idle to 850-900 it just about stall the truck when I put it in gear because the idle falls so low. At that point, it sounds like a built Harley Davidson. To overcome that I have to set the idle at a minimum of 1,000 rpm. It still drops to maybe 650 rpm or so (give or take a little). At that rpm, it still lopes quite a bit. Sure it sounds cool and turns heads, but it is a bit too much for the street in my opinion. At that point also, I'm not making very much vacuum. So you can imagine how driving it in stop and go traffic is like. SORT OF SCARY and probably dangerous. Luckily I've got strong legs. I end up switching back into neutral and revving it to gain a little vacuum and keep it from falling on its face. But I'm sure I just sound like a punk by doing that.
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