Will Vortec heads bolt on and function correctly on 1975 383 stroker short block - Hot Rod Forum : Hotrodders Bulletin Board
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Old 04-07-2013, 04:53 PM
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Will Vortec heads bolt on and function correctly on 1975 383 stroker short block

I have a built 1975 SBC 383 stroker short block that I want to put in my 98 Silverado 4x4, since it is EFI and Vortec heads, I am hoping that it will be a simple fit but I don't want to go to the expense of rebuilding the Vortec heads if there may be a problem. If not Vortec heads then I am thinking perhaps 2.02 but it will have to work with the EFI, computer etc.
Trying to keep it simple, but awesome. Any suggestions or input would be appreciated.

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Old 04-07-2013, 05:09 PM
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The heads will bolt on and work. BUT most used Vortec heads are cracked. So at least have them checked out by a qualified shop.
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Old 04-07-2013, 05:15 PM
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Every vortec head thread...Bob comes in .. they re cracked...all of them.
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Old 04-07-2013, 06:13 PM
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Yup, not all, but about 85 percent of them. 15 years and 150+ thousand miles of heat cycle on a GM, too thin casting..
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Old 04-07-2013, 06:23 PM
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Would the old school 2.02 be better? And if so, with the 98 intake and throttle body efi?
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Old 04-07-2013, 09:09 PM
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In my limited experience about half are cracked. As for better head, a cheap set of Chinese heads will be better than any factory sbc head. Cheaper too.
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Old 04-07-2013, 09:45 PM
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I swear they a patented a casting process that allows a head to last for ever but crack as you're taking the bolts out. I seen several motors that were running fine but had crack heads when they were tore down.
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Old 04-08-2013, 03:25 AM
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From your description it sounds like you have an assembled 383 stroker short block and want to install Vortec heads. If so, I assume you have also figured out the right piston combo so that compression is not too high with the smaller 64cc chambers on the Vortec heads. That same limitation also applies to aftermarket heads if they use 64cc chambers.

Bruce
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Old 04-08-2013, 05:42 AM
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Quote:
Originally Posted by FOIDIL View Post
I have a built 1975 SBC 383 stroker short block that I want to put in my 98 Silverado 4x4, since it is EFI and Vortec heads, I am hoping that it will be a simple fit but I don't want to go to the expense of rebuilding the Vortec heads if there may be a problem. If not Vortec heads then I am thinking perhaps 2.02 but it will have to work with the EFI, computer etc.
Trying to keep it simple, but awesome. Any suggestions or input would be appreciated.
The Vortec heads off the 5.7L SBC engine now in your truck will bolt onto the 383 SBC engine. If stock, the Vortec heads will need new springs (details on that and other things that need looked at in link below).

Two main things can get in the way: Compression ratio (CR) and camshaft duration.

If the CR is too high the engine will ping, causing the knock sensors to retard the ignition timing. Retarded ignition timing will help stop the knock but it will also take a big chunk of power w/it.

Hopefully you know the 383 stroker piston type- flat top or dished, and if dished what the volume of the dish is. Along w/the bore and stroke, you need to know how far down the hole the piston is at TDC, the head gasket thickness and bore, and the head combustion chamber volume. That will tell you the static compression ratio. Adding the rod length and the intake valve closing point will give you the dynamic CR.

If the cam duration is such that the vacuum is lower than the factory cam, the ECM will not allow the engine to make full use of the cam and economy along w/performance will suffer. There are companies who specialize in custom chips for the computer to allow a bigger than stock cam (and other mods like long tube headers, etc.) to be used. Also there are cams designed to work w/the factory computer and sensors- but these cams are not high performance in the traditional sense, although they will perform somewhat better than the stock cam in most cases.

Some info on Vortec heads here, including compression ratio calculators.
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Old 04-08-2013, 06:22 AM
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This is great! Very good info and discussion!
The block has flat top pistons and .450/.460 cam.
Sometimes the only confusing part about these blogs is misinformation, but I can't determine if it is misinformation, I have been out of this game for a long time, so thank you all for you patience.
I had read that Vortec heads may have a different/additional cooling jacket that won't coordinate with older blocks(?) It is alot of time, money and frustration to be puting them on ebay, so I am trying to get straight info from you guys that have been at it better.
My mind set has been that the Vortec, being a newer design with more 'science' with matched Vortec intake system would create an awesome power plant for pushing and pulling. However, with my 'old school' knowledge, the new science of computers and technology in this newer truck is forcing me into a new education, which is good, but I am afraid of making a very big and costly mistake.
I am at the stage of purchasing heads, and I only want to do it once.
Thanks again guys for the help.
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Old 04-08-2013, 06:59 AM
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Quote:
I had read that Vortec heads may have a different/additional cooling jacket that won't coordinate with older blocks(?)
You may be thinking of the SBC Gen 2 LT1/LT4 heads that have decidedly different coolant passages (they're designed for reverse coolant flow, and are not compatible w/the Gen 1 engine block w/o extensive mods).

The Vortec engine does use a different coolant bypass, you can do a search on that for more info.
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Old 04-08-2013, 07:31 AM
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Quote:
Originally Posted by FOIDIL View Post
This is great! Very good info and discussion!
The block has flat top pistons and .450/.460 cam.
Sometimes the only confusing part about these blogs is misinformation, but I can't determine if it is misinformation, I have been out of this game for a long time, so thank you all for you patience.
I had read that Vortec heads may have a different/additional cooling jacket that won't coordinate with older blocks(?) It is alot of time, money and frustration to be puting them on ebay, so I am trying to get straight info from you guys that have been at it better.
My mind set has been that the Vortec, being a newer design with more 'science' with matched Vortec intake system would create an awesome power plant for pushing and pulling. However, with my 'old school' knowledge, the new science of computers and technology in this newer truck is forcing me into a new education, which is good, but I am afraid of making a very big and costly mistake.
I am at the stage of purchasing heads, and I only want to do it once.
Thanks again guys for the help.
The own efi intake that came on your truck is a pos and should be thrown away. A tbi throttle body on a rpm intake would be a better combo but a multiport ram style intake would be even better. All this requires money though.

That's the problem with old sbc's the cost to update them is so far beyond the cost to just drop in a used LS type engine. An lt1 is a decent middle ground but still isn't that wonderful.

Good luck on your project, take your time and you should get the results your after.
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Old 04-11-2013, 11:07 AM
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I have recently done a 400 sbc with vortec heads. The flat top pistons will not be enough to get the compression down. you will need some sort of dish.. i ran -4cc dish and that still put me pretty high compression. The vortec heads will also need to be redone to aceppt a larger cam. The original springs cannot open as much as what your going to want. There are a couple of ways to fix it. I used beehive springs but there is a way to machine them to handle better springs also. If you have any questions or need any part numbers just private message me.
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Old 04-11-2013, 11:49 AM
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It is to late to change to dish pistons. I take it that I will need to go with a larger cc head? Would the 64cc be big enough? or is there a larger one?
It is looking like I will be going with the vortec heads after all, now I am finding there are several different castings that relate to different specs. Any help in narrowing them down?

Thanks again to all who have posted, this has been a BIG help.
Even though this is going in the 98, I will have to post pics of my 1st series when it gets done, but I am having a hard time finding a body man that isn't just doing insurance work. Frame is powder coated, engine is done and cab has been rebuilt, now just remaining body then reassemble.

Too many projects to little money!
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Old 04-11-2013, 01:11 PM
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How about a little math.....
383 with flat-tops (7cc eyebrows) and 64cc heads will create 11.1:1 static compression ratio, requiring a camshaft in the 240@0.050" tappet lift range that makes power from 3200 to 7000. The L31's would have given up way back in the 4K range somewhere due to their tiny little 170cc intake runners trying to feed 383 cubic inches, so you'd be left with a detonating turd. Bad plan from the git-go in my opinion. L31's will make a nice torque motor for the street when bolted on a 383 with 9.0 to 9.5 static compression ratio, where you can use a mild cam and take advantage of the low-end grunt of the combination.
Same motor with 68cc heads creates 10.4:1
Same motor with 72cc heads creates 9.98:1
Same motor with 75cc heads creates 9.68:1
Same motor with 76cc heads creates 9.58:1
Same motor with 78cc heads creates 9.4:1
Same motor with 80cc heads creates 9.2:1
I recommend running the lowest static compression ratio possible so you can run a mild to modest camshaft that the computer will tolerate. FYI, a 383 will want ~200cc intake runners. Even if the L31's would allow a lower SCR, they have 170cc runners that will run out of air pretty quickly, compared to an aftermarket head like an AFR195 or a good ProFiler 195 head.

Last edited by techinspector1; 04-11-2013 at 01:31 PM.
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