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Old 08-20-2019, 10:58 AM
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I've also been curious how the Voodoo 702 would run in an engine like this. Something I may try in the future.

For the OP, I think anyway you slice it, you'll need to deck the block anyway if you're going for a proper rebuild and want things square. I guarantee it's going to be off on one end or the other. How much you want to deck it though is going to determine the route you take. I personally wouldn't start with a piston .040 in the hole though. Which means new pistons requires a rebalance of the assembly. And before decking the line bore needs to be checked and honed.

Kind of got backed into a corner with pistons in the hole that far. One way or the other, even if just replacing pistons and getting them closer to deck, then a rebalance and call it good enough, it's going to be a spendy fix, and the block still won't be square.

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Old 08-20-2019, 11:01 AM
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#64 heads;
https://www.ebay.com/itm/Pontiac-197...MAAOSwR29ZMysx

  #23  
Old 08-20-2019, 11:21 AM
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"He wants it to remain basically numbers matching and stock as far as block and heads go, but stated he would like maybe a bit of a camshaft upgrade to get a little more out of it, but nothing too radical."




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Old 08-20-2019, 11:27 AM
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Quote:
Originally Posted by STEELCITYFIREBIRD View Post
"He wants it to remain basically numbers matching and stock as far as block and heads go, but stated he would like maybe a bit of a camshaft upgrade to get a little more out of it, but nothing too radical."



Sometimes you get what you want and sometimes you get what you need.
Close as it's going to get for a better compression ratio to use pump gas.
He can keep his numbers matching heads on the shelf.

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Old 08-20-2019, 11:28 AM
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I hate to break it to the seller of those 64's but they are not worth half of that asking price.

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Old 08-20-2019, 11:29 AM
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I hate to break it to the seller of those 64's but they are not worth half of that asking price.
Right. Just an example. They are still out there. 70 GTO heads.

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Old 08-20-2019, 11:31 AM
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  #28  
Old 08-20-2019, 11:32 AM
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Options. More is better.
What would you do to get the compression down into the 9's?

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Old 08-20-2019, 11:40 AM
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I'm building an engine very similar to this. I have decided to go with the factory 068 cam. It should be very easy on the valve train and should allow me to run pump gas with the stock 10:1 compression ratio. I am running a 744 cam in a 421 engine with 10:1 compression and 670's. I think the 068 cam would have probably been just as quick though. It does run good with the 744 but I think there would be more power to be had with a summit 2802 cam or something similar.

However, I don't think you could go wrong with that Crower 60916 cam either. Just use some big block Chevy rocker arm studs and nuts to change the valve train to an adjustable valve train. It should be a good runner.

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Old 08-20-2019, 11:54 AM
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I would take a degree wheel and dial indicator and get some idea of what the present cam has for max lobe lift and 0.050" duration. No way to know what is an upgrade without knowing what you have now.

Stan

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  #31  
Old 08-20-2019, 12:08 PM
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Originally Posted by TransAm 474 View Post
Hi, we are building a 1970 YZ Ram Air 3 400 in a 1970 Trans Am for a customer. He wants it to remain basically numbers matching and stock as far as block and heads go, but stated he would like maybe a bit of a camshaft upgrade to get a little more out of it, but nothing too radical.

It is a YZ block, stock #12 Heads, factory rods, and cast "8" eyebrow pistons with no markings, but it appears the bore is .020 over when measured with a caliper. The pistons appear to be around .040" in the hole as well. The camshaft that is currently in it is unknown. The only stamping I can find on it is the letter "A" stamped in the rear on the camshaft, along with "MAP" stamped in the rear as well. There is nothing else anywhere on it, front or rear. I would like to talk him into letting me replace the pistons with normal Flat Tops, and try and get it atleast close to zero deck, either with the pistons, or having the block decked. I am going to also try and talk him into letting me replace the factory 50 year old rods with a better set of 5140 rods, this build doesn't need 4340. Compression should be up around 10-10.2 I believe, if I were to do those upgrades, and I was thinking about using the Crower 60916 camshaft, but then I suppose that would require an adjustable valvetrain?, so the cost just keeps climbing for him. This is just a street restoration project, so he doesnt really want to go all out with this build, which is understandable, although he did say he wouldn't mind a few upgrades. We are also thinking of buying the carb kit and Jets/Rods from Cliff to build the Qjet, and maybe have someone put the factory Points distributor on a machine and set up a custom curve for it.

So my question is, what would be a good camshaft for this application on Pump Gas without running into problems with pinging and detonation, while using the stock, non adjustable valvetrain. The valve springs will be Crower 68404. I like the idea of the 60916, just wish it didn't require an adjustable valvetrain.

How much compression do you think it has in its current configuration, and what camshaft would you recommend for it with its current parts and compression?(just in case he wants to use what he already has.)

Thank You
As is my guess would be the compression is around 8.7:1 the way the engine was. Not great, but if you rounded the edges off the tops of the reliefs on the pistons, ground the crown between the reliefs down a bit and ran a voodoo 702 it should run ok if the owner punts on the upgrades.

I do not see anything wrong with the proposed upgrade plans. Only comment I would mention is there is a good chance the engine has the original balancing yet on the crank. Most shops that use those 8vr cast pistons would not balance something. So if you can not talking him into the forged rods, use the originals, run arp bolts and get some 2vr pistons should be fine with out rebalancing.

Does not sound like the owner is wanting a finicky pump gas engine. The smaller aggressive cams like the 702 voodoo or something similar do fine with less compression. The 60916 though would like a little more compression than where it currently sits. I would only use the 60916 if they go for the upgrades.

  #32  
Old 08-20-2019, 12:36 PM
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I've been using Icon pistons in most builds, but there may be other varieties out there for 400's that don't end up so far down in the holes at TDC.

Lowering compression is always an option, but even with lower compression the cam choice is still critical to make sure it makes optimum power and still manages pump gas w/o issues.

We've seen several Pontiac engine build with no more than 9.3 to 1 compression pound the rod bearings right out of them simply because they put enough camshaft in them.....FWIW......Cliff

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  #33  
Old 08-20-2019, 12:49 PM
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Quote:
Originally Posted by TAQuest View Post
Quote:
Originally Posted by unruhjonny View Post
...
Compression first, cam second.
...
... if you have all your choices on the table why not dictate the compression you want first then make a list of the parts that would help you attain that?
...
see what I did there?

you are essentially saying the same as me, except I've removed what I can only guess was misinterpretation.

where you lose me is here:

Quote:
Originally Posted by TAQuest View Post
Pick a cam more dependent on what you want to use the car for, not for the compression your pile of parts dictated.
Where does this purported "pile of parts" come from?
Are they not parts that you (the engine builder) has chosen to use to get your long block to your desired compression?

I agree the cam should be chosen to compliment the compression and intended use, but weather you are deterimining where the compression will be, or where you want it, you are still first looking at the compression;

If by chance you are replying to this:

Quote:
Originally Posted by unruhjonny View Post
I would deck the block, but not worry about getting it zero decked - just freshen it up;
...
It was a response to this:

Quote:
Originally Posted by TransAm 474 View Post
... I would like to talk him into letting me replace the pistons with normal Flat Tops, and try and get it at least close to zero deck, either with the pistons, or having the block decked. ...
If this is intending to be a street motor, you can go too much compression very quickly going this way.

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  #34  
Old 08-20-2019, 01:04 PM
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Quote:
Originally Posted by unruhjonny View Post


Where does this purported "pile of parts" come from?
Are they not parts that you (the engine builder) has chosen to use to get your long block to your desired compression?

.
Basically was leading up to a different set of heads. The 12's are in the present 'pile' of parts.
The 64's would make things more manageable. Along with the autotech pistons. Summit 2801 Cam.
That's what I would do if I was stuck with iron heads and could pick what would work best with pump gas.

  #35  
Old 08-20-2019, 01:24 PM
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Originally Posted by Formulajones View Post
Pretty much what Cliff described the short block is how I built my 70 RAIII.

I used old style TRW flat tops and as they come out of the box they are only .015" in the hole or there about. I then deck the block near zero. Think I left mine .004 or .005" in the hole and with a .039" gasket I end up with decent quench. Compression was 10.13:1 on mine with the #12 heads.

For me adjustable valve train is a must so I can set lifter preload to what I want or what the lifter manufacture recommends. Making them adjustable is a piece of cake. I simply swap over to big block chevy 7/16 rocker studs and the appropriate poly lock to fit. This also provides a little more valve train stability with the larger studs. I do it with every Pontiac here regardless of cam or spring pressure choices.
I like this post.

What might be beneficial, is is someone can find a good compression calculator, I seem to be having trouble finding a good one any more.

Even with the wallace racing one, I must be doing something wrong, because I seem to be getting 6:1 when I put in specific parameters which should yield closer to 10:1... I think it's the 'head cc' spot that really bunked me on that calculator.

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  #36  
Old 08-20-2019, 01:24 PM
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Default Another Option

I know what I'm about to post goes against common wisdom but.... I recently build an engine for a friend that has a 400 in a 72' Ventura. I just did it as a favour at no charge. The car is for his teenage son and he wanted to do it on a tight budget. We tore the engine down and it was .030 over, 8 valve relief pistons and had #16 big valve heads on it. Piston deck height was around .030. The engine had a lot of piston to wall clearance too so I tried to get him to bore it and use "better" forged pistons in it. Wouldn't do it. Just hone and rering it. So I warned him it's going to ping, probably use oil, etc... We wound up putting a 2802 Summit cam in it and a used 2500 torque converter I had laying around.

End result is this car runs very well, no hint of detonation anyplace, and no oil use. Car just ran a 13.80 1/4 mile too! I wouldn't have believed it but in this case it turned out great!

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  #37  
Old 08-20-2019, 01:50 PM
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It's obvious the heads have to stay. On an engine like this, with this type of bird, and with restoration in mind, the 12's need to be on the YZ block. So I understand the OP's purpose entirely.

The compression isn't going to be outrageous even if a flat top piston was at or very near zero deck, and could manage pump fuel fine with the right camshaft, I'm doing it with an 068, but I'd recommend a little bigger to keep things a little safer at that compression ratio.

It's really going to come down to how much money the owner is willing to spend to accomplish his goal. If he wants to leave it the way it is and use a non adjustable valve train then I see no other choice but to stick an 068 in and button it up, hope for the best. With pistons .040" in the hole the compression has to be pretty dismal anyway.

  #38  
Old 08-20-2019, 02:06 PM
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Originally Posted by unruhjonny View Post
Even with the wallace racing one, I must be doing something wrong, because I seem to be getting 6:1 when I put in specific parameters which should yield closer to 10:1..
Can you take an image capture of your values?

  #39  
Old 08-20-2019, 02:12 PM
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Originally Posted by unruhjonny View Post
I like this post.

What might be beneficial, is is someone can find a good compression calculator, I seem to be having trouble finding a good one any more.

Even with the wallace racing one, I must be doing something wrong, because I seem to be getting 6:1 when I put in specific parameters which should yield closer to 10:1... I think it's the 'head cc' spot that really bunked me on that calculator.
This calculator (download it from bottom of page) works for me:

http://cochise.uia.net/pkelley2/DynamicCR.html

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  #40  
Old 08-20-2019, 02:13 PM
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Originally Posted by Formulajones View Post
It's obvious the heads have to stay. On an engine like this, with this type of bird, and with restoration in mind, the 12's need to be on the YZ block. So I understand the OP's purpose entirely.
It all depends on what you use the car for. The 12's look like the 46's except for the numbers. If you aren't getting judged then they are the same. The car is still numbers matching with the originals on the shelf.
If I'm not married to the 12's then I would use the 46's.

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