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Old 08-27-2010, 12:36 PM
Bonger
 
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Need Head Opinions and Suggestions!

Hey guys........

Right now I have a 355 in my old 70 GM that I want to make a little more street friendly.........ex - can run at least pump fuel!!!! It was primarily built to be a strip motor so it the compression is way up there at 10.65 - 11:1.

---- I wouldn't mind keeping it as is but access to anything but 91 is pretty slim where I am.......even aviation fuel is tough to come by.

It currently has a set of Vortecs (1.94 intake valve, 1.5 exhaust, 64cc chamber) so I figure that my best bet to knock back the compression into pump gas range would be to go with a different set of heads. I'd love to try and stay with a vortec style head since all my accessories (covers, intake, etc) is of course designed for that style........but I'm pretty sure they don't come any larger than 64cc.........so if anyone knows of some please direct me!!!

SO, since I'm likely going to have to go to a different style head, intake/etc/etc............I'd love to hear some suggestions about what type/brand of heads some of you guys have used and recommend!!!!!!
-------- I don't care about $$$$ so a nice set of aluminum heads would also be in the cards

Based on my current compression......can someone also tell me where I would be (guestimate) based on going with 72cc, 76cc, etc??? I still want to push my hp but just want to be able to fuel up at the pumps!

--- New intake suggestions would also be appreciated but I'd like to go back to a polished or chrome.........just cuz I like to keep it looking shiny under there!!!!

Additional info about what I'm going to be putting together to help suggestions is:

1973 350 4 bolt block, decked, line honed, bored 0.030 - 355cu in
Forged crank .010/.010, Forged Flat Top Pistons, HD stock rods with ARP bolts
CAM - Comp Cam Ex286C, .282/.484 Lobe Center 109, Valve Overlap 64
Rebuilt Holley 650 4777C Double Pumper
GM Stinger HEI Distributor

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Old 08-27-2010, 01:31 PM
Bonger
 
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The guy that built the motor knows his stuff and the heads may have been shaved down since I know he had them pocket ported and bowl hawged and when I talked with him last he told me:

The static comp ratio of the pistons is 11.25/1 and combined with those particular heads and the .040 thick head gaskets it worked out to a real compression ratio of 10.65/1, a little high for 91 octane.

As I said, he had originally built it to be a strip motor, not a street.......I'm really not trying to invent a problem because as it currently sits, on 91 I've adjusted my timing numerous times but the only way I can avoid detonation is to have the motor running like a dog since the timing is too retarded. And I definitly won't claim to be any expert which is why I'm looking for opinions, but with the compression ratio that high (and I have no reason not to believe him since he's been nothing but helpful) all I've seen is that lower octane like 91 is just going to be a problem unless it's being mixed with 100 or 110.
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Old 08-27-2010, 02:51 PM
Bonger
 
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10.63 is about where the engine builder was guessing so you're spot on F-bird!

I'm actually up in Canada and the availability of decent fuel is pretty F'n lousy. Especially in my area...........so 91 is pretty much going to be it at the pumps. I haven't done a total search of in the city yet but my hopes of finding 93 are slim. The airport can hook me up with 20 gallon jugs of 100 but thats as good as I'm going to get!

And the distributor suggestions are something I'll surely look at ASAP. It does make alot of sense because even when I was doing adjustments on my timing it didn't seem to make alot of sense (how it was reacting).

Plugs were going to be up for a change as well. I have my headers off right now being modified to accomodate for the spark plug wire looms since the bolt holes on the sides of the heads weren't accessible with the headers on so I'll try that as well.

Just re-installed the intake but it was clean underneath and seemed to be sealed well...........carb right now is at 69 primary and 78 secondary.

******THANKS A TON for the info though F-bird!!! I'll start with my Distributor and plugs for sure. Before this I was actually just using a 600cfm Edelbrock performer as well and since have installed a Mallory GP140 electric pump and regulator to use with the 650.
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Old 08-27-2010, 05:10 PM
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Once again, thanks a ton F-bird!

It's not that the builder doesn't know whats up.......it's just a matter of getting all the info from him as he doesn't live in town and internet is not really his friend if you know what I mean! He's more of a have coffee and we'll sort it out since the e-mails that I receive do not have a single period or spaces.......tough to sort through.

The pistons are flat tops but I don't know exactly what other machining was done to the heads..........so they may have actually been milled down.

BUT, I will get the exact cam as this was info I got off a pile of papers that I had sitting in my desk.

As for the stall, 2400 was what I had available when the trans was rebuilt so I could definitely look at getting a higher converter. But I am trying to keep the truck fairly streetable and I've heard that 3000+ aren't as friendly for the average drive. Even as is right now........I'm hesitant to believe it's actually working properly! It seems to be fully locked up at alot lower RPM than 2000.

But if I do need to upgrade the converter.........it shall be done!

As for the fuel, I've been checking myself and just quizzed a buddy who says that one station in town carries 94. I haven't seen any Sonoco or Pioneer stations in Canada at all! They may be around.......but not here in Alberta so we get stuck with Husky, Shell, etc. The Husky is where it's supposedly 93 or 94, but thats an ethanol blend as well.

------Lastly, I'd rather not be pulling the heads either since I've already been spending an abundance of $$$ on the old girl already!!!! So if I can get it running primo with no detonation I"ll be smiling.
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Old 08-27-2010, 05:55 PM
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If you're looking for large chamber heads, Patriot makes aluminum heads with 72cc chambers. Jegs sells them, here's the link: http://www.jegs.com/i/Patriot+Perfor.../2171/10002/-1
They're worth a look and they are a reasonable price.
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Old 08-27-2010, 09:36 PM
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Everything fbird posted is spot on. I'll only add that polishing the chambers can turn a 62cc head to a 66-68cc head if your fairly aggressive. That'll be better across the board if done right. Another option is a smaller carb with annular boosters- more finely atomized fuel helps some, and a restricted intake helps lower the cylinder pressure.
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Old 08-27-2010, 11:59 PM
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Quote:
Originally Posted by turbolover
Everything fbird posted is spot on. I'll only add that polishing the chambers can turn a 62cc head to a 66-68cc head if your fairly aggressive. That'll be better across the board if done right. Another option is a smaller carb with annular boosters- more finely atomized fuel helps some, and a restricted intake helps lower the cylinder pressure.
All good advice here. Have you considered Aluminum heads? they're getting cheaper and vortecs Ebay good...

Ps Aluminum is generally considered to reduce octane requirement equal to nearly full cr point.
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Old 08-28-2010, 12:34 PM
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I'll try and get on top of getting my Distributor set up in the next couple days if I can get ahold of a limitable/adjustable vac can and then I'll limit the mech advance, check my timing tab, change out to a cooler plug, and go from there.

The 2400 converter is coming out and I"ll see what timeline I can have at the trans man in town to get ahold of a 10" stall, 3200 minimum.

The rear end is a 3:73 locker, with 275/60R15 (approx 27").

Lastly, thanks again to all, especially F-bird and I'll get back on here to post after I get everything back in place. It might still be with the 2400 for the time being but at least I can verify that I'm going to be able to run these heads!

------- It's the first project of this type for me since so thanks for the patience! Loving it though and can't wait to get everything on the road. I'll post a pic of the old girl in my profile so you guys can check out what I'm up to!
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Old 08-28-2010, 04:06 PM
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Quote:
Originally Posted by Bonger6
The 2400 converter is coming out and I"ll see what timeline I can have at the trans man in town to get ahold of a 10" stall, 3200 minimum.
I missed it if you said what transmission you have?
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Old 08-28-2010, 05:14 PM
Bonger
 
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TH350, Stage 2 Shift kit and the 2400
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Old 08-28-2010, 09:51 PM
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high stall converter

Quote:
Originally Posted by Bonger6
TH350, Stage 2 Shift kit and the 2400
One of my customers has a converter like you're thinking of and wants something closer to stock. But we live in South Carolina and I suppose it would cost more to ship and import custom than is practical. Not sure.
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