# 400 + l2262 +041+670=????



## mbspeed (Sep 25, 2012)

Hi Guys.I have a 67 400 .30 over i am putting back together it has l2262 pistons new compcam 041 ramair cam and 670 rebuilt heads my ?? is can i run this motor on pump gas with a can of 108 octane booster or will i need replacement heads ???? and if i do need replacement heads what would be the best cast# to look for dont have much $$$ to spend so new is out i am going to try and sell this motor to re coop cost of the 467 stroker motor i put into my GTO thanks any info would help ........


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## Chris-Austria (Dec 23, 2010)

This combination will be at about 9.9:1 SCR which is a bit high for pump gas but may be okay with premium fuel. The 041 cam will reduce the DCR a bit.. I'm pretty sure it would be good with the fuel over here where I live. (would be equal to 95-96octane in the US).


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## BearGFR (Aug 25, 2008)

Key questions:
Did you zero-deck the block (if not, do you know what the deck clearance is?)
Which head gaskets did you use?
Did you cc the chambers to see for certain how large they are?
If I assume nominal dimensions everywhere (.045 compressed gaskets, .020 deck clearance, 6.70 cc's in the valve reliefs, 65 cc's in the chambers)

That works out to 10.6:1 static compression. My opinion... you don't stand a chance of being able to run it on 93 octane, even with large amounts of booster. You _might_ be able to squeak by if you retard the cam a bunch (6 degrees or more) and pull a bunch of timing out of it, but that's going to kill power and bottom end torque. (Retarding the cam pushes the torque curve higher into the rpm range, and that 041 cam is already "up there" to start with. 670 heads like lots of timing, 40 degrees or so - and pulling out timing is going to make them very unhappy.)

If you want to change heads, you need to be around 78 or so cc's to be safe. Year model 1970 casting #16's are nominal 78 cc's, but they have the smaller valves. Very important to get year model 1970 16's --- other year 16's have smaller 72 cc chambers and still wouldn't be big enough.

Bear


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## Chris-Austria (Dec 23, 2010)

Don't the 670 heads have 72cc chambers?
I'm not sure if the SCR did kill my engine, it was a 428cui with 670 heads and 38° of timing. It started to knock, but at the same the the head gasket and the camshaft were bad. The pistons didn't look like they had a big detonation issue, but I wouldn't risk it if Bear says it's not safe!


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## BearGFR (Aug 25, 2008)

Depends on which web site you believe  The 670 chambers with their closed design sure LOOK smaller than the 72 cc open chamber heads. With Pontiacs though like has been said many times, you never know for sure unless you cc them yourself.

Bear


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## mbspeed (Sep 25, 2012)

BearGFR said:


> Key questions:
> Did you zero-deck the block (if not, do you know what the deck clearance is?)
> Which head gaskets did you use?
> Did you cc the chambers to see for certain how large they are?
> ...


 Hi Bear i did cc heads like 72/75 cc ...the head gasket is buttler GM repro ...motor is stock deck.... and i have a set of 061 heads cc close to 80 open chamber heads i could use if needsd. and cam is new not installed yet i could return and get a low pro cam if i could make this combo work need to sell this motor to get more parts for 467 stroker motor :confused


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## geeteeohguy (Feb 2, 2008)

The 061 heads would be a much better choice here. 670's are useful for numbers matching restorations or race cars run on race gas. Their combustion chamber shape needs a TON of timing to produce optimum power, and that means super high octane. The only octane booster that actually works is TEL 130, and it's about as expensive as blending race gas. "bleeding off" compression with a big cam is really a myth: lower cylinder pressure at low speed helps at low and cruise rpm, but it'll bite you when you hit the power band and start to stuff the cylinders. I'm running 87cc #15 1970 455 heads on my +.030 '67 400 in my '67 GTO, after having years of failure with various 72-75cc heads. If you want to drive it, you need to run less than 9.5 CR, at least where I am, in the land of 91 octane. Even with the 061 heads, you'll probably need about 93-96 octane to make it happy.


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## BearGFR (Aug 25, 2008)

:agree with the wise man.

I also understand this is a budget build that you are using to raise money, not an engine you're going to keep so you don't want to put a lot of money into it.

You _could_ build it with what you have and use the 670's, just be honest when you sell it and make sure the buyer understands it's not a street engine but is set up for race gas _only_ and will not survive on pump gas. That might limit your potential market though....

Bear


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## Rukee (Feb 8, 2007)

I wouldn't say it wouldn't survive, I've been running mine for like 18 years at 10.75-1 compression with forged pistons. Sure it's premium only and sure I have the timing backed off about 10*, and yes I still get a slight pinging at WOT, but it's still streetable.


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## BearGFR (Aug 25, 2008)

Well, I 'spose I should have qualified what I said a little bit. True, you will _occasionally_ find someone who's able to 'make it work' for them. Just like you'll _occasionally_ find someone who's able to get an engine to live while making power with factory rods. The odds aren't in favor of it though. For every 1 engine that stays together with factory rods and making significant power, you'll find 500 or more that weren't so lucky and had a rod let go, taking the block and everything else along with it

I'll just say that given the choice, I wouldn't try it myself.

Your mileage may vary, void where prohibited by law, slippery when wet, past performance is no guarantee of future returns, batteries not included.... 

Bear


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## Rukee (Feb 8, 2007)

I have the factory rods too. 
Balanced, but I never buzz it over 5k.


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## mbspeed (Sep 25, 2012)

well i guess i will change my plan and use the 061 heads and sell motor as high CR motor not good for pump gas thanks for all the info guys:cheers


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