Pontiac GTO Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
15 Posts
Discussion Starter #1
I have a 66 GTO 4 SPEED with a 1973 400 block and 93 heads, stock rear end gears. I am gioing to have the engine rebuilt and I was wondering if anyone can recommend what cam lift I should have installed. I want a nice Lobe and I love the muscle car ( cam sound) when a car is at a stop. would like to keep gears stock and drive on the freeway. any help would be appreciated.
 

·
Super Moderator
Joined
·
5,744 Posts
Which transmission (and converter, if it's an automatic) do you have? Does it have power brakes and/or factory a/c? What rear-end ratio are you running?

Bear
 

·
64-67 Expert
Joined
·
8,561 Posts
Also, with a 400 block, you have 400 pistons, which have their valve reliefs cut for a '67-up head. The 093 head is a '66 GTO closed chamber head, with different valve angles. To put it simply, a big cam in this engine will cause the valves to hit the pistons. You should be able to run an 068-type of camshaft without issue. Also, be advised that you will need to use race gas or boosted fuel with these heads...if they are 093's. They are only about 64-69cc, and are ping-monsters. My advice would be dished pistons, forged rods, and decent heads. AFTER you decide the car's main purpose. Comp cams XE 262-268 cams work well with a nine to one 389 or 400.
 

·
Super Moderator
Joined
·
5,142 Posts
Also, with a 400 block, you have 400 pistons, which have their valve reliefs cut for a '67-up head. The 093 head is a '66 GTO closed chamber head, with different valve angles. To put it simply, a big cam in this engine will cause the valves to hit the pistons. You should be able to run an 068-type of camshaft without issue. Also, be advised that you will need to use race gas or boosted fuel with these heads...if they are 093's. They are only about 64-69cc, and are ping-monsters. My advice would be dished pistons, forged rods, and decent heads. AFTER you decide the car's main purpose. Comp cams XE 262-268 cams work well with a nine to one 389 or 400.
:agree

IMHO

I would move from 1966 93 heads (1.92/1.66) to 67-70 (72-75 cc) heads with 2.11/1.77 valves. Before buying dished pistons try .051" or .060" head gaskets to lower the CR.

Pontiac Cam Specs;
9779067 duration @ 50% 200/213; Lift .410/.410 LSA 114. mild street
9779068 duration @ 50% 212/225; Lift .410/.410 LSA 116. H.O. Cam
a more agressive cam would be,
9794041 duration @ 50% 231/240; Lift .470/.470 LSA 114. RA-IV
 

·
Super Moderator
Joined
·
5,744 Posts
Another appropriate question would be, how much are you willing to spend? If you go much over stock lift there's a point where things start to rapidly snowball on you. You have to run different valve springs because the stockers aren't strong enough to keep the lifters on the lobes, and they also go into coil bind before the valves can get fully open - so you need taller/stronger springs. To install the taller/stronger springs you have to have the spring seats in the heads machined to make room for them. You probably have to have the tops of the valve guides cut down to keep them from getting hit by the bottoms of the retainers, and cutting them means different valve stem seals. All that also puts you into territory where you must have an adjustable valve train, so then you need poly-locks. And then the bottleneck studs are suspect because they tend to break at the neck with higher spring pressures ---- so you replace them with 7/16" studs. It's kinda silly to spend all that on the top of the motor and still run stamped steel rocker arms, so next you pop for roller rockers. The maybe some stud girdles... then new valve colvers because the factory ones won't clear --- or you have to find some spacers. The you need custom length pushrods after all the other changes...

Get the idea?

I'm not trying to talk you out of it, just be aware there's a lot more to it than just swapping out the cam shaft.

Bear
 

·
64-67 Expert
Joined
·
8,561 Posts
There is no reason to run 389 heads on a 400 block, IMO. They are inferior in every way to the later heads. I am running them on my '65 GTO because it's a '65 389, and that's the only reason. I need race gas, too. If the engine in question was indeed a 389, then yes, for appearance sake. But for a 400, it would be a huge improvement to install 400 spec heads....and go from there. Lots of previous threads on this topic, and "Mr P-body" (Jim Lehert of Central Virginia Machine) can help you pick the right parts and services for a good running, long lasting engine. Or, since it's a '66 and you seem to have all the correct parts except a block, locate a '66 389 and build it up with low compression pistons. Done a couple now, and they run great.
 

·
Registered
Joined
·
15 Posts
Discussion Starter #9
Would these heads work and would you recommend these?

Pair #670 Heads 1967 high performance 72CC. Complete, magnafluxed & ready to ship. DC's L076 & L086
 

·
64-67 Expert
Joined
·
8,561 Posts
Excellent heads for a 400, IF you go with custom dished pistons. But, 670's are "closed chamber" design heads, and they need a lot of ign. timing to work. You need to drop the compression to about 9:1 to be ok with today's gas.
 

·
Super Moderator
Joined
·
5,744 Posts
Would these heads work and would you recommend these?

Pair #670 Heads 1967 high performance 72CC. Complete, magnafluxed & ready to ship. DC's L076 & L086
I know people who love these heads, but personally I've never understood why. Like GeeTee said, they're closed chamber heads and as such they need a TON of ignition advance because of that. The earlier you "light the fire", the more likely you are to give up some potential torque due to the effect of negative work (the piston is still rising as pressure is building from the ignited fuel/air, so pressure that would otherwise go towards building torque is actually working AGAINST you, trying to make the engine run backwards.) 670's do have excellent quench characteristics (lots of mixture turbulence) and that's a good thing for helping avoid detonation. However there are other ways to acheive that without having to also run so much ignition timing.

I'm not going to say that these are BAD heads, just that there ar other Pontiac iron heads that are better.

Bear
 

·
64-67 Expert
Joined
·
8,561 Posts
I agree. 670's flow great, and are good performance heads, but--- there are MANY open chambered heads that flow the same and are a lot more user friendly. Not to mention, cheaper, too, because 670's are for the '67 GTO (and 428) and are sought after by collectors.
 

·
64-67 Expert
Joined
·
8,561 Posts
With stock pistons, something in the 87cc-96cc range. Consult the charts.....Wallace Racing and others....I'm running some modified #15's with an 87cc chamber. If you go with custom pistons, you can run any 72-80cc head you want. A lot of good ones: #12, #13, #62, etc. etc.
 

·
Super Moderator
Joined
·
5,744 Posts
... If you go with custom pistons, you can run any 72-80cc head you want. A lot of good ones: #12, #13, #62, etc. etc.
:agree If you're changing pistons anyway, that opens up possibilities for you because you then have the option of using dished pistons. That let's you get by with smaller chamber volumes in the heads because you're "making up for it" by adding volume in the pistons.

Bear
 
1 - 16 of 16 Posts
Top