Marx3

Okay, I know this subjet must have been covered a thousand times, but I cant make the search function find me good answers to my questions.

Here goes:
I have a completely stock 403 in a Trans Am. I have a set of completely stock 7 heads.
The engine is out of the car and will be getting new gaskets etc, so heads are coming off regardless.
Would you say that it is worth it to put the 7 heads on as is? Would they be an improvement over the 4A's as is?
I might mill them a bit to hit 9.5:1 and ofcourse find a good cam to go along. Something like 210/215@.050 ? and I might port them and bowl blend them.

Will I have to do something about the holes for the headbolts to make this work?
Is there anything that I should know, when if doing this swap?

brownbomber77

17/32 drill bit for the bolt holes. Yes they will help. 330 heads will help more with smaller chambers. Yes. Worth it.

Marx3

short and sweet :-) so bolt holes will have to be opened up a bit.

olds 307 and 403

Bolt holes and one dowel hole needs enlarged on each head. The 4A heads are awful on the exhaust side and have huge 84+ CC chambers. Mill the 7's to achieve your desired compression. If you cut the heads a lot, the intake side or actual intake will need cut. If you go to 9.5 to 1, 215+ duration shouldn't be a problem.

joe_padavano

People use early small block Olds heads on 403s to bump the compression, but they don't realize that you really need to install larger valves in those heads. 2.070/1.625 fits no problem and is what Olds used in the big block 400 motors. For that matter, consider using BBO heads. C heads were factory installed on the 400 motors and will flow better for the 403. Yeah, they have the same large chambers as the 4A heads, but CR isn't the only thing that makes HP. Mill the heads and port-match a Performer RPM.

Marx3

I have been thinking about putting on big block heads, but the thing is, these 7 heads are very cheap and big block heads are hard to come by in my country.

The goal is about 300 horsepower. Would it be equally possible to achieve with both the 4A's and the 7's? or would it be easier with the 7's?
I have noted to install larger valves.
I will also take care of the valve geometry if end up milling them alot.
Can I install polylocks and make the valvetrain adjustable, like you can on Pontiac engines?

joe_padavano

300 HP is realistic with the 7 heads. You can convert to adjustable rockers, but you'll need to have the heads machined for larger screw-in rocker studs and guide plates.

Octania

I put #6 heads on my 403 and failed to enlarge the valves, and now I wish I had. But, I have a really puny exhaust system so there is a lot left on the table there.

I would go with at least 2.000 and possibly the big BB valves at 2.072" if your intake manifold and exhaust and cam are in place to match.

olds 307 and 403

Bigger valves and the bowl blending to make use of them, as said 2.07/1.625". It is way easier with #7 heads to hit your goals. More important than the 300 hp will be the 350+ ft lbs of torque.

Marx3

Thanks for all the info. I am not sure they will be milled much more than a clean up.
I sounds like a smart move to install bigger valves. I will definately port and blend them. Valves will get an anglejob too.

A cam will be chosen carefully to match the rest of the combo including rearend gearing. I guess 300 hp is not to be considered a wild build.

btw. 350+ ft-lbs of torque? typo? didn't these engines have like 330 ft-lbs from the factory? I would expect an increase of more than 20 ft-lbs by upping the compression, porting and adding a good cam?

captjim

Doesn't the Comp kit use 5/16" studs on the lower part that screws into the head?

Marx3

hmm, the 7 heads were sold.
There is a set of 8 heads on ebay. Would it make sense to do work on these over the 4A's?

67 Cutlass Freak

The #8 heads are not very good castings. Not much better than the 4a's. You should keep looking for better castings. How much are these core heads selling for, and how much is shipping to your country? I may be able to help you find a good set of cores.

Marx3

That sounds interesting. Thing is, the engine in question, actually belongs to a friend of mine, who does not have an account in here, so I am helping him out.

Actually I just sold a set of 7's here in denmark. I got 2500 dkr for them. I think that kind of iron heads would be worth a bit more here, but no one was interested but this one guy, who gave an offer.
2500 dkr equals 370$.
To have something to compare this with, I can tell you that a set of stock double hump SBC heads in working condition would go for about the same.
2500dkr/370$ aint that much here.
67 cutlass freak, what do you have in mind? can you include a shipping quote to Viriginia beach in your price?

( btw, worship your porting threads... I am going to follow these when doing these heads )

67 Cutlass Freak

Thank you! I really hope I've helped a lot of people breath life into their Olds junk.
Best of luck to you, Dave - The Freak

Warhead

I limited my milling to .030 on the #5 heads I bolted to my 403, had a 65cc chamber, factory pistons ended up being 9.2:1. No fitment issues whatsoever. 2" intakes, 1.56 exhausts. Factory A4 intake, factory iron exhaust manifolds, factory valve gear and pushrods.

The compression increase made an astounding difference in power.

This engine needs compression, I say SBO heads with factory dish pistons, BBO heads with a flat top piston.

I have bare castings I am getting rid of, but I am just too damn far away.

olds 307 and 403

I disagree on the #8 heads being not very good. The exhaust is plain terrible on the 4A. Once the lip is removed under the exhaust valve on the #8's, they are decent. Doesn't take much grinding either to remove it. My #8 chambers measured 77-78 CC vs 86 CC for my 4A. That said, early heads have about 10 CC smaller chambers and need less work to flow decent so pay accordingly, #8's are worth less and much more common.

Marx3

Yeah, I figured If I hit about 65 cc , that should give me just over 9:1 cr with stock dish pistons.
This 403 will definatley get some better flowing heads and as big a cam as possible with 2.73 gears.

btw the 7's in question milled out at 69 cc.

Cutlass freak, I am shooting you a pm.

307and403: would you say it is worth it to spend money on 8's when I can just start grinding on th 4a's ?
300 hp is the ( usual ) goal here. The car is a Trans Am and the owner ( my friend ) want's to wake it up. I mean, 300 is not the limit... :-)

olds 307 and 403

If they are cheap, get them. The chambers are 5+ CC smaller and they already have the 1.625" exhaust valves. Mill them .060", that will put them around 70 CC and do the bowl work necessary for the larger intake valves. Just take your time and cover the seats with tape if you plan on reusing 1.625" exhaust valves.

Marx3

They are 200$ :-)
http://pages.ebay.com/link/?nav=item.view&alt=web&id=271826846398