dman0712

Can the olds 403 heads be ported to flow numbers that will support 500 hp? Is it true that the stock 4a heads intake flow more than the c heads and its the exhaust that really chokes the 4a heads? I would be installing 2.075 int valves and 1.710 exh valves.

Warhead

Maybe, No, and Yes.
Do NOT worry about power numbers, they are only there to inflate ego's.
Et is the true measure of power.
Do the 2.075 intakes, but stay with a 1.625 exhaust, put in hard seats.
You will not notice the difference in power. The stock exhaust valves are just way too small.
Jim

dman0712

im putting in the 1.710 exh valves because i already have them. I want to make that power because it has been a goal and i enjoy the challenge. nothing to do with my ego.

cutlassefi

Huh?

380 Racer

Jim I really have to disagree with these statements. A dyno produces HP & TQ figures and graphs them out. How high to shift, what to launch at, what stall to use for a torque convertor, plus other aspects.

Yes the track is the most important...........but. There are too many variables to test accurately week to week or track to track. The weather first and foremost, track prep (spin/perfect hook), how the timers are set up (not all tracks are set to specs). So in reality yes my ego got a big boost but not only with the dyno but also the time slips this year they went hand in hand. Almost forgot you also need a good chassis to get any HP to the ground.

Warhead

At your level-I agree-is HE there too?

What I am saying IS, how fast do you want it to go?
A lot of people (usually Chevy guys) say "it has 500 hp", but will only run 12.80's.
There is more to it than that.
Once again, after seeing a number of posts than skirts this issue,
How fast do you want this thing to go?
Do you want elapsed time (if you are even drag racing it)?
High top speed?
Are you going to fart around on the street, with occasional track time?
Or are you planning on a competitive car like Nick has?
I took it that you will be farting around on the street, and take it to the races once or twice for fun, by the posts you have made.
Can the 403 heads support 500 hp...sure they can.
C heads are way better starting point in MY honest opinion.
The exhaust valve is way too small on a std 4A head, I never found an et difference going to the larger 1.71 exhaust, although I never ran nitrous, or boost. I would rather run a larger intake valve (2.125) and the 1.625 exhaust.
That is just me.
Keep up with your efforts.
Jim

dman0712

I found some c heads for $100 so i might go with those as long as they havnt been milled. I just need them to flow like 260 cfm. I would just be polishing the exhaust runners, chambers, and porting the bowls. Im hoping that will be good enough. I was told not to cut down the egr bumps because they really dont make a difference. If i caould get the same results with those 4a heads i would lioke to do that because I already have them and i like the stock look.

MI455

I still think a 403 is gonna grenade if you actually get that kind of power out of it...

dman0712

There not as bad as you think. Ive seen a 600hp olds 403. lots of money invested but its possible. You just got to keep them under 6 grand. im running a forged crank and 5 cap girdle to just ease my mind

380 Racer

Points well taken Jim.

J-(Chicago)

D man, if 500Hp is your goal, why don't you start with a better block?
I'm not raggin' on ya, it sounds like fun, but I'd rather see your pile money go into something more concrete.

J-(Chicago)

11 flat in a 3600 pound car will be about 500 HP.

If you do it..... it would be one of the meanest 403's I've ever heard of.

MI455

Those windowed mains just scare me way too much, but I like to over build everything I have too so starting with the strongest foundation you can find makes more sense to me.

dan2286

How much does J&S Machines car weigh? They have their 403 into the 11's. I have no idea how much power they make though.

dman0712

il do my best. i have the forged crank and im getting the 5 main halo girdle. the full block girdle is just over kill for me. The car will be a weekend fun street car. It wont be at the track very often. Ive seen 500hp 403's that run the stock crank with no girdle and are still holding together after many passes. Just have them balanced and keep them under 6000 and there will be no issue.

dman0712

I like a challenge and attempting things many people dare not to. I also want to do this motor because it was in a 79 trans am and I want to keep the original engine. il keep you posted and let you guys no how it turns out. Im ordering the 455 c heads this weekend.