403 heads to 455 heads

[DarkStar]

Hi guys, Im new this to forum this is my first post. Well i have spent some good amount of time doing some research and I remember back about a year or 2 I read about being able to swap the heads of my olds 403 to some olds 455 ones to get some more power. I just want to make sure that this is acurate and what to look for when looking for a set of 455 heads. They will be going into a 1978 Pontiac TA.

[Oldsproject]

According to Mondello Tech referance catalog, you can swap 403 heads with 455's but need to drill the head bolt holes to at least 17/32nd's. The problem won't be the head but the intake. The 455 heads have a taller intake profile so your 403 intake won't match up. You'll need to go to something like a an Edlebrock 7111 which can be ported to fit. There's an outside chance an intake of a 1977 will fit but again will need to have the intake roof raised. Don't think your really gaining anything by doing it unless you change pistons and raise the compression.

[70 cutlass s]

I would stay with the 455 heads. Go 9.5-1 or higher compression pistons. Nice cam, roller tip rockers, good flowing exhaust.

[DarkStar]

Yeah I already have the 7111 intake from edelbrock and was planning on sending them over to a machine shop to get the head bolt holes opened up and port matched to the intake.

[svnt442]

What 455 heads do you have? (large letter on them)

[DarkStar]

Originally Posted by svnt442

What 455 heads do you have? (large letter on them)

I dont have them yet. What should i look for?

[Oldsproject]

Originally Posted by DarkStar

I dont have them yet. What should i look for?

Depends what your trying to accomplish but can't go wrong with A-B-C Heads. 2.070 Intake and 1.625 Ex. 80cc. Arguably the best olds made. A, B & C's were on 65-69 400's, 425's and 455's. Also D's with 2 ribs (68/69 W-30), GA with 3 ribs (72 W 30's) and G's with 3 ribs (72 L-75). Others are good too.

[Eightupman]

Actually you are going about it a little backwards. What you need is a good set of #5, #6, or #7 SBO heads with large valves.

Compression increase is what you are after if all you are going to do is bolt them on and leave the bottem end alone. The 403 heads and the BBO heads offer the same cumbustion chamber size. The small block heads offer nearly 20 less CC's (each). So unless you are planning a total rebuild and going to sling some Keith Black domed pistions, you are sort of wasting your time. (IMHO of course)

John

[Eightupman]

Originally Posted by Oldsproject

According to Mondello Tech referance catalog, you can swap 403 heads with 455's but need to drill the head bolt holes to at least 17/32nd's. The problem won't be the head but the intake. The 455 heads have a taller intake profile so your 403 intake won't match up. You'll need to go to something like a an Edlebrock 7111 which can be ported to fit. There's an outside chance an intake of a 1977 will fit but again will need to have the intake roof raised. Don't think your really gaining anything by doing it unless you change pistons and raise the compression.

Yes you have to drill the heads for the head bolts. The 403 manifold has PLENTY of meat to raise the roof. Its the ONLY SBO intake with enough meat to do it. You nailed it when you mentioned the compression. Its a waste to go with the BBO heads UNLESS you are digging into the motor. Early 350 SBO heads 5/6/7 heads. 330 #4's are the BEST but require one more step during the machine process. they need the push rod holes elongated due to the different cam bank angle

Of course if WEIGHT is an issue, then use the Ebrock manifold. if cash is an issue, port match the cast one.

John

[DarkStar]

Originally Posted by Eightupman

Actually you are going about it a little backwards. What you need is a good set of #5, #6, or #7 SBO heads with large valves.

Compression increase is what you are after if all you are going to do is bolt them on and leave the bottem end alone. The 403 heads and the BBO heads offer the same cumbustion chamber size. The small block heads offer nearly 20 less CC's (each). So unless you are planning a total rebuild and going to sling some Keith Black domed pistions, you are sort of wasting your time. (IMHO of course)

John

Yeah thats what im going for, compression increase. So im going to try and find a good set of SBO heads with smaller CC's. Im really just trying to find something better than the stock 403 heads that i can just bolt up. The compression ratio on these engines is really low.

[Eightupman]

Originally Posted by DarkStar

Yeah thats what im going for, compression increase. So im going to try and find a good set of SBO heads with smaller CC's. Im really just trying to find something better than the stock 403 heads that i can just bolt up. The compression ratio on these engines is really low.

You don't have to look very far. There are options. I have a set of #7 heads and a set of #6 heads for sale. They are core heads, meaning they are a clean slate for you to do whatever you want to them. I JUST sold a complete ready to bolt on set of #7's last week. The #6 heads are about to go up on Ebay. They are complete with valves, springs rockers and bridges but need to be gone through. I have #7s as well, but will have to look at them to see what they need. I may just spring for them to get done for occasions just like this.

Or you can spring for a super sweet set of heads from http://www.jsmachineoldsmobile.com/home.html I just did!

Shop around man. heads are pretty inexpensive to buy cores; they range from $100-150 (or less) but shipping is the killer. Upwards of $30 per head to ship. So if you can find them local its the way to go.

John

[sethj78]

How much did you give for the heads from j&s?

[Eightupman]

Originally Posted by sethj78

How much did you give for the heads from j&s?

I don't want to come off as prudish here, but even if I said exactly what I spent, your figure may differ based on any "extras" you and Jim would agree upon. I had the exhaust dividers welded up, and different valves put in, etc. I can say his Stage 1 heads start in the $800 range.

If you are really interested in them, call him. First thing in the AM is better. He will be more than happy to answer any questions and give you an idea of how much lighter your wallet will be. That goes for the original poster as well.

John

[Warhead]

Please make sure to open up the smaller alignment dowel to 5/16ths inch, or the heads will not bolt down on the block. If you mentioned what you are doing to Jim, I am sure he has probably already taken care of it for you.

BTW, he has a special this month...castings for free with Stage II and up head service.
He has #7 heads.

Jim in Phx.

[oldsracer]

Originally Posted by Warhead

Please make sure to open up the smaller alignment dowel to 5/16ths inch, or the heads will not bolt down on the block. If you mentioned what you are doing to Jim, I am sure he has probably already taken care of it for you.

BTW, he has a special this month...castings for free with Stage II and up head service.
He has #7 heads.

Jim in Phx.

yeah i found out about those dowel pins the hard way but at least I dont have to worry about lining them up any more!
I just put a set of stock #8 heads on a 403 with mondello springs to finish up this season . over the winter I have a set of #6 heads that I am porting to go on it.

[Eightupman]

Originally Posted by Warhead

Please make sure to open up the smaller alignment dowel to 5/16ths inch, or the heads will not bolt down on the block. If you mentioned what you are doing to Jim, I am sure he has probably already taken care of it for you.

The #7 heads are going on a 1972 block so for me this is a non-issue. But good point for the 403 guys.

John

[DarkStar]

Originally Posted by Eightupman

You don't have to look very far. There are options. I have a set of #7 heads and a set of #6 heads for sale. They are core heads, meaning they are a clean slate for you to do whatever you want to them. I JUST sold a complete ready to bolt on set of #7's last week. The #6 heads are about to go up on Ebay. They are complete with valves, springs rockers and bridges but need to be gone through. I have #7s as well, but will have to look at them to see what they need. I may just spring for them to get done for occasions just like this.

Or you can spring for a super sweet set of heads from http://www.jsmachineoldsmobile.com/home.html I just did!

Shop around man. heads are pretty inexpensive to buy cores; they range from $100-150 (or less) but shipping is the killer. Upwards of $30 per head to ship. So if you can find them local its the way to go.

John

Thanks for the info.
After doing to more research, im going to go with some 7a heads from a 72 350.

[Eightupman]

To open your respective possiblities, the differences in the 6, 7 or 7a head are negligible as far as flow numbers. There are differences in springs, and valve rotators. I think you are making a much better choice with the SBO heads.

I guess the biggest notable difference in the 7a head is the hardened valve seat. Well being that Olds used a very high nickel hardened casting its very difficult to destroy the seats on the earlier heads. Plus you are not going to run it every day all the time so the wear factor will deminish.

And there are naysayers on that topic as well.

And whatever you do, do NOT let a Chevy builder install seats in your Olds heads. He will "think" Chevy seats are the same, cut your heads and find water jackets making the heads boat anchors.

John

[Warhead]

Originally Posted by DarkStar

Thanks for the info.
After doing to more research, im going to go with some 7a heads from a 72 350.

Make sure to put at least a 2" intake valve in them.
You may even want to get a set of 2.072 intakes to feed the 403.
Good luck with your project.
Jim