Small block heads vs big block on 403
May 26th, 2015, 04:06 PM
#1
Small block heads vs big block on 403
I have a set of large valve big block heads I was going to use but I have a street dominator which I've read doesn't have enough height on the runners for a proper seal. I can get it welded to add some meat but I'm wondering if I'd be better off having my bb valves put in a set of sb heads. I'm only looking for 9:1-9.25 comp ratio. Also wondering if the larger ports on the big block heads will make it lazy down low or not, I know they came on the bbo 400. Also if I go with the big block heads will I have to port match my intake or will it run ok without.
May 26th, 2015, 04:45 PM
#2
Registered User
Join Date: Apr 2010
Posts: 978
This is just MHO, but I feel unless you are going for all out racing, the SB heads would be better for you. I recently finished porting a set of #5 heads going on a 403. You have to drill out the head bolt holes, and guide pin holes with either set you want to use. With the BB heads there's only 2 intake manifolds on the market right now that have enough material on the roof to match the BB head port: the edelbrock RPM Performer, or the Victor. If you do decide to go with the BB heads, you should pick up one of those two intakes. Don't mess around with welding up the Holley. The effort is just not worth it. I do like the Street Dominator intake, but only with SB heads. I wouldn't bother pulling the large valves out of the BB heads. Just buy new stainless steel valves that are .100" taller than stock. If you try to use the big stock valves the stem height ends up too short. Been there - done that.
The key to performance with your build will be getting the compression ratio up to where you already said you want to be. 9:1 - 9.5:1 would be ideal for a pump gas street thumper with cast iron heads.
If you do end up going with the BB heads you should match port the intake to raise the roof or you won't gain any benefits. The other thing to remmber is you will have to mill the BB heads so far to get your compression back up that you might weaken the deck's sealing surface, and be prone to overheating/ warpage. You would also have to mill the intake to match the heads. That's just another expense.
If you really want to learn about cast iron Olds heads, you should check out the "Home Porting Techniques" thread-
https://classicoldsmobile.com/forums...echniques.html
I know it's real long, but it's full of good information. In fact all of these questions that you just asked are answered in that thread.
I hope this helps, Dave - The Freak
The key to performance with your build will be getting the compression ratio up to where you already said you want to be. 9:1 - 9.5:1 would be ideal for a pump gas street thumper with cast iron heads.
If you do end up going with the BB heads you should match port the intake to raise the roof or you won't gain any benefits. The other thing to remmber is you will have to mill the BB heads so far to get your compression back up that you might weaken the deck's sealing surface, and be prone to overheating/ warpage. You would also have to mill the intake to match the heads. That's just another expense.
If you really want to learn about cast iron Olds heads, you should check out the "Home Porting Techniques" thread-
https://classicoldsmobile.com/forums...echniques.html
I know it's real long, but it's full of good information. In fact all of these questions that you just asked are answered in that thread.
I hope this helps, Dave - The Freak
Last edited by 67 Cutlass Freak; May 26th, 2015 at 04:47 PM.
May 26th, 2015, 06:13 PM
#3
The street dominator is already at the limit for Height in my car. I also am trying to keep cost as low as possible, the engine I just put together for it sounds like it has a knock. I'm trying to get it back together as cheap as possible while still running well
May 27th, 2015, 05:15 AM
#5
Out of Line, Everytime😉
Join Date: Dec 2006
Location: Melville, Saskatchewan
Posts: 8,911
You will only need slight milling to hit 9 to 1 with early 350 heads. Pretty sure the Felpro's are .041" thick. I would bet your piston to deck clearance is around .020". I use KB pistons calculator to figure out compression for builds.
Last edited by olds 307 and 403; May 27th, 2015 at 05:18 AM.
June 1st, 2015, 12:01 AM
#11
Registered User
Join Date: Apr 2010
Posts: 978
I whole heartedly dissagree with this ^^^
First of all when you get the E-brocks, the first thing you will need to do is send them to your machine shop to have the valve to guide clearance loosened up. They are all set up too tight out of the box. You should also have them do a valve job, because out of the box valve job SUCKS! Then make sure they mill them down pretty far to get your compression back up. Now get out your dye grinder or pay a machine shop to raise the roof on your intake to match the BB intake port on the E-brocks. Before you do that you will need to mock up the intae on the heads because you will most likely need to mill that too. Then you better call up Jegs or summit and order a full fuel system with an electric pump since your mechanical one will not clear the Edelbrock heads. Yeah to bolt the Edelbrocks on a SB will probably set you back $4000 when it's all said and done. For what, you will have lost all your port velocity. They would probably slow you down.
Go back and take another loo at the "Home Porting Thread". I showed you how to do a simple port job on some #5 heads, for J-Chicago, that flowed 247 CFM on the intake @ .6" lift, & 200 CFM @ .6" lift on the exhaust. Edelbrocks out of the box supposedly flow 255CFM @ .6" lift intake & 179 CFM @ .6" lift on the exhaust. This is a BB head vs a SB head mind you. Those SB heads could support a 500 HP engine.
Now save yourself a **** ton of cash and get out the die grinder.
You don't have to spend a ton of money to go fast, Dave - The freak
First of all when you get the E-brocks, the first thing you will need to do is send them to your machine shop to have the valve to guide clearance loosened up. They are all set up too tight out of the box. You should also have them do a valve job, because out of the box valve job SUCKS! Then make sure they mill them down pretty far to get your compression back up. Now get out your dye grinder or pay a machine shop to raise the roof on your intake to match the BB intake port on the E-brocks. Before you do that you will need to mock up the intae on the heads because you will most likely need to mill that too. Then you better call up Jegs or summit and order a full fuel system with an electric pump since your mechanical one will not clear the Edelbrock heads. Yeah to bolt the Edelbrocks on a SB will probably set you back $4000 when it's all said and done. For what, you will have lost all your port velocity. They would probably slow you down.
Go back and take another loo at the "Home Porting Thread". I showed you how to do a simple port job on some #5 heads, for J-Chicago, that flowed 247 CFM on the intake @ .6" lift, & 200 CFM @ .6" lift on the exhaust. Edelbrocks out of the box supposedly flow 255CFM @ .6" lift intake & 179 CFM @ .6" lift on the exhaust. This is a BB head vs a SB head mind you. Those SB heads could support a 500 HP engine.
Now save yourself a **** ton of cash and get out the die grinder.
You don't have to spend a ton of money to go fast, Dave - The freak
June 1st, 2015, 06:33 AM
#12
Registered User
Join Date: Jan 2014
Location: Barre,VT
Posts: 621
I whole heartedly dissagree with this ^^^
First of all when you get the E-brocks, the first thing you will need to do is send them to your machine shop to have the valve to guide clearance loosened up. They are all set up too tight out of the box. You should also have them do a valve job, because out of the box valve job SUCKS! Then make sure they mill them down pretty far to get your compression back up. Now get out your dye grinder or pay a machine shop to raise the roof on your intake to match the BB intake port on the E-brocks. Before you do that you will need to mock up the intae on the heads because you will most likely need to mill that too. Then you better call up Jegs or summit and order a full fuel system with an electric pump since your mechanical one will not clear the Edelbrock heads. Yeah to bolt the Edelbrocks on a SB will probably set you back $4000 when it's all said and done. For what, you will have lost all your port velocity. They would probably slow you down.
Go back and take another loo at the "Home Porting Thread". I showed you how to do a simple port job on some #5 heads, for J-Chicago, that flowed 247 CFM on the intake @ .6" lift, & 200 CFM @ .6" lift on the exhaust. Edelbrocks out of the box supposedly flow 255CFM @ .6" lift intake & 179 CFM @ .6" lift on the exhaust. This is a BB head vs a SB head mind you. Those SB heads could support a 500 HP engine.
Now save yourself a **** ton of cash and get out the die grinder.
You don't have to spend a ton of money to go fast, Dave - The freak
First of all when you get the E-brocks, the first thing you will need to do is send them to your machine shop to have the valve to guide clearance loosened up. They are all set up too tight out of the box. You should also have them do a valve job, because out of the box valve job SUCKS! Then make sure they mill them down pretty far to get your compression back up. Now get out your dye grinder or pay a machine shop to raise the roof on your intake to match the BB intake port on the E-brocks. Before you do that you will need to mock up the intae on the heads because you will most likely need to mill that too. Then you better call up Jegs or summit and order a full fuel system with an electric pump since your mechanical one will not clear the Edelbrock heads. Yeah to bolt the Edelbrocks on a SB will probably set you back $4000 when it's all said and done. For what, you will have lost all your port velocity. They would probably slow you down.
Go back and take another loo at the "Home Porting Thread". I showed you how to do a simple port job on some #5 heads, for J-Chicago, that flowed 247 CFM on the intake @ .6" lift, & 200 CFM @ .6" lift on the exhaust. Edelbrocks out of the box supposedly flow 255CFM @ .6" lift intake & 179 CFM @ .6" lift on the exhaust. This is a BB head vs a SB head mind you. Those SB heads could support a 500 HP engine.
Now save yourself a **** ton of cash and get out the die grinder.
You don't have to spend a ton of money to go fast, Dave - The freak
Aside from the cost (which I do understand that they are expensive)
I would think these heads would help you out by bumping up your compression without having to be as concerned about detonation and the weight savings is nice as well!
June 1st, 2015, 07:40 AM
#13
Registered User
Join Date: Apr 2010
Posts: 978
Funny I've never heard of their heads valve job "sucking" from the factory. I've always been under the impression that Edelbrocks Olds heads are one of the best precision heads available! That said I've never knew that the heads hung over too far so you can't bolt a mechanical pump on.
Aside from the cost (which I do understand that they are expensive)
I would think these heads would help you out by bumping up your compression without having to be as concerned about detonation and the weight savings is nice as well!
Aside from the cost (which I do understand that they are expensive)
I would think these heads would help you out by bumping up your compression without having to be as concerned about detonation and the weight savings is nice as well!
You are wrong about bumping up the compression. The combustion chamber on the E-brocks is close to 80CC. Your compression will go down.
OK Madmax, I am done busting your *****, but please, next time you try giving advice like this, I suggest you attempt to do it yourself first.
Have a great day guys, Dave - The Freak
June 1st, 2015, 10:48 AM
#14
Registered User
Join Date: Jan 2014
Location: Barre,VT
Posts: 621
Well first off Cutlass Freak I am by no means an engine builder but from the sounds he isn't doing a monster build so 9cfm intake and 16cfm exhaust probably won't happen since he isn't going to have a .600 lift cam. Second, I'm sure it would be cheaper to shave the head, deck the block or add thinner gaskets. Am I wrong? What I meant by the bumping up compression comment was that the Edelbrocks would be more forgiving to increased compression due to them being aluminum instead of cast iron. I get that the bigger chambers would lower it. Sorry I wasn't clear on that. No problem on busting my *****. I'm not afraid to take a beating! Lol
June 1st, 2015, 11:45 AM
#15
ok, this is where im at right now. i didnt get the 403, got a 350. heres what i want to do, mill my 7a heads to bump my compression to 9:1 and i have a set of large valves from some c heads id like to put in as well as a little pocket port action. is that doable? i already know ill have to mill .060 of the heads to get the comp with .045 felpro's but will the large valves from c heads fit or will to much of the seat have to be removed?
June 1st, 2015, 12:46 PM
#16
Registered User
Join Date: Apr 2010
Posts: 978
ok, this is where im at right now. i didnt get the 403, got a 350. heres what i want to do, mill my 7a heads to bump my compression to 9:1 and i have a set of large valves from some c heads id like to put in as well as a little pocket port action. is that doable? i already know ill have to mill .060 of the heads to get the comp with .045 felpro's but will the large valves from c heads fit or will to much of the seat have to be removed?
June 1st, 2015, 02:39 PM
#17
I already have full roller rockers and everything that goes with it. I'll prolly just get them cleaned up and leave them as they are, I don't want larger valves bad enough to buy new valves. I'd rather just enjoy the car finally
June 1st, 2015, 04:03 PM
#18
Just cause I'm curious, how could using factory valve cause an installed height problem when if you get a valve job and keep your same valves it ok? Are the big block valves not the same length as small block?
June 1st, 2015, 04:12 PM
#19
Registered User
Join Date: Apr 2010
Posts: 978
It's hard to explain why. I've tried to do it on SB heads. I believe the valves are the same length, but when you open up the seat to accomidate the larger valve face, it ends up lowering the valve. The only way you could get the correct installed height would be to sink the valve. That is not desirable.
Last edited by 67 Cutlass Freak; June 6th, 2015 at 10:59 PM.
June 2nd, 2015, 04:49 AM
#21
Registered User
Join Date: Nov 2008
Location: Central Fl
Posts: 7,824
I whole heartedly dissagree with this ^^^
First of all when you get the E-brocks, the first thing you will need to do is send them to your machine shop to have the valve to guide clearance loosened up. They are all set up too tight out of the box. You should also have them do a valve job, because out of the box valve job SUCKS! You may want to tell Bill Travato that. He's routinely posted builds with out of the box Edelbrocks with nothing more than a spring change. Then make sure they mill them down pretty far to get your compression back up. Now get out your dye grinder or pay a machine shop to raise the roof on your intake to match the BB intake port on the E-brocks. My guy here charges $200.00 to do that, reasonable I think. Before you do that you will need to mock up the intae on the heads because you will most likely need to mill that too. Then you better call up Jegs or summit and order a full fuel system with an electric pump since your mechanical one will not clear the Edelbrock heads. You can buy a good electric pump for $100.00. New fuel line from the tank to the front isn't that much more either. Yeah to bolt the Edelbrocks on a SB will probably set you back $4000 when it's all said and done. No way, more like $2500.00, while being lighter and with a much better combustion chamber. For what, you will have lost all your port velocity. They would probably slow you down. Not necessarily, compare the low lift flow vs a set of ported irons.
Go back and take another loo at the "Home Porting Thread". I showed you how to do a simple port job on some #5 heads, for J-Chicago, that flowed 247 CFM on the intake @ .6" lift, & 200 CFM @ .6" lift on the exhaust. Edelbrocks out of the box supposedly flow 255CFM @ .6" lift intake & 179 CFM @ .6" lift on the exhaust. This is a BB head vs a SB head mind you. Those SB heads could support a 500 HP engine.
Now save yourself a **** ton of cash and get out the die grinder.
You don't have to spend a ton of money to go fast, Dave - The freak
First of all when you get the E-brocks, the first thing you will need to do is send them to your machine shop to have the valve to guide clearance loosened up. They are all set up too tight out of the box. You should also have them do a valve job, because out of the box valve job SUCKS! You may want to tell Bill Travato that. He's routinely posted builds with out of the box Edelbrocks with nothing more than a spring change. Then make sure they mill them down pretty far to get your compression back up. Now get out your dye grinder or pay a machine shop to raise the roof on your intake to match the BB intake port on the E-brocks. My guy here charges $200.00 to do that, reasonable I think. Before you do that you will need to mock up the intae on the heads because you will most likely need to mill that too. Then you better call up Jegs or summit and order a full fuel system with an electric pump since your mechanical one will not clear the Edelbrock heads. You can buy a good electric pump for $100.00. New fuel line from the tank to the front isn't that much more either. Yeah to bolt the Edelbrocks on a SB will probably set you back $4000 when it's all said and done. No way, more like $2500.00, while being lighter and with a much better combustion chamber. For what, you will have lost all your port velocity. They would probably slow you down. Not necessarily, compare the low lift flow vs a set of ported irons.
Go back and take another loo at the "Home Porting Thread". I showed you how to do a simple port job on some #5 heads, for J-Chicago, that flowed 247 CFM on the intake @ .6" lift, & 200 CFM @ .6" lift on the exhaust. Edelbrocks out of the box supposedly flow 255CFM @ .6" lift intake & 179 CFM @ .6" lift on the exhaust. This is a BB head vs a SB head mind you. Those SB heads could support a 500 HP engine.
Now save yourself a **** ton of cash and get out the die grinder.
You don't have to spend a ton of money to go fast, Dave - The freak
Last edited by cutlassefi; June 2nd, 2015 at 10:25 AM.
Thread
Thread Starter
Forum
Replies
Last Post
