Couple of small block chevy questions

[79loserbluebu]

Hey all, thinking about picking up a set of GMPP cast iron Vortec heads to go along with the 280H camshaft I'd like to run. We had a 355 in the car with flat top pistons with 4 valve releifs and a 280 cam, and it ran pretty good for the time it ran. However, it spun a rod bearing and that was about it. The new goal is to build it to the same specs except throw in a taller crank and put it at 383 ci. As of now we have a Goodwrench 350 crate in which came in the car when we bought it. Here's the questions I have...

Right now on the car is a set of Hooker competition long tubes, and the headers fit okay, but we had to beat them quite a bit with a hammer and torch to get them to clear the upper control arm and frame section before the firewall. Is there any set of long tube headers that have some pretty good clearance in the G-bodies? And with a set of Vortec heads, do they use the same exhaust port pattern as traditional small block heads?

Second, the angle that I'm looking at the heads shows that they are also straight spark plug heads, can anyone confirm this?

Third, I'd like to keep the car very streetable with maybe a visit to the track once or twice a year. So what kind of compression ratio do you think I should shoot for? The part number on the pistions is L2256 .030. From what I've found, it's an aluminum cast piston Speed Pro used to make but doesn't anymore. The pistons will be used from the engine that spun a bearing (as well as the block) and they look to be in good condition.

And finally, I found that the Edelbrock Performer RPM Air Gap does wonders on a small block with stock heads, does anyone know how well it does with the Vortec heads? I found that Jegs sells them for around $250 and if I choose to go with Vortec heads, I'll need a new intake.

As said before, I'd like to keep the car streetable.

Thanks again to anyone who can answer any of these questions

 

[mebe007]

i would just pick up non vortec heads. you can get big valves in them and the intake is cheaper.

 

[Blake442]

Right now on the car is a set of Hooker competition long tubes, and the headers fit okay, but we had to beat them quite a bit with a hammer and torch to get them to clear the upper control arm and frame section before the firewall. Is there any set of long tube headers that have some pretty good clearance in the G-bodies?

Have you replaced your motor mounts?
A sagging motor kills the already tight tolerances.
When ever I put headers on cars at the shop, or my own stuff, new mounts go in too.

 

[86Cutlass383SR]

Hey all, thinking about picking up a set of GMPP cast iron Vortec heads to go along with the 280H camshaft I'd like to run. We had a 355 in the car with flat top pistons with 4 valve releifs and a 280 cam, and it ran pretty good for the time it ran. However, it spun a rod bearing and that was about it. The new goal is to build it to the same specs except throw in a taller crank and put it at 383 ci. As of now we have a Goodwrench 350 crate in which came in the car when we bought it. Here's the questions I have...

Right now on the car is a set of Hooker competition long tubes, and the headers fit okay, but we had to beat them quite a bit with a hammer and torch to get them to clear the upper control arm and frame section before the firewall. Is there any set of long tube headers that have some pretty good clearance in the G-bodies? And with a set of Vortec heads, do they use the same exhaust port pattern as traditional small block heads?

Second, the angle that I'm looking at the heads shows that they are also straight spark plug heads, can anyone confirm this?

Third, I'd like to keep the car very streetable with maybe a visit to the track once or twice a year. So what kind of compression ratio do you think I should shoot for? The part number on the pistions is L2256 .030. From what I've found, it's an aluminum cast piston Speed Pro used to make but doesn't anymore. The pistons will be used from the engine that spun a bearing (as well as the block) and they look to be in good condition.

And finally, I found that the Edelbrock Performer RPM Air Gap does wonders on a small block with stock heads, does anyone know how well it does with the Vortec heads? I found that Jegs sells them for around $250 and if I choose to go with Vortec heads, I'll need a new intake.

As said before, I'd like to keep the car streetable.

Thanks again to anyone who can answer any of these questions

I'll add some quick comments as I go down your list.

If you do go to a 383, you'll have to get differant pistons as well. It sounded as though you wanted to re-use the 355 pistons. A 355 piston with a 383 (400 3.75" stroke) crank will have the piston sticking out the top of the block by 1/2 of the added stroke (3.75" - 3.48" = .27" divided by 2 = .135" out the top).

Vortec heads use the same headers as any other SBC and they are straight plug heads.

With cast iron heads and no knock control I'd keep compression at no more than 9.5 - 1. With alum heads and timing control (like found on fuel injection setups) you can go up to 11-1 depending on your cam (actually your dynamic compression ratio). Bigger cams will bleed off some of the compression at idle so it can be raised. With a smaller cam, I'd stay in the 10 - 10.5 compression range.

 

[pjpj1979]

I just did a olds to chevy swap and I put Hedman headers on my non-vortec heads and they fit perfect in my car.

 

[megaladon6]

i used flow-tech afterburners on mine and have no clearance issues. but there is a clearance issue with the #3 spark plug--i had to use a shorty plug.
i'd stay under 10:1 so you can use regular fuel and have full streetability.
x2 on the pistons needing to be changed. and i'd go with d-dished for the better quench=better knock control
on the heads, don't forget to have the proper machine work done to the valve guides for the extra lift of the 280h
vortechs are good heads and dollar for dollar beat many other heads (even after the machine work and intake) and if you can afford them, the bowtie's are pretty sick!
i'd definately go with the rpm air-gap. i wish i had and will be when i can afford it.

 

[mebe007]

is there a noticable difference in power between the rpm and rpm air gap? also will a phenollic spacer make a difference, i have a brand new one sitting in floor of car. sorry for hijack

 

[megaladon6]

i don't know the difference between the intakes but a cooler air charge will definitely help things.
phenolic spacers have been to show a SLIGHT increase in HP at the top end. they have a greater effect on race motors than street motors

 

[79loserbluebu]

Wow guys thanks for all the help!

Yes, we did replace the motor mounts with brand new ones, we just used OEM rubber mounts and then later on put a poly trans mount in.

I didn't know that about the pistons but then again I never really thought of it like that, so thanks for bringing that up and reminding me. My friend has a 383 small block with Edelbrock aluminum heads and he put in a set of Dynomax I beleive it was, headers and they fit easily in his Monte Carlo (85' SS). I also did not know about having to machine the guides to allow the lift of the 280H. I didn't think .480 lift was going to be that much more than stock, but it is what it is. Basically I'm just trying to build a budget small block and not get stupid with it and save some money, get the car painted, the interior in good shape, and start building a pretty cool 6.0L.

Thanks again for all the questions, if anyone wants to add more feel free I will keep reading this thread.

 

[mebe007]

anyone know if a 1" spacer will fit under stock hood with rpm manifold