jojobanks

It's really that close? I'll admit the combustion chambers are pretty small and something like this doesn't suprise me too much, but having never done something like this before, I have to ask, how much material do you have to remove off the deck to actually make a difference in compression? Do you think I would have a better chance going with slightly smaller valves?

If this is the case then it seems I have a choice of oversizing the valves for better flow or decking the head for more compression. Anybody have a comment on this?

Thanks for all the comments already posted! When I actually get down to tackling this I'd like to know as much as I can.

Iskwezm

The TFS 170 head is the only head i have seen that you can use a 2.02 with a stock piston and cam up to .550 lift..EVERYBODY else recommends flycutting the pistons, which you can do with the block in side in the car still, if you must have 2.02's.

jojobanks

would rather not cut the pistons if I don't have to. Thing is I'm just trying to match specs by aftermarket heads to a degree. You wouldn't happen to know how big of a valve I can go with without cutting the pistons would you?

Also just got around to checking the number on the heads. They're actually 302 heads. Does this make any difference?

Iskwezm

1.90/1.60 will work, but again, that is dependent on the lift of the cam and if you deck the heads.

jojobanks

thanks for the advice. Seems I'm gonna have to wait to deck the head until after I get everything put together and see how much initial clearance I have between the oversized valve and the piston.

I should probably be talking to the machine shop about all this, but they tend to talk up whatever makes them more money, instead of what's actually better for me $$/hp wise.

frdnut

Have you done the math to see what compression you have now?..That way you can calculate how many CCs you want to end up with when the new heads are finished..Also 2.02 valves are too big for a stock 289 head..You will want to go with a 1.90 intake valve..

frdnut

There is much more to it than just matching valve sizes..Aftermarket heads also have much bigger runners to move much more air than a stock head could ever hope too...
Yes the 302 heads probably have bigger combustion chambers than a 289 head would which hurts compression..If you give me the date code and casting numbers off of the heads I can tell you what size the combustion chamber is..

OCHOHILL

Isn't it called mill the heads? The deck is the surface of the block the heads bolt to. For posterity the old holley heads had 2.02 valves. I have after market pistons in mine at about .53" lift net.

If cutting the pistons for valve clearance is a no go you should consider a proven build.

MonsterBilly

I have not read the whole post, but you will have to remove the studs tap the holes and install screw in studs, you will also have to drill out the oblong holes that the push rods go through and install guide plates as well.
I know because i had a ton of issues with them.
I have them dialed in now but i have well over $800 in parts and machine work and they are much less of a head then even the Procomps or the E Street.
I have now switched to Trickflow heads. You will also need new rockers, mine were $200.

If you want more info please let me know and i will send you a ton of details.

jojobanks

they're D4AE heads. So they have to be a 302 head rather than a 289.

Not hoping to precisely mimic an aftermarket head. I know that is impossible. But it's easy enough to mimic the port flow to an extent. I'd like to cram as big of valves as I can into there, but the reason I don't want to cut the pistons is because I don't have any others to replace them with as well as the fact that if I mess it up then I have to yank the whole motor to replace them. Too big of a PITA for the gains IMO. Considering the fact that I've never done this before, I fulley expect to screw it up the first time. That's why I'm planning to do this on a set of spare $50 I picked up. I don't mind trimming a little material off of the pistons if need be, but I would really rather avoid any real cutting.

From what I looked up on the heads the intake/exhaust ports are the same, the valve sizes are the same, but the chambers are 58.2cc instead of 49.2cc(hi-po heads). So in theory I should be able to shave off about 9ccs worth of chamber, but it all depends on what the bigger valves give me clearance for.

installing the screw in studs won't be a problem. i'm pretty good with tapping new threads. The info on the guide plates is well recieved though. I'm still debating whether or not to go with a hydraulic roller setup though.

From what i've seen as far as flow bench stats on ported 289 heads, you can get pretty good power out of the stock heads. Since i can't afford $1800 PLUS all the valvetrain components(most aftermarket heads I see only come with the valves already installed, some even completely bare. All the valvetrain you have to get yourself). Basically I'm looking at about a budget of around $25-2800 to get what I want with a set of aftermarket heads. Whereas I can go crazy with my stock heads and have to try real hard to break $1k as long as I do all my own cleaning, porting, and milling/decking.