Porting heads

[predator5100]

Hey i have a question i've done a search and have seen to many different answers to even say. What will i see exactly from port and polishing heads, 3 angle valve job and cams from a 3.4 firebird

How much additional horse power will i gain

[strange_trp]

<blockquote>quote:</font><hr>Originally posted by predator5100:
Hey i have a question i've done a search and have seen to many different answers to even say. What will i see exactly from port and polishing heads, 3 angle valve job and cams from a 3.4 firebird

How much additional horse power will i gain<hr></blockquote>

the HP you gain depends on the other mods you have that will supplement or benefit from the gains provided by the head job. you really feel the power when you want it, definately a noticable gain. you may want to have a VERY SMALL amount milled to SLIGHTLY increase comp. ratio. you'll have to run higher octane fuel, though.

if you're not experienced in valve grinding and such, i'd suggest leaving the whole job to the machine shop. it's real easy to port yourself right into a water jacket if you don't have experience.

[3.4-Wraith]

Hey Strang_trp, exactly how much would be a very small amount, and how much of a bump in comp. would that equal?

Josh-

[strange_trp]

<blockquote>quote:</font><hr>Originally posted by 3.4-Wraith:
Hey Strang_trp, exactly how much would be a very small amount, and how much of a bump in comp. would that equal?

Josh-<hr></blockquote>

hummm. well, i don't have valve to piston clearance specs in front of me, so i can't say for sure. the info may be available on this site in engine specs or something. i'm sure robert would have these specs around somewhere. you don't want to mill much. the stock combustion chamber (for the 3800, i see you have 3400) is 64cc, giving you about a 9.4:1 compression ratio. the main concern with milling to increase compression ratio is that you want to give yourself a safety margin so that if you happen to float a valve at high rpm's you don't smack that valve with a piston (causing serious damage). i would keep the ratio below 9.75:1. i think (someone correct me if i'm wrong) that you can get by with 93 octane fuel running 9.75:1.
don't forget about the thickness of the head gasket material also. you can slightly increase compression without milling at all, by reducing the thickness of head gasket. just make sure new head gasket will handle increased pressures.

i would recommend milling no more than .012 (inch)so you can still fill up the tank at any gas station, and i speculate that you'd still have a little room if a valve were to float. milling .010-.015 from head or cyl block deck will give you around a 9.65:1 or so CR. (check out the links in the tech specs section under engine specs).

as i mentioned before, the benefits you'll see depend on what you have done already. i also want to add that i did not design the engine so i do not know how strong the connecting rods, bearings, and crank are (not to mention the wear you have on your cyl walls and rings; incresing compression will increase blowby, especially if you have a lot of miles on your stock piston rings and are not planning to rebuild/recondition block assembly). but guys are putting 50-shots of N20 on 3800's with 60k miles and its working out fine for them.

so to answer your question, check out the tech database, engine specs section on this site. you'll just want to be sure you 1: have sufficient valve to piston clearance after milling, and 2: are moderate enough to use pump gas and not destroy engine.

***this is all figured for a 3800. the 3400 has lower stock CR, so look at the available info and figure accordingly***

[ February 05, 2002: Message edited by: strange_trp ]</p>

[Tiago]

if you mill the heads, remember you have to mill the intake manifold to match, or else it wont fit right.

[3.4-Wraith]

Thanks for the info. I only ask because I am in the process of buying used heads and plan on having them ported. I believe stock cr on the 3400 is 8:1 and I don't want it much higher. Although my car has only 49k miles. (The new heads have 90k) Maybe I will just get slightly shorter gaskets, I run 93 anyway because of the jet chip. Thanks,

Josh-

[2WISH4]

<blockquote>quote:</font><hr>Originally posted by 3.4-Wraith:
I believe stock cr on the 3400 is 8:1 and I don't want it much higher.
<hr></blockquote>

9:1 not 8:1

at 8:1 without forced induction you would experience serious lllllllaaaaaaaaaggggggggggg in throttle response. ;)