Head Resufacing for more compression??

[grandprixgtp_91]

OK heres what i got, i have a brand new 91-93 3.4L DOHC gm crate motor. i have it at work ripped down to the block on a stand i am going to port the heads out and i was wondering what is the max you can resurface the heads on these motors? i heard somewhere that it was .010" , what happens at that point? do the valves hit the pistons? also if i do like .005" how much would that up my compression? enough to notice anything? anybody that knows or has done this please let me know i would like to take them to the machine shop this week to have them done. also another thing that i wanted to have done was have the cams reground to a performance spec, but due to the fact that nobody will help me come up with a spec then i am going to scrap that idea, what i want to do though is have the bottoms of the cam carriers machined down which will increase the lift in the valves, has anyone done this? if so did it work? what im wondering about is will i cause interference with the valves and pistions if i increase the lift? and if i machine the bottoms of the cam carriers down will it force the valves open a little without the cam pushing down on them, because i know that the lifters are compressed on the valves as it is , how much more can they go? please any info anyone has please post. and one more thing, right now i currently have the 6/6 cam timing mod, which i like but the problem is i lose power at like 6000rpm , has anyone done a 6/13 mod before? or even a 6/8 or a 6/10? if so how did that work out for you? anyways anything else that you guys can suggest would be great, i want this motor to rip. thanks

Jake

[SappySE107]

Milling the carrier won't increase your lift. It will increase your lifter preload and probably fuck everything up. If you ground the cams you might possibly get away with that but you really should use lashcaps to make up the difference.

You can take .011 off before its interference but I wouldn't take more off than you need to for it to be flat. You won't gain enough in compression to notice unless you go to maybe .020.

[grandprixgtp_91]

have you experimented with different cam timing like the combos i listed? i like the low end of the 6/6 but i would like some more high end, have you experimented with like 6/10 or anything like that?

Jake

[SappySE107]

No, I haven't had much luck with widening the seperation angle further like that. 12 or 13 degrees seems to be the sweet spot from my experiments. Do the 13 degree exhaust retard with stock intake if you want more top end.

[dohcfiend]

if you want compression you can install a later set of heads with the smaller chambers.

it will not give yuo much though. about .2 -.3. i hear using bigger pistons give you more compression but as to how much i am not sure. also i wouldn't bore out your block unless it was necessary.

as for your cam query. if there is a place that will regrind them, then let them regrind the cams. tell them what you want out of the cams(ie drivability, hp/tq and powerband).

as far as research and info:
id give them a flowbench sheet of your heads ported and stock, your stock engine specs( 210 hp@5500 215 tq@4000 and 7000 redline), tell them about the interference, tell them your stock cam profile and let them work.

i am sure they know a thing or two about cam profiles. it beats the hell out of going through all the time that you would spend coming up with a profile which may as good as the one they would recommend or even inferior to it. researching and knowing your shit goes a long way but there is no substitute for experience.

[Fierobsessed]

The downsides to milling the heads for clearance... The belt looses some tension. you loose .004" of belt tension PER .001" of milling of each head. It still isn't a heck of a lot but it's something to think about. Also, consider how milling the heads will effect the alignment of the bolts in lower intake manifold. I say, only mill the heads enough to get them flat, if needed. The valve clearance isn't as bad as people make it out to be really. But decreasing the clearance is always a bad idea if it can be avoided.

A good set of pistons is the best answer. However you get 0.25:1 increase per .010" shaved. That makes a difference.

[grandprixgtp_91]

yeah i wanted to shave them .010" but thats the limit you can go, i was watching the gm CPT video on this motor and it gave all the specs on that. i dont know if i want to go that much, these are brand new heads, but its an automatic motor and i want to get the compression up for the power of the 5 speed motor, well i guess im gonna have to think about my options here, i was at the machine shop and they said that they can open up the bowl in the heads, and where the air enters the cylinder at the bottom of the port will be opened up and they would do a 5 angle job and they said that it should flow better and give it some hp that way, so i am definatly gonna do that for sure.

Jake

[grandprixgtp_91]

oh and do they sell high compression pistons for this motor? i never heard of them if they do, if they do where would i get them at?

thanks
Jake

[dohcfiend]

the 96-97 pistons have a dome that will increase your compression. the 96-97 engines have 9:7 to 1 but that is counting the different heads.

[grandprixgtp_91]

ok, so ive ported the heads and i brought the heads to the machine shop and they were gonna grind and blend the bowls out but they said that they were opened up already as much as they can go, they told me not to waste my money , my question to you guys is this, they said they will do a 5 angle valve job, is this worth the money? will there be any performance increase, if so how much? and im going to have the heads milled down .010" has anybody done this? is it safe? did you notice any power? is there anything i can bring them to machine to gain any power? what have you guys done to get some added power, i want to get this all done while i have the engine stripped down.thanks for any info.

Jake

[SappySE107]

5 angle will smooth the seat/port/combustion chamber transition so id have that done. Milling won't make any noticable difference, especially since you ported the heads as well. .010 is fine if they haven't been cut before.

[grandprixgtp_91]

do you think that there will be any noticable power gain having the 5 angle job done?

Jake

[series8217]

Uhhhh we took .014 off my heads and I've spun the cams all the way around with the motor at TDC. I didn't bend anything!

[grandprixgtp_91]

good to hear, i just wanted one person thats done it, thanks

Jake

[SappySE107]

good to know I was told .012 was when it became interference. Of course, your lifters might not be pumped up? I know there is a difference for pushrod motors between sitting on the stand and running in the vehicle.