Head Rebuild. OEM Valves or oversize?

[mharrison]

OK, Timing Belt broke on my 97 Eclipse GS. I'm pulling the head tommorow to take it to a local cylinder head shop that I've dealt with for years.

This is an NT car with 105K. Factory other than some cosmetics.

While I'm having the head reworked, is there any point in putting oversize valves in? I'm not even sure if the head has room for bigger valves. I'm counting on some of you experienced DSM guys to chime in on this one.

BTW, doing all new belts, new tensioner bearing, water pump while I'm there. Anything else I need to do on this while I'm in there? And what is the black box behind the intake that's such a PITA to take off to get the intake stays off?

Thanks,
Matt

 

[BigRand]

well if your going for performance, you might as well go with a whole valvetrain kit. 1mm oversized valves, pt crusiers rocker arms, and upgraded springs and retainters.

If your just doing it to get your car up and running again, no point in switching to oversized valves.

IMO, if your going to do oversized valves, then your going to want to do the whole valvetrain as well.

 

[VelocitàPaola]

Black box = cruise control

The head can take at least 1mm oversized valves (possibly larger, I'm not sure). I wouldn't get them, though, unless you have extensive other headwork done too.

Don't forget a new idler bearing.

 

[conceptillusion]

No sense in going with oversized valves unless you are pushing a turbo, even then oversized valves dont do any good unless your doing extensive port work.. id go with a set of oem valves and be done with it.. as far as how far the valves seats can be cut,, we have had a custom set of 2mm made and fitted into our 420a head

 

[dr1665]

Larger valves result in reduced air velocity into and out of the combustion chamber. This can reduce performance in the low end. Given extensive port work, a lot of boost, or both, larger valves allow more air and fuel to be ingested/expelled per combustion event, translating into greater power output.

Basically, this is one of those things which, along with heavy duty headwork, will move your power band higher up on the tach. I have the headwork and +1mm SI valves with a 5 angle and I have to cross 4000rpm before my engine is anything more than a metal turd in the engine bay with a really cool idle.

Food for thought...

 

[mharrison]

Black box = cruise control

I thought that might have been the cruise control. Man, what PITA place to put it.

Don't forget a new idler bearing.

I'm putting in the Parts Dinosaur's kit with new idler bearing and mechanical tensioner.
I'm also using new head bolts. I may re-ring it and put new bearings in while I'm there. I'm still undecided.

It sound like from the comments that there's not much point in oversize valves. I'm not ready to drop the $ for extensive headwork on the 420A. Is there anything else I need to do while I'm in here?

-Matt

 

[dr1665]

It sound like from the comments that there's not much point in oversize valves. I'm not ready to drop the $ for extensive headwork on the 420A. Is there anything else I need to do while I'm in here?

I'd get some very mild port work done, Matt. Maybe just have the shop clean things up in the ports a little bit to help what you've got without getting a full-on port job done. Then, I'd support that with a nice valve job - 3 or 5 angle depending on budget - and finally, a set of cams - Crane 12s or Crower 2s - and the bits to make them work reliably - PTCruise lifters and followers and upgraded springs. You'll get the slightly lumpy idle, which is cool, but you'll also get a nice bump in the mid- to upper-range of things without needing a lot of tuning. (I run a completely stock fuel system with nearly 190,000 miles on it daily.)

If you had to shave some money off a list like this (it's gonna run around $1,000, imo), replace the stage 2 cams with a stage 1 and skip the springs. That would shave about $200 off the price. You could also save a bit more money by leaving out the followers and just upgrade the lifters. It's all up to you in the end.