I think I have a head gasket leak and may have to pull the heads to get 'em milled. I was thinking since the car is high mileage (117k) that I would have them redone. My compression last time I checked was 195 - 205 on all 8 cylinders so I have some confidence in the bottom end. I was thinking of porting and 1.6 roller rockers, new springs and valves. I'm not going to change my cam now and I'm not touching the bottom end now.

What do you guys recommend best bang for the buck?
What perf gains if any, should I expect?
Will this raise my redline and what will new redline be?

Any and all advice welcome. My car is still completely stock and I want to massage it a little. Thanks in advance.

 

There are some standard L98 mods, some free mods and some little mods. The latter two along with exhaust mods and results are on my site; I'm sending you mail with data on results of ported heads.

 

you can look up a post i did in archives for flow numbers on the ported heads. in my oppinion your best bang for the buck is either the 2.00/1.55 valve or the manley pro-flo in 1.94/1.50 the guides on these heads last forever so they should be okay. expect to spend a lot of time porting these heads. also the combustion chambers need work. if you blend where the quench goes into the chamber & polish the entire chamber you'll help prevent carbon build up. a .039 gasket would also be my choice, it's .012 thinner than stock but it tightens up quench and gives you a slight compression increase. since your running the stock cam just a comp cams single dampened spring would be my choice. the hotcam springs are okay but i don't like the fact they have no dampers. make sure you don't port through the intake short turn radius & hit a water jacket !! just start with a carbide bit or stone if your a little shy. take all the casting flaws off & pull metal out of the short turn on the intake and exhaust, blend the intake bowls into the runner & remove the edges, take down some of the casting hump in the intake runner & give the exhaust a good polish. once you have your basic shape you can move into cartrage rolls & finish off with cross buffs & cotton along with some mothers mag polish to get the chamber and exhaust up to snuff. the intake runner can be left with just a sanded finish. smooth but not polished. that's about what they should look like before you take them in for a valve job and shop work.



[Modified by gtsyellow, 3:03 PM 9/15/2002]


[Modified by gtsyellow, 3:04 PM 9/15/2002]


[Modified by gtsyellow, 3:05 PM 9/15/2002]

 

If the bottom end has never been freshend up, you stand a chance of oil consumption with fresh heads on top. I have seen it several times that when using new or rebuilt heads on high mileage bottom ends, the engine started to smoke a little and use oil. What happens is with tight new guides, new seals and valve that are seating tight, you create higher cylinder pressures and vaccum draw the can now overcome the seal og the old rings. It doesn't always happen, but if your luck is like mine, I'd atleast consider freshening the bottom end(new rings/bearings) with just standard replacement parts. You can do this for $100-$200. It is cheap insurance! :cheers:

 

I know you said you don't want to change the cam right now, but in my opinion that would be the best bang for you dollar. Since you are pulling the heads anyway it would be real easy to do, and probably not much more expensive than roller rockers. A good port job may cost as much as new heads, but a freshen up with new vavles and maybe pocket porting would give some good gains. Unfortunately one of the major problems with the L98 is the intake. Anything you do without working the intake will yield smaller returns. Changing to a superram or miniram would be ideal, but even porting your tpi will help.

Don't know how much you want to spend, but because you feel the heads need to come off I would:
Freshen the heads - get better valves and springs, if possible do some porting. Maybe $100-$500 depending on what you do. 30+ hp
Change the cam - there are many cams you can choose from - just make sure you match the new valve springs to the lift, and match the cam to your intake. $100 - $375 (maybe you can get one off the forum even) 20-40 hp.
Work over or replace the intake - Port and polish the tpi setup $300 - $600 maybe (I've never looked at the price for this) 30+ hp
Or replace with MR or SR for $1300. 50+hp
1.6 Roller rockers $160 - $270 10-20hp

Those are just guesses, and that's really only if they are all done together. If you only do a couple they will yield less power as gains are more or less cumulative. Good luck with what ever you decide.

 

good stuff except the 1.6 rockers, those are totally dependant on the cam used. the 113 casting chokes at .500 lift, on a stock cam 1.6's are wonderful, on a zz4 cam they are boarderline, anything with more lift than that and it's working backwards creating more lift than the head wants to flow.

 

sinistervette is getting REAL close to the what you can expect by pulling the heads on a high mile engine like yours.

The real reason you're likely to experience increased oil consumption after you rebuild the top end is this:

Although you will retorque the heads to the reccomended torque, the block will not go back to the position it was in before the heads were removed.
It will go back close but no cigar.

The rings have long ago seated and CONFORMED to the bore shape you have before head removal.
After replacing the heads, the cylinder shapes will all be different than before they were removed.

The rings are already worn, the croshatch is gone and the rings will not seat.
You'll be down on compression and up on oil consumption due to oil scrapers that don't work as well with the "changed" cylinder shape and same for the compression rings.

Unless you do something to reduce the volumne of the combustion chambers the comprression is likely to be LESS than before you had the heads rebuilt (assuming there are no catastrophic failures in the valve seats or valve heads). Your compression test shows the engine to be in "normal health" for the miles that are on it.

Compression is NO indicator of condition of the "lower end" of the engine.
Case in point: I had an engine that would puke oil out the vents at higher RPM. Compression was great. Oil looked good. No consumption at lower RPM. The problem was a BENT ROD....the piston rings weren't sealing at high RPM and a lot of the compression from that cylinder found it's way into the crankcase.
Had another engine that had a high speed vibration. Compression was fine.
Four rod bearings had welded themselves to the rod journals.
(my fault, I knew the clearences were a little below limits) I thought it might wear in ok and in a street driven engine it probably would have.
On the circle track running at 7000 RPM it didn't have a chance....
That one taught me that too little can be as bad as "not enough" when it comes to engine clearences.

Anyway, it's not much more work (or expense) to pull the engine and freshen up the bearings and put in a new set of rings.
You're going to wish you had anyway, if you don't.

There'll probably be a ton of folks here that tell you about how they changed out their heads and never had a problem.
That ALL the speed shops do it, etc, etc., etc.
They also probably gamble a lot in Vegas and buy a lot of lottery tickets.

Good luck with your rebuild however you decide to do it.