What gains would i see by installing the zz4 on my stock l98. the only other things i might do would be to open up the plenum and lower intake and maybe an afpr. also should i instal 1.6rr's?

 

You will have to have your stock L98 heads reworked to accept the higher lift of the ZZ4 cam. The exhaust side has a .510 lift with 1.5 rockers which is to much for your stock heads. You will break something without reworking the spring areas. If you are going to have the heads rework I would go with 1.6 RR's on the intake side only. This would bring the intake lift up to .505".

Every thing that you do will help. Port match everything and have the heads cleaned up.

 

so is that something that a machine shop will have to do?

 

New springs are needed. You can do 'em, but I had a machine shop do mine for my ZZ4 cam. Got a valve job too.

...oh, and you might want to consider screw in studs instead of press in studs, since there gonna be at the machine shop anyway.

 

Like said above, you will have to have the heads worked over. The biggest issue is lift. 1.6, 1.5, the ratio you use doesn't matter for this, you will need to have them machined for more lift. This usually means milling the guide bosses a bit. This would be a prime time to have them machined for positive valve seals (teflon type). Depending on what springs you use, you may or may not have to enlarge the spring pocket. A popular spring is the 986 or 987 spring. Either of these would require the spring seat to be enlarged to roughly 1.45" (the spring OD is 1.43"). A personal favorite for me, when it comes to hydraulic roller springs that fit the factory pocket are the Isky 235-D springs. They have the 1.26" OD and a large .886" ID. They have 130 lbs of seat pressure at 1.750" installed height and 320 at 1.200" The spring rate is 350 lbs/in and they coil bind at 1.150". That gives a total of .600" between the installed and coil bind. Take away the safety margin and you are left with roughly .550". Thats enough to run 1.5's. It's cutting it close with 1.6 rockers, but it could probably be done.

If you get rockers, just get a set of 16. Don't bother with the intake side only or what not. You're machining for more lift, right? Why not use the advantage you're machining for. Besides, you are still using factory castins and the exhaust ports, by all means, are far from magical. They need all the help they can get to get the exhaust out.

As for the actual gains, it would be kind of hard to say. The gains would really open up once you open the breathing side of the car. I'm assuming you already have the full exhaust.

For rockers, the best budget piece that aren't aluminum are the Comp Magnum roller tip rockers. I have a set ready to go on my Vortecs.

My last suggestion: While the heads are off, do yourself a favor, port them up nice and good. Your engine and ZZ4 cam will thank you in the end. As for the intake, it leaves a lot to be desired up top.

 

I agree with Abubaca. After about 3 weeks on the new engine i pulled 3 stock rocker studs out with that cam. This led to the rocker becoming very loose, it proceeded to ruin the tip of the valve, the rocker, and the pushrod put a groove in the aligning slot in the head (non-self aligning rockers) Because of the groove i had to either run a self aligning rocker on that valve or run guideplates and hardened pushrods. I choose the second. I'm not saying you should get guideplates and hardened pushrods. I'm saying you should prevent a possible diaster and install screw in rocker studs. Mr. Gasket makes some that don't require machining to the rocker boss.
http://store.summitracing.com/defau...-1076&x=20&y=11
Only $28, i wish i installed screw in studs while the engine was being rebuilt and saved the $300 to fix my heads. Vader has an article on how to install these studs while the heads are still in the car.
John

 

wow i didnt realise how much it took just to upgrade the cam. since the car is my daily driver i think my best option would be to find a cheap set of factory heads and take the time to get them done right so that all i have to do is swap the heads in with the cam.

 

Thats a great idea, stock L98 heads can be had for $100 in the classified section all the time. Then you can resell yours to make all the money back.

 

I'm running a ZZ4 cam in my stock L98 block. It has 150K miles and the only change has been the intake -- Stealthram -- and the ZZ4 heads "113" castings with 1.52 magnum roller tip rockers. The torque converter is a Vigilante with a 2400 Stall.

So far, this combo has helped me get a 12.85 ET. Not bad if you ask me.

Hope this helps your plans!

 

what is the difference between the zz4 aluminum heads and the l98 iron heads?

 

ZZ4- "113 casting" (also know as Aluminum Corvette Heads)

PORT SIZE: 163
CHAMBER: 58cc
VALVE SIZE: 1.94 / 1.5
LT4 springs
Screw in studs
O.E guideplates

L98 head specs depend on the casting. Do a search for your particulars and I'm pretty sure you'll get something.

 

it is my understanding that i have the "083" castings. what im confused about is, what is different about the vette heads that they can handle the zz4 cam, but the iron heads need work.

 

You will need screw in studs if you don't want your originals to be yanked out of their sockets. Aslo, you need to get the springs that handled the lift of the ZZ4 cam. The stock springs on your Fe heads only handle .500" lift. The ZZ4 will put you over that with 1.5 rocker arms. If you decide to use 1.6 then you will add additional stress on your springs.

The ZZ4 heads were designed for the ZZ4 cam. They are compatible becuase the springs on the ZZ4 heads allow for the lift of the ZZ4 cam.

The O.D. of the original springs you have is smaller than the O.D. of the ZZ4 springs. That's why you will have to go to a machine shop to have your head machined for new springs. There is however, per my understanding, springs that handle the ZZ4 lift without any machining to your Fe heads. You will need screw in studs though -- if you do a search on all this, you can get part numbers and all the gravy!

Hope this helps.

 

Stock springs will hit clearance issues before .500", more like .480" tops. Take them to a shop and have them machined for clearance issues. They will probably end up milling the guide boss down. This would be a pretty good time to have them set up for teflon positive type valve seals. However, if you do not feel like doing that, Fel-Pro does offer viton seals that do not require machining. Part numbers for these are SS72527 for the intake sides and SS72877 for the exhaust. Keep in mind, they are inteneded for the factory diameter guide boss. The spring pockets CAN be enlarged, however, like above, there are springs that can fit in the factory pocket and can handle the lift. One of my personal favorites, and I have them ready to go on my Vortecs, are the Isky 235-D springs. They have the factory 1.26" OD and a generous .886" ID. 130 lbs @ 1.750" seat, 320 lbs @ 1.200" open pressre, 350 lbs/in spring rate, and they coil bind at 1.150". This gives about .550" of net lift (lift after clearance factors are added in). With these springs one could probably take the ZZ4 cam up with 1.6 rockers, which puts .544" lift on the exhaust. The only down side about the Isky springs is that, well, like all other Isky products, they are not cheap. Summit lists them for 92.99 (p/n ISK-235D). With those springs, I use a steel retainer, part number 707-STA (also from Isky) to achieve a 1.750" installed. VL-32 is the part for the 7° lock from Isky, standard 11/32" valve stem.

As far as screw in studs, taking them to a shop would end up in them milling aobut .400" off. As an option (like said above), Mr. Gasket makes a screw in stud that doesn't require machining, just tapping. Part number MRG-1076.

I think that's all the part numbers.

 

I ran a ZZ4 cam on my STOCK heads without Machine work with the stock 1.5 rockers. I used the short ZZ4 retainers for more Guide clearance with the ZZ4 springs. I ran this cam with press in studs for 90,000 miles and never had a problem.I did this on my 91 Z28 when it had the 350 in it. It worked for me but you should check clearance before you put the cam in with stock heads. I went 13.11 with that cam in my 350TPI.

 

geese I was thinking I would only get a 14.0 with my setup



Is our elevation THAT different ???

 

what other mods did you have at the time?

 

I ran a 13:17 ET with this zz4 cam,L98 ported heads, Edelbrock manifold, 1 5/8 Mac, 3:73,SLP runners... Convertible 91 Z28 wich is know to be heavier! As from me, I only changed the springs and had no clearance problem.

Happy built!

Pat

 

I also had, 3.42 gears, no cats, 1 5/8 headman headers, 160 stat, underdrive pulleys, 50 psi fuel pressure, 12 degrees timing advance, 92 octane fuel, Stock chip, Stock induction except for ground down Lumps behind the throttle blades, Air foil, home made ram air, head light covers, throttle body coolant bypass and Slicks. I had a 1.73 60 ft when I went 13.11 at 101.6. I think that is everything.

 

For the record, I've heard of more people NOT getting screw in studs than people that have, when swapping in a ZZ4 cam on an otherwise stock L98. Most seem to have no problems, but some obviously have.

...I'm not "suggesting" anything, obviously they can't hurt, but you should be safe without them. The ZZ4 isn't that crazy of a cam, and unless you plan on seeing higher RPM's a lot, the stockers should be fine.

...but like I said, it can't hurt. Take if for what it's worth.