Getting L98 heads ready for Hotcam
12-02-2003, 11:46 AM
#16
Registered User
Join Date: Jul 2002
Location: Friendswood, TX, USA
Posts: 3,769
After clearly stating that I have done this, we get two post that say it can't be done!!! Interesting, no?
So, for anyone interested, this is what can be done.
I had a high mileage 87 Corvette with a stock L98. Rather than rebuild the two bolt main block I purchased a new ZZ4 short block form GM.
This block has the stock bore and stroke, the stock deck height, and the stock piston to deck clearence.
I had a new set of L98, aluminum heads, that I had machined for over size valves, both intake and exhaust, 5 angle valve job, LT4 hot cam springs, 7/16 studs, pocket port, port matched, and combustion chamber worked to unshroud the valves.
I installed these heads with the stock Felpro head caskets. And used the 1.6 ratio rocker arms.
There were NO clearence issue with any parts, and no special modification had to be done.
With after market intake and exhaust the engine dino to 401rwhp, on pump gas.
insomniac 92z28 and 90rocz,
Please explain to me why the
What do you mean by this.
And why,
So, for anyone interested, this is what can be done.
I had a high mileage 87 Corvette with a stock L98. Rather than rebuild the two bolt main block I purchased a new ZZ4 short block form GM.
This block has the stock bore and stroke, the stock deck height, and the stock piston to deck clearence.
I had a new set of L98, aluminum heads, that I had machined for over size valves, both intake and exhaust, 5 angle valve job, LT4 hot cam springs, 7/16 studs, pocket port, port matched, and combustion chamber worked to unshroud the valves.
I installed these heads with the stock Felpro head caskets. And used the 1.6 ratio rocker arms.
There were NO clearence issue with any parts, and no special modification had to be done.
With after market intake and exhaust the engine dino to 401rwhp, on pump gas.
insomniac 92z28 and 90rocz,
Please explain to me why the
1.6s won't clear the head
And why,
Stock TPI heads will safely only support aprox .480" lift
12-02-2003, 08:49 PM
#17
Registered User
Join Date: Jun 2002
Posts: 48
Christ man (Z28SORR)chill out! He has iron heads THEY ARE DIFFERANT.
The 1.6 rockers will throw the geometry of your pushrod too far towards the rocker stud to clear the head through the pushrod clearance hole in the head. The head will need milled or at least have the hole drilled out larger to clear the pushrod.
The .480" lift on the L98 head is because of the interferance between the spring retainer and the valve guide boss. Mine had .570" clearance when I check them, which would be good up to .520" lift.
You will more than likely be fine if you stay with the 1.5 (stock)rockers. The extra lift won't do anything anyhow, and if you don't want to pull the heads you really don't have much choice.
Later,
Charlie
The 1.6 rockers will throw the geometry of your pushrod too far towards the rocker stud to clear the head through the pushrod clearance hole in the head. The head will need milled or at least have the hole drilled out larger to clear the pushrod.
The .480" lift on the L98 head is because of the interferance between the spring retainer and the valve guide boss. Mine had .570" clearance when I check them, which would be good up to .520" lift.
You will more than likely be fine if you stay with the 1.5 (stock)rockers. The extra lift won't do anything anyhow, and if you don't want to pull the heads you really don't have much choice.
Later,
Charlie
Last edited by insomniac 92z28; 12-02-2003 at 09:27 PM.
12-02-2003, 11:55 PM
#18
Registered User
Join Date: Feb 1999
Location: Springfield,OH. U.S.A.
Posts: 2,947
I didn't mention a fact that "insomniac" did about the pusrods. Clearance must be checked there also b/c if the pushrod slot is not long enough it will rub the head and eventially fail. Not to mention the fact that they will increase lift by aprox .030"...risking coil bind or retainer interference.
If you remove your valve spring and measure the distance from the retainer to the to the seal, WITH the NEW seals installed.
You come up with a number like .570 exhaust/ .530 intake. Now subtract a saftey margin for coil-bind of .010" between each coil, 6 coils = .050", and use that same saftey margin for the "retainer-to-guide SEAL" clearance. Even if ehaust is OK, you'll have to machine the intakes, so you might as well do it right...Or your playing "Russian Roulette"...If the valvetrain gets a little loose something bad WILL happen..
Thwy will cut the spring seats at the same time as the guide bosses, so tell them your cam/spring specs!!!
I know there's always someone getting by, chancing it, but I wouldn't sacrifice my motor betting on it...this car is my current project, not my first...a work in progress...when money allows.
If you remove your valve spring and measure the distance from the retainer to the to the seal, WITH the NEW seals installed.
You come up with a number like .570 exhaust/ .530 intake. Now subtract a saftey margin for coil-bind of .010" between each coil, 6 coils = .050", and use that same saftey margin for the "retainer-to-guide SEAL" clearance. Even if ehaust is OK, you'll have to machine the intakes, so you might as well do it right...Or your playing "Russian Roulette"...If the valvetrain gets a little loose something bad WILL happen..
Thwy will cut the spring seats at the same time as the guide bosses, so tell them your cam/spring specs!!!
I know there's always someone getting by, chancing it, but I wouldn't sacrifice my motor betting on it...this car is my current project, not my first...a work in progress...when money allows.
Last edited by 90rocz; 12-03-2003 at 12:01 AM.
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