L98 Heads? Reverse flow cooling? Compression Ratio?
Thread Starter
Instructor
Joined: Jun 2002
Posts: 218
Likes: 0
From: Winnetka CA
L98 Heads? Reverse flow cooling? Compression Ratio?
Just some questions as I get closer to having the money to rebuild my engine.
First, how good are the stock aluminum heads on an 87 L98? I was looking at porting and polishing and I was wondering how good the stock heads are cause I dont know if it is worth it to spend the money on porting.
I am keeping the stock intake, but going with a better cam. Not sure which one yet. I know I will need a new chip other than the hypercrap that is in it now.
Are the L98s reverse flow cooling? I was told that if it is I can go up to like 11.5:1 compression ratio. What is the highest ratio you would go with? It is sounding like a choice between 10 and 10.5 if they are not reverse flow.
I have an automatic tranny and I know I need to do torque converter and shift kit, especially with a new cam. Anything else that you would do to the tranny? I wish it were manual, but oh well...
I am trying to balance cost and perfomance. For example, if it is $350 to port the heads and it only yields 10 hp, its not worth it to me. Thanks in advance!
First, how good are the stock aluminum heads on an 87 L98? I was looking at porting and polishing and I was wondering how good the stock heads are cause I dont know if it is worth it to spend the money on porting.
I am keeping the stock intake, but going with a better cam. Not sure which one yet. I know I will need a new chip other than the hypercrap that is in it now.
Are the L98s reverse flow cooling? I was told that if it is I can go up to like 11.5:1 compression ratio. What is the highest ratio you would go with? It is sounding like a choice between 10 and 10.5 if they are not reverse flow.
I have an automatic tranny and I know I need to do torque converter and shift kit, especially with a new cam. Anything else that you would do to the tranny? I wish it were manual, but oh well...
I am trying to balance cost and perfomance. For example, if it is $350 to port the heads and it only yields 10 hp, its not worth it to me. Thanks in advance!
Melting Slicks
Joined: Jan 2003
Posts: 2,167
Likes: 0
From: What did the 5 fingers say to the face? SLAP!!
Re: L98 Heads? Reverse flow cooling? Compression Ratio? (amswak)
The L98 is not reverse cooling. The 87 heads are not the best, but depending on what your goal is, they can be used. Depending on cam selection, porting them should yield more than 10 HP.
[Modified by flyersfan1088, 4:42 PM 10/14/2003]
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: L98 Heads? Reverse flow cooling? Compression Ratio? (amswak)
The big change from '87 to '88 was the #113 D-port heads, and they netted a 10chp gain that was masked by addition of the "frisbee" in '88.
Porting and working the #113 heads is worth about 25chp so I would expect some nice gains from porting your Al heads too. The heads are NOT reverse cooled; that came with the LT-1 heads in '92. I think you can go to 10:1 or maybe a bit higher if you reduce the quench area and remove any sharp edges from the combustion chambers.
For the later L98s, the TPIS ZZ-9 cam is worth about 30chp.
For a nice performance/feel improvement I suggest a 2,000rpm lockup TC along with a TransGo shift kit.
If you want your "new" L98 to pull to 6,000 rpm with those new parts I suggest you try the siamese base to improve top end breathing. The slight loss of low end torque will be more than compensated by the 2,000rpm TC.
Porting and working the #113 heads is worth about 25chp so I would expect some nice gains from porting your Al heads too. The heads are NOT reverse cooled; that came with the LT-1 heads in '92. I think you can go to 10:1 or maybe a bit higher if you reduce the quench area and remove any sharp edges from the combustion chambers.
For the later L98s, the TPIS ZZ-9 cam is worth about 30chp.
For a nice performance/feel improvement I suggest a 2,000rpm lockup TC along with a TransGo shift kit.
If you want your "new" L98 to pull to 6,000 rpm with those new parts I suggest you try the siamese base to improve top end breathing. The slight loss of low end torque will be more than compensated by the 2,000rpm TC.
Team Owner
Joined: Sep 2001
Posts: 62,160
Likes: 1,733
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Re: L98 Heads? Reverse flow cooling? Compression Ratio? (amswak)
reverse flow started with the LT1
the 87s 128 heads are pretty good, probably good for say, 300-325 untouched
I would go with something like a Accel 211 or Tpis ZZ9 cam, or with similar durations.
I wouldnt run more than 10.5:1 compression, but thats just me.
Other than a 2000-2200rpm converter and shift kit, I would add a tranny cooler, that will really relieve some of the stress off that transmission.
the 87s 128 heads are pretty good, probably good for say, 300-325 untouched
I would go with something like a Accel 211 or Tpis ZZ9 cam, or with similar durations.
I wouldnt run more than 10.5:1 compression, but thats just me.
Other than a 2000-2200rpm converter and shift kit, I would add a tranny cooler, that will really relieve some of the stress off that transmission.
