is porting the runners and the intake worth the hassle on an otherwise stock L98?? I looked at the runner/plenum transition looks as big as the gasket I just don't want to open a can of worms. I will be cleaning up the EGR area and putting a AFPR on before it goes back together.
THNX THE SHAGGY IROC

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'89 SHAGGY IROC
L98 7r4, all free stuff,T.E.S.,HOOKER CAT BACK,KYB,ACCEL8.8,JET fan sw. etc.
so much to do , so little money

 

If you have the time, it's worth doing the intake and runners. If you add up the little you take out of the runners, times 8, it adds up. I did my entire intake, plenum and runners on my old L98 and it make a big difference. I also did my 305TPI in my 92 Z28. I ran 14.21@96mph with 3:08 gears and the peanut cam. I think its worth it.

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Rob P
89RSconvtZZ4TPI
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

14.2 with the peanut cam?

I doubt that.

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91 Trans Am WS6
Bright White
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

Built on Wednesday

 

that was w/ the 150 shot dude. just kidding...what other mods did you have to run that number?

shaggy, you should at least grind down the "wall" directly behind the tb. If you have the time fool w/ the runners, but definitely do some work behind the tb.



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87 IROC-Z, 5.7, auto, 3.27, leather, !cat, Holley fpr, K&N'S, SLP 1-3/4" Jet-Hot coated headers, SLP .218/.224 .495/.502 cam, Comp 1.5 roller tip rockers, $uperPITAram, Edelbrock lower intake, Holley 52mm tb, Dynomax\Flowmaster catback. Coming Soon(?)- Fasttrack/Accell DFI

1989 Pontiac 20th Anniversary Turbo Trans Am - 161,000 miles, !cat, 9" K&N

 

Why do you doubt it? Cause your car won't run that fast? If you like, talk with Bob Cosby over at the mustang boards. He writes articles for Fast Fords and Mustangs and has a daily driven low 11 sec LX coupe. He was there the day I pulled it. Track was Maryland Intl Raceway on a nice spring day with good air. Track is almost at sea level.
The car also has a hollow cat, alum drive shaft and center force clutch. That was my best run, she runs 14.5's all day. I know it pisses a lot of people off that my heavy *** , 92 Z28convt with a 3:08 rear runs fast than most L98's.

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Rob P
89RSconvtZZ4TPI
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

IROC,

The plenum porting make an even bigger difference on the L98 than on the smaller engine. Pay attention to the area shrouding the EGR ports in the floor of the plenum right behind the TB, and the transitions from the plenum to the runners.

You can easily increase the size of the runner openings from the stock average of 1.500" to 1.575". It really doesn't pay to go much farther than than, since the I.D. of the stock runner tubes is 40mm (1.574"). If you do this, you need to be aware that the stock GM gaskets AND the Fel-Pro replacements are both too small to allow correct port matching. The gaskets will have to be punched open to allow flow without obstruction. A 1¼" trade size conduit punch works great for this, since the gaskets have a metal liner.

The same can be done at the lower ends of the runners that mate to the intake base. There are some irregular transitions there as well, and the sizez can be matched to the runners with some minor machine or grinder work.

The difference can be a "free" 15HP gain.

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Later,
Vader
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"No matter how hard you try you can't stop us now"
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