L98 Intake porting

[Mart]

Just curious if anyone has ported and polished thier own L98 intake.

Any pics or info appreciated

Mart

 

[JT ZR-Won]

I don't have any pics but I've done 3 of them. Pretty easy but requires a pretty hefty air compressor. I would have to stop every now and then to let the compressor charge back up. There are 2 large chunks of aluminum directly behind the butterfly openings of the plenum that you will want to remove. I found that the metal dremel bits work the best for removing them. After that I'd go over it with a sanding dremel bit and then wet sand it for the smoothest flow possible. It is a job you can do yourself with a bit of patience.

Jay

 

[bossvette]

I ported my SLP runners

By going inside the runner it is supposed to shorten the legnth and raise the rpm limit, mine will pull strong to 5500 I have a cam matched to that rpm peak also. The finish is not supposed to be a critical since it is a "dry" system. I also opened up the mouth of the plenum as discribed in the previous post.

 

[Mart]

Thanks guys, how about the intake, apparently that is the real bottleneck on the L98 as it was made for the 305.Mart

 

[JT ZR-Won]

I "heard" that if you port the manifold out to it's fullest potential it is still a lot smaller than TPIS's big mouth manifold. The only true way to know is through dyno results.

Jay

 

[vetteboy86]

I have been thinking of doing this mod myself, since all it requires is my time. So you just grind down the ridges at the opening of the plenum. Is there any other spots that would require grinding. To the guys that have done this, is there a noticeable increase in performance?


thanks

 

[Edmond]

I "heard" that if you port the manifold out to it's fullest potential it is still a lot smaller than TPIS's big mouth manifold. The only true way to know is through dyno results.

Jay

That's the same thing I read, unfortunately, it was from the TPIS catalog! :L That Big Mouth isn't cheap either, $425 and $75 for the "port matching." TPIS claims that this manifold "will flow enough air to make over one horsepower per cubic inch-375 HP 350's and 440 HP 400 CID's." They also claim that "it will give you a 22 HP increase (when ported) on a stock 350 CID TPI motor..." Taken from page 15 of the TPIS catalog.

vetteboy86,

I don't think the increase will be that noticeable until you get into the cam and heads too. It really stinks that our TPI intakes were designed with the 305 in mind.

 

[Moonunit 451]

I don't have any pics but I've done 3 of them. Pretty easy but requires a pretty hefty air compressor. I would have to stop every now and then to let the compressor charge back up. There are 2 large chunks of aluminum directly behind the butterfly openings of the plenum that you will want to remove. I found that the metal dremel bits work the best for removing them. After that I'd go over it with a sanding dremel bit and then wet sand it for the smoothest flow possible. It is a job you can do yourself with a bit of patience.

Jay

I'd agree here, take some time. I did a BigMouth intake and some large tube runners. What bossvette is showing is a "rough" Siamese job. I would have claened it up a lot more than that, but, that's JMHO.

I think that a real nice Siamese job would be benificial on your car, add a cam ,RR's, headers, free flowing exhaust, and you probly got some good HP

Oh Yea! I forgot the heads, but I still think you can pick up some. BTW don't forget the MAF, that's the REAL choke point, when you get for real

 

[JT ZR-Won]

That's the same thing I read, unfortunately, it was from the TPIS catalog!

Ha! I think that's where I read it also. I actually never noticed a difference, but it's one of those things where every little bit helps......especially if it costs next to nothing to do

Jay

 

[bossvette]

I will be putting mine on the Dyno at Cruise-Fest 2004 I don't have anything to compare with though. The short block was built in 1990-91 for a Street Rod project and was transplanted into my Vette in 2000 when I converted it to a TPI and has better then 60,000 miles on it so I don't expect real impressive numbers but do expect a decent torque curve.
I will post the results after the Dyno-run.

 

[fast.asleep]

"it will give you a 22 HP increase (when ported) on a stock 350 CID TPI motor..." Taken from page 15 of the TPIS catalog.
.

funny, their "Insider Hints" propaganda states that it "will result in a 14hp increase" .
The least they could do is be consistent with the figures they pull out of their a** :eyerole

 

[Vettelt193]

before you get into it all, make sure the mods you do work best with the driving you do.... I love massive low-end torque that the L98 cars have, and when I had one, I didn't want to lose it, or shift the torque higher because I loved the seat of the pants feeling it gave. I have seen many un-happy L98 owners after doing mods because they lost that feeling to gain high revving HP.

Most of my driving is done in the low RPM range, so I love torque... it is nice to have high revving HP for that 5% of the time when I run it really hard, but if I had to have one over the other I would take the low end torque... this is why I didn't like my LT1 as much as my L98. (Love my LT4 though, best of both worlds)

 

[Mart]

I'm not looking for massive gains, just trying to clean things up and reseal the intake and figured while I was in there I could do a mild port and polish and grab a couple of ponys while at it.

I figured there would be more guys with pics and tips about porting and polishing the L98 intake.

Thanks guys
Mart

 

[vetteboy86]

After reading this post i was discussing the plenum mod with a guy that has an 85. He told me he ported his plenum with it on the car. He told me he stuffed red shop rags behind the area he was porting, then when he was done he pulled the shop rags out. He also used a vacum to try to collect any loose shavings. This kind of worried me, I dont believe i would try this with the plenum on the car. I plan on trying to do this before the Crusie Fest. My question is if i remove the plenum should i try to salvage the gaskets, or will they be destroyed in the process?


Thanks for the help

 

[bossvette]

New gaskets are a cheap way to insure no leaks;personally I would not reuse any gaskets.

 

[JT ZR-Won]

New gaskets are a cheap way to insure no leaks;personally I would not reuse any gaskets.

I agree. I also wouldn't attempt to do this on the car. It would make more sense to take it off because of how easy it is to remove.

Jay

 

[vetteboy86]

Yes I think I will take the Plenum off the car. It doesn't look to bad. Where do you suggest I buy the gaskets from. Does anybody have a particular part number for the Throttle body to plenum gasket, or the tube runner gaskets. I think while i have the plenum off i will clean the throttle body. I remember a post i read some time ago about doing this.


Thanks to all

 

[bossvette]

Where do you suggest I buy the gaskets from.
Thanks to all

any auto parts store or your local Chevy dealer