Siamesed base...THUMBS UP!
Thread Starter
Safety Car
Joined: Dec 2000
Posts: 3,767
Likes: 5
From: Jacksonville Fl
Siamesed base...THUMBS UP!
I siamesed the stock base manifold on my 87 L98 to cut depth of about 1.25" over the last two days. After a few drives...it was definitely worth it. I can tell a nice improvement in midrange pulling. :cheers:
I didnt do the job just for the siamese...that would hve been a little too much trouble than it's worth, but since I had to reseal the intake manifold ends...well, I just couldnt help myself. :crazy:
The biggest reason I wanted to do this was I really noticed the absence of high RPM power in the L98 after pulling the 2.59 gears and putting in a 3.31 gear. The gear change resulted in blazing tires from any stop and then falling on the motors proverbial face once the car started moving...it just didnt have the RPM range to pull! Now it pulls right through. (but it still blazes the tires :steering: )
It was an easy job, all I did was get a few 4" cutoff wheels for my die grinder and made two cuts in each runner pair...then popped the material out between the cuts with a light tap of a hammer/chisel. Then cleaning it up with a burring bit only took a few minutes more. I would say the total time doing the mod was less than an hour, and when your talking thats just the better part of a long lunch in the big scheme...it's worth it!
I didnt do the job just for the siamese...that would hve been a little too much trouble than it's worth, but since I had to reseal the intake manifold ends...well, I just couldnt help myself. :crazy:
The biggest reason I wanted to do this was I really noticed the absence of high RPM power in the L98 after pulling the 2.59 gears and putting in a 3.31 gear. The gear change resulted in blazing tires from any stop and then falling on the motors proverbial face once the car started moving...it just didnt have the RPM range to pull! Now it pulls right through. (but it still blazes the tires :steering: )
It was an easy job, all I did was get a few 4" cutoff wheels for my die grinder and made two cuts in each runner pair...then popped the material out between the cuts with a light tap of a hammer/chisel. Then cleaning it up with a burring bit only took a few minutes more. I would say the total time doing the mod was less than an hour, and when your talking thats just the better part of a long lunch in the big scheme...it's worth it!
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Re: Siamesed base...THUMBS UP! (BBA)
I did the same thing in 2002 and got the same results.
I used my reciprocating saw with the longest blade I could find at ACE. Not only did I do the intake manifold, but the runners as well. I tried to remove all of the dividing wall from the runers, but the balde wasn't quite long enough to reach all of it; so I took out as much as I could.
They are not stock runners though; BBK siamesed jobs.
The mod gives each intake port more volume to draw from.
Jake
I used my reciprocating saw with the longest blade I could find at ACE. Not only did I do the intake manifold, but the runners as well. I tried to remove all of the dividing wall from the runers, but the balde wasn't quite long enough to reach all of it; so I took out as much as I could.
They are not stock runners though; BBK siamesed jobs.
The mod gives each intake port more volume to draw from.
Jake
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Siamesed base...THUMBS UP! (BBA)
Good to hear that mod worked well for you too.
With the siamese base, exhaust mods & 1.6:1 RRs I find that my L98 now pulls strongly into the mid 5k RPM range.
With the siamese base, exhaust mods & 1.6:1 RRs I find that my L98 now pulls strongly into the mid 5k RPM range.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Re: Siamesed base...THUMBS UP! (65Z01)
Right now I'm working on siamesing my plenum to runner holes, and smoothing out the runner entrances. I can't siamese them since they're stock runners. I'd be thrilled if I noticed any improvement, but every little bit helps.
Le Mans Master
Joined: Jan 2002
Posts: 5,320
Likes: 4
From: Kyle TX (Because Mojo Made me fill it in)
Re: Siamesed base...THUMBS UP! (CentralCoaster)
you can kinda siamese them even if they are stock.
Just make sure not to knife edge them like I have in these pictures. Evidentally that causes some turbulance or something. I rounded them off before installing them.
Just make sure not to knife edge them like I have in these pictures. Evidentally that causes some turbulance or something. I rounded them off before installing them.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Siamesed base...THUMBS UP! (CarAteMyMoney)
I have stock size plenum, runners and base with a 52mm TB.
The plenum has been ported to match the TB and the upper runners & plenum sides have been ported. The intake base and lower runners have been siamesed; there are pics on my site along with dyno pulls before & after the siamese work.
The plenum has been ported to match the TB and the upper runners & plenum sides have been ported. The intake base and lower runners have been siamesed; there are pics on my site along with dyno pulls before & after the siamese work.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Siamesed base...THUMBS UP! (CarAteMyMoney)
Well since I have an A4 the dyno operator couldn't mash the pedal till the engine was above the 3-2 shift point so I realy don't have data down low but ou can see that it gained about 10% or 20rwhp at 5,400rpm.
My short times were roughly the same after the siamese base so I conclude that any low end torque losses were minimal. Shortly thereafter I had the A4 rebuilt with a 2,000rpm TC which brought down the 60' times substantially.
My short times were roughly the same after the siamese base so I conclude that any low end torque losses were minimal. Shortly thereafter I had the A4 rebuilt with a 2,000rpm TC which brought down the 60' times substantially.
