New runners on a L98
Thread Starter
Instructor
Joined: Jul 2007
Posts: 236
Likes: 0
From: Mobile Alabama
New runners on a L98
I have a 1990 L98 Auto it has muffler elimiators and thats about all. I am going to change to a set of Jon's injectors and am wondering if installing siamised runners would help performance. I have a chance to get some but don't know if they will help or hurt performance with my mostly stock setup. I will be adding a open airbox in the future.
Le Mans Master
Joined: Jun 2006
Posts: 5,642
Likes: 5
From: One day you're a Comet...the next day you're dust... Arkansas
I have a 1990 L98 Auto it has muffler elimiators and thats about all. I am going to change to a set of Jon's injectors and am wondering if installing siamised runners would help performance. I have a chance to get some but don't know if they will help or hurt performance with my mostly stock setup. I will be adding a open airbox in the future.
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Depending on the specific type of siamesed runners you're talking about, you may or may not notice a little difference.
If they have a larger bore and are siamesed at least 3"-4", you should see a small improvement especially from 4300-4800ish rpms.
Above and below that range will remain largely unaffected. You can decide if that's worth it.
A couple of members like to recommend siamesing the base for a small top-end gain.
I agree with the exhaust and free-mod suggestion from BADDUCK. Consider replacing your cats with hiflo versions and going to a 2.5" front "Y"
If they have a larger bore and are siamesed at least 3"-4", you should see a small improvement especially from 4300-4800ish rpms.
Above and below that range will remain largely unaffected. You can decide if that's worth it.
A couple of members like to recommend siamesing the base for a small top-end gain.
I agree with the exhaust and free-mod suggestion from BADDUCK. Consider replacing your cats with hiflo versions and going to a 2.5" front "Y"
Team Owner
Joined: Sep 2001
Posts: 62,178
Likes: 1,740
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
It would help, and certainly not hurt. However you may not feel the difference. Since youre going to do the injectors, I would go ahead and do this while the runners and such are all off....but you should do the exhaust and free stuff as well.
Pro
Joined: Jan 2008
Posts: 584
Likes: 1
From: Near Lockport NY Black 1986 Coupe
The only way you will feel a difference from the runners is if you port them and the intake as you are changing the injectors. Clean them up with a dremel and they will flow a lot more than stock. Wouldn't hurt to touch the plenum as well, that thing just begs to be ported.
The exhaust side of the equation is much easier, as removing the backpressure creates a lot more torque for the motor to use. Get rid of the pre-cats if you have no limits on smog, and either gut out the main cat or get a high-flow one from summit or MA motorworks - either have decent prices.
The exhaust side of the equation is much easier, as removing the backpressure creates a lot more torque for the motor to use. Get rid of the pre-cats if you have no limits on smog, and either gut out the main cat or get a high-flow one from summit or MA motorworks - either have decent prices.
Drifting
Joined: Dec 2005
Posts: 1,313
Likes: 2
From: High Ridge Missouri
It really depends on what you mean by siamesed.
This?
OR THIS?
A set of stock SLP runners will do very little over stock, but they do have a considerable amount of potential with some work.
This?
OR THIS?
A set of stock SLP runners will do very little over stock, but they do have a considerable amount of potential with some work.
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Drifting
Joined: Dec 2005
Posts: 1,313
Likes: 2
From: High Ridge Missouri
Safety Car
Joined: Oct 2007
Posts: 3,816
Likes: 0
From: :45 minutes from everywhere / E-I-E-I-O
They say the intake flow design is for a 305TPI, and intake mods should be before exhaust mods.
http://forums.corvetteforum.com/show....php?t=2063375
Instructor
Joined: Dec 2005
Posts: 142
Likes: 2
From: Centerport NY
The ported SLPs push the power band up into the
RPM range and you lose a little low end torque but you also lose the
TPI wall @ 4500 RPM. I happen to think this improves the fun factor for the car. However, it's been said before -unless you do heads and a cam you are not going to see hugh performance gains
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
6k WOW. Did that hurt lower end any?
