Vader86’s Minor Mods Page

Minor’ Modifications that work

  • K&N Filter w/cut lid

You’re looking at about 5-10hp gain on a dyno from running this on the L98. People are quick to point out weblinks that say its the worst filter ever, but ignore the longterm performance of this filter. If you compare a brand new K&N to a new paper filter, they’ll flow about the same. If you wait 10K and compare them again, the K&N is ahead by leaps and bounds, and you shouldnt have to clean that K&N for another year.

The cut lid is basically what it says, you take the stock air lid off and cut a big square hole in it. If you dont want to snip yours, get one from a junkyard. 85-89 and 91-96 are the same respectively.

  • MAF descreening

The MAF sensor is the sensor between the airbox and the accordian intake. It has 2 screens on either side of the sensor element, and it’ll flow about 200cfm extra air (total of about 650-700) with these screens removed. I would not, however, remove the heat sink fins inside it, youre taking a big risk by getting near the sensor element, and this is not a cheap part.
Some make the mistake of assuming these screens are for preventing debris from hitting the sensor….thats what the air filter is for, and why would they need a screen after the element if that was the case? They are primarily for straightening air over the element, but on Corvettes that shouldnt be an issue with our straight intakes.
Unfortunately, this doesnt seem to help LT1/4 that much, so I wouldnt bother with it.

  • TB Bypass

Coolant (which is hot) is routed through the throttle body to warm it. This prevents frost from building on the butterflys during extremely cold weather. Unfortunately it hurts the car’s performance the rest of the time. Bypassing the coolant flow from the throttle body can be done with a 5/8″ hose. I routed mine around the TB completely.
Dont worry about icing on the TB vanes, its got to get DAMN cold for that to happen, and it could only then happen if the engine is cold. Is it a noticable improvement? no, and it wont show on the dynojet either. However, if you do it you will notice that you will be able to touch the plenum on a hot day not long after shutdown, which tells me its doing ‘something’.

  • Exhaust

The L98’s exhaust system is so inadequate that its funny. The ports on the exhaust manifold are tiny, the pipes have precats built in, and the mufflers on most models only have one functional outlet of the two.

So, as you might expect, the L98 responds extremely well to exhaust mods. I changed over to a Power Effects adjustable catback. Its got alot more deep bass than most of the others, and sounds like a big block. If you ask me, the adjustments might as well not be there, its not that much quieter, and the resonance is worse (i think) with them closed. Still, nearly any catback system will net about 10-12rwhp on a dyno (conservatively).

Next is those 2 precats and the manifolds. The L98 basically uses ’70’s converter technology, with 2 precats in the front Y into a large main cat. All of them are terribly restrictive compared to cats used on LT and LS engines.

So the best bet is to install longtube headers, like TPiS, Hooker, or Lingenfelter. Most will show the same 10-15rwhp gain, and the major difference is fit & finish between all of them. Hooker 2149s are emissions ready, with EGR and A.I.R. hookups, as well as an O2 sensor bung already installed….and they come ceramic coated. The 2151s are bare headers, and you can order them coated if you want. The correct Y pipe PN is 16720. Note, Hookers do not allow use of the rear alternator support on most models, so you will need to fab something up or you will eventually crack your alternator. TPiS allows use of it, and they come with emissions ports already. Lingenfelter is out of production but its a good header, you may find them on ebay.

Header size? It doesnt really matter, you won’t feel the difference between 1 5/8″ and 1 3/4″ primaries, and your track results probably won’t show any. Hooker and TPiS are both 1 3/4″ headers.

All of these delete the precats, which are not doing the bulk of the work for emissions anyway. You should still pass testing in any state besides CA, except perhaps a visual check.

The main cat. Its a huge heavy piece of junk, designed in the 70’s. Removing it entirely will get you back about 10hp on the L98 (only 5hp on the LT1/4’s smaller dual cats), but I decided to put a new one in that would keep the resonance bearable and the new ones are built so much better that they aren’t a big restriction. There are several brands to choose from: Random Tech, Car-Sound, Magnaflow, Catco, etc. Most will bolt right up to catbacks and slipfit to header Y’s.

  • AIR eliminator

I debated putting this here, since its not going to give you any measurable power. Its mostly a cosmetic modification, as the pulley thats on the AIR pump is spinning pretty free already. Its also going to save some weight when you remove it.
The purpose of the AIR is to inject air into the cats so they light off quicker, more of a stopgap ’70s-era thing. The car starts up running in open loop, which makes it richer, and theres unspent fuel in the exhaust. The AIR injects air into the exhaust to try and burn the rest of the fuel. It pumps air into the manifolds in open loop, but in closed loop it switches to the main cat to help it burn anything left. Modern cars rarely use this. You will still pass a sniffer test if the engine is hot, once you remove it.

  • AFPR

This is only going to help those who have done several minor/major mods, and don’t yet need a chip change. It will also help those who’ve replaced their injectors with larger units, as the ECM needs a little help in maintaining A/F ratio.

An adjustable FP has a adjustable spring in it that sets the fuel pressure.. I wouldn’t raise it much more than 3 or 4 psi. Fuel pressures can range anywhere from 37 to 47 psi, 45 is good for Ford SVO’s. To high of a fuel pressure setting will prevent the fuel rails from purging vapor lock conditions back to the gas tank. If you’re going to play with the fuel pressure I would recommend that you do it at a shop where the car can be analyzed, or on a dyno preferably.

If you look in the Superram installation page, you’ll find data on flow numbers, at the bottom of this page is information on fuel pressure changes.

  • Timing Changes

Most people forget about this, and its the easiest thing you can do, the base timing is 6* BTDC and you can set it to 8-10* without issues. This can get you .1-.2 gain in the 1/4mi by itself.

  • Underdrive Pulleys

Personally I dont like this mod, because I dont like the idea of my Alternator spinning any slower than it already does, especially since the C4 eats alternators. However, track tests show that you could get .1 in the 1/4mi just from this, which equates to about 10hp.

Stuff that DOESNT work
1. airfoil
2. TB spacer plate
3. “adjustable” MAF’s, like Granatelli
4. Larger Throttle Body-this isnt needed on a 350 and definitely not on a TPI. The 48mm stocker flows more than the engine can use anyway.
5. MAT relocation
6. Power Couplers
7. The Tornado
8. A hypertech chip, or any other non-custom chip.

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