as we all know, a stock l98 runs out of breath way too quick. its frustrating on my 89. the right thing to do is tear the motor out and do a cam, heads, and all that stuff. but of course, im going to be cheap and try to do things easier (and probably get frustrated when i get poor results). anyway, im planning on porting the stock plenum. but while i have it apart, i figured i might as well put on high flow runners. and why stop there, maybe bolt on a high flow base while im at it! not so cheap anymore. heres what im looking at:

http://www.ebay.com/itm/TPIS-High-Flow-Base-Big-Mouth-Intake-Manifold-Tuned-Port-Injection-Corvette-L98-/151058448054?pt=Motors_Car_Truck_Parts_Accessories&hash=item232bc8feb6&vxp=mtr
http://www.summitracing.com/parts/ed...model/corvette

now, should i go with one of these or both? or maybe neither and just stick with the plenum porting. id also like to get the tuning software so i can make adjustments myself.
http://www.moates.net/apu1-autoprom-....html?cPath=64

 

Those prices make me cringe!

Look around and take your time.. You can find deals on entire intakes occasionally. I paid substantially less for my complete superram than you're talking for just the base and runners.

 

Buy a Miniram. It will handle the heads and cam, you will add later. I started with the aftermarket base and runners. Ended up going to the Mini later. And, damn the install is easy.

 

Have you thought about an LT1 intake converted for an L98?

 

Porting the plenum might be worth 3-5hp on a good day provided you did runners base etc. Imo a finishing touch not a real mod youll ever feel on its own.

 

To answer your question, if you don't do a cam change and run stock heads, just the ported plenum and large tube runners will suffice. For the tuning, it will always be best to do a dyno tune. Yu can do it on the street, but it is difficult to run the rpms to max on the street. Other beneficial mods would be the underwrite pulleys and exhaust upgrades.

 

I agree. David Frederick sells these here in the Parts for sale section. Beautiful work and free advice over the phone or by PM. As an example he noticed on one of my posts about an install that I needed a different fuel rail than the one he sent me. Mailed it to me the same day at no cost to me.
You will have to purchase a remote thermostat housing, fittings to route the coolant from the housing to the rear of the manifold, a small cap distributor and wiring adaptor, LT1 fuel pressure regulator and have fuel lines fabbed up. Total cost for you to do it yourself is in the $450 range. You can sell your current system to defray the cost though.
Also be forewarned that you will be stricken with "Oh well, while I am in there I might as well.........disease". This disease has cost me a few extra bucks already.

 

Hands down, no question that's the route I'd go. By far the best bang for the buck. If I have to pull the intake on my IROC, that's what's going on it.

 

i have thought about the lt1 intake, but it really seems like alot of molestation. maybe the mini ram is my best choice. its just so god damn expensive. how would a ported plenum and high flow runners compared to a mini ram?

 

You can port and polish the plenum until your blue in the face, it will NEVER flow as much air as the engine needs. It is by far the most restrictive part on an L98, and it just can't be reasonably modified to flow enough air to provide to volume of air you need. The modified LT1 intake is very well worth the molestation IMO.

 

See this EFI intake comparison ( done on a 383)
http://xtremecarzone.com.au/index.php?showtopic=386

Don't look at the raw numbers;
look at the graphs to see where each intake , starts working , it's working rev range and were it runs out of puff
Note most TPI based setups are dead around 5K.

If it wasn't for the hood clearance problem on a C4 , the HSR is the best all round bang for buck performer ( next to the used only SR )

 

What a great article, thanks...

Do NOT do BM base only; I'm not sure about runners only. The combo of BM base & AS&M runners will give you 10chp gain.

Do some exhaust mods too: mandrel-bent Y, hi-flow cat and cat-back or better 2 1/2" true duals.

Cut the air filter lid and add a K&N filter.

Add an AFPR and bump fuel pressure to 48psi to match WOT fuel to new air flow.

If you still have the "frisbee" on the front of the WP pulley, toss it for another free 10chp.

Install a 160deg T-stat & fan switch for another 10chp.

If you get better breathing up top install a HyperTech coil/cap/rotor and some low resistance wires to fire the charge up around 6k RPM.

Cut back some stock AC Delco spark plugs for a "free" 8chp gain.

 

There is no comparison TPI to LT1 or miniram

Its well worth it
Just do the LT1 youll love it. No real molestation....hey they are cheap and they work.

 

Cut plugs are probably worth it, but I gotta think the stock high-power electronic ignitions on our cars are about as good as it gets -- unless mods get crazy. OTOH, having new(ish), good working parts is never a bad thing.

Ehhh...to the stat idea. Unless the switch controls the main fan, who wants their aux fan running all day. Plus, I'm not impressed with what mine can do.

I think the frisbee mod was proven far less than 10chp. Seems like it was half that amount...though worth if -- if you're certain it won't cause premature wpump failure.

We've all decided that a K&N doesn't do squat...that the restrictive part of the intake is actually the neck of the air box. K&N won't help that.

Stock WOT tables are already over-the-top rich. Bumping up FP seems like it would just make it even richer. OTOH, maybe it causes triming of normal ranges...which brings DOWN WOT fueling. Combined with better atomization, there's a small chance I believe higher FP works...though not for the reason most would think.

Any exhaust mod is worth it on an L98. As mentioned before, I vote for 2.5" front Y, magnaflow bullet cats, no main cat, and a glass-packed rear Y.

None of this would change the top-end RPM limit though. I think the large-tube runners -- especially TPIS/ASM are the best -- w/o porting. Beyond that, everyone is right about a superram (SR) or short-runner intake. OTOH, w/o a cam, there's a chance you'd be more satisfied with the largetubes vs a non-cammed short-runner intake. Less torque in normal "useable" range. (That's what the intake comparison is designed to show.)

 

I started with a LTR and ended up with an HSR. I should have done the HSR or Miniram to begin with. There is also the FIRST.

 

i have no plans of ever camming my motor. so it looks like the stock ported plenum and high flow runners would be my best bet cost wise. without a cam, the miniram will never work to its potential. not to mention, its more more expensive than just slapping on high flow runners.