I hear you are the resident expert on L 98's, and wondered if you could help me out. I love my 88 convertible, but naturally wish it had a bit more horsepower. I have a couple small mods, K & N, open air box, throttle body foil, AFPR. Short of a total rebuild, bore, etc., what kind of mods can I do. I only have 39,000 miles on the motor now. I'd like to end up with around 300 rwhp. What should I do, and about how much should I plan on spending. I can do all the mechanical work myself, not too hot on the computer end of it tho.

Thanks for any info you can give me.

Bob
:yesnod:

 

Hi Bob,

I don't really consider myself a L98 expert... still learning like most.

But your question is fairly straightforward and easy. The L98's biggest weakness is the stock long runnered TPI System... while due to the strong low rpm air velocity those long runners create they make respectable off idle torque, however they cannot feed a 350 with a good set of heads enough air to make any HP above 4500 rpm, therefore without rpm and/or a lot of cubic inches you're bottlenecked in power. With that said, I recommend the 1st thing you do is get rid of the stocki tpi, and invest in a Lingenfelter Superram manifold. The new base intake, runners and plenum will set you back about $ 1100 give or take a bit. If you browse the various forums you can sometimes find a used, but perfectly good Superram for about 30 % off that price.

The Superram will now allow your motor to make a broader and stronger overall torque band that will allow your motor to spin up to roughly 6000 rpm with your HP peak somewhere around 5500 rpm. Therefore, now that your manifold breaths somewhat, all of the traditional small chevy hop-up tricks actually start to work. With your 88 you could either have a competent local head porter work over your stock aluminum heads or you can invest in a new set of aftermarket heads such as the popular AFR 190's or Brodix appears to have some great flowing heads too. Just keep the intake runner size down below 200cc with your 6000 rpm 350 and you will be complementing your torquey motor rpm range. AFR 190 heads are around $ 1200 out of the box, head porting is more of a who's doing the work thing, but I would think you could easily invest $ 1200 in the heads too. The results between the two will be very similar from what I have noticed, but I'd probably give the AFR 190's the edge, and in addition if you have them ported, they probably jump solidly ahead of the D-ports in potential.... but I'm guessing.

Add in the very popular and well proven LPE 74219 cam profile which is very docile and will pass even the strict California emissions. This cam seems to also compliment the SR rpm band with its moderate 219 duration, but agressive lobe ramps. There are probably other cam profiles just as good as the 74219 for this type of set-up, but I just haven't found them yet. This cam is on the expensive side though at $ 314 last I checked, however the nice thing about having this cam in is if you have problems on your initial start-up, you can pretty much eliminate the cam as the problem, thus you're kinda paying extra for "piece of mind. "

Go as far as you dare with the exhaust... this motor will like all restrictions you get rid off. A set of 1 3/4" headers are advisable. A good set of Headers for a C4 are somewhere around $ 450... I'm running Hooker 1 3/4" Super comp ceramic coated headers and they've worked out well for me.

As far as a custom chip for your set-up, there are a lot of places to get them, I have 2 chips, A Formato Chip and a TPIS Level 5 chip, they both work well, just need to change the timing, idle screw, FP and TPS setting between the two. There chips are expensive though at $ 500... I think you can get them down towards the $ 300 area from some other vendors such as Ed Wright... and also forum member Craig Marcho has been dabbling in EPROM chips, thus maybe he can help you as well.

If you have an automatic transmission, I recommend you run a slightly higher stall torque converter... if you plan on visiting the dragstrip frequently I recommend a Vigalante 2800-3000 rpm lock-up torque converter ( Or a Pro-Torque which also is a quality piece), however these 9.5" smaller diameter torque converters are not cheap and in the $ 700 territory. If you do not plan on seeing much strip duty, a lower cost 12" 2500 rpm SLP torque converter will be just fine. Its in the $ 300 area.

The nice thing about the above set-up is that its basically happy with whatever gears you are running, 3.73's are not necessary and I would venture to say they would probably wouldn't do anything positive for your et's anyway. 3.07-3.45 seem to perform the same.

Depending on how far you opened the exhaust and pay attention to the little things, you'll make between 350 flywheel HP all the way up to a hair over 400 HP. (280 rwhp to 340 rwhp) Due to the strong torque in the low and mid range rpm and a good torque converter you should be able to run anywhere from mid 12's to high 11's at a 3400 raceweight.... which is pretty darn quick for a street car. My gas mileage with my Stroker is pretty darn good too with 27 freeway and 17 combined. Yours with a 350 and 3.07 gears you should be even better.

Some of the little things which really don't do a lot by themselves, but when added up at the end of the day really do make a difference are items such as: Port the Superram manifold and base, clean your injectors and/or install 24lb inectors, good cold air box, March Pulley, disconnect the knock sensor, Air pump eliminator kit, MSD6A ignition.... there's others. Most of these individually will only add anywhere from 0-10 HP, but all of them can really make a difference.

The above set-up is not a secret... its a well known and popular set-up that is recommended by not just myself but many on the forum..... simply because it works everytime.

Forum Member "Ralph" runs the above set-up with the AFR 190's and he has done most of the little things and has seen et's as quick as 11.7 @ 116 when he is in tune.

hope this kinda helps.

Cheers,
Beach Bum

 

Hey Beach

I was wondering if you have ever come across any L98's Vettes that made it into the 12's with a stock longblock ? I have looked all over this forum, and don't see any examples. A couple of people are close, but not quite there.

Vic

 

Vic, i can't remember who, but i believe there is at least one forum member who claims he ran high 12s with the stock L98....well not exactly stock; but just simple air flow improvements and a good converter.

 

Hi Vic,

I've never heard of a truly stock L98 in the 12's... but I think its doable.... the following is a brief breakdown of what racing buddy and forum member 90vette has done: (I don't think he has internet access anymore though)

When I first met him he had: Cold air box, airfoil, Magnaflow mufflers, hypertech coil, AC delco rapid fires, K&N, auto, 2.59 gears and he was running right around 14.0 @ 97 with 2.0 60 foots.

Then he added Nitto Drag radials, 52 mm TB, ported plenum, AFPR, MSD6A, 8.5 mm spiral pro wires, 2.5" exhaust pipe all the way back, High flow cat, eliminated the pre-cats and he ran a best of 13.5 @ 101 with 2.0 60 foots With a 13.6-13.7 avg. He also experimented with an aftermarket chip, but it seemed to slow him down, so he scrapped.

He then installed my old 3.07 gears: Which still left him with a 13.5 best... I think he averaged about 1/2 tenth better with them vs the putrid 2.59's.

He then installed a Vigalante 2600 rpm converter: Which gave him a best et of 13.17 @ 102 (best mph was 103 I think) with a best 60 ft of 1.77 He averages right around 13.3 @ 102 nowadays.

Point to all of this, in my opinion, if he eliminated the single cat, slapped on skinnies and/or headers, I think he could see 12.9 @ 106 mph with an untouched internal motor, unless you count the removal of the ridge in the plenum entrance or the 52mm tb as a internal motor modification.

His is the best running L98 I've seen out here.... most others are 14 second racecars.

Just food for thought.

later
Beach

 

Thanks for that great example Beach.

With a stock long block, I meant more in terms of stock heads & stock cam.

So my idea is to use the stock long block with an aftermarket (Accel) TPI base & runners. Also I want to run a aftermarket Ypipe with no main cat.

I have run a couple of times this summer in crazy heat and my times have been in the 13.4 to 13.6 range.

I want to hit 12.9's in cold air.

Vic

 

I have seen a 91 vette at the track that was running 13.0 with the usual bolts ons, headers, 1.6 RR, SR, and Drag radials. His luanch wasn't all that impressive either, I hung with him with my street tires and a 1.9x 60' I think with a good torque converter and luanch he could have run 12's.