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1991 c4 corvette L98 engine questions, options, mass confusion.

General engine tech -- Drag Racing to Circle Track

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midnightbluS10
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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by midnightbluS10 » Sun Sep 01, 2019 9:12 pm

SpeierRacingHeads wrote:
Sun Sep 01, 2019 8:35 pm
midnightbluS10 wrote:
Sun Sep 01, 2019 8:30 pm
Good thing that isn't a C4 :mrgreen:


Did you already sell that engine you had listed for like $2k on Facebook, Chad? You think it made 300?
Yes, sold it. I think it made more than 300hp
I figured it would go quick. Nice!

Back to your regularly scheduled topic...
JC -

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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by SpeierRacingHeads » Sun Sep 01, 2019 9:13 pm

Orr89rocz wrote:
Sun Sep 01, 2019 9:00 pm
peejay wrote:
Sun Sep 01, 2019 8:44 pm
midnightbluS10 wrote:
Sun Sep 01, 2019 8:30 pm
Good thing that isn't a C4 :mrgreen:


Did you already sell that engine you had listed for like $2k on Facebook, Chad? You think it made 300?
I'm no expert, I'm not even a never-was-pert, but I had more fuel injector than that and didn't even make 275 at the clutch before the injectors were running static. Unless I'm doing my math wrong again.
I’ve seen 350 whp on 24’s but it all depends.

But chads combo should be closer to 375 whp imo but i thought he had bigger injectors
I have a set of Bosch 0280-555-715's I got from Motorwest Performance.

This sheet came with them.

24lbs/hr @ 43.5psi
25.7lbs/hr @ 50psi
27lbs/hr @ 55psi
28.2lbs/hr @ 60psi
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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by MadBill » Sun Sep 01, 2019 11:05 pm

I'm amazed no one has suggested headers (just because) plus a small blower.
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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by BOOT » Sun Sep 01, 2019 11:50 pm

MadBill wrote:
Sun Sep 01, 2019 11:05 pm
I'm amazed no one has suggested headers (just because) plus a small blower.
I almost said SC it but fuel system, tuning and trans made me keep it simple.
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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by gmrocket » Mon Sep 02, 2019 2:27 am

that slug needs gears. it probably has the stock 3:31 that came in the manual cars...with two overdrive ratios and final being .5, you can still do 150 mph with 4:10's and only be turning barely over 4000

your overall first would go from 8.87 to 10.99

best bang for the buck in that car..to get the same acceleration from engine mods alone, you'll probably spend 5 or 10 times the $$ to get it done

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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by Bill Chase » Mon Sep 02, 2019 8:41 am

Car has the 3:45 gears, at least according to the rpo build list, I suggested a blower, this is a joint father son project for my recently retired father.for a lot of reasons he is against forced induction.

Think a solit 10 to 1 383 shortblock, lt4 hotcam, headers, and aftermarket runners, ported base, with the right injectors and a tune would put this car over 300 rwhp with a nice fat torque curve??

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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by Bill Chase » Mon Sep 02, 2019 8:45 am

Also, no emissions checks here, so egr, a.i.r. injection etc can go. Big thing here is keeping the outward appearance of OEM, meaning all guage and ac etc work. Any intake setup is fine provided if can be tuned with the OEM computer, obviously with a new prom burnt and time on the dyno.

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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by peejay » Mon Sep 02, 2019 10:27 am

Bill Chase wrote:
Mon Sep 02, 2019 8:45 am
Also, no emissions checks here, so egr, a.i.r. injection etc can go. Big thing here is keeping the outward appearance of OEM, meaning all guage and ac etc work. Any intake setup is fine provided if can be tuned with the OEM computer, obviously with a new prom burnt and time on the dyno.
EGR and AIR don't hurt power, though, so there's no reason to remove them unless any aftermarket parts can't accomodate them.

EGR also helps fuel economy in the 99.9% of the time you aren't looking for max power, and if budget is a concern then fuel economy should also be a concern. The difference between EGR functioning and EGR not was about $400 in fuel per year on the last car I owned with EGR. Every bit counts.

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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by gmc406 » Mon Sep 02, 2019 10:40 am



Did this in my 91 GMC 1/2 ton. 19/lb injectors feeding my 406. Will literally do 20mpg with the cruise set a 70mph, a/c blowing in my face while listening to my favourite AC/DC song


3.73 rear gear and a 700-r4 with a 2400 stall. Peak power at 5300 and 5500 shift

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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by Orr89rocz » Mon Sep 02, 2019 11:26 am

Bill Chase wrote:
Mon Sep 02, 2019 8:41 am
Car has the 3:45 gears, at least according to the rpo build list, I suggested a blower, this is a joint father son project for my recently retired father.for a lot of reasons he is against forced induction.

Think a solit 10 to 1 383 shortblock, lt4 hotcam, headers, and aftermarket runners, ported base, with the right injectors and a tune would put this car over 300 rwhp with a nice fat torque curve??
Typically a cam that big on a good 355-383 with aftermarket tpi parts will do 300+ whp and alot of torque
I would suggest a FIRST tpi system as its the best bang for buck out and old tpi parts are hard to come by

Last one i did was using tpis bigmouth base and arizona speed and marine large tube runners. Afr 180 heads and lt4 hotcam clone by lunati. On stock shortblock that had some blowby out the oil dipstick it made 272 whp and 351 wtq i believe it was. Honestly expected 300 whp but oh well. Shortblock may not have had best condition cylinder seal idk. But ran great. Felt like stock manners but alot more power and torque. 87 maf system.

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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by BOOT » Mon Sep 02, 2019 11:27 am

Bill Chase wrote:
Mon Sep 02, 2019 8:41 am
Car has the 3:45 gears, at least according to the rpo build list, I suggested a blower, this is a joint father son project for my recently retired father.for a lot of reasons he is against forced induction.

Think a solit 10 to 1 383 shortblock, lt4 hotcam, headers, and aftermarket runners, ported base, with the right injectors and a tune would put this car over 300 rwhp with a nice fat torque curve??
TPI intake is kinda too small for a 350 let alone a 383, unless you desire low end galore. The TPI was designed for a 305, gm almost got rid of the 350. I like the TPI for a mild street 305/350 but it is the most co$tly low power intake there is! I have a modded TPI intake on my C4 but if I didn't have the stock unported heads, stock exh manifolds and stock cam I'd use a diff intake.
Channel about my projects https://www.youtube.com/user/BOOT350V

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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by SpeierRacingHeads » Mon Sep 02, 2019 11:33 am

BOOT wrote:
Mon Sep 02, 2019 11:27 am
Bill Chase wrote:
Mon Sep 02, 2019 8:41 am
Car has the 3:45 gears, at least according to the rpo build list, I suggested a blower, this is a joint father son project for my recently retired father.for a lot of reasons he is against forced induction.

Think a solit 10 to 1 383 shortblock, lt4 hotcam, headers, and aftermarket runners, ported base, with the right injectors and a tune would put this car over 300 rwhp with a nice fat torque curve??
TPI intake is kinda too small for a 350 let alone a 383, unless you desire low end galore. The TPI was designed for a 305, gm almost got rid of the 350. I like the TPI for a mild street 305/350 but it is the most co$tly low power intake there is! I have a modded TPI intake on my C4 but if I didn't have the stock unported heads, stock exh manifolds and stock cam I'd use a diff intake.
The OEM TPI is great for a street rod. It has a timeless classic look, and some might say ahead of it's time. However performance wise it's a disaster, IMO. The bottom isn't even big enough to match the factory head, and you can't port it big enough without weld.

Mini Ram all the way or something similar.

I sold my OEM on eBay for $300.
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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by Bill Chase » Mon Sep 02, 2019 3:44 pm

I know I sound like I am just bench racing, truth is I have the car, fuel economy is not a concern, and this isnt a budget build per se, all told there is about 9 grand to put into this car it needs tires, some shocks and basic maintenance stuff done, the big criteria are keeping ac, cruise, and not having something so wild that it cannot be tuned adequately with the stock computer. So exceeding 4 grand isnt that much of an issue, and I have no illusions, what starts as 4 grand ends up being 6 grand before the car is drivable,

Like mentioned previously, too much info from bench racers and internet users ( which is why I came here)

Perhaps a better approach would be to pose the question like this... if you had a customer that wanted to add 75-100 hp to a 1991 c4 corvette 6 speed car that runs good, has solid compression on all cylinders. Must keep ac, cruise, and forced induction is not an option, furthermore wants to avoid the additional costs of an aftermarket efi setup, and the nitemare of integration to the c4 bcm, what would you suggest.

I mean basically I can port the stock heads build a stout 383 shortblock, or do heads, cam, intake, tune on the l98 stock shortblock.

How would you 3way your customer? I keep telling dad even 270 rwhp is a lot, but he is hell bent on a solid 300 rwhp.
I just have info overload, what would one of you fine engine builders do with a starting budget of 4 grand for a customer with these goals?

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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by SpeierRacingHeads » Mon Sep 02, 2019 3:56 pm

Bill Chase wrote:
Mon Sep 02, 2019 3:44 pm
I know I sound like I am just bench racing, truth is I have the car, fuel economy is not a concern, and this isnt a budget build per se, all told there is about 9 grand to put into this car it needs tires, some shocks and basic maintenance stuff done, the big criteria are keeping ac, cruise, and not having something so wild that it cannot be tuned adequately with the stock computer. So exceeding 4 grand isnt that much of an issue, and I have no illusions, what starts as 4 grand ends up being 6 grand before the car is drivable,

Like mentioned previously, too much info from bench racers and internet users ( which is why I came here)

Perhaps a better approach would be to pose the question like this... if you had a customer that wanted to add 75-100 hp to a 1991 c4 corvette 6 speed car that runs good, has solid compression on all cylinders. Must keep ac, cruise, and forced induction is not an option, furthermore wants to avoid the additional costs of an aftermarket efi setup, and the nitemare of integration to the c4 bcm, what would you suggest.

I mean basically I can port the stock heads build a stout 383 shortblock, or do heads, cam, intake, tune on the l98 stock shortblock.

How would you 3way your customer? I keep telling dad even 270 rwhp is a lot, but he is hell bent on a solid 300 rwhp.
I just have info overload, what would one of you fine engine builders do with a starting budget of 4 grand for a customer with these goals?
AFR 195cc heads, Big runners and aftermarket lower can be found on EBay or Third Gen sitr, camshaft. Use the stock L98 bottom end. Maybe a 58mm TB. You spent $4K and have a nice engine.

Then you will need gears, and a few other mods.. :)

I just found out the hard way a stock L98 isn't worth anything. I just sold a ported 113's, new stainless rockers, LS valves, new HYD cam, new lifters, complete 350 with a conventional manifold for $2000. Sucks but needed to go.
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Re: 1991 c4 corvette L98 engine questions, options, mass confusion.

Post by BOOT » Mon Sep 02, 2019 4:11 pm

SpeierRacingHeads wrote:
Mon Sep 02, 2019 11:33 am
The OEM TPI is great for a street rod. It has a timeless classic look, and some might say ahead of it's time. However performance wise it's a disaster, IMO. The bottom isn't even big enough to match the factory head, and you can't port it big enough without weld.
A bit harsh, the problem is most don't build to it's strengths and try to make it do what it won't. Still most the time I try n caution anyone not to go too big on a combo piece they just go bigger! People always think my C4 is a LT1 car cause I beat basic moded LS cars and it's fun to pop the hood n show them the TPI.
Channel about my projects https://www.youtube.com/user/BOOT350V

I know as much as I can learn and try to keep an open mind to anything!

If I didn't overthink stuff I wouldn't be on speedtalk!

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