1990RS350

Hey, I'm pulling an L98 out of a 91 z28. I'm also going to stick with the TPI setup, what kind of gains would I look at with:

Air foil
CAI
52mm TB
Large tube runners from TPIS
Big mouth manifold also TPIS
1.6 RR on intake, 1.5 exhaust
Also 1 5/8 Hooker headers into 3" without a cat.

Going over everything individually, it seems I'm looking at roughly 75-100 hp.

That's after a full tune up is done.

Would 330-350 hp at the crank be overly optimistic?

Also, how much benefit is there in going to a custom chip at this point, if any?

Orr89RocZ

iTrader: (20)

I'd get a tune for that but it be more beneficial if you did it yourself with a wideband to verify and dyno time or track time.

Most L98's i've seen with those mods will put down 245-260whp depending on year. I think 265 well tuned is certainly doable and thats probably realistically 310-320 crank hp. Still good numbers for a bolt on car. run low 13's to possible high 12's with a great chassis setup on a good converter/geared combo.

Airfoil and TB likely wont do anything so you can skip that for now. Big gains will be made with the TPI components and exhaust. Tune will also add a few since theres a chance the 1.6 rockers combined with the increased air supply will lean things out abit. Good news is GM made these cars more rich to begin with, so it may lean out right in line with where it needs to be.

Only dyno/track testing will tell.

Artisan

I agree with Orr on this. I made 226 on my bolt on 305 manual car. That is pretty much the same level of improvement with a 350 car. The 350 being a natural 15 -20 HP improvement over the 305. I did mine with a mildly ported stock intake so another 15 to 20 hp with the better base? I think Orr's numbers are on the money.

Orr89RocZ

iTrader: (20)

I had an HSR on my L98 and it made 254whp running very lean. My friends 88 L98 with full TPI bolt ons was running side by side with me, so I'd venture to say he'd be in around the 250whp range too. 91-92's should have abit more power with a touch more compression but its close

1990RS350

Well that sounds good, short of cam and heads, is there anymore power to be squeezed out of this engine? I'd like to be as close to ls1 territory as possible with stock long block and internals. I was looking at tpis super l98 cam but would rather keep it stock. Thanks for the input thus far.

What about aluminum or electric water pumps?
Already wont have AC.

Orr89RocZ

iTrader: (20)

underdrive pullies with an electric waterpump could free up some hp but i dont think all the bolt ons will put you near LS1 territory..they make 300whp stock and I dont think an L98 will do much more than 270 if all goes well, but i'd be curious to see all the bolt ons maybe even 1.7 rockers and well tuned on a good condition shortblock. Could definately make good power and run in the high 12's

You will need a cam to do much more than that.

1990RS350

Alright well that gives me something to aim for then. Im going to shoot for around 300 whp. Should be a fun ride either way. Ill post back in a few months when I piece everything together. Thanks

Orr89RocZ

iTrader: (20)

try to get a before and after if you can but really focus on the after... as that is what counts. Good tune and good selection of parts will make some interesting numbers I think.

ninetyone

iTrader: (2)

how are u making 254 rwhp? i think you mean 254 at the crank. so are u saying an l98 motor with a hsr intake and bolt-ons is going to make like 320hp at the crank? That sounds like a little too much.

ninetyone

iTrader: (2)

254 crank hp is about 205 at the wheel.

SiCkRs

iTrader: (6)

He had bolt ons with the HSR, i believe. IIRC

VincentZ28

iTrader: (2)

What would really get you close to 300whp are these mods. Dyno Don 1 3/4in headers, dual cats or dual 2 1/2in pipes the that connects to a Y-Pipe near the tail end of the Trans to a 3in cat back Magnaflow system, Ported,TPIS Intake, any aftermarket ported runners, ported Plenum and a tune. This will get you close to 270-280whp. ITSMikey 89 L98 GTA G92 N10(dual cats)made 251whp with just Dyno Dons headers and Magnaflow exhaust and tune. Since the engine is out of the car, maybe pull the heads and do a valve job with mild bowl work and port match the intake to 1205 intake gasket, then you should be in the 290-297whp range with the stock cam. Headman Headers will not get your HP this high.

Also these numbers can be done if your car is an 89-92 with performance equipt G92 N10(dual cat) 240-245 rated HP. Subtract 10-20hp for 87-88 L98.

88fastgta

iTrader: (9)

im just curious how much are dyno dons headers and what kind of headers does he sell.... i may be interested in buying some..

ninetyone

iTrader: (2)

How did Mikey add 50 hp with just Dyno dons headers? Sounds a little fishy. You gotta stop saying whp. You mean at the crank.

VincentZ28

iTrader: (2)

This is WHP not crank. They are very good shorty headers. Look at the entire post I made and you understand where I'm coming from. Those other headers are restrictive and they are only 1 5/8in tubing. The HP was made with all the smog and A/C working.

ninetyone

iTrader: (2)

My car does have the N10 dual ypipe. I have all those mods except for the ported tpis intake. I also have headers and a tune

ninetyone

iTrader: (2)

1 3/4 headers? and a 3" catback? On an otherwise stock motor? What about all of your low end torque. IMO that just doesn't seem like enough motor to need an exhaust system that big.

VincentZ28

iTrader: (2)

What headers do you have? Like I said before the construction of those other shorties are restrictived.

ninetyone

iTrader: (2)

Edelbrock TES

VincentZ28

iTrader: (2)

Ok! But you didn't use the headers I mention. TES are the worse headers. If you the exact route I mention, you will see the results. I sent Dyno Don an email to see if he can post up ItsMikey Dyno graph. Did not loose any torque.

88fastgta

iTrader: (9)

im running headman long tube headers.... they are 1 5/8th in size.... how much are those holding me back compared to dyno dons headers...

VincentZ28

iTrader: (2)

Don't know! Have you dynoed your car yet?

88fastgta

iTrader: (9)

i havent actually.... i will soon... im sure my longtube headers cant possibly flow worse than short tube headers....

ninetyone

iTrader: (2)

Headers on a car adds about 10% more hp. I don't think dyno dons are some magical solution that add 50 hp

ninetyone

iTrader: (2)

sorry, guess its not so private any more Vincent.LOL I do agree tho about how it is nice to be able to rev higher into the rpm's with a better intake.

Abubaca

iTrader: (3)

Everything I've ever read about Dyno Don's headers has been good. That being said, I don't find 250 whp (on our cars) with just a full exhaust and tune to be all that amazing really. Good, for sure, but that's what I'd expect for a good set of headers, dualcats-back and a tune. Gotta remember that headers don't add horsepower, they just don't take away as much! ....the tune can be magic though!

....if you gave me a stock L98 car, the first thing I'd do would be exhaust. Second would be to check my rear gear and make sure I had at LEAST a 3.08. My car had a 2.77!!!!! I found a 3.27 9 bolt for a few hundred bucks. Then without a doubt, a new torque converter, and I say do this AFTER the rear only because the rear is so cheap and easy to do. Far more fun to be had with a TC and good gear!!!!

yaj15

iTrader: (3)

I agree with the post above. My car has a stock L98. I've gutted the factory air box and added a 52mm bbk throttle body. I also have ceramic coated 1 5/8" hooker headers, high flow cat, and 3" flowmaster catback. When I did all the exhaust work the car still had the stock trans. The headers really woke the car up all through the rev range. The best mod was putting in a stall and aftermarket trans after the stock trans pump went out. I have small stall, only 2200rpm. The converter with the other mods I did have really woke up the car even though I still have the 2.77 gears.

itsMikey

okay..yes, the numbers vince posted are correct..dons headers are without a doubt the best, really no competition. and yes just headers, exhaust and kevins tune added near 50hp for me

88fastgta

iTrader: (9)

really wish yall california guys could tune my gta... i used to live in cali about 14 years ago....

VincentZ28

iTrader: (2)

I think they thought I was making it up. Did you do a video that day? Can you post up a picture of your engine bay? Explain to them about the power and torque it makes.

Shadow Z

iTrader: (2)

This thread is making me want a nice L98 car, just to see how quick/powerful I could make it at full weight, and with a stock L98 short block.

GTA matt

iTrader: (1)

Stock L98 short block? You can go pretty far on one of those. Even with the stock TPI intake I've said it before, with shorty headers, there's not much difference in performance from one manufacturer to another. I may have gone faster with bolt ons and edelbrock tes headers then anybody else has with any other header

Going back to the original post in this thread: If you were to do everything listed there, you would have a very nice solid bottom 13, possibly 12 second full weight car with the right suspension, good transmission, gears, converter and tires.

ninetyone

iTrader: (2)

Mine weighs 3551 with me in it. Power everything, no cruise control. Ha ha

ninetyone

iTrader: (2)

idk, that seems like an awful lot from just "freeing up " exhaust. I would say it adds about 25 hp tops and that is with exhaust.

ninetyone

iTrader: (2)

Vincent, isn't Dyno don one of your friends that sells headers?

88fastgta

iTrader: (9)

i believe dyno don actually makes the headers...

SiCkRs

iTrader: (6)

Exactly what bolt ons did you have to get into 12s with only a bolt on tpi?

yaj15

iTrader: (3)

The converter is a good mod. I've still got the 2.77 gears and I have a 2200rpm stall and bolt ons. Even though I still have the freeways gears I have had good gains with the higher stall. I haven't noticed a change in the fuel economy to any great extent. Get a converter that locks up like stock one does and there shouldn't be a change with fuel economy. It may go down depending on how you drive when you get the new converter put on. The car is a lot more fun to drive with the higher stall converter though. I would have a hard time going back to stock stall now. Are you going to get the trans rebuilt to?

freaky

i hate to keep sounding like a ebl flash fan boy but in all honesty the best gains i've got come from the ebl flash an the ability to tune the engine ...

GTA matt

iTrader: (1)

Sorry, just realized I never PM'd you back the other day. Back when I had a bolt on motor I had Edelbrock tes shorty headers, dual cats, and flowmaster american thunder 3" catback. I also had a 52mm TB, underdrive pulleys, 1.6 rockers, adjustable FPR, 3.73's with the stock converter and B&M transpak. There was no porting done on the intake. I knocked down the little bump behind the throttle body in the plenum, but that was it. With that setup I went 13.12 in good air on stock size drag radials mounted on the stock wheels. Also had a Spohn torque arm and LCA's and relo brackets. I removed the ac, ps, air pump and installed an electric wp, removed the spare tire stuff and added the pro stars and slicks, a very tight B&M converter and went a 12.85 in good air.

Thirdgen89GTA

iTrader: (5)

Yes. 350chp would be overly optimistic. I'd estimate you'd be around the 300-315hp range at the crank. I'd spend the $$$ from the 58mm TB on something else though. You won't be putting down enough power to make use of the 58mm TB. You won't lose power, but you really won't gain anything either.

Your largest gains will be the the CAI, plenum porting, larger runners, base, and the exhaust. The 1.6RR's will give you slightly more duration and more lift but not much power there. The Air Foil also is a very small gain.

I'm putting out about 320-330hp at the crank with my B-body LT1. It has the small baby cam. Stock to Stock my LT1 has better heads and made about 15hp more than the best L98 in the thirdgens. I expect you'll see similar gains as me.

You should be able to run mid 13's on average street tires. I expect with DR's you could get lower. But I wouldn't expect it to trap more than low 100's. Probably in the 99-101mph range. This is roughly at 1200ft elevation which is the average of what runs I've made.

I did know of a 89 Formula 350 that had every bolt-on known to thirdgen F-bodies. With a Vigilante 9.5" 3200 stall, Jimmy's Transmission (local guy VERY good with 700r4s) and slicks he was trapping 13.0x @ 99mph all day long. I can't remember what the Air was like that day, but he might have broken 12's @ 100mph with better air. This car was in pristine running condition. It was the FASTEST L98 thirdgen I've ever seen that had full interior, functioning AC, and all the bolt-ons.

Thirdgen89GTA

iTrader: (5)

Good running STOCK l98's make 200-215rwhp. I have video proof too for what its worth. Yes, I do have the full video, no I don't have it in better quality.

http://home.comcast.net/~thirdgen89g...rottleDyno.m4v

GTA matt

iTrader: (1)

Found these floating around in my photobucket from 6 years ago. Obviously it spun on the .22 run. This was a full weight gta, Nothing removed. Stock Firebird air intake lol.

SiCkRs

iTrader: (6)

Thanks for being specific im half way down of those bolt ons hopefully i get good results like those

itsMikey

the numbers dont lie >.>

ninetyone

iTrader: (2)

Thats funny i just looked at some Slp 1 3/4 Headers,which are similar to Dyno Dons. They say they help free up 12-20hp and the Slp catback helps add another 10,but of course,they probably ran that test on a modified car anyway,which always gives better results. No header adds 50hp ,not even with full exhaust. On our cars the Slp systems probably free up more like 25hp if even that.

ninetyone

iTrader: (2)

Look at it like this, on a stock L98 350,aftermarket heads add 20-30 hp. Now add headers,exhaust and better intake and you may end up adding 100hp OVERALL to your car. That is how it works. So, i can beleive that adding headers to a car that has just aftermarket heads would then give you about a TOTAL 50-80hp increase.

yaj15

iTrader: (3)

How much power and torque will a ported plenum, larger throttle body, aftermarket intake runners and base add to a stock L98?

Thirdgen89GTA

iTrader: (5)

Yes, some headers can add that much with a full exhaust. LT1's and LS1's are well known to make serious gains with LT's and a cat-back.

Mostly because the intakes already flow so well compared to a stock TPI. The exhaust is the greater restriction.

ninetyone

iTrader: (2)

Aftermarket intake on an otherwise stock car might add 20hp. Not sure if it would be much fun on a stock car tho,unless you are at WOT .Larger throttle body will add nothing unless you have a need for it,like if u have better heads,cam,intake together. Ported plenum on a stock car might add 5hp