Brother wants to increase performance of his 91 to try and keep up with my 98. Any suggestions?

I have an LT1...

...but I would start on the exhaust (Long tube headers, true duals, X-pipe, etc.), then look at a heads/cam package.

There ARE also a bunch of little mods that he can do to pick up a few HP here and there (ie. Underdrive pullies, electric water pump, etc.), but we're talking fairly small gains with each.

Hopefully, some of the L98 guys will speak up...

Definetly exhaust mods. The L98 has probably the most restrictive exhaust system of any C4 model. A nice free flowing exhaust system will really wake it up. The intake system is also pretty restrictive. A K&N air filter and an open air box lid will let it breathe better. There are lots of little stuff that can add up to adding some ponys. Besides what has already been mentioned. Remove the "frisbee" at the water pump pulley. That's about 10 lbs less that the motor has to spin. If it's an automatic, a high stall converter can help. Or if it has the 2:59 rear gears, a gear change up to 3:07, 3:54 or even 3:73 will really help it shoot outta the hole. (I wouldn't recommend the 3:73 for an automatic if it sees quite a few highway miles)

If you're going to open up the engine, definetly get the intake system better.
You can port the existing intake and heads and with a cam swap probably get near 300 rwhp. But, you'd have to go with aftermarket equipment to get beyond that.

I agree. Exhaust on these engines is the #1 restriction.

Long Tube Headers
High-Flow cats
x-pipe
Cat back exhaust of your choice. I like Corsa, simply because it is less boomy.

That setup would be worth upwards of 50hp. Yes, the stock exhaust is THAT restrictive.

I personally hate the TPI setup. It won't breath past 5000 RPM worth crap. I would ditch it and go with a SuperRam or MiniRam setup.

Add a cam, roller rockers (1.6:1) and life should be good. With all those mods, I see 300RWHP in your future. If you want more, then you have to mess with heads and dig deeper into the motor.

The L98 has a ton of performance available to it.

If you have the cash, and you really want to keep up with an LS1 equipped 98, it will take cash.

you are 100hp short, and a generation of chassis behind!

I would recommend the following upgrades:

performance cam

performance heads

super ram intake

This would cost a lot of $$$, no doubt, but with exhaust mods and a stock bottom end, you would be in the 350hp range in no time flat. Seriously.

The throttle response would be insane, and, with a higher torque peak, it would be a much more drivable and launchable engine (too much torque too low would cause the tires to toast and you don't do anything that resembles forward progress... that would suck :D)

This is the problem... the C4 is a GREAT chassis, but it is now the old chassis, and to make up for it, we have to have more power. The C5 can get it's power down better, we can't.

There are other things you can do to the chassis, disconnect the sway bars helps, I have been told.

Oh, one last thing to consider... gearing... if you have a stock automatic
L98, it is more then likely a 2.59:1 rear gear ratio... I would upgrade that to at least 3.31:1. Better yet, if you have the $$ (about $2k), I would upgrade to a Dana 44 with 3.45:1 rear gears.

Whatever gearing options you use, don't go about 3.73 with the automatic... beyond that, it really doesn't work well. If you have a manual, go with 4.10s and really rock!!!

If you have an automatic, a torque converter will help, too. I don't know enough about them, so I suggest you search around CF or check with the various TC manufacturers, or, call summit racing. They have experts who will really help you make a good selection.

I hope this helps you get an idea of what it will take.... Oh, and practice your driving skills!!!

Lingenfelter liked the ss 1 5/8 primary stock headers though. the cats are the real problem. check out the sosn (something old something new) tech article @ gmhightechperformace.com site for an eye opener. hint over 400 hp and enuff tq to (add funny thing)for days Also Lingenfelters book is a must read! the superram is awesome but be prepaired for poor casting and machining from accel and it's a pain to install (there are mods/ tools to make this easier though. avoid changing only one or some parts of the intake system as the gains will be marginal, think of it as a whole. accels dfi gen 7 computer has plug and play interface available for most performance cars and for your year. this is the first thing I would reccomend as the chip thing sucks so bad I would never even consider it, making changes is a breeze with a stand alone system. with plug and play you only get bank to bank fueling but it is all most street cars will ever need. the gen 7 allows for nawzz and boost also. the wide band innovate settup is cheap and will only let you down in high mileage use or 10 psi and higher boost apps by a small margin in lag times reading slightly richer than should. use for tuning and replace with narrow band for street use, or leave in permanently for richer than stock (14.7 to 1) for best power (no cats!) finally I always wrap my headers (scavenging effect and lower underhood temps. IF you do go with other than stock headers make damn sure they are ball and socket type (can add to cheesy three bolt types) exhaust leaks suck on efi. remember this block can handle almost 500 hp stock! avoid cams with too much lift for your springs and it's not always about gaining hp/tq but not losing it as well! performance is not breaking parts also Aloha