olefam

I'm just toying with this idea right now. First, I'm not a mechanic, but I have some skills and some tools and some minor repair/maintenance experience. My goal is to get a '91 L98 from 250 HP up to approx 300 HP. Since I don't have this car yet, this concept is pure speculation. But perhaps someone on this forum has done something similar.
1) Would a mild street grind cam, roller lifters, and roller rockers be hard to put into this engine?
2) Would the engine have to be removed to put in the cam, or could the radiator be removed to get the room needed to pull the cam?
3) I would like to pull the heads, resurface the seats, and replace the valves and springs for reliability and better breathing. Any special concerns I should be aware of? Any reason why the engine couldn't remain in the frame during this process?
4) Are the aluminum heads used on this engine free breathing from the factory, or do the ports need to be cleaned up or polished?
5) I would like to use the stock intake plenum, injectors, throttle body, etc. Is the factory unit already at its limit, or will it flow more air if the engine gets the cam?
6) I would like to use either the stock exhaust manifolds or shorty headers. But I would probably add an aftermarket cross-over pipe and free flowing mufflers.
With these modifications, would I get reasonably close to 300HP?
Thank you for your thoughts.
Glen

redwing76

Vortech!

vader86

91 heads are fine, capable of 350hp untouched. Although porting them will help you get that goal.

The Engine doesnt have to be removed, but everything else in the way does and then you have to tilt the engine up to remove it. Scorp did his with the engine in the car.

Adding longtubes will be the easiest way without a cam change. Full headers and exhaust should net about 20-25hp at peak.
1.6rr, 10-15hp....fully ported plenum/runners/intake should get you very close to that goal of 300.

If you dont go with longtubes, you might have to change cams to something like Tpis ZZ9 or Accel 211. Then you would need a chip change, and also all new valvetrain parts on the heads.

jdog0411

Or you could save yourself the trouble and get an LT1 Corvette. I guarantee you'll get to 300 HP that way. :D

c4cruiser

How many miles on the engine?? If you are going to replace the cam and do some head work, you may as well pull the whole thing to do the rest. Consider going to 383 CID with a good set of rings and pistons and do a balance and blueprint. I Fyou go to displacement above 350 consider a 52mm throttle body or 58mm for 383 0r higher.

The factory heads should be good with porting, polishing and bowl cleanup and add a good set of springs and 1.6 roller rockers. Cam could be a ZZ4 from GM. See if you can find a SuperRam to replace the factory TPI setup. Otherwise you will need to do some port matching to help with airflow. The factory design is one of the limiting factors in getting big HP numbers.

Hooker Super Comp headers (#2149) and a free flowing exhaust system should round out the package. The factory manifolds or most shorty headers won't perform like a set of long tubes will.

There is computer software available that will allow you to enter various mods and engine combination and provide virtual dyno numbers. Summit Racing should have something like that.

With the engine out, you also get a chance to clean everything up and while you're at it, have the radiator cleaned and inspected. Modded motors will put an extra strain on the cooling system so get that part done too. Check out all the engin accessories at the same time. It's a PITA to have to back a few weeks after you get everything buttoned up and replace the water pump, starter or whatever else can go wrong.

Depending on what transmission you get with the car, consider beefing upthere too. For a 6-speed, a new clutch/pressure plate to handle the increase or for an A4, shift kit and maybe higher stall converter if drag racing is in the cards.

50HP is doable with just a mild cam, head work and headers, but if the car you're considering has lots of miles, it may not last with the mods, especially if you're going to be hammering on it.

TA

Many have gotten 300hp out of their L98s relatively easily. My rwhp/tq numbers and mods are in my sig. My heads and cam are stock. I haven't done the conversion for the hp/tq, but I'm sure it would be more than 300 at the crank.


[Modified by TA, 6:13 PM 1/25/2004]

Vic'89

You better get more than 50 HP from a Cam/Heads/Headers combo.

Vic

Kieran Cox

:sad: Makes me think of all the time I spent fixing up my '86 L98 that left me in a ball of fire!. Anyway here's what you gotta do:

1. Pull the engine. Believe me it is worth it. You can spend untold hours fooling around with clearances or just 3-4 pulling it out so you can do the job right. In fact that engine comes out so easy there is no point doing much mod work with it in the car. Save your back! Pull it out and stick it on an engine stand. Hell, I'll talk you though it.

2. Order yourself a Super-Ram intake and big-breather base $1300, a 52mm throttle body $200-300. This mod alone is worth gobs of power on even an unmodded engine. DON'T upgrade cam or heads until you get more air in that sucker. The long tube runners on the L-98 suck choke it to death. The LPE Super-Ram set-up kicks behind.

3. Do the coolant bypass. Cheap trick worth 2-5hp and the intake stays cooler.

4. Gut the MAF sensor if it is a MAF system. THis is worth a few hp too.

5. Get the K&N air filter and cut the air lid, another cheap way to get 2-5hp.

6. Lose the mufflers, go with straight pipe. The 3-way cat system is plenty to quite it down those mufflers in the back are only adding weight and heat to the rear area. They only do anything at WOT anyway.

7. 1.6 in/out Crane Roller Rockers. Trust me.

8. Get a slightly more aggressive cam, the ZZ4 is a good choice.

9. Go to the Chevy parts counter and order the Canadian EPROM and the Austrailian one. They are worth a few more HP too at a cheap price. I think they are like only $30 each.

10. That should be enough for a start, put it all back together on the stand, nice and clean like. Then re-install the engine. You should be at about 300rwhp.


Of course if you want to spend some more money you can get those AFR 190 heads and then really hold on!!!!

The best way to go is to start off with a good rebuild. You may get bummed if you spinn a bearing and then have to go pull it out to spend more bread on a rebuild. If you wanna go that route post some more and I'll be happy to make some recommendations for pistons/rings, bearings, oil-pan, oil-pump and all the other nice TUFF-engine stuff!!! :D

scorp508

Go for at least 300 at the wheels. :smash: :steering:

65Z01

If you do heads, cam, headers (and exhaust) along with a BM intake base & LT runnners plus some odds & ends you should get a '91 L98 to about 370chp and it will be very streetable.

Check out the results of mods to an L98 page table on my site to see what various engine mods can do and take a look at what Vic'89 has done (well over 300chp) with stock cam & heads on an '89 L98 (stock 240chp).

MrSpeedyBob

You'd have some electronic help controlling wheel spin also. Now if you wanted 800 I'd start with an L98 since it's a 1'st gen block.

olefam

Thanks for all the great feedback. As I said, this is in the "Dream stage" and everything is possible. My concerns were that I be able to spend my limited resources on go-fast parts and do the labor myself. I am not sure that I would want to tackle a complete engine rebuild. But I agree that after all is said and done, it may be the best way to go. Also, I imagine a time may come when an engine would have to be rebuilt because it wore out. That may be the time to come up with some additional dollars for go-fast parts versus stock parts. We'll see...
Thanks again.
Glen

ZF Six

320hp, 454 ft, lbs. of torque, according to my calculation :D

Bilyk

does anyone have any flow numbers for the stock TPI? how much power can it support with the stock long runners? I also need to bump up the power a wee bit but want everything to look completely stock
i was thinking about dart iron eagles (85 vette) with a lumpier bumpstick, exhaust, and the free mods

metropolis

One of my fraternity brothers got to this place with his IROC, with just a straight bolt on Paxton supercharger kit. He had a flowmaster catback and 3.73s as the only mods. The Paxton was a Saturday job, very clean, with no messing with the motor. That thing would scat, and no messing with rebuilds, head swapping, or cams.

I don't know if Paxton makes a kit anymore, but I think Vortech does, but it requires pluming oil lines and such, so it's probably not as clean an install.

To tell you the truth, the 3.73s made the car fell like it had another 80hp. So if you want subjective power, start with the gears.

scorp508

An L98 with anything more than a 3.45 is useless unless the engine has been modified to enable more power in higher RPM ranges.

Give us a budget and we'll help you squeeze the most out possible. :yesnod: I'm at 380hp & 445ft/lb & spent $3200. Then another $1400 for nitrous and ignition which when I finally get to use it should hopefully make around 500hp & 600 ft/lb.

olefam

The question about budget is very appropriate. I want to try to pay for this as I go. That's one reason why I thought the "components" approach would work. For example, to add roller rockers I don't think I need to change anything other than the rockers. And since they should have a pretty long lifespan, when I am ready to tackle polishing the ports in the heads, for example, the rockers wouldn't add any additional expense, as I would already have bought and paid for them. Same would be true of the camshaft, valves, springs, etc.
What I want to avoid is paying for the same thing twice. If I were to pull the heads and only polish the ports, I would have time and effort and gaskets, etc. for an incomplete job. Why imcomplete? because at some point I would want to either do a valve job, or replace the valves, and I would have to go through the time, expense, etc. of pulling the heads again.
That's also the reason why I believe that pulling the engine would probably be the ideal method of doing this project all at one time. But I don't know if I want to wait till I have $3,000. or more before I start seeing some power gains. Does this seem like a good plan to anyone else, or is my thinking a little "off" ?
Glen

scorp508

I'll tell you what I did. I made a plan and started purchasing parts as I had $ available. I'd buy a cam here, some heads a few months later, an intake when I found one I liked. I think I spent 1.5 years buying parts. I waited for good deals and snatched them up. Thats how I spent relatively a good amount of money less than some other people have to get the same thing. I ended up with a pile of parts waiting to be installed and then installed it all at once.

Considering the order of your implementation is a great thing to do. I also did not want to waste time, money and gaskets pulling the heads twice because i could only afford install heads/intake and then a cam down the road.

The Dingo

Australian EPROM? Does GM make one of those? :confused:

On the main subject, with my mods (see sig), I have run 254.9rwhp. The way I figure it, that's about 309 flywheel hp allowing for 18% drivetrain loss with my six speed. Can't wait to dyno it when my headers are finished and my 1.6 rockers arrive. :)

The Dingo

:iagree: I'm already started doing the same thing for my next motor.

If I did my mods again I would start from the bottom up. I probably would also wait and install everything in one go to minimise time spent pulling things down and rebuilding several times.