I've got a 89 coupe with 76K miles, overall it still runs good but has a couple small issues.

• I've got a small coolant leak from a hose and I've considered replacing all hoses as most are original.
• I also have a few annoying oil leaks here and there
• Oil pressure is a bit low at idle, due to wear I assume.
• Finally, I'd like to just put some spunk back into it

I did use the car in AS Solo but now I've got a 04 Z06 for SS and don't plan to run the 89 anymore. But as you can imagine the 89 feels downright slow now. I can mod the engine a bit now not worrying about stock classing.

My thought is a rebuild of the existing L98, I'd like to do some of the work myself to manage the cost, but I'm not the complete rebuild guy! I'd feel good replacing the heads/intake/etc. But I'd like the bottom end professionally done.

As the stock spec on the motor is 245HP I'd like to think I could get it to 300HP without going crazy, don't really want to change exhaust, I want it very Daily driver, AC working good and predicable idle.

OK, any thoughts on what direction to go and the associated costs.

 

The single most thing you can do to help the wishes of both you and your car is to get rid of the FI and put a good ole fashion Edelbrock dual plain intake and maybe a 670 avenger holley on it. Youll bring the HP up dramaticley to about 340 and increase your dependability by about 100% over and 89 with on going computer problems.take it and go back to the ole days, thats were your performance and dependability is.

 

Wow interesting response.

I should have noted that I've owned this C4 since 1990 at 7K miles and in those 17yrs or so I've had next to no problems with the engine. Dead batteries due to sitting, wouldn't start due to a bad battery cable, and 1 dead ECM about 10 years ago, couple alternators???? My experience with this base setup has been solid, no abnormal issues. Maybe mine was built on a Wednesday :-)

Also, right now in mixed ATL driving it gets 19.7 mpg, not to shabby. I would expect that to drop with ditching the FI and ECM.

Thanks for the input, I'll watch for all ideas coming in, I'm not in a rush.

 

Your bottom end should have a lot of life left in it at 76k miles. I wouldn't worry about the low oil pressure reading at idle unless there are other problems (knocking sounds, warning light flickering, etc.). I do a leakdown test and see if the rings are holding, but they should be fine, too, if you've maintained the car well.

For your goals, I'd just do a cam and exhaust and save the rest for later. If keeping TPI, don't go wild with the cam - somewhere around 210 duration. Put LT4/ZZ4 valve springs on and shoot for around .500 lift. At a minimum, replace your cats with modern hi-flow units (or ditch them), or do the headers/dual exhaust thing for more bang. But, you really need to improve the exhaust if you're improving breathing since the stock L98 setup is pretty wimpy. A stock LTx system is cheap and a big improvement. You could probably install all the above yourself for $5-600 and be around 300 crank hp.

If that's not enough, you need to change out the intake, go to an even bigger cam, and then get into heads. Cost will go up a lot and you'll start to lose the good street manners you want to keep.

 

Cam, full 1.6 RR's, and better exhaust and you are there. It is important to fix the L98 exhaust. My exhaust looks/sounds almost stock but isn't.
High flow cats and dual outlet mufflers will help.

 

My dyno pulls and trap speed showed 298chp and I hadn't opened the engine and still had stock headers.
-2 1/2" front Y, hi-flow cat, hi-flow cat-back
-160deg T-stat and fan switch
-cut lid with K&N
-toss the frisbee from the water pump pulley
-under drive crank & over drive alt pullies
-1.6:1 RRs, springs, etc
-cut back spark plug electrodes
-AFPR set to 48psi
-base timing at 8deg BTDC

If you more street feel add a TransGo shift kit and 2400rpm TC.

If you do FL headers, dual cats, heads, cam and some intake mods you will be looking at maybe 375chp or more.

 

I get most everything people are saying here and most of it makes sense to me.

I agree with improving the exhaust, doesn't help to put more in if the exhaust is the bottleneck, I'd probably try to stay away from headers and just go with high flow cats and true duals.

ditching the frisbee is a definite.

Mild increase in cam makes sense as I would prefer to stay with the current intake/TPI, even though it isn't the greatest.

What does going to the 1.6:1 RR accomplish? is this a more aggressive ratio giving more valve lift? other?

Why change the stat to 160, sounds odd in a performance discussion?

AFPR set to 48psi? I assume this is a higher level to increase the performance of the injectors?

Thanks great info here!

 

1.6 RRs are a cheap and easy mod. You should install better springs when you are in there. The RRs should add 10 or 15 CHP.

Ditch the frisbee and install downsized March pullys. I like the power and Amp series. That should give you another 10 HP.

I would not jack up your fuel pressure.

You could port your plenum and get a set of high flow runners. TPIS will port your plenum for $100.00. I would install true dual exhaust with high flow bullet cats. This should get you another 30 HP

Before you start any rebuild check your compression. Your engine may be OK.

 

Quote:
Originally Posted by 87stocker
QUOTE ;Based on my experience with my '89, I agree with the previous posts that indicate 300 rwhp is approaching the upper limits with a stock cam. My car made 268 RWHP/345 RWTQ with the stock cam. I have an ACCEL base, large tube runners, ported plenum, 1.6 rockers, and high flow exhaust. I did do a clean-up port on the heads but I still have the factory shorty headers and an iffy tune (old TPIS stage 4 chip). Long tubes and a proper tune would most likely have gotten me right around 300 rwhp. My car was reasonably fast at the dragstrip (13.3@105 in 90+ degree heat), but it really shone on the street and at the race track. The car was just awesome coming out of corners.

Keep in mind -- the TPI system is designed to make tons of torque. A highly modified TPI may make "only" 300 rwhp, but its average horsepower throughout its RPM range is very high because of the torque curve. For example, my car made a peak RWTQ of 345 at 3400 rpm, but it also made over 300 ft-lbs at the wheels between 2000 and 4500 RPM. There were very few cars on the road that could stay with me in "real world" conditions.

The trick to making a TPI run really strong is to carefully choose your parts combination so that all the parts enhance the torque producing potential. Even with high flow intake parts, the power peak is going to occur at 4800-5000 RPM. Big cams and heads really won't make a difference because the total amount of air flow will be limited by the long intake tubes. If you choose to upgrade the base/runners/plenum, you should also plan on a set of long tube headers and a tune that is optimized for your combo. This combo should be capable of high 12's with the stock heads/cam and will be an awesome daily driver.

Based on my experience with my own car (hindsight is always 20-20), I would do upgrades in the following order and grouped as shown. These recommendations are based on using a stock L98 short block. Please note that a tune will be needed with each successive grouping:

High flow exhaust
LT headers

Big mouth base
High flow runners
Ported plenun
1.6 rockers

Ported 113 heads or 180cc aftermarket heads
Cam (no larger than a LPE219, aim for .500-.550 lift)

Wider rear wheels and sticky tires to handle all the torque



Here is what i think you want!!!!!!!!!!

 

With that low mileage, I would do a basic rebuild which is a rering and new bearings. Maybe a little cylinder hone, but no need for a bore. Should suffice for another 100k miles until the next time.

 

400 HP is pretty nice with my combo...and isn't really that radical.

While you MAY get away with a hone, a .030 over bore can correct casting shift and square the bores to the crank.

Critical when it comes to getting the most power and the least amount of stress to the bottom end.

I did my upgrades all at once. Sent the motor to the shop and got it fully assembled and ready to drop into the beast.

Check my web site in the signature...good luck!