Hi all
New to forums here. About 27 years ago i bought a 1988 5.7 359 iroc z. Loved it but had to sell it a few years later do to needed a car to drive all year long for work. I payed 4500 at the time and dropped about 3000 into it.
Now with kids in college out of the house I'm looking for my gen 3. Love gen 1 and the new gen but pipe dream to afford. I have the opportunity to purchase an 87 5.7 with minor rust on rear wheel well from what i have seen in pics. Price was $7000 got it down to $5500. Or 1990 mint but 305 for a $1000 less. I'm leaning obviously towards 350 since closest to what i had. Wanted to see what other bowtie lovers would do. Sorry long winded.
thanks

 

Rust = Run like Hell

If you can see rust in the pics on the rear fenderwell then it's all over the car in other places and for sure underneath it. Unless your day job is a paint and body man and you can do all the repair work yourself for cost and your time run away from it.

Why a 90+ is better then a 85 to 89.

(1) No mass air flow sensor. Can be problematic and hard to find a replacement MAF that is properly calibrated. No MAF burn off relay or other wiring that goes with a MAF system. 90+ is Speed Density and a simple, readily available MAP sensor is easy and cheap to replace.

(2) No 9th cold start injector system. 85 to 88 have CSI. 89 MAF and 90+ MAP doesn't. Can't get them new and don't know if available aftermarket.

(3) 88+ has a serpentine accessory drive belt system. 87 down is multiple multi-rib belts or V belts

(4) 87 IROC-Z will have a Borg Warner 9 bolt rear axel with a cone style limited slip and a 3.27 gear ratio with Delco-Moraine rear disc brakes. 90+ will have a GM 10 bolt 7.625" ring gear with 28 spline axels with limited slip, 2.73 gear ratio, and drum brakes. BW 9 bolt rear axels have harder to find parts and probably more expensive. Thousands of toothless rednecks can rebuild a GM corporate 10 bolt rear axel but look at a BW 9 bolt and go WTF is that. They have a problematic cone style limited slip differential. Delco-Moraine rear disc brakes SUCK. Drum brakes are better than Delco-Moraine rear discs. The later model GM 10 bolt like is in the 1990 IROC-Z has an easy upgrade path to a better limited slip differential and 3.42 gear set out of a late model 4th gen F body. Not the entire 4th gen rear end. Just the Zexel Torsen limited slip differential with 3.42 ring and pinion gears.

(5) Nothing about a 3rd gen F body was designed for a 5.7L L98 (350) TPI engine. The 5.7L L98 engine was an afterthought. GM just slapped a 2 bolt main cap, cast iron head L98 long block with the 5 speed manual transmission camshaft from the 5.0L H.O. TPI engine under the TPI system with bigger injectors, different knock sensor & ESC module, a tune for the bigger engine, and the same exhaust system as a 5.0L TPI engine and sent it down the production line with some 5.7L badges on it.

1987 5.0L H.O. camshaft (305) LB9 TPI engine = 215 HP@4400 RPM & 295 FT-LBS@3200 RPM vs 5.7 (350) L98 TPI engine = 225 HP@4400 RPM & 330 FT-LBS @2800 RPM. Wow 10 more horsepower and 35 foot pounds of torque. LOL

(5) 1990+ 5.0L (305) LB9 TPI engine = 230 HP@4400 & 300 FT-LBS@3200. There was only one version of the 5.0L LB9 TPI engine from 90 to 92 and they all had the 5.0L LB9 H.O. camshaft just like the L98 did. GM choked the power out of the 90+ 5.0L LB9 TPI automatic transmission cars with the low output exhaust manifolds, catalytic convertor, and exhaust system from the 5.0L L03 TBI cars. The LB9 5 speed and L98 automatic cars had a high flow N10 dual catalytic convertor exhaust system with the H.O. high flow exhaust manifolds.

MagnaFlow makes a 409 stainless steel high flow single catalytic convertor exhaust system that you can swap onto the 90 IROC-Z with a low output single catalytic convertor system that will even out flow a factory GM N10 dual catalytic convertor exhaust system and unlock all the power and more that GM choked out of the 1990+ LB9 automatic transmission cars. It will require the TPI H.O. exhaust manifolds used on all 85 to 89 TPI engines and 90+ L98/Auto and LB9/5 speed/N10 TPI F bodies. It also requires the passenger side exhaust manifold spacer used with the H.O. TPI exhaust manifolds.

MagnaFlow 16450 - Y Pipe - Performance Exhaust System
MagnaFlow 93441 - Direct-Fit - Performance Catalytic Converter
MagnaFlow 16829 - Cat-Back - Performance Exhaust System

GM GENUINE Torque Convertor #24202310
DBLF = 1995+ L35 H.O. S10 truck torque converter has a GM rated stall speed of 2025 RPM and will probably stall around 2200+ RPM in the 1990 IROC-Z

Zexel Torsen limited slip differential with 3.42 ring & pinion gearset out of a late model 4th gen F body.

You swap the H.O. TPI exhaust manifolds with H.O. TPI passenger side exhaust manifold spacer and MagnaFlow high flow single catalytic convertor exhaust system, that GM high stall torque convertor, and the late model 4th gen Zexel Torsen 3.42 rear differential and your 90 5.0L TPI automatic IROC-Z will rock.

Start with the nicest car you can afford. If you can't afford a nice one now then wait and save up until you can. Don't start with a rust bucket because it will always cost more to repair than you thought it would, take more time than you thought it would, and once you get into repairing the rust you will find more rust than you thought it had to start with.

1990 IROC-Zs are cool because it's the last year GM made an IROC-Z and it was a low production year with all of them being made in 1989.

EDIT: The above information assumes the 1990 IROC-Z is a 5.0L TPI automatic transmission car. If it's a 5 speed car and in better shape than the 1987 then it is a no brainer. Buy the 1990 IROC-Z.

Note: If the 1988 IROC-Z you used to own was a non G92 Performance Axel Ratio car then it came standard with a 2.77 axel ratio instead of the 3.27 axel ratio. If the car had factory CC1 T-tops then it for sure wasn't a G92 car. If a hardtop the standard gear was 2.77 and it had to be ordered with the G92 Performance Axel Ratio to get the 3.27 gear, The 1990 IROC-Z with the exhaust, torque convertor, and 3.42 gear ratio modifications I described above would murder a stock 1988/1989 2.77 geared IROC-Z.

 

Thanks for taking the time and advice. This will be a slow project that i will be working with my kids on. It's been a while since I've really worked on a vehicle so hopefully I can secure it before end of year. Thanks again.
Thanks to the others on votes

 

So which one you getting?

 

Like said above, wheel well rust likely means more rust you dont see. I'd go for the 90 in a second over the 87. If you really want a 350 you can swap one in. Or build the 305 a little. Let someone else deal w the rust!

 

I took a look at the 87 inner wheel well pretty bad and noticed a bit more rust on corners of doors. The real kicker after i ran vin came up as total loss in 1999. Going to go take a look at the 90 this weekend . The price is right and would give me some time to do some things to it and eventually do a swap. The plan is for a weekend ride and to go to meets. No plans for daily driver. Definitely need to add more HP. We'll see.
Here are some pics.

 

Hope all goes well when you check out the 90 IROC-Z. Good luck.

 

Didn't pan out. so hopefully something comes along. Thanks guys

 

Sorry you missed out on them. As others have stated, run away from rust. Drivetrain changes are easy. Rust repair & body work is a whole different ball game altogether.