LilTimmy

Hello,

First let me say that I apologize if there's a thread exactly like somewhere which I am sure there is. About a year ago I bought a 91 z28, 305 TPI, WC T5 5 speed, dual cat exhaust (I didn't know much about the car at the time, guy who sold it to me said cat was actually off and I didn't find out until I got 2 hours home it had 2 cats on it which I assume are shot.)

After the car running great for a month or so, it lost all power and felt like it was towing a house, started missing and I lost compression in one cylinder. So I tried to be an adult and pull the motor to rebuild? it (my first time doing such) After a while it threw an EGR code, so I blamed that and the cats for it not even making power past 1500rpm.

Fast forward to now.....the original 305 short block and transmission have sat on the side of my house since then....I live in CA so they haven't been totally thrashed, covered up....

What do I do with this car? I want to keep it.....I love my 3rd gen and totally intend on restoring it.....just had a lot of life issues which have come up and now Im ready to tackle the project and have the money to do it finally. I don't want to keep the original 305. What block do I put in it? What else would I need? I've heard the WC T5 transmission is good but not too strong, is it gonna get shredded? Its also got a posi rear end, can that hold up? I'm also curious as to if this car is rare or not because finding info on it is sometimes hard, not sure if it's like that for all z28s with TPI or what.

Any other questions I have no problem answering, this would be my first swap and I very much appreciate any input.

Injuneer

In 1991 they sold 12,458 Z28 coupes. About 1/2 of them had the 305ci engine, and 6,080 of them had the optional 350ci (B2L) optional engine. The WC T5 was used behind the 305ci engine, but was not considered strong enough to put behind the 350ci engine, so those were only available with an auto trans.

The obvious upgrade would be 350ci (Gen 1 SBC) engine, ranging from stock to a 383ci stroker build, and up to 500HP. Depends on your budget. The T5 might survive behind the stock 350, but for any sort of power upgrades, you would be looking at an upgraded T5 or a conversion to a T56 6-speed manual.

The stock 10-bolt rear will survive behind a stock 350 with manual trans, until you try to drag race it with sticky tires and high RPM clutch dumps. But the only real option would be a Ford 8.8" conversion, or a 12-bolt conversion, as available from Strange or Moser. But now you're looking at $2,000 - $3,000 for the rear axle assembly, unless you can find one used.

Just curious.... did you check for plugged cat converters when your engine seemed to lose power?

LilTimmy

I was in a tight spot life-wise when it was going down and I had no time, I pulled the o2 sensor and it didn't seem to breath any better....guy I bought it from said he rebuilt it and did a can of paint rebuild basically.....said it had no cats that's why it sounded all throaty.....but it had both cats on it still lol ....also lost the cylinder and had a low end miss I couldn't fix. I do plan on putting a nice 350 in it since I don't have the cash for a stroker, just not sure the direction I want or need to go with it to have this car still perform nice on the street....sorry for not mentioning my intentions, its gonna be a daily most likely

Mr.Gordon

A mild to moderately built 350 will be fine with the trans and rear you already have. As long as your not thrashing the throttle at every stop light. The 7.625 rear in the '91 has the better axle's than earlier model's, 28 spline axle's instead of the 26 spline. If your concerned about it falling apart on you, there are some simple mod's to the rear to strengthen it. Welding the axle tubes all the way around the housing is the first one, then a rear diff. cover that has bolt's that secure the cap's on the carrier. Then a Zexel / Torson carrier will bolt right in, and a gear ratio of at least 3.55. The WC trans, in my opinion, is not as potent as the non WC, because of the lined syncro ring's.
I am running a 383 in my '86, with the non WC trans, and I haven't had any problem's so far. I do have 3.73 gears with the Zexel carrier, and did the mod's I described.
The money spent is worth it, you get a car that will perform good for not a whole lot of money