What can the standard '87 autobox cope with?

[Kiwi Bloke]

Hi gang,

When I finally do come over to buy an '87, I'll be looking for one that someone has "sensibly" uprated to about 300bhp. I'll be wanting an auto, partially because I love the sound a V8 makes when floored into kickdown from about 20mph. That almost instantaneous change from "just above idle" burble, to a full-throated roar, with a hard gearchange a second or so later. Shiver!

Anyway, my question is this: '87s were designed with (according to my literature) about 240bhp and 345lb-ft. Does the standard autobox cope with the higher outputs of uprated engines, or does it need some work too? Sort of - what power and torque can the unmodified 'box cope with?

Adrian

 

[Vettefan87]

I think I have read somewhere that everything would hold up until about 400 hp and 400 torque. I could very well be wrong, someone will step in with more accurate info.


Justin

 

[Kiwi Bloke]

Sounds encouraging! What power/torque does your '87 generate?

Adrian

 

[c4cruiser]

The GM 700R4 auto tranny should handle up to around 400HP and a similar amount of torque assuming it's is good condition. It's amazing how so many folks do not do regular maintenance on automatics. A simple fluid and filter change every 30K miles or so goes a long way to insure long life.

The 700R4 is very common in GM rear-wheel drive vehicles and I would think there are competent transmission repair shops worldwide that could work on them.

When you test drive some cars, make sure the tranny is operating properly. The upshifts should be firm and with no hesitation; the same with downshifting. Use the shifter to manually select gears for both upshifting and downshifting. The tranny should hold each gear until the lever is moved. Try (with the owners' permission and no police cars around ) a couple of full-throttle upshifts to make sure everything works right. There should be no "clunk" when you put the car in gear (something like this could be u-joints or even the differential).

Some people will have a "shift kit" installed to make the clutches last longer. this provides for a quicker shift between gears but the shift becomes very firm, even to the point of feeling like being kicked in the rear each time the tranny shifts. B&M makes a very good kit that can allow degrees of shift firmness. They are relatively inexpensive and don't take a lot of work to install. A tranny shop can do it with no problems and the kits come with detailed instructions.

Now after all that, my 87 is a 4+3 and I have a modded 350 with a older ZZ3 cam, good 3-angle valve job, ported and polished heads, the intake runners are port matched to the heads and plenum and it's balanced and blueprinted. It puts out about 310HP at this point with the pre-cat and main cats and muffler eliminators. The tranny is holding up quite well, thank you, to autocrossing and the occasional track day.

The 4+3 is a hoot to drive as the 87 version of the tranny and ECM allows the engaging of the overdrive unit in all 4 gears, so I effectively have an 8-speed! I like to play with the local ricer-driving kids and their Hondas in city traffic when I get next to them. Start in 1st low, let it shift into 1st OD, then quickly shift to 2nd low, then OD, and so on. With no mufflers, it sounds great and the kids really look confused when I just keep shifting.

 

[Kiwi Bloke]

Thanks for that great info! I'm enjoying learning these basics on the cars that I have so long admired, but never technically investigated. (Most of my automotive knowledge is based around late '80s to now Jaguars.)

I've just Googled shift-kits for this box, and they do look inexpensive and straightforward. And reversible too, I guess!

The mods you have with your 350 sound pretty good. How common is it to find vettes with such mods? And I love your "8 speed" story. Gotta keep them rice-burners on the run!

Adrian

 

[Vettefan87]

Sounds encouraging! What power/torque does your '87 generate?

Adrian

I am not really sure, I have not had it dynoed. I have a first generation GTech that I ran it with and I got right around 270 to the wheels give or take a few. With the Ram Air done the chip and the air foil. I have not been able to run it with the rebuilt motor and the ported plenum due to not making it past the break in period.....long story though.


Justin