syc0path

I have an ’88 Trans Am w/ a 305 TBI and a 700R4 trans w/ about 109k miles. It’s rated at 170HP, and the only performance mod is a Hypertech computer chip and K&N air filter. I’ve always felt the car is underpowered relative to how well it handles, so I’m thinking about an upgrade. This won’t be a drag strip car. I’m basically looking for the same kind of smooth, tractable, reliable power that I have now – just a lot more of it.

I’ve done a fair number of engine swaps and even helped w/ a few rebuilds, but I’ve never really modded an engine. So I’m thinking a crate engine (w/ all the computers and associated wiring) is the way to go. MI doesn’t require vehicle inspections, emissions tests, or anything like that.

The idea I have in my head is a SBC/LSx 350 w/ about 400-450HP (which, I’m assuming, will also require a new trans), and replacing the rear end w/ a posi unit w/ rear discs. But I need guidance… is that a reasonable amount of power to expect from a 350? Is it too much for this car on a stock chassis? Is there better or more practical approach? And finally, what kind of ballpark cost are we talking about?

cmiller2014

Building a SBC is definitely the cheaper route to go, but I personally went the LS route. LS swapping is one of those things where you think you have everything you need, but then that makes you want to change the next thing, and the next thing, and before you know it you're over $10k in the swap.

There are a couple LS swap threads on here that outline what's involved but if you have the cash, I'd go LS and never look back. You just have to figure out if you want to keep your 700r4 and build it up a little, or go with a 4l60 or (even better) a 4l80. I personally went the T56 route but that will cost you a lot more money, usually.

But above you said you want smooth, reliable power, and an LS is the epitome of that. Regardless of which engine you choose, you'll definitely want to swap that 10 bolt rear out with a 9" or 12 bolt.

syc0path

I did some more research on this, and the LS6 6.0L looks appealing. As for the trans, the existing 700R4 works fine, but it's never had any service but a filter change and fluid added. It's 30+ yrs old and has 109k on it. Putting 2.5x the power to doesn't seem like a good idea w/o beefing up the internals, and that's not really something I want to get into.

And u make a good point about changing the next thing and then the next thing. W/ that much extra power, I bet the handling won't keep up anymore. The front brakes certainly wont! So that's engine, trans, driveshaft, rear axle assembly, brakes, and probably springs, sway bars, and control arms as well.

Modding the existing engine to get into the 250-300HP range is starting to look more appealing. It's been probably 25yrs since I looked into it, but back then the problem was that any1 who wanted to go fast already had the 350. There really weren't a lot of performance parts available for the 305. And even if there are now, could I get that much extra power w/ just bolt-ons?

cmiller2014

You're going to be hard pressed to get that much RWHP out of the 305. At a minimum you'll need new heads, cam, and intake, and at that cost you're way better off to buy a new or used long block or crate SBC.

Do you know what your budget is? That'll help diagnose what your best bang for the buck is in regards to what you want to do.

Kingtal0n

The only two ways I would LS swap a(nything really) thirdgen for reliable daily driving are

1. Use an aluminum LS engine, the largest displacement possible (6L+ ideal), with a 0.5:1 sixth gear ratio T-56 transmission for optimal fuel economy (400-500hp easy w/ 25-30mpg economy)
OR
2. Use any LS engine (e.g. LM7 or L33 or 4.8L) with a turbocharger & 4l80e to make around double the power (700-900rwhp) feasibly in a reliable daily driver (as #1 above) however economy suffers 12-16mpg at 3800lbs is typical with the 4l80e, so that is something to consider

The LS is far superior to anything prior, in many ways. girdle, oil control, oil pan support, seal design, pcv interface, the list of 'fixes' over SBC is enormous and... get this... they don't leak