gta90

iTrader: (1)

I've posted on this topic over the past years, when I didn't really know anything, but after doing some research and getting good insights from this community, I believe I've narrowed down what I want to do to gain horsepower with budget in mind. I'd like to run my plans by you all and get a solid plan in place and find out any items of importance that I will need to consider... and modify my plan as needed.

Disclaimer: I'm not a professional mechanic, but do most car maintenance myself (fluid changes, belts, brakes, etc).

What I have: a stock 1990 T/A GTA w/305 TPI and 4 speed auto and a highway rear end (2.73 gears) which is sluggish and bottom line not an exciting ride.

What I want: A naturally aspirated and reliable street car that is comparable performance-wise to a modern V8 Camaro. Not looking to build a drag car with slicks, NOS, open headers, intended for track purposes only.

My plan is to get a complete junkyard drop-out from a 2WD truck/van (Sierra, Tahoe, Express Van). So essentially I want a 6.0 LS (LQ4, LY6, etc.) with the LS3-style rectangular port heads. I would like to run all the truck accessories if possible (are there any fitment issues with this?), and I want to SHAVE the truck intake so that it will fit under the stock hood and run the stock truck injectors/fuel rails. Truck everything essentially. I believe this is the most cost effective approach. If there is a 6.2 L LS available for similar pricing (doubt it), I'll just assume go with it instead.

I will plan to notch the K-member and use a short oil pan. Also plan to do a VVT-delete if applicable.

I plan to tear the LS engine down myself, send it off to a machine shop to make it like brand new (re-deck the head-mating surface, hone the cylinders, polish/balance the crank, and anything else they recommend). I'd also like to rebuild it with some upgrades (new cam bearings, bigger cam, longer pushrods, upgraded rocker trunions, and forged pistons).

In addition will like to use the truck auto transmission (4L80 or 4L85). I'm OK with sacrificing a little power to use an auto trans. Can the rear-end from one of these donors also work with a third gen T/A? What about drive-shaft?

Will plan to use a throttle cable (use the truck intake mount point) or go with the E-pedal depending on what I can find. Will plan to use the truck computer and harness. And plan to get it re-programmed/tuned for sport car application.

Please let me know how crazy this plan sounds and any insights that you can share to make this work. Or any items that I have not yet considered (sure there's a ton).

Thanks

Tibo

iTrader: (15)

That sounds like a sane goal, having an LS powered Thirdgen that is comparable performance wise to a new Camaro. You'd only need 400-450 wheel horsepower to keep up with any stock engine N/A Camaro, Mustang or Challenger. But if you only have average hand tools and your experience has been limited to fluid changes, belts and brakes this is either going to be a very long term project or an expensive project. IMO its a waste of money to rebuild a truck LS engine unless you're going for big boost or big hp. Under 500 hp you will be fine with a stock 5.3L. Rebuilding an LS is just going to make the project longer and more expensive. Perform a leak down test and if it's in acceptable limits then buy the engine. Also, skip the 6.0L and just buy a 5.3. I see complete (all accessories and electronics) 5.3s on craigslist for $500 but a 6.0L will be only the short block for $800. Put peak horespower numbers, cylinder head flow numbers, connecting rods and all that other minutia aside because they are all (yup even that 4.8L) better engines that will leave your current engine in the dust. You already said it's not a track car so there is no real reason to pay the 6.0L tax. Buy a 5.3L and swap out the cam, put on good exhaust and stick it in the car. That alone will get you to 400 wheel horsepower which can break your rearend. Is the extra $1500-2000 rearend expense in the budget? Later down the road if you find a good deal on an intake or cylinder heads go for it.

QwkTrip

iTrader: (22)

Seems like you've been doing homework and have the gist of it. Not sure you can fit that truck intake under the Trans Am hood but I'll let you sort that out.

I think the Gen III engines, like the LQ4, have cathedral port heads, cable throttle body, and 24x timing systems; and the Gen IV engines, like the LY6, have rectangle port heads, drive-by-wire throttle, and 58x timing systems. There might be an oddball hybrid somewhere in there, but in general the engine controllers are not interchangeable so you'll be using whatever ECM comes with the engine you choose. If you want cable throttle body with rectangle port heads, then you'll probably need to do a head swap on an older Gen III engine, or use aftermarket EFI.

Seems a shame to have rectangle port heads and not use an LS3 intake manifold. Best damn intake GM ever put on an LS engine, and still an affordable junkyard find. But it would necessitate changes to the accessory drive.

Most 6.0L builds I've seen at this site end up around 400 RWHP. Seems the 5.3L builds end up around 350 RWHP. If you read too many magazines and forums then you'll probably think any dummy can make 500 RWHP. Most the people saying that have never done it and are quoting somebody else's exceptional achievement.

Aviator857

There is a guy on youtube that has a video of shaving down a truck intake, it gets rid of all the random crazy bits on top of it. Its a pretty involved process but makes them look much nicer. Though your hood clearance on that intake will be the front where the throttle body is if you have the flat or louvered hood.

I will say this, take your best estimate on how much this is going to cost you and add $1000 to that also factor in cost for subframe connectors.

The rear out of a truck will not work without a lot of fabrication, Your rear should be fine as long as you are not doing crazy launches on sticky tires. You probably also don't have posi-traction on that rear. A cheap but not perfect solution is a 4th gen rear (its 3 inches longer so it will stick your tires an 1.5 inch out on each side) Before I spent money on modifying a truck or 4th gen rear to make it perfect I would build a ford 8.8 or 9"

If you have the space, one thing you can do is buy a donor car, from auction this will cost you about what the engine cost you from the junkyard and you can make money back by selling parts off it. You will also find that you will have all sorts of little parts, bolts, etc that save you money over time off the donor. You can use alot off a 4th gen but the 5.7ls1 is a little old tech these days.

gta90

iTrader: (1)

Tibo,
Thinking I'll be OK as far as tools and time go. Will pick up any additional tools needed for this project. Since I'm planning to lift the car off the engine/trans/front-suspension I'll for sure be buying an engine hoist, hopefully second hand. Not sure if an engine stand is needed anymore as I'm liking your advice about avoiding tearing into the engine and just do a cam swap, but probably will want one of those anyway (seems convenient and not too pricey). Guessing if I don't go too big on the cam then there is no need to change to longer push-rods and upgrade rockers, etc. Do you know the max size of cam that can be used without having to upgrade the other internals?

Will also be building a dolly-pallet to set the engine/trans on to roll it out from under the car.

350 RWHP would put a big enough grin on my face, but feeling the magic numbers for this project are 400 RWHP/400 LB-FT. My concern with 350 RWHP is that there will be a HP loss since I'm going with an auto trans - any idea how much HP will be lost with an auto trans? If a considerable loss that may be enough of a nudge to go with the 6.0 setup.

Yeah, will want a new rear end too. Save the headaches later down the road. What is an affordable rear-end for 400 RWHP? Heard that 3.73 gears are good for a street car.

Time to read up on leak-down testing.


QwkTrip,
There is a youtube video showing a shaved truck intake fitting under the stock 3rd-gen hood, but man is it tight, and depending on the motor mounts used can imagine there could be a scenario where it won't fit (murphy's law). I'm thinking the drop-out that I get will come with the truck intake so I'll give it a try, but also will be looking for a LS3 intake.

Great information. I don't want to mix-n-match as much as I can help it. I'll be happy with an LQ4 or an LY6, but with preference towards the LY6 w/drive by wire.

What is the issue with using an LS3 intake on a LQ4/LY6 that necessitates a change to the accessory drive? Pretty sure I recall learning about this but can't recall details... thinking something to do with the throttle body getting in the way of something like the water pump. This info would be helpful if you can provide it, and what I need to work around it.


Aviator857,
I've watched a couple good ones out there on shaving the truck intake. Looks like a fun project. Will definitely use a face mask to avoid breathing in all that plastic particulate though! That plastic welding kit from HarborFreight appears to be the ticket for this job.

Yes indeed... sub-frame connectors will probably be the first thing I do once this thing is gutted.

Good to know about the truck rear-ends. Thanks.

Will a Ford 8.8 or 9" be reliable with 400 RWHP/400 torque?

Guessing we can't do a engine leak-down test on an auction.. otherwise I'd go that route for sure.

Tibo

iTrader: (15)

The Ford 8.8 is really only a great swap if you (or a friend) are doing the work (research, measuring, cutting and welding) yourself or you have a place that will do the work inexpensively. I'll be doing this swap in the near future, many people have had them behind 400-500 wheel hp cars without breaking them so it's a great mid-level performance rear end. The Ford 9" or Strange S60 are going to be rearends if you can't do the work of an 8.8 yourself or you want to be making over 500 wheel hp.