Bought a LS3

Over the past 2 days I hunkered down and did an extensive search for a motor. I narrowed my search to just the GM LS2 or LS3. I searched all over the web and in ebay. Then I picked up the phone and called about 2 dozen salvage yards within driving distance of Charlotte NC. I was having no luck at all until I called a yard in the little town Henrietta, NC. Bingo…They had both a low mileage LS2 and a low mileage LS3.

Long story short, I bought a LS3 that was in the 2010 Corvette with only 11K miles. Heck, it was still under GM warranty and the interior still had that new car smell! It’s a full pick with all the peripherals such as Assy drive, belt, Alternator, Accelerator E-pedal, ECU, harness, O2 sensors, MAS sensor, headers, etc. It was $7.2k delivered....not great, but a fair price.

So 9 calendar days after purchasing the SLC kit, I now have the motor and transaxle lined up…Not bad


Next I need all the bits to connect the trans and motor:
  • G50 to LS Adapter plate – This comes with the SLC kit
  • Adapter plate bolts – Fran, Do these come with the adapter plate? Its not clear in the manual.
  • Clutch, pressure plate, flywheel – Fran, when I was at your shop 3 weeks ago you mentioned that you had a cost effective suggestion here.
  • Starter – Do I use just a stock Porsche starter?
  • Throwout bearing - I assume I need stock a Porshe part
  • Clutch release slave cylinder and fork – These are included in the G50/21 I bought
 
Re: SD vs MAF Engine Mgt

Just for some feedback on tunedbyfrost - Steve speed density dyno tuned my LS6 and I had no issues on the street or track. He does do mail order pcm tunes and has a very good reputation and knows what he's doing. I got lucky in that his shop location is about 8 miles from me. Highly recommended -- Mike

Fair points above.

I wouldn't say SD is for track only though, I would run it on the street without issue and have driven several cars that are that way. The throttle response is much crisper with SD vs MAF in my opinion, do some searching on driveability and see what you find. SD also helps tame larger cams to get more precise on the tune so improved drivability with bigger cam as well.

Also keep in mind a MAF will not help with a vacuum leak either. That is air being introduced after it is metered and therefore the computer doesn't know about it and will not adjust to fix it. If you're altitude is changing a lot, I could see where SD could be challenging, but my home is in the midwest and I rarely drive the cars outside that altitude area.

My point in commenting on doing SD is it will help you save cash in sourcing the MAF and still being happy with a solid tune. This is my opinion, I'd tell you to reach out to this guy, he does this for a living and does mail order tunes, I will use him to get my initial SD tune on the L33 in a few years when i'm ready to start this project. TunedByFrost.com - Professional Tuning For Your LSx Powered Car or Truck
 
I checked out tunedbyfrost.com. Very impressive!

I may contact them when I get to the point where I need a mail order tune.
 
The motor arrived

I was off on vacation last week in San Fransisco, Napa and Yosemite.

I had arranged for my LS3 motor to delivered on my first day back home, and it arrived in good nick.


Looks like I'll have plenty to do over the next week or so:
  • Reverse the intake
  • Modify the water pump
  • Remove the un-needed peripherals such as the power steering pump, AC compressor, starter, etc
  • Clean the motor up
  • Get the ECU flashed
The one thing I could use some guidance on is the GM engine wiring harness. Its all there, including half-a-dozen additional mystery plugs.

Can anyone point me to a pin-out diagram for the GM harness, or guidance on how to modify the GM harness to interface with the ISIS system?
 

Attachments

  • IMG_2634.jpg
    IMG_2634.jpg
    93.8 KB · Views: 706
  • IMG_2632.jpg
    IMG_2632.jpg
    95 KB · Views: 662

Ken Roberts

Supporter
I modified a 2007 Z06 engine harness for stand alone use. I wouldn't do it again. It will take many hours of studying the schematics. I'd recommend sending it to this place for conversion for $450. Engine Management harnesses by Current Performance Wiring

Sell your complete front accessory drive and put the funds towards a CTS V accessory drive. GM Performance Parts - 19155166 - GMPP Accessory Drive System Without A/C - Fits LS1 & LS6 Engines or http://www.summitracing.com/parts/NAL-19155066/ Summit will match the Pace price.

Some of the additional plugs in the engine harness are the front wheel speed sensor wiring and ABS wiring.

Also sell the LS3 headers/cats and buy the Z06 style of headers/cats. Post all of these items up for sale on LS1tech. They should sell quickly.
 
Last edited:
Re: The motor arrived

Not really seeing the savings here? You could buy an ls 525 (which is supposedly closer to 560hp at the crank with exhaust and tune, we'll see) for 7400shipped. Another thousand for a complete wiring package (which includes pedal, O2 sensors, maf, yadda yadda) and a few hundred bucks to Fran for the front dress and you've got everything, plus another 120hp plus a longer warranty, a brand new engine and an ecu that works from the getgo (you'll have to get the harness trimmed and computer flashed to remove all the security and whatnot from it)

, or guidance on how to modify the GM harness to interface with the ISIS system?

It doesn't. The only "link" between the two is the switched 12v power to give it power.
 
I checked out tunedbyfrost.com. Very impressive!

I may contact them when I get to the point where I need a mail order tune.

Mail order tunes are a pile of bullshit. I've seen enough cars go boom from them to know not to trust them. Heck, I tried to cheap out on my 04 cobra and did a canned tune from a local mustang shop that had dyno tuned dozens of them. My car must have been the odd-bird because when I did eventually put it on the dyno at WOT my a/f was 13.8!
 
Mail order tunes are fine as long as the combination is "normal". The biggest thing outside of normal on an SLC would be the MAF position. I would suspect that a canned tune would be ok as a starting point, but at the very least I would rescale the MAF table.
 
The G50/20 or 21 is probably what I am going to end up getting and have the first and 6th gears swapped out for a 2.81 and .656 respectively. Of course I have no idea what that would cost and probably will not be able to afford it right off the bat. I have an email into GBox so well see what they say. Is the one in the picture the one you bought? Where did you acquire it from?

When I spoke to Erik about the feasibility and cost of swapping the gear sets, he mentioned that a swap of first gear is more pricey than the others because the gear itself is welded to the shaft. So there is more cost involved as far as that goes. But if that's not an issue, then it makes sense to make the switch.

I know in my 5 spd (G50/03 on an LS2), First gear is pretty much used only for pulling the car into the garage, or maybe going up a trailer ramp.

In my mind, it doesn't make a lot of sense to use 1st out on the streets, since you'll be shifting again in less than 100 feet.

4th and 5th have been switched in my gear-box, to give better ratios at cruising speeds. (between 70 & 80).

It seems that the quote for changing 5th & 6th in a G50/20 (6spd) was somewhere in the 2500 to 3000 range. If you add a 1st gear swap, you'ew looking at around 4000 to 4500. But I'm not sure if I'm remembering 100% correctly.

The gear box has to be set up to be run "inverted". Some people do this themselves, but I have Erik set mine up for me. It's not overly expensive to have done, but it definitely needs to be done.

And don't forget about upgrading the side plate to something that won't twist off when you apply the 400 or 500 ft/lbs of torque through your newly rebuilt gearbox. CMS makes a very nice billet plate for the Porsche boxes. I think it ran me about $450.00. I'm also running a transmission oil cooler, in order to help reduce the transaxle temp, and hopefully pro-longing the life of the gear box. $300.00 or so if I remember correctly.

It's not an inexpensive prospect.

I have around $12,500.00 in my (5spd) transaxle. If the Griffin, or Mendeola had been available when I bought mine, I would have probably gone that route... But they weren't.

I think if I were to do it all over again, (with a Porsche transaxle); I would buy one that didn't need the gear swaps. That limits you to the G50/50, G50/52, G64/51, and I think G96/96. These were used in the Turbos, GT2, and GT3 cars.

These all use a 9" Ring gear, where every other gear Porsche Gearbox uses a 7.5" Ring. The 9" Ring holds the torque of the LS engines much better than the smaller ring gears do.

Most importantly, (or at least equally important), they have gear ratios that are very comfortable when used with V8 engines.

They cost more on the front end, but after you buy them, you're only faced with a posible rebuild, instead of a rebuild and gear swap...

If you're planning on putting your car on the track at all, you may really want to give this some thought.
 
Mail order tunes are fine as long as the combination is "normal". The biggest thing outside of normal on an SLC would be the MAF position. I would suspect that a canned tune would be ok as a starting point, but at the very least I would rescale the MAF table.

I've seen enough stuff with just basic bolt-ons (e.g., pulleys, longtubes, exhaust, intake, etc..., not for advanced stuff like heads/cam) having nothing but problems with canned tunes to ever trust them.
 
When I spoke to Erik about the feasibility and cost of swapping the gear sets, he mentioned that a swap of first gear is more pricey than the others because the gear itself is welded to the shaft. So there is more cost involved as far as that goes. But if that's not an issue, then it makes sense to make the switch.

I know in my 5 spd (G50/03 on an LS2), First gear is pretty much used only for pulling the car into the garage, or maybe going up a trailer ramp.

In my mind, it doesn't make a lot of sense to use 1st out on the streets, since you'll be shifting again in less than 100 feet.

4th and 5th have been switched in my gear-box, to give better ratios at cruising speeds. (between 70 & 80).

It seems that the quote for changing 5th & 6th in a G50/20 (6spd) was somewhere in the 2500 to 3000 range. If you add a 1st gear swap, you'ew looking at around 4000 to 4500. But I'm not sure if I'm remembering 100% correctly.

The gear box has to be set up to be run "inverted". Some people do this themselves, but I have Erik set mine up for me. It's not overly expensive to have done, but it definitely needs to be done.

And don't forget about upgrading the side plate to something that won't twist off when you apply the 400 or 500 ft/lbs of torque through your newly rebuilt gearbox. CMS makes a very nice billet plate for the Porsche boxes. I think it ran me about $450.00. I'm also running a transmission oil cooler, in order to help reduce the transaxle temp, and hopefully pro-longing the life of the gear box. $300.00 or so if I remember correctly.

It's not an inexpensive prospect.

I have around $12,500.00 in my (5spd) transaxle. If the Griffin, or Mendeola had been available when I bought mine, I would have probably gone that route... But they weren't.

I think if I were to do it all over again, (with a Porsche transaxle); I would buy one that didn't need the gear swaps. That limits you to the G50/50, G50/52, G64/51, and I think G96/96. These were used in the Turbos, GT2, and GT3 cars.

These all use a 9" Ring gear, where every other gear Porsche Gearbox uses a 7.5" Ring. The 9" Ring holds the torque of the LS engines much better than the smaller ring gears do.

Most importantly, (or at least equally important), they have gear ratios that are very comfortable when used with V8 engines.

They cost more on the front end, but after you buy them, you're only faced with a posible rebuild, instead of a rebuild and gear swap...

If you're planning on putting your car on the track at all, you may really want to give this some thought.

I don't mean to hijack the thread, but thank you for the lengthy write up. In my e-mail exchanges with Eric I have pretty much come to the same conclusion. When Griffin released their prices I will be honest, I was a little shocked. I had to change my mindset on gearboxes, they are expensive, and for good reason. Even if I could get a G50xx for $2000 I will easily bring it up to the ~$9000 Griffin is asking just rebuilding it and swapping gears. Since my order is a year or so out I will probably go with the Griffin and be done with it. Hopefully they are in full production by then :).
 
Hey Bill,
Good to see you making headway and back from your vacation. Did you get the other parts purchased from Kennedy?
Awesome write-up on the '32!

Doug
 

Howard Jones

Supporter
A couple of ideas for ya. First, 1st gear is never used at the track except to idle around in the paddock and get on/off the trailer. Same sort of thing in traffic. 1st gear isn't a gear I would spend limmited funds on. If you leave the standard 3.xx 1st in the box, it is perfect for leaving stoplights, paddock crawling, trailers.

Second, 2nd gear is used on track in very slow corners and is the gear you will use a lot around town between 25-50mph if it is long enough. 1.70 or thereabouts is pretty good for this with a 3.44 final.

Third gear in my R21 is 1.38 and the rev drop to 1 to 1 (really it's .98) in 4th is near perfect on track.

Fifth in my car (GT40) is .85 and gets me 2800 at 80MPH with the 3.44 diff ratio. It is also useful as a speed gear on long fast straights.

So if I was short of money I would change 2nd to 1.7 ish and leave 3rd and 4th alone at lets say 1.4 and 1. Then if the final was 3.4-3.5 I would want a .8 5th.

These gears will net you a 175 mph car that is good on the track, easy to get on or off the trailer and mild mannered in stop and go traffic.

The most important thing about gearbox questions is limmited slip. IMHO this is the single most valuable perfromance improvement you can make in a high powered mid engined car.

I personally love the the Quaife TBD in my Renault R21. So much so I had one installed in the Porsche G50 that's in my under construction SLC.
 
Hey Bill,
Good to see you making headway and back from your vacation. Did you get the other parts purchased from Kennedy?
Awesome write-up on the '32!

Doug

I'm holding off untill my G50/21 arrives. I want to ensure the transaxle is as adverstized and in good shape before I dig deeper for the Kennedy flywheel, pressure plate, clutch & starter.
 
What about just getting the LS3 crate with transmission for simplicity reasons? Especially if you think that you would be happy with 430hp because you would be using the car for mostly street use. I am in the process of learning as much as possible. Also, wouldn't it still get you 0-60 in less than 4?
 
Dnrice,

Welcome! As you go through the forum threads and visit the RCR site you will see that the transmission will need to be changed out for a transaxle. There are several transaxle options to choose from.
 
Back
Top