5.7L Gen III iron Block by Thompson Motorsports
07-05-2015, 07:48 PM
#1
On The Tree
Thread Starter
5.7L Gen III iron Block by Thompson Motorsports Just finished breaking in my TMS built 350 (5.7L) engine at 525 miles.
Specs:
The Good:
The Bad:
Conclusion:
Solid 350, GREAT low-end torque truck engine. Once the warranty runs out, I will replace the cam, likely with the Cammotion Stage 2 cam for 5.3L truck engines. It will have to be tuned at that time. Fresh air box and better exhaust will be added sometime along the way.
Specs:
- 5.3L LM7 core
- Bored to 3.898
- TMS pistons and rings
- Late model floating piston pins
- Reconditioned 24x crank
- 317 casting heads (milled)
- 2.00 intake, 1.55 exhaust valves
- LS3 "blue" springs
- Stock LM7 cam
- 10:1 compression
- Summit 25% under drive harmonic balancer
- Installed by a professional mechanic
- Stock tune
- No Intake changes
- No exhaust changes
The Good:
- Reliability has been flawless
- Startups are quieter (no piston slap)
- Gas Mileage is improved over the stock 5.3L
- Works perfectly with the stock computer as-is
- Truck now squeals B.F. Goodrich Radial TAs on 3.73 limited slip rear end
- Acceleration is noticeably improved
The Bad:
- Warning citation for exhibition of speed (great cops in this small little town)
- Premium fuel required (I haven't even tried mid-grade or regular)
- Initial issue with Oil O-Ring for Melling pump cost me an extra $1200 at the mechanic's shop.
- TMS said they sent it
- mechanic said they didn't
- SLOW replacement
- TMS could have done better
- I wanted the GM 6.0L cam, I was willing to pay for it, I got the LM7 cam
Conclusion:
Solid 350, GREAT low-end torque truck engine. Once the warranty runs out, I will replace the cam, likely with the Cammotion Stage 2 cam for 5.3L truck engines. It will have to be tuned at that time. Fresh air box and better exhaust will be added sometime along the way.
07-05-2015, 11:50 PM
#4
On The Tree
Thanks for the write-up. I've been looking at the same engine from them to replace the short block from my '00 Yukon when the time comes but I've got a TBSS intake and set of 243 heads sitting on the shelf waiting for it. Nice to hear some positive feedback from someone who's used one.
07-06-2015, 01:39 AM
#5
On The Tree
Thread Starter
5.7L Gen III iron Block by Thompson Motorsports You're welcome. In my case, it HAD to run on the stock tune for a while. It does that perfectly on premium gas. No tuners within 150 miles of here.
07-06-2015, 10:46 AM
#6
On The Tree
I feel your pain on the lack of local tuners... Have you looked at some of the mail order tuners like Black Bear? I bet you'll be amazed at the difference once you get a good tune for new engine 
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07-07-2015, 07:58 AM
#9
On The Tree
Thread Starter
5.7L Gen III iron Block by Thompson Motorsports When the vehicle has to be reassembled and disassembled needlessly because it takes over a week for a replacement o-ring to be delivered and the shop didn't have the real estate to let the truck sit in the bay waiting for the part to show up.