I am a long time lurker, but getting more active recently. I have used this forum to answer a lot of questions over the years (thank you!) but never had much to post about. I had a C4 Corvette for a long time and have just been doing LS stuff in the last 10 years or so, buying my C5 in 2020 to replace the C4 track car. I decided to start a build thread as Im changing things up a little for next year.

I have been competing in SCCA Time Trials and some GridLife events in Street GT and Track Mod (most recently). I have been running the stock LS6 (for the most part) since I bought the car in 2020. In 2022 I added headers and an intake manifold which was all I could do within the class rules for each series. This year the car has felt slower and slower without any changes from last year. At the end of the year I was about 3-5mph down in Vmax on all the straights at Pitt Race, and about 2.5sec off my personal best there. I think 12k track miles and occasional runs past 7000rpm has made the original engine a bit tired.

For 2026 I am building an engine with the help of Summit Racing, Cometic Gaskets and Klotz lubricants. The class rules for Max 2 limit NA engine displacement to 6.4L or less. This makes an LS3 build the perfect fit. I found an L92 truck block to use as the base for the build. Then we are going to fill it with the full line of Summit Pro LS parts (crank, rods, pistons, cam, etc)! I will be documenting the process in here with all the parts used. Our goal is to make 550 wheel hp on pump 93 octane. The basic outline will include around 11.5:1 compression, TrickFlow 280 heads, short runner intake and a cam and valvetrain capable of around a 7500rpm redline.

So far all I have is the block. Since the L92 is a truck engine with DoD/AFM, I had to plug the towers in the block the oil flow. I tapped the holes for a 3/8-24 set screw vs the hammer in plugs or rivet type kits. I used the BTR plug kit in my Gen V truck AFM delete, but I like the more mechanical retention of threads for this engine.

Next, I dropped the block off at Cragon Automotive, a shop around here that does a lot of Chevy and Corvette work. They are going to clean it up, line hone, bore, deck etc. Rotating assembly parts are order from Summit Racing and should be here soon to hand over to the machine shop as well.






This is my car:

 

What manifold are you looking at? Is Brian working on the cam for it?

 

Yup Brian has spec'ed a cam (S.P.5 I believe - SUM-8744R1), and we are going to use the Summit Max EFI low intake for hood clearance. This will likely shift at 7500rpm, sacrificing some low end for more top end power. Given the "displacement limit" to only a stock 6.2L, spinning it more with help make more overall power. Since I race on 200tw tires and not a Hoosier or full slick, traction is limited in the low speed corners anyway, and this engine will still have more than enough to pull out on corner exit.

 

I would have the machine shop balance the pistons, rods,brgs and crank. Always easier now.

 

Hi, Yes I would like to help with your project.
My racecar was the Inteped (Garven Brown owned, Driven by Danny Sullivan)
I bought the "roller" from Whittey.
My first tip is the NEED for Crankshaft Acceleration.
I would fit Ti Piston pins And Ti Rods if Affordable?
I would fit a High Compression "flat top" piston and use a low-volume head.
Ti Valve Intakes
Lance

 

Is there a compression ratio limit? Can you run e85?

What is your rear gear ratio, and can you change it to 3.90 or 4.10?

280cc seems quite large for a stock displacement 6.2. Can you afford the AFR 260's?

 

That's the plan!

There is no compression ratio limit, but I would prefer to keep it on pump gas. E is harder to find driving across the country at different tracks. I know I can get 93 anywhere.

Rear gear is the stock 3.42 but a built diff by RPM.

The large head is to help airflow at higher rpm. I'm sticking with either the TFS 255 or 280 head per Summits recommendation.

 

The pistons will have a small +2cc dome, but Ti rods are not in the budget. I am using all Summit Racing brand internals to show even budget builds can be reliable and make good power.

 

I have a hard time imagining that a 6.2 will benefit from heads with ports that large. Richard Holdener did a test with James Short on an LS7 where the TFS 255s actually outperformed the LS7 head that they put it up against. Running a short runner intake like you are, I would want the smaller port for the low end, but to be honest, I think it will also make more power all the way out at 7500 rpm too. The TFS 255s are a really nice head.

 

I would suggest (and I'm sure Brian would too) using the 255. A 280cc head is huge for a smaller na motor of your goals. It'll be lazy with a 280. That head was made for big na motors, but mostly the lsa/ls9 cars.

 

Cool build, look forward to the updates.

 

Another way to solve a "large port" head Torque Curve Problemm
Run a SHORT ROD and Max Compression

 

Brian is who picked the 280, but I'll talk with him about it.

 

Really?? That's surprising.

 

As others have already screamed, the heads are waaaay too big. I made right at 600 wheel recently with a 403. 6.2 block with a 3.9” Molnar crank. I think in good air, the thing would have done 615 wheel, which is decent LS7 territory. The beauty of the build was the explosiveness of throttle response. Car was crazy torquey…C6 GrandSport. I did a build thread here if you’re remotely interested. Those heads you’re looking at will make big numbers with the right intake and a big enough cam, but you’re going the wrong direction with that intake….but you’re limited with intake in a Vette. Torque matters in what you’re doing a lot, as you’re coming out of corners a lot. I’ve had my hands in everything from Cup engines to 24 Hours of Daytona engines through the years and I’ll tel, you that in road racing, torque wins….fastest guy out of the corner is always the fastest guy down the chute. Heck engine is the easy part. Brakes and chassis matters a lot also, but I digress. AFR Mongoose heads with the PD XS intake and a 108 or 112 TB will make big power. Do not over cam it! Contact Tony Mamo if you want the best Mongoose program out there. They flow almost as much as a good LS7 head, with much smaller intake ports. That gives you crazy fast intake air speeds, which makes torque. Simply the best out there. I also just sent a sleeved block build with those heads to Portland for a guy who road races his car. Phenomenal powerband.

 

Scott, I did see that GS build you did and it was very impressive numbers! After the holidays I'll talk with Summit about going with the 255 vs 280 as they are helping with the parts selection as well.

 

Another ITEM not often spoken about is Engine Location.
Would it be possible to MOVE your engine towards the rear of your car ?
Lance

 

It's a C5 Corvette, and it's already a tight fit. No real room to move ANYWHERE.

 

Others have recommended the AFR 260s and Mamo 260s, and I must agree.

For heads at $3,000 range, AFR 260s have out dynoed many heads tested by Holdener and Weingartner including the TFS 255s.

For heads at $4,000 range, Mamo 260s.

Just my 2 cents. Good luck with your project.

 

Hi Again, I would ADD A KERS system
I was the first to nvent this ELMO (Hybreed)
Would be legal in your Class ?
Lance