TorqueHD

L8T rotating assy ordered. 4.020 x 3.858. Got the oil/timing gear with it and the 8 bolt flex plate, and ARP main studs. Pistons are flat top with valve relief and Wiseco spec's them at -1cc. LS3 heads on order from ebay, factory 823 castings with valves/rockers. This will be 392 CID, 6.4 liters (I suck at math so tell me if I'm wrong) If budget goes well and I can do the LSA blower, the increase in displacement will probably be negligible. But if I run out of money due to moving to a new house, and have to go all motor, every little bit will help. If I end up going NA, I will probably get the heads milled to raise compression as well. The heads were only $500 on ebay, from the little bit I have been able to read about LS3 heads, they are rock solid heads and don't become a limiting factor until you're in the 900hp range.

I need to pick a Cam. The guy on the line at Mast told me I should get a Franks Red Hot cam, specs:

0.604/0.604 Lift 222/234 Duration- Lobe Sep 112+2

Or one of the supercharger cams. I told him I was interested in the BTR Truck norris cam (212/22X, .552/.552, 107 LSA​​). He said it was a great cam for a stock engine but with a bigger bore and stroke I'd probably run out of cam over 4500 RPM. I don't know enough to make an informed decision. I want big midrange power, I don't want to have to run the motor up to 6 grand before it starts really making power.
I've heard that the BTR cams are very "streetable" and have soft profiles for longevity. I don't know how far you can go before a cam isn't "streetable". I do love a good chop though. And I plan to get a Circle D convertor before the motor is finished.

Oh also I talked to my engine guy, he uses a guy here in Fayetteville NC (where I live) named Robbie Draughon for engine machining. I guess the guy has a good name and has been doing this for a long time so I feel good having him machine the block. He also does head work. Spoke with him on the phone and looking forward to having him work my motor once I get the rotating assy in.

Sorry I've edited this thing like 7 times. Even the "mild" stroke of the L8T crank will require clearancing the block; I watched some youtube videos and it looks easy. I'm pretty handy with a die grinder. Anyone have a good reason why I shouldn't do it myself? I'd like to do as much of this build myself as possible. Part of the fun of building a motor is in learning how to do it. I think the part you clearance is low enough that even if I mess it up a little and over-clearance, it shouldn't really be an issue? Or am I wrong here?

TorqueHD

OK I'm retarded and need some help determining compression ratio please.
Bore: 4.020
Stroke: 3.858
Comb Chamb CC: 70
Piston Dome: -1cc
Head Gasket Dimensions: 4.1" bore x .054" thick.
Head gasket volume: (.5x4.1) x (.5 x 4.1) x 3.14159 = 13.203 x .054 thickness = .713CID x 16.837 = 11.682CC

(.5 x 4.020) x (.5 x 4.020) x 3.14159 x 3.858 = 48.97 CID per jug
48.97 CID x 16.3871 = 802.43 CC per jug
802.43 / (70cc comb chamber +11.682 head gasket) = 9.82:1 Compression Ratio

I don't know what I'm doing wrong. I used to be so smart on this stuff after I went through Engine Rebuild & Performance at Motorcycle Mechanic's Institute. Now the math never seems to work. I checked my formula against the stock numbers for an LQ4 and I'm coming up with 9.1:1 instead of 9.4:1.

strutaeng

Summit Racing has a handy calculator on their website. Check it out:
https://www.summitracing.com/popup/c...ion-calculator

TorqueHD

Yeah I did the summit calc and it's telling me 11:1... even if I use .075 head gaskets it's saying 10.49:1. Damn I wish I was smart. Those pistons may have been a mistake. Mast has to custom order them from Wiseco, I wonder if it's too late to change the order.

strutaeng

I was curious about the Summit Racing calculator and used this website to create a quick Excel spreadsheet to double check and looks accurate: https://www.motortrend.com/how-to/ca...ression-ratio/

Your piston-to-deck clearance is unknown, so I used 0.005" out of the hole.🤔🤷
The Summit Racing calculator doesn't have HG diameter, so I guess it assumes it's the same as the cylinder diameter?

TorqueHD

The sales guy from Mast (I think his name is Hank?), said the piston that comes with these kits is a special deal they have with Wiseco and they are set to deck at 9.230", which is where he said most blocks get machined to. So zero for that value assuming the block decks at 9.230".
The piston would be "dished", because they're flat top but they have valve reliefs. So +1 instead of -1.
I can run a .060 head gasket and get 10.62:1 according to the Summit calc.
I can order different pistons but he said it would take 12-16 weeks to get them... Suddenly wishing I hadn't done the L8T crank.
I think I could run it 10.62:1 low boost... E85 would sure help. I wish I was smarter on all this stuff. But, I tend to learn by doing. Learning what NOT to do next time.

strutaeng

I hear you. It's like trying to solve for two unknowns when selecting these internal engine parts. I think it just comes from experience. Guys that do this on a regular basis already know what combination yields what.

I'm also having similar issues with my engine build. I calculated a compression ratio of like 10.6:1. It looks like Lingenfelter has some Cometic HG that are 4.100x0.075" for these engines specifically for reducing compression. How much does that reduce on your combination?

What does "Cometic" mean anyways? I've heard that on those engine building shows. Is it just a brand? You ain't the only naive member here OP! 🤣

TorqueHD

.075 would put me at 10.27:1
Part of me just wants to say "Send it" and just run NA high compression now. If I'm not buying an LSA blower I could get a cheap catfish Camaro.

silentbravo

iTrader: (1)

I think your "high" CR is looking correct, I did some of that figuring a while ago and and you are looking very close to what I came up with. The static compression is less of a big deal it seems, the dynamic compression ratio is more important and everything is even more critical if you are throwing boost at it and are octane limited. The cam you pick can help bleed off pressure and lower your dynamic compression. Here's a good article on it, https://www.chevyhardcore.com/tech-s...compatibility/

When I was trying to figure this out, I was using the summit calculator and also the wallace racing one here, Wallace Racing: Dynamic Compression Ratio Calculator

With the numbers I was trying I came out around that 10.2:1 static CR also, but the dynamic is what I was really trying to get lower because I also want to throw an LSA on top and I want this to run anywhere, so it should be safe on 91 octane. Obviously there is a lot of tuning that can be done for octane limits but getting the "hard parts" right is important also.

I'm thinking more like a -8CC piston is going to be better if adding boost and using common 70ish CC heads.

Bluecollar Hotrods

iTrader: (18)

JMHO - the TN cam would be a horrible choice for that combo. I have a similar sized cam in an LQ4 with 862 heads. It doesn't make very good power, drives fine for a daily. I'm eventually going to a 228/236 and different heads. That 222/234 they recommended is the smallest cam I'd want in that combo.