Hey all, I am currently building my first LSx. It's a used 2004 GTO LS1 block to swap into my 1990 Mazda Miata track car.

I am a bit confused on something and it could just be that I am doing my math incorrectly as I am new to internal engine work.

I recently purchased the Eagle Specialty Part #12804.

This is a 383ci stroker kit for the ls1 with the following specs

383 Cubic Inch
3.905 Bore
Arais -3.1 Flat Tops
Pin Height 1.050
Crank Stroke 4.00
Rod Length 6.2
Deck Height 9.24 (as far as I know)
Head Gasket .051 GM Part #

I have not decided on heads yet but I will probably pick up a set of TSP 6.0L heads with 68CC chambers to keep the compression under 11:1. I want to run pump gas as race gas is not available here.

After using the calculator on Eagle's website this setup puts the piston .01" above the deck. It seems that I have a problem, unless I am mistaken of course.

This also puts my compression ratio near 11:1.

If It helps I already have a cam also,

LS7 lifters
TSP Tsunami 111LSA 235/240 .648"/.609"

Any help is appreciated

 

Ls pistons are usually "out of the hole" meaning they are above the cylinder deck, but I'm unfamiliar with those pistons so I'm not sure. I've never been able to calculate compression until at least building short block and measuring the piston to deck clearance...

 

That's weird, 6.125" is usually the norm for the rod length. I suppose its fine though.

As far as .010" out, it shouldn't be a problem and neither should 11:1 on pump gas. I built my engine with 11:1 CR and it runs on 91 just fine. Just be sure to keep an eye on how far the piston really does come out of the hole on your build and whomever decks the block needs to know what gasket you're running so as not to take off too much.

 

You can run more than 11.1 in an LS platform. This isn't a SBC with iron heads and a carb.

With that cam, you'll want to run more compression anyway - and the cam has a lot to do with how much compression you can ultimately run. With any cam, you need to look at the intake valve closing point (IVC) and it's calculated off advertised duration at .006" and the intake centerline (ICL). With that cam, I believe it's 285 duration and 109 ICL if it has 2 degrees of advance if installed straight up with your timing set. That gives you an IVC of 71.5 degrees. Now, we can use that to determine the calculated dynamic compression ratio (DCR).

If so, and you're at 11.2:1 with a .040" gasket (it's 10.9:1 with stock GM) then you'd be about as high as you want for 91 octane with a DCR of 8.5:1. With 93, you could actually mill the heads down to 66cc and be perfect at 11.5:1 and a DCR of 8.7:1. 93 gives you more headroom with that cam.

Should drive nice and build a lot of power under the curve in a 383.

 

Fortunately here in NC and nearby in TN we get 93 octane with no ethanol most of the time.

Thank you for figuring that DCR, I wasn't sure how to do that.

The more compression the better, this is a race engine and will not be on the street but abused on the circuit. In fact it doesn't even need much power, I only built the 383 because I got the kit for cheap and I prefer forged internals on a road race motor. I've seen a few LS1's and 5.0's blow up under stock power at VIR. I also work at the airport, I suppose I could mix in just a little 100LL if necessary.

Not to mention my full V8 race weight in my Miata is only 2,300lbs, possibly even a little closer to 2,200lbs. This setup will eventually be put into my tube chassis at some point which should bring the full race weight down to 1,500-1,600lbs depending on if I add or take away a few things. So ultimate power is not the goal.

What kind of power could this engine make with just an LS6 manifold and a nice throttle body? I was planning on using the Holley HP EFI Standalone for tuning and as my harness solution. MSD coils if I can find them, 1 7/8 headers with full 3" exhaust, no mufflers or cats.

The transmission is a "dogbox" Ford T5 with custom ratio's and the rear end is a new Getrag unit out of the 2013 Cadillac CTS-V. Everything else has been custom machined and ready to go (bellhousing, clutch, flywheel, driveshaft, axles, hubs, subframes, ect...) It was all built as light as possible and with as little rotating resistance as possible without spending $30k+ for a custom transmission.

The tires are my largest limiting factor. The largest I can fit on either the Miata or tube chassis is 15x10 forged wheels with 275/35/15 Hoosier R6 or A6 Race Slicks

 

LS6 would be fine. I'd get 6L Truck coils tho. The MSD coils have had issues in the past. I don't know if they were resolved. But on here in the classifieds you can usually get the truck coils, harness, and bracket for $110 or so. And they're a step up over the regular LS1 coils.

Powerwise, you'd be looking at 440rwhp give or take 10hp through an F-Body driveline with that setup. In your car you'll probably see more power to the ground.

 

I can probably detune that to 400 or so just to keep the reliability up. I don't want to rebuild it anytime soon. Engines ain't cheap and this is the most I have ever spend on a car, the cost are getting absurd and I'm going on 2 years of collecting parts now with very little progress.

I also have a new set of Comp Cams 1.72 Ratio Gold Series Rockers, they claim that these free up power. It also seems like the TSP Stage 3 6.0L heads flow very well. Any other recommendations as far as cylinder heads?

 

That's not bad at all. And I keep forgetting you have the 383 forged rotating assembly. You might be closer to 460rwhp.

As a race engine, I'd look at several things very closely: RPM, oiling issues, and valvetrain harmonics is what will destroy the engine.

My advice is keep the RPM limited at 6500, even with the forged internals. Run the best oil pan you can or run a stock F-Body pan with an Improved Racing baffle to help with oil control. These engines are notoriously bad for keeping oil up top, so you can starve bearings without some improvements to the oiling system or even suck the pan dry. I'd also seriously consider going to a dry sump setup. Katech has several different stages and that would alleviate most of the oiling issues. But it cost $$$.

Change the cam to something with much milder lobes. You're running a super aggressive cam designed for the quarter mile. Talk to Brian Tooley or Martin @ Tick on here for a custom cam that is designed for the 4" stroke of the 383 and the weight of the car and for racing. You want mild, endurance lobes with relatively low lift and slower ramp speed. I'd run stock rockers w/upgraded trunion, lightweight valves, lightweight springs w/adequate pressures, and the biggest pushrod you can fit in the head. I'd aim for a 3/8" and machine the head to accept those. I'd also run a quality lifter like a Morel or a short-travel race lifter from Johnson.

 

Good to know. The cam was free if i drove to pick up the block, I kind of assumed I wouldn't be using it though as it is very aggressive and the 111LSA had me worried right from the get go.

I had a very nice custom oil pan built with a diamond baffling and trap door setup with a custom pickup tube to provide maximum ground clearance and good capacity. I do not think I will need a dry sump, this pan is super nice with very aggressive baffling designed for road racing. I'm also utilizing dual external oil filters, cooler and an oil thermostat. What other oil modifications would be useful? I built a Mitsubishi engine awhile back and had the oil passages in the block machined out, I'm not sure it helped any though

Why not run the rockers I have and the LS7 lifters? All my research tells me these are adequate to handle the power I will be making, especially if I keep it under 6,500 RPM. I really try not to abuse my cars, especially not this one. I feel like WOT will be more like WOTHFS (Wide Open Throttle, Holy F***** S***), lol

I'm not trying to go cheap here, dont get me wrong but I am on a very limited budget do to job, ahhhh... I lost my job, haha. Currently working an awful temp job until I get back on my feet.

Between the suspension and external engine parts I have had to purchase or have made I am getting awfully close to the $20,000 mark already just in parts. That was more then I intended to spend at this point and it just keeps adding up quickly. My goal is to keep it under $30,000 assembled but I have a feeling that won't happen

 

Well the stock rockers are what I'd run. I'd just do the trunion upgrade for $130 to keep the needle bearings from spilling into the engine.

And the LS7 lifters are fine as long as the rest of the valvetrain is built with them in mind. Lightweight is the key here. Brian Tooley has some slow rate leakdown lifters "SLR" that might be worth a look for $200.

I'm just thinking some short-travel lifters would be worth their money, due to the fact they they don't bleed down at sustained higher RPM.