Ok so about what I remember, I actually expected closer to 500 on your build and I have to say your build is what convicted me to revert my focus back to rectangle port heads. Guess I expected the lift to make up the low overlap but it didn't. You might still get much closer, idk; last year I actually tried all kinds of different intakes and don't remember them changing my Kpa drop at all. Usually drops by 3-4 and it stayed that way. Your result remined me of reading all those old threads comparing rectangle and cathedral port heads saying cathedral ports can make as much power as rectangle ports but they need more cam and overlap to do it. I bet your heads are capable of 520/530 with more overlap but I remember your focus being different like gas milage etc. so you got what you wanted, not like the Miata needs more.

You can do small port heads that flow great and have great efficiency through smaller valves but if you want to make rectangle port power up top you will need to lean on the cam more or you can do the opposite and lean on the bigger rectangle ports with a smaller cam for the same outcome while still keeping decent throttle response. You start losing noticeable throttle response though when you start doing big cams, with later intake valve closing points, on the rectangle ports without more compression; idk, that's at least my conclusion from reading all those professional opinions, different head build threads and driving different combinations.

 

I totally agree withe the above.

Rodney and I have almost identical setups except my short-block is LS2 (05 vette). We talked several while I was planning my build. Bang for the buck ported LS3 heads, intake and throttle body with 1 7/8 headers and a moderate cam are a killer combo.

I've got a dyno planned for the 21st, will give results when done.

 

Bringing this thread back from the dead. But, this is a very good option imo for heads that don’t cost 3500-4k… they come cnc ported, has an 11° valve angle for better flow and more camshaft and PTV. The ports aren’t hogged out. They even have a 255cc version that’s not ported under 1800 bucks….

https://smedingperformance.com/colle...39309244792890

 

What's interesting about these is what they said about comparing them to a competitor. That sure sounds like they compared them to AFR 260 12 degree heads I talked about earlier in this thread. Those valves are probably still heavy as hell but so are the ones on the AFR head.

"Below is a dyno comparison of our 11° 260cc CNC cylinder heads vs a competitors 12° CNC 260cc cylinder heads. The test engine was a mild 11.0:1 441" LS engine with our 245/256 Rectangle Port R4 Stroker camshaft. Both dyno pulls were done the same day, with both tunes optimized for each combination. As you can see the 11° Smeding heads outperformed the 12° competitor's heads across the entire curve."

 

they aren’t as heavy as the afr. And afr needs roller rockers which adds even more weight to the valve train. Lightweight valves have their place if you are spinning above 8k rpm’s. For the most part it’s not necessary.

 

Do you know the weight of the valves? It doesn't say on their website, but it looks like they have bronze valve guides just like the AFR heads so they need roller rockers as much AFR heads do meaning if you want to prolong the life the guides otherwise both heads can use stock rockers.

Also, imo you want the valves as light as possible so that you can use lower spring pressures to prolong the life of the lifters, cam, guides, etc.

 

I don’t have the weight of the valves. Billet Rocker Arm Stands Included - Compatible w/ OEM LS3 Rocker Arms.

Spring pressure puts stress on the lifter, guide and pushrod. Hence the reasons for hardened pushrods for deflection. Lightweight intake valves benefit over 8k rpm where instability can greatly occur and have valve float appear. Exhaust valves are always steel due to extreme temps. For a street car. The valves are fine. Regardless the stock ls3 intake even ported falls off at 6600 rpm’s… unless you go to a high ram which requires that no hood gang and destroy your bottom end torque.

I like the smeding head’s because of price. The ability to mill chambers to 62cc and have plenty of ptv. If you had to take the heads off I’d get these if funds allow. If you wanna save money and had to take the heads off, I’d send them to txspeed. Stock untouched ls3 heads flow up to 800whp under boost….

 

I am also looking at the Smeding 11 degree head. I have a 5th gen Camaro SS. Already have ported heads and healthy SS3 camshaft.

I am wanting more out of it. The 11 degree head will allow up to .200 of Piston to valve clearance, I believe. I am thinking of going to the GPI SS4 cam and milling the smeding head and adding a ported intake with 4.10 gears.

I am just wondering how much I can mill for 93 Octane only? It is a 69cc chamber to begin with, I am pretty sure.

Would anyone know what would be the best mill for 93 to maximize hp/tq without leaning it out too much on 93?

 

I’d run pat g’s stage 3 cam. 233/242 111+2 .621/.604 cut by cam motion over gpi cams. They are way too big for stock cubed ls3. The overlap will make you hate the car.

I’d run the smeeding heads milled to 62cc and .040 headgasket. Should be 12:1 compression. I’d run e85 for max effort.

Also I recommend the performance design intake ported by Mamo with a katech 102 TB.

3.90’s would be much better.

You still want to measure PTV. Never guess or think it’s ok. I’d also run 2116 link bar lifters for valvetrain stability. You will need to measure each pushrod. You may have 2-4 different pushrod lengths.

 

So, the car's current setup which I should have mentioned:
Ported LS3 castings
GPI SS3 Cam
3.91 gears
Full bolt on's with Stock manifold.

I am at 480 Wheel currently.

Not bad to drive with the gears, but was planning on doing a trutrack and 4.10 gears along with the ported manifold and Larger SS4 cam. I do already have upgraded valve train .660 Ti springs, Oil pump, and the fore mentioned Johnson Link bars installed. I had an LS7 swap which failed rather quickly. Can't get over the power difference from the extra cubes. It was also Heads/cam/Intake.

I want to gain over 500 wheel horsepower and try to bump torque with the compression in the 11 degree head. I don't have e85 stations near me, so sticking to 93.
The SS4 cam actually has a bit less overlap vs. the current SS3 that I am well familiar with.

Pat G builds do intrigue me, but I want a quick turn around as the weather is getting nice and want the car ready for the spring. Is that cam capable of over 500 wheel with 11 to 1 or 11 to 5 compression and the Smeding Head?

The SS4 with a Frankenstein 11 degree head and a bit of milling is doing 520wheel 470wtq. That was the goal here.

 

Pat G’s cam will be better down low and both similar top end.

BOTH will make 500whp.

Mill heads to 65cc w/.040 headgasket. 11:6ish compression. Wouldn’t run any more on pump.

I recommend Greg Huggins for tuning. You can find him on HPtuners forum. You’ll really need to dial in the ve tables on these cams and EOIT/SOIT or they will run like a bag of wieners. Will require a blend of sd/ and MAF.

leave the 3.91 in the car. You’ll kill your whp goal the bigger you go.

 

This is on an LS3?

What is the full set up? What did it dyno whp/wtq?

 

Yes, it's an LS3.

FAST102 intake (ported by Tony), stock LS3 throttle body ported by Tony, 1-3/4" long tube Kook's headers (can't fit bigger in a Miata), and 2-1/2" exhaust out the back (hard to fit bigger in a Miata).

It made 471/425 on a Mustang dyno, and gets 31+ mpg highway because of the mild cam, high compression, and long gearing ... I run a 3.23 rear end.

 

Just FYI, watching a guy on YT who does a lot of LS swaps. He has a cammed LS3 in 350Z with a LSA on it but before he did the LSA he was running 2-1/2 exhaust and didn't like his dyno numbers, switched to 3" exhaust picked up a considerable amount of power. Don't remember how much but it was like over 30, didn't believe it. He just swapped another cammed LS3 into a G35 sedan with dual 2-1/2, made like 440, expected 485 so is now doing custom dual 3" exhaust which isn't cheap, but he's convicted it will be worth it. Apparently an LS3 needs dual 3" pipes to breathe otherwise it's being choked. I'm pretty sure that 2-1/2 is choking your Miata out of a considerable amount of power from what I have seen.

Can you post that dyno sheet?

 

I'm sure you're right. My exhaust is 3" back to the trans crossmember, and then 2-1/2" after that. I could probably run the 3" back to the differential and then neck it down. I'm about to lose a bit of clearance around the diff because I'm upgrading from a Getrag (CTS-V, Solstice, etc.) diff to a Ford 8.8. Realistically, 30 more horsepower in a Miata would just give me 30 more horsepower worth of wheelspin at 100 mph. Might be usable on track, though ... after the track tires are nice and sticky, it will actually hook 2nd gear, which it never does on the street. On the street, depending on tires and temperature, I've seen wheelspin at 100 mph in 4th.



On this same dyno, a completely stock LS3 with a GMPP ASA cam made 462/425 ... but it had horrible street manners. This engine only made 10 horsepower more, but is actually reasonable in daily driving.