The original dilemma:



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The newer build, fresh with a much simpler setup:

1990 Mazda Miata - V8Roadsters LS Mounting kit with LS3, T56 Magnum, and Ford 8.8
T56 Magnum wide ratio transmission (2.66 1st /.50 6th)
Ford 8.8 rear end with limited slip 3.27 rear end (03 Cobra housing, aluminum driveshaft, 31 spline miata swap axles)

The engine setup:
Crate LS3
(Intake manifold?)
Summit Racing Camshaft 8710R1 or Texas Speed F35 Camshaft
PAC 1207X Valve Springs
Long tube V8 Roadsters Swap headers (IIRC these are 1-3/4" primaries and 3" collector)

For anyone who is jumping in now, I'm trying to choose a cam and intake manifold package that pushes torque up as far as possible with a 480-500 RWHP goal on a stock bottom end LS3 running to 7000 RPM.

 

If this will be used for road racing, you want to keep the cam flexible throughout the effective rev range.

 

I'm looking to build it for a 9" tire class primarily as a drag car but also with some capability on the street/highway. This car will probably never see any sort of road course or autocross use

 

There’s a guy who drag races an LS swapped Miata, still using the IRS, on the FB V8 Miata group. The car goes by “Turtle” or something like that. Runs high 8s. His is turbocharged, but he seems to know what he’s doing. You might try to contact him.

 

Yeah, that's Matt Lamphier, and that's the 5.3+Turbo I mentioned

 

Call BTR, they will have a good recommendation. If you want to get more sophisticated, call Bullet. Summit has nice shelf cams, as well. The Saturn stage V would be ok in this, maybe they will chime in. The valve springs are going to limit you the most. Go PAC 1207x, you'll thank me later.

 

With that combination, I'm thinking one of @Summitracing 's new big guns cams would work well for occasional street use:

Big Gun 1 SUM-8729R1 is a 10 I/O, 50 I/C, 65 E/O, 3 E/C for 13 degrees of overlap. (240/247 115.5 LSA + 5.5 Adv. .625/.605)
Big Gun 2 SUM-8730R1 is a 11 I/O, 51 I/C, 67 E/O, 4 E/C for 15 degrees of overlap. (242/251 116 + 6, .625/.605)

With it's light weight, and the fact you'll only be using it for occasional street, I think maybe the larger 8730R1 would match well in this case (even with the 2.66 1st and rear 3.27 gear). Should soften the bottom end @ launch, since you'll be traction limited on tires that'll fit in a Miata, yet still have some street manners.

 

Do you think going with the close ratio 2.97 1st gear version over the wide ratio Magnum with the 2.66 or a different rear gear would help? I think I'm on the right path of pulling as much out of the bottom end as possible to help with launching, as I'm very aware that a 9" tire is about as much as I can get under the car without doing at least a mini-tub. I've tossed around a bunch of ideas:

1st was going with a destroker- 6.2 block with a 4.8 crank to move the power band way up high and doing everything I can to pull as much torque out of it as possible
2nd was just taking a stock 6.2 and shoving a cam, long tube headers, and a good 93 tune on it
3rd was doing an aluminum L33/LM4 and slapping a large single turbo on it- but it's been done and I wanted to be a little different
I even thought about just slapping an LS7 in and calling it real, but option 2 got me to the same place for less money, which meant I could spend that money in other places.

and then, after driving one of the new LT1 Camaros I decided I really wanted a stroker- I loved the power delivery and wanted all of that but more of it so I felt like the stroker LS3 build was the way to go.

I would like to see the car hit 11.00 to start and see if that's enough for me. The car is a convertible, so it needs a full cage to comply with chassis regulations at 10.99. This car can get away with a roll bar (which would keep it streetable to me). and that seems to be the edge of the rabbit hole- A custom cage that would allow me to use the factory soft top (Which is important since I don't fit in the car with a hard top on it- My head would contact the roof with a helmet on, the soft top has a bit more clearance) is in the neighborhood of $3000 (I can't weld, and I definitely would not take chances with my own life like that).

My budget on this build is roughly $25,000 with about $14,000 of that being dedicated solely to the engine after adding everything else to the car (Suspension is a WIP but I'm going to need to adjust the final details of that when I figure out where my actual goals are, but I figure around 2k for that setup at most). Thankfully I'm not worrying about labor costs since I'll be doing the whole build with my fiancée in our garage.

Another note- I'm capped by Pump gas locally as the one semi-local E85 station is half a tank of gas away, the car has a 10 gallon tank on it and I don't feel like driving an hour to get crappy (as in low ethanol content) "E85." I think I can get away with a 12.0:1 static compression ratio on this build but don't want to push too hard since the average temperature in summer is easily 90+ and closer to 100 and the humidity is pretty nasty.

 

If you want to street drive the car, the .50 ratio in 6th will help the fuel economy a bunch. My LS3 Miata puts down 471 rwhp and gets 31 mpg highway with a .5 6th and 3.23 rear gears.

Looking back, knowing what I know now, either that approach or a 5.7 rather than 6.2 makes a lot of sense in such a light car. Depending on conditions (tire temp, pavement temp, passenger or not) data logs show that my car has spun the tires at up to 100 mph in 4th gear on dry pavement. This is on good quality street 200TW tires. On warmed up track rubber, with an instructor in the car, it will hook second gear at full throttle. Forget second gear on the street, and it's not unusual for the tires to break loose around 85-90 mph in 3rd as it comes up to the torque peak. A smaller engine (destroked 6.2 or 5.7) would also get better fuel economy, which might matter to you since you plan to street drive it.

That's mostly what I've got. A 6.2, upgraded heads, cam and headers. I **love** the way the car drives, I'm sure it's fast enough to get in the 10s easily with drag rubber and a decent run (but I'm a road course guy).

Re: the cage ... a cage would detract a lot from the streetability of the car. Can you run a hardtop at the strip? My car has a roll bar and door bars, but no cage. The trouble is, almost any Miata with an LS will go under 11, and if that forces a cage, then you immediately have a much less street friendly Miata.

 

Do yourself a favor and go milder instead of wilder, unless you are racing for money or life and death...LOL

Andrew

 

With 12:1 static compression ratio, then the SUM-8730R1 gets the nod. If I did the math right, should put you around 8.7 dynamic compression ratio and ~182psi cranking compression which should work on premium with the right tune.

Probably stick with the close ratio 2.66 transmission. Close ratio should work well at the track. Going steeper on 1st defeats the purpose of softening the bottom end for launches. With the 3.27 and 22" tall tires the combined ratio is good for launching.

Definitely need some safety upgrades for how quick it's going to be.

 

That's actually better than what I get now- about 25-26 average highway.

I think I might be better off Just throwing a mildly massaged LS3 in the car with a set of long tube swap headers and a good size cam. If I don't need any more that's great, but if (when) I do eventually feel the itch for more I can do heads when I get the build going since they'll have to come off anyway to do the rest of the build. Seems like most of the milder builds I'm seeing are just cam/intake/long tube headers/tune. and that should be plenty to start. It's not like I can't throw the money I'll save into a high yield savings account and have a little more when I'm ready to go ham.

Unfortunately, the helmet I'd need would hit the roof of the hardtop in the factory seating position. In theory, I could mount the seat directly to the floor in a fixed position to give myself enough clearance with a helmet to at least not hit my head on the roof over any sort of bump- but then the issue becomes the hardtop isn't a fixed hardtop (It's still removable) so it doesn't save me any headaches around the roll cage rules from what I gather. It's about a 3/4" to 1" from the top of my head to the bottom of the hardtop at most, but the soft top sits at least another inch higher. I do realize the aerodynamic benefits a hardtop gives, and I'd really like to use one, but it's really a spatial limitation.

 

Sounds like you need a Dan Gurney bubble. :-)
http://race-car-replicas.com/parts/gurney-bubble

But seriously, considering it's not a true fixed roof, it's not going to pass tech without a cage.

 

You’ll need to do the drop floor no matter what. Helps you fit with a hard top and a roll cage.

 

One thing to consider (I am NOT a cam expert) would be to have a bit less lift than that 0.650". It will help the engine live longer and I think you have enough cylinder head and flow to drop to .600 or .580 and still make the power you need.

You may also consider a slightly wider lobe separation angle, but that is up to you, as its a relatively minor choice.

 

I would go with a destroked 6.2, 6.0, or 5.7 over a 416 stroker. The 416 will make torque on accident and the short wheelbase of the Miata is going to make it a handful to keep straight. The smaller displacement will feel right at home in the Miata and it is still going to rip with its light weight. The softer torque delivery will allow you to hammer the throttle without the *** end wanting to act like you just hit a banana peel on Rainbow Road.

 

I had a FC RX7 back in the day. It made 390rwhp and eventually ran a 10.95@125mph

How quick do you want to go?

Andrew

 

I think rather than a stroker, just build it as a stock bore/stroke LS3. A camshaft like Cammotion's Stealthy Stroker LS 230/242-117+5 Rectangular Port or similar would work well in a very lightweight vehicle and 6.2L.

https://cammotion.com/camshafts/stea...ectangle-port/

Very broad/flat torqueband and with the 1st gen Miata weight with decent driveability thanks to the IVC. With the mild overlap, it'll be more linear and easier to manage, and long durations will still give it top end charge out to 7k.

 

It depends. I'm 5'11", with a long torso (my head hits the roof or is close in a surprising number of vehicles, given my modest height). My helmet clears the hard top in my Miata with an Ultrashield seat bolted directly to my stock, unlowered floor.

 

Ideally I'd like to run 9s. But for now, I'd like to keep it to 11s- gotta learn to crawl before you can walk.


The more I look into this, the less I want to actually do the stroker build. For the money i'd spend pulling the engine apart to do a stroker build I could add a mild single turbo setup and do a boost by gear tune- and dual tune it at that. I can have a 4-6 psi "street tune" and a higher 8-10)psi "race tune" for when I'm at the track, etc. I think what I really want is to be faster than anything I'd realistically come across on the average drive to work- plenty of v8 challengers, mustangs, and camaros around here, and I think realistically a C/I LS3 would be enough to do that, given the utter lack of weight in the car.