To build ,or not to build
 

Ok guys, Ben lurking around this site for a while , first post. Haveing a delma . I want a v8 miata so bad but only if I can achieve around 500 crank HP. Upper 400s anyway. Research tells me this is a realistic goal. But the dino # I see on this site seem low. One question is the 25% loss for drivetrain. Wouldn't that be a set # ? Ie. Autos take x HP to turn not a % of motors HP. Doesn't make sence to subtract 25% off crank HP . Next question or concern is the headers. How much are these short little headers choking the exhaust? Doesn't matter what heads or how much $ you spend on them if you can't get the exhaust out. So my 500 crank HP gets cut to less than 300 rwhp hard to swallow. Or is it just the efi engines can't produce like the carbed ones ? I have the motor, the heads the transmitions ( t5s and toploaders) just have not decided on a car yet . A miata is top of list just lots of work , especally if I can't get my motor to its full potental . Thanks for any input

You're pretty much on the mark with both of your statements. A 500 hp at the crank engine is only going to read 375 or so at the wheels with a 25% loss. I'm reading 270 rwhp on a Mustang dyno which translates (loosely) to about 360 at the crank.

Keep in mind as well that a Mustang dyno typically shows about 12% lower than a Dynojet. My car would read 306 rwhp or 408 crank on a Dynojet.

Both the LSx and 5.0 kits use pretty restrictive headers. On his engine dyno, my father has tested long tubes headers and similar shorties to the Monster kit's on his 306 test engine. He found the long tubes gave about 30 more (crank) hp over the kit headers. The only solution here is to modify the tunnel to make room for a modified set of long tubes. It's been done with 5.0 builds already, I'm not sure the LSx has enough room to do so.

500 crank is probably easier to get to with a LSx than a Ford. With the LSx you may only need a cam and head change, a Ford would probably need a blower to pull this off. You can get the Ford up to 450 or so with the right displacement, heads, cam, intake and tuning.

Good luck and welcome,

-Jason McCully

There is so much aftermarket support for a 5.0 you shouldnt have any problem with any thing your looking for. My question for you is why does it have to be 500 hp?? Have you ever driven a 500 horse car? how about a 500 horse car that weighs 2600lbs ( miata)? I think you might be underestimating the weight of the miata. I built my Big block mach 1 so radical its baically a pain in the ass to drive. With 500 horse you will break more things than you will have fun with. Just some food for thought, disregard this if your building a drag car or something you only plan on driving once in a while. To each his own tho.... build away

I concur with Mach1460. With the widest avaiable street tire being a 225 any power over 300 or so rwhp is almost just for dyno bragging.

-Jason

I have 245/45zr16's under the rear of my dyno queen. LOL!!

I have had a few cars with 300 to 400 HP. One was a monza , I miss that car!

More power the better. I have a 68 bug with 500 hp. with me and a full tank of gas 2600lbs. Runs 10.80@130mph. I could use more power in that. When i convert my wife's 2000 Miata to lsx power i want another 500 crank hp. Doesn't really matter what the power numbers are though....i can smoke cars that have 7-800 hp at the strip because of weight and traction. I would imagine Miata would be similar but could still turn a corner. The bug likes going straight only.

We need pictures and some details on this little bug! It might be just a bit more odd then a V8 Miata!