Hey guys,

I run a boosted 5.3 in my Miata for Time Attack road racing. I�ve been contemplating going NA for a variety of reasons. It�s a 2003 block, 6.098� H beam rods, 11.5:1 +2cc dome pistons, ARP main/head studs. It currently has a ls6 cam in it, new stock lifters, stock length Comp Cams push rods, upgraded rockers, I forgot what springs I put in it but they aren�t dual springs. 706 heads, stock valves.

it worked well boosted, made over 720 whp. The problem is I don�t need that much power, I would like to be around 500whp NA, we run 112 fuel in it. Is it possible with this bottom end? Obviously a proper cam, and probably cylinder heads? This car doesn�t get driven on the street we currently run it up to 7800rpm. If it�s possible to make that power I save 80+lbs of turbo ****, more reliable, less overall heat in the car to try and manage

 

The bottom end WILL handle the power.
It DOES handle the present 720+ HP, so I'm not sure why you are asking the question.
A good pair of nicely ported 243/799 heads will handle the power, but you will need a serious cam with good mid range for road racing.
Call Cam Motion or TSP for good advice there.

 

With current heads and bottom end I dont forsee 500whp being possible.

Not enough compression to run a cam large enough to spin high enough to make the power. Of course if you did have the rpm you'd need the cyl head to support it.

 

And gm lifters spinning to 7800? Geeeeez.

 

I agree. At least not with 7800 redline. Why not run a centri and keep the boost to about 8 psi? Probably a lot less work given the way your motor is already set up.

*insert DDnSPider surprised reaction at my suggesting boost here...*

 

sorry I should�ve been more specific, I know the bottom end can handle it.

I guess I was asking if it�s possible with the current compression ratio or if it was too low. If we kept the 11:5.1 pistons, got a better head and cam if it is was going to be possible. Seems like all the reading I�ve done suggests it�s not enough compression. I�ll give TSP today and see what they recommend. I did a dcr calculator this morning and with the ls6 cam it�s only 6.75:1. That�s seems terrible lol

 

 

What boost are you running to make 720whp?


If you dont need that much power, can you not just turn the boost/timing down?

 

that was around 26lbs on old 5.3 stock dished pistons. It hasn�t been back to the dyno since we put the new bottom end together. But we have the timing turned down already because I raised the compression. Before I we had around 18-19� of timing in it. I think now it was somewhere around 12� I don�t remember exactly. But it�s a dog out of the corners now. That�s why I was thinking if it could make the power NA we could crank the timing back to it and get the drive off the corner again.

other option would be to go with a smaller turbo so it lights off quicker. This is an old on3 88mm, probably not suited for road racing

 

ok. I ask because I�m building a 5.3 right now and was thinking about going with a stock(ish) cam. I�d be happy with about 750whp but not at that boost pressure.

so you say the lower compression motor was more responsive because of added timing? If so, that�s good to know because I�m doing the opposite of what you did, I�m going from high compression to lower compression.

 

Only way you're making 750 wheel on a 5.3 is 20-25# 🙏

 

The problem is you have the wrong power adder. It's either larger cube NA or PD supercharger for road racing. 5.3 won't touch 520whp NA and have any kind of power under the curve. I would put a TVS 2300 on it and run 8-10psi. You will make the power under the curve you need for accelerating out of the corner.

 

Good *** advice ! Or run a very small 70mm ish turbo that only makes 550 ish wheel on your 5.3 MAXED out . That spools instantly

 

He wants more jams out of the corners not less, centri blowers are dogs down low, worse then a properly sized turbo.

They love it!

5.3 has zero chance of making 500whp. I would 100% ditch the 88mm for your needs as its way overkill. Get something like the next gen billet 78/75 run a bit lower boost and more timing, make for a more responsive combo overall.

 

If your set on going N/A and you want to get off the corners, I�d personally go with cubic inches. That car is begging for an aluminum engine to get weight off the nose. Look into an LS3 or an LS7 block with a set of heads that produce crazy fast velocity, cam the thing properly and spend money on valvetrain. Your just not gonna find the torque you want with a N/A 5.3 for road racing. Prolly not the answer you wanted, but it�s what I�d look into...

 

Could have heads ported and hollow valves put in by texas speed. Then have then spec a torquey cam for it and put a fast 102 ported on top Should make 420 wheel hp and 390 torque (guessing) and have a usuable power curve. 720whp seems like a lot to handle in a miatas for a road course...and I know enough about road course to understand that high hp cars aren't always the fastest.around the track

 

Swap in an S362 and run like 14 PSI. You'll make 550whp and 650wtq with twice the responsiveness.

 

it has an aluminum 5.3 in it already, the original engine was an iron block 5.3 that we used when doing 1/2 mile racing. That was replaced with this aluminum 5.3

yes, I spoke with Texas speed on Friday and it�s not looking great NA with the little 5.3 that couldn�t lol. Going to go with a BW S372SX I think. The turbo will end up getting moved and possibly thinking of going to a w2a with an ice box. Get the nose of the car sealed up.

420 hp isn�t enough. These boys are making serious power in the Global Time Attack series, big turbo 2jz, twin turbo ls stuff, nasty big cubic inch NA ls stuff. We are gonna downsize the turbo, work on better boost control and get back after it.

this is the car

 

Youre able to put that HP to the ground ? Car looks like its 2500Lbs. What kind of speeds are you doing out of the corners ?

 

Helped a friend do a road C5 corvette with a standard crate 350 in it,, the recipe was to build a motor with RPM's ..
It was a 406 Sprint car buildup,, with the rev limited to 8200 (On the oval this motor would be turning 10,500)
Iron block aluminum heads, and the rotating assembly was scat/carillo/Mahle IIRC..
Good luck