Race Motor Re-build Questions
 

I have been running the motor combo described below for the past three years. Run about 20 track days per year (most with a dual driver so the car rarely rests). The short block is starting to get a little tired as the oil pressure starts to drop once the motor gets hot (from 50 lbs to 30 lbs at throttle).

• Stock 2001 bottom end with Maruha oil pan baffle, ARP head studs
• 2000 head with 1mm larger exhaust valves, slight porting/head shave
• Adjustable cam gears with exhaust cam on intake side
• Reworked 2000 intake with upper intake camber machined out
• Skunk2 Pro Series 64mm throttle body
• M-Tuned fuel rail with fuel pressure regulator (set at 60 lbs)
M-Tuned coolant re-route
• RB Header, Spec Miata exhaust system
• MegaSquirt PNP with Toyota COPS
• Self imposed 7,200 red line
• Dyno’d at 155 rwhp, 127 ftlbs torque

Time to throw a new(er) 2001 short block under this setup - before I do I have a few questions.

Have access to a Square Top intake manifold - will this stock Square Top outperform the reworked/machined out 2000 manifold.

What are the differences between a 2000 and a 2001 head gasket? Which one should I be using with a 2001 block and 2000 head.

Any performance gains in going with a thinner than stock head gasket? If so any recommendations on the best available?

if you gutted the vics manifold and vics is inoperable - then yes
you need the 94-00 gasket and use a proper coolant re-route
no. stock mls is best

Squaretop will make more power than gutted VICS.
94-00 gasket
CR depends on fuel. Here in Cali (91) we stick to 10.25 unless it has polished chambers, then maybe 10.7 at most. States where you can run 93, I hear guys reaching MBT in stock cammed BP's with 11.0:1, YDMV. E85, shave .060 and/or 11.0:1 Supertechs.

As a side note to OP question/s, at won't point should someone strongly consider a BE oil pump and/or SuperMiata/ATI damper?

Can you get by with one of the other or ?

Emilio also has said you will get more results on opening up the intake side of things on BP's, so what is feeding that Skunk2 TB of yours?

Short (10") homemade intake with a large K&N on the end terminating where the right front headlight used to be. I remove the turn signal to get more air in there as well as using "Will Martins" louvered headlight cover.

Add at least 3 inches to that pipe length.

SuperMiata damper might solve the oil pump issue. BE oil pump definitely solves the oil pump issue. I put an oil pump on every bottom end that leaves Trackspeed. SPM dampers are recommended for anything above 250whp or 7500rpm.

Thanks for the info. If I end building an engine, I'd likely do both to try to maximize longevity.

So, if I just grab a junkyard engine, don't spin it above ~7100 and use it til pukes?

Cant' answer for the two pro's in this thread but that seems to be the deal here in socal. Unless you're going balls out build it seems the best dollar/performance balance is to copy the 95r project that emilio did (yard engine included). Iv'e seen it on track and it's faster than it should be for hte money that was spent... (of course it doesn't hurt to have a 2x Nasa national champ behind the wheel).

Pretty much.

We built forged bottom ends for two reasons:

1. Insurance against money shifts/mechanical over rev.
2. Because the engine breathed well enough to have normal shift points above ~7200rpm or so.

We purposely restrict the rev limit on the SuperMiata race series to 7000 in the interests of engine longevity and reducing operating costs. Even with a high dollar build, perfect cooling frequent oil changes with Amsoil, carefull warm ups, everything, BP engines just don't like being revved past 7500 and wear out faster when you do.

Even a mistreated junkyard BP with so-so compression will last a season usually. They are tough engines. So perfect junkyard BP (from Japan usually) deserves to be taken better care of with a good oil cooler, big radiator, reroute, high zinc race oil and no overrevs. Still need to keep revs below 7500 though. A few here have revved stock NB engines closer to 8000 on a regular basis but that's high risk. Bottom end usually goes first with those kind of revs, spun mains usually.

For the record, the JDM NB1 and NB2's had 7500 rev limit. Every single part of the long block is the same as the USDM (I checked). Only different part is the mass damper hung off the TB on the JDM models. I presume that's to keep the throttle shaft from breaking as they like to do without the damper. Can't find a damper? Either epoxy the OEM shaft or swap in a Skunk2 TB.

Thanks for all the great info.

I've now found a super cheap, running '99 engine locally, so I may go ahead and do a mild build.

Is there any point in using more cam than a BP5A if the head will be stock? (IE no porting, stock sized valves)

Yes

To keep more info in one place.

You mentioned running custom JE 13.5:1 in another thread for an E85 build.

I assume this is a better scenario than 11:1 and shaving the head? I'm not knowledgeable enough about headwork/squish area, etc. to have any idea.

Essentially, I'm strongly considering a build like this:

Manley rods
Supertech valvetrain
SPM Damper and BE oil pump
Squaretop (already on the way)
13+ Compression (whether custom or 11:1 + shave)
Cams for best 4500-7500 power, not sure on this either


Do you have any plans on offering a piston designed for "E85 N/A", ie 13:1+ compression?

You'll need custom pistons to get to 12.0:1. For 13.5:1 you need them custom built with foreknowledge of the chamber design and valve lift. Not OTS stuff but a custom build by someone with a lot of BP specific knowledge. Keegan Engineering in this case.

Where is 11:1 Supertech's and a 0.060 shave going to end up (comp ratio), assuming an otherwise stock combustion chamber?

0.060" is a crap ton of shave, I have no idea if it's even possible to take that much off. But if you can and don't have clearance issues, it would bring your 11:1 supertechs up to around 13:1.