BP-T or BPT

[Identity_X]

I've been doing a lot of reaserch lately trying to figure out if I should swap the GTX motor I have sitting in the garage or just use all of the turbo components to turbo my existing motor. The GTX motor seems to be in great condition and it looks like it certainly has less miles than my current BP motor. My 1991 LX has 100k at the moment and the car has been driven well, never abused, so I figure that I still have a few good years left on the BP. Now, if I do decide to turbo my current motor, what can I use from the GTX? Obviously the exhaust mani, the turbo itself, and the injectors, but can anything else be used? As far as I know the pistons are lower compression. Would they be worth swapping? Is there anything to be gained from the cams or any other internals? Somewhere on the Miata board I read that the the GTX has hotter cams and a better flowing intake manifold. Can anyone else confirm this? I am just trying to figure out what route to take and it's proven to be a harder decision than I expected.
And yes, I do know that the BP has a better flowing head.

Any suggestions will be gratly appreciated!

[bam]

If you already have a gtx motor just use it. The NA BP doesn't have a knock sensor. You'd be swapping a lot anyway. Just not the engine. I almost guarantee the cams are different and the gtx cams should be swapped into the NA BP(dsm turbo and NA cams are different.) The gtx engine has a friendlier compression ratio, but 9 to 1 on the NA Bp isn't too bad. And yes the gtx will have a better flowing intake manifold because it doesn't have VICS. You could turbo your current motor, but especially since you already have the gtx engine you might as well use it.

[Protoss]

you already have the engine just swap it in. honestly it will be less work than rewiring, and what not.

[itzkcatz]

Swap the gtx motor in and if u feel ambitious swap the na head on.

[Stefan]

fully agree with above comment........the n/a head is definitely worth the trouble if you can.

[Identity_X]

Well if I do decide to swap the complete motor I'll definately put in the better flowing n/a head. I am starting to lean towards a whole motor swap mainly because I can do everything at once and get it over with (including a clutch replacement). Wiring the ecu will most likely be much easier with the motor out of the car. Another quick question since we are on topic: How much is a good P&P job? I remember Branden was selling P&P heads + 3-angle valve job for around $600 + core back in the day. Will this be approx. the same price if I go to a local shop? As far as I know, P&P is a well worth modification regardless if n/a or turbo.....

[JDMProtege311]

what are ya gonna do with the bp if you put the gtx engine in?

[Identity_X]

Originally posted by JDMProtege311
what are ya gonna do with the bp if you put the gtx engine in?

Although it would probably be a good idea to have a spare engine sitting around just in case................. I don't have that much room in the garage so I'll probably end up selling it.

[JesseSays]

I don't see the point in swapping....or ever buying a GTX motor unless you don't have an NA BP to begin with.

do NOT lower the compression.

[Identity_X]

Originally posted by JesseSays
I don't see the point in swapping....or ever buying a GTX motor unless you don't have an NA BP to begin with.

do NOT lower the compression.

I have been looking for just a VJ-20 with manifold for a while and I could not find anyone selling them for a good price, that's why I bought a whole motor.

Mileage difference is another reason. If the BPT is actually around 30-40k as they advertise it, that's a 60k difference between motors, which is not bad at all.

Why not lower the compression? So you are saying if I decide to turbo the BP, just throw on the turbo, exhaust manifold, and injectors and forget about everything else?

[Stefan]

i think jesse means that the n/a compression ratio is almost perfect for a turbo car, rather than the lower gtx ratio.
the lower ratio just gives you an added safety buffer for crappy fuel and management....

i'd want aftermarket engine management with a higher compression ratio - you'll be much less likely to detonate and blow the engine up....

[JesseSays]

Personally, I don't think turbo motors should have static CRs below 9.5:1 and they SHOULD BE 10.5:1

I like cylinder heads that don't detonate too... and good tuning.

[bam]

The reason a lot of people want lower compression is to run more boost on pump gas. No matter how well tuned you are there's a limit to what can be run on 93 or 94 octane no matter what the compression. Boost makes more power than compression, at least to a point. Higher compression does help spool times, but I'd rather run more than 10 psi on pump gas. If you're a fan of running race gas all the time, more power to you, run all the compression you want. 93 octane and 10.5 to 1 compression wouldn't let you run more than 10psi. I'm a big fan of about 8.5 to 1. Seems to make a nice balance. Oh yeah, I have no problem with 9 to 1 either.

Just my 2 cents.

[JesseSays]

you have a mindset that's at least 10 years old....


cylinder heads need to be worked to reduce hotspots. This allows FAR more dynamic compression, boost and static CR than typical regular combustion chambers. This is something the DSM world doesn't like, so it's easy to see where you're coming from.

11:1 and 1 bar is NOT that hard, and will make a kickass motor ON PUMP GAS.

Mechanical Octane...

[bam]

This may seem like I'm trying to start problems, but, trust me I'm not. It seems most people make more power running 8.5:1 C.R. and 1.5 bar rather than 11:1 and 1 bar. I know all about hot spots, that's why I love sodium filled valves, that kills 2 right there. I know 4 valve cylinder heads and pentroof combustion chambers help too. There's also water injection, and intercooler sprayers which are a big help. Most dsm'ers aren't as agianst static compression as I am, I just want to run lots of boost on pump without water injection, or race gas. I'm wondering if or where you've seen a street car running 11:1 and 1bar without race gas or water injection? I'm not trying to be rude, I'm just curious. I know the srt-4 motor and most of the new turbo motors use an a-symetrical pistons, as mechanical octane. I remember reading about it and getting all excited. But it's not a miracle, the aricle about the srt-4 siad it only allows 1 or 2 more psi before knocking. The point I'm trying to make is more boost and less compression usually makes more power on pump gas. This is just max power, big spool times can make a pretty ****ty autocross car, which is where i think you're coming from.