alex 2550

Hi Everyone,
Firstly I wish you all the best for the festive season.
I have searched for answers here and around other forums but I haven't found anything that really answers my question with my setup or similar in the last decade so I thought I would ask, this is the first question I have posted on Miataturbo (not my first post) so go easy on me....... but not too easy.

I'm located in Australia, my car is a 12/95 NA8 and not my daily driver, I have owned it for a few years and it has all the usual suspension and bracing mods.

It has the standard bottom end which is the NA8 9:1, it's very healthy and has roughly 120,000 miles on it (200,000km).

The top end (head ect) is currently disassembled but has the following.

- Fully ported BP4W race head shaved 60 thou by Gary Stewart. Gary is a very well known entity in "upside down land" race circles.
- Supertech back cut and under cut standard size black nitrided stainless intake and exhaust valves.
- Supertech light double valve springs with titanium retainers.
- Supertech bronze valve guides.
- Mazdaspeed SUB's.
- TODA 256/9mm solid profile intake and exhaust cams.
- TODA adjustable cam gears.
- Flowforce EV14 640 injectors.
- Flat top manifold.
- NB8A fuel rail.
- Spartan 2 wideband.
- Toyota COP's
- Cowl intake.

I will shortly purchase an MS3 of some description. Just looking at all the options and researching but possibly an MS3 basic from Rev' or one of Brains MS3X units.

With the 60 thou shave on the head i'm working on roughly 1/4 point compression increase for every thou shaved so my 9:1 compression will be up at around 10.5:1 static. If the head was together I would CC the combustion chambers but I think this 10.5:1 is pretty close with genuine Mazda head gasket.

I was building the car to be an N/A track and street build but I just can't find the time to get to the track anymore (3.5 hours away) so I have decided to go a street turbo set up that's responsive and not that wild, around the 250WHP mark for now.

This is not my first turbo setup, not by a long shot. But it is my first turbo Miata set up so I need people with more knowledge on the BP motor than what I have.

Keeping in mind i'm looking for a responsive street only maximum of 250WHP for now.

What do you all think of this setup running a GT2560 on a tube manifold (NitroDann) and 3 inch exhaust on wait for it................Pump fuel?!


The fuel will be Australian 98 Ron (minimum) which works out to be 93 "State side". E85 isn't common over here and the nearest pump is about 130 miles away.
It will obviously be intercooled.

Do you think this is possible or am I going to be fighting detonation to the point that it becomes a nightmare?

Thanks for your time everyone, again all the best for the festive season.
Alex

ryansmoneypit

iTrader: (6)

That's a lot of compression for that fuel. If all you wanted was 200 hp, then it might be a little better. Stock rods, 10:1 and 93, you get one short chance with detonation.

irollgen4s

If your goals are around 250 wheel and you are already running relatively high compression I personally at the least would add in some forged rods with the stock pistons if money is an issue, throw in pistons if you don't want to open it up ever again. The stock pistons on a good tune will hold to around ~300hp but the rods will bend long before that with some detonation.

Otherwise i think you will be fine, a 2560 will fit the quick spool and 250 wheel requirements.

2manyhobyz

iTrader: (4)

You could check into if Cometic or someone else makes a thicker head gasket. Also maybe there is more material to be reshaped/removed in the combustion chamber. Otherwise, yet gonna hafta do the rods.

sixshooter

iTrader: (12)

I would do rods for durability and lower compression pistons for detonation resistance and durability, especially if you have such a heavily built head. It will be counterproductive to mate it to a stock block with weak rods.

tomrev

Pretty sure Cometic will make you just about any thickness head gasket, as long as they have a pattern, which is easy (sure they would, but you can send a stock gasket, for lay out.). That's the easiest way to back off on the comp. ratio; but I agree with others, that if it's out, and the head is off, I'd go thru the bottom end with forged rods and lower comp. pistons. I see combo kits with Eagle rods and Wisco pistons for under $900. US. Your goal of 250 RWH will be very obtainable. Good luck!

emilio700

iTrader: (3)

I can never understand the rational for spending thousands of dollars and hundreds of hours on a build with a semi-worn out bottom end.

In my book, "very healthy For a used NA8 block is 185psi and <4% leakdown. Whatcha got? Anything under 170psi and 6% I would rebuild before adding a blower.

alex 2550

Thanks everyone for the replies, I really appreciate it.
You have all confirmed what I expected but I kind of hoped I was being overly cautious, I obviously don't want to destroy a bottom end and risk taking a fairly expensive head setup with it if the valves and pistons have an intimate moment together.

Thanks for your comment Emilio, its good to know what someone with your experience considers healthy, also thanks for the countless times you have shared your knowledge on here it's a credit to you and your business.
In answer to your question, compression test last year with the BP05 head had a high of 183psi (sorry cant remember the cylinder but I think it was 2) and low of 178 on number 4, I can't remember the leak down test numbers but 4 was higher so its the problem child.
Also I also agree 100% with you on the built top end on a used factory bottom end, I'm a mechanic by trade and it doesn't make a whole lot of sense but I had a reason.

I have always done the whole motor in one step, the reason I just did the head on this bottom end was that it was going to be just a standard BP4W head swap, nothing special and then I eventually planned on doing the bottom end when it needed it, just balanced with a set of light rods like Carrillo's or similar and leave it at that. the NA for me is just cheap fun.
I not long ago sold a WRX with around $40k US put into it and still have another project with considerably more in it than that plus bikes ect and if I go crazy on the NA the wife will kill me...... I did say to her I was going to leave the NA stock when I bought it ..........she didn't believe me lol she actually said "I bet it either ends up with a turbo or a rotary in it".

For the record nothing gives as many smiles per dollar compared to the Miata and I wish I had got one years earlier.

I considered a thicker head gasket as a band-aid solution but messing with the quench area may mean that detonation is still an issue and not solve the problem anyway.

So the only real solution now then is build the bottom end with some lower compression pistons and forged rods but I was hoping to delay this till the end of next year as I don't want to do the bottom end rebuild by halves and have a couple other projects I want to get finished.

So the items I have in mind for a rebuild is.
- ACL race rod and main bearings, always used them.
- Supertech pistons 8.6:1 with Wiseco rings, thinking of going out to 84mm. I have never used Supertech pistons but have read they are a little more quiet the Wiseco's which I have used and because i'm not shooting for crazy numbers i'll give them a go.
- ebay rods, maybe the Maxpeeding ones or a set of Eagle's.
- Boundary pump.
- ATI damper.
- ARP main studs, will most likely need a line bore I suspect.
- Maruha sump baffle, while the sump is off it makes sense.
I already have ARP head studs.

I guess the bonuses is the sump will be easier to drill for the oil return on the bench and more time N/A to learn settings on Megasquirt so not all bad.

If I am building the bottom end the turbo will most likely end up being a GTX2860R and shoot for 250-300WHP, I have a GTX in another vehicle already and i'm happy enough with it.
EFR turbos are certainly better but the price difference down here is huge.

Thanks again everyone for your input and time replying, it's not the advice I was hoping to hear but the advice I was expecting to hear. I'll enjoy what I have for now, boost will have to wait a little longer.

Cheers.
Alex

adryargument

iTrader: (1)

Last time I bought a cosmetic gasket pretty sure I had options for 20 / 40 thou thicker. Straight on the website.

I think I remember seeing that/a Stewart head/motor for sale a while ago. Nice piece of kit for NA power. Would be a shame to kill it.

There's always the option of getting a cheap decent compression 2nd hand motor and whacking the turbo on that until you either learn more about ms3 tuning or blow it up 🤣

At least you wouldn't be babying it and probably enjoy the process more.

alex 2550

Thanks heaps mate,
The thought had crossed my mind on a second motor but I think i'll just keep it N/A with this set up and bite the bullet and build the bottom end before going turbo because I agree it would be a shame to kill what I have by cutting corners on a turbo setup.
Still fun but not as fun as turbo power.
There is always the other option..... just buy an NB8B turbo it and have 2 of them ...... my wife will kill me. lol