Engine upgrade question

[Zorix]

Hi everyone. I have been researching this topic for a few days and found some answers, and also had a few more questions in the process as well. I have the BP DOHC engine from a 91 LX and due to poor compression, I want to rebuild it. I want to put some good pistons and rods in place so I can eventually tune it for performance. From my research I have found that Wiseco seems to be the favorite here as well as Eagle rods. I also found mention of FlyinMiata's custom parts but those are very much out of my price range.

After some searching I have found what appears to be a pretty good deal on Wiseco pistons and Eagle rods: http://www.ebay.com/itm/270771668724...84.m1423.l2649

My questions are:
- Will I have any problems with the stock piston oil squirters? (Some forum searches said yes, some said no)
- Will this change the engine to be an interference design? (Possibility of valves making contact with piston)

Also for later upgrade options, I have the following questions:
- How can I increase the engine performance without using some form of boost. (Cams, intake, exhaust?)
- What kind of performance numbers can I safely expect without boosting?
- What are recommended manufacturers/parts for headers/exhaust upgrades?

I realize these are a lot of questions but the more I research, the more questions I have and if I am going to go down this path, I don't want to use any substandard or dangerous parts and ruin my engine block or waste my time and money. Thank you all for your help.

[atomicEGT]

contact the seller to ask about the reliefs for the oil squirters. if they don't know, buy from someone else.

you'd have to really **** something up to make a BP an interference motor, especially with pistons that lower the CR from stock.

N/A power upgrades: cams, shaved head, increased CR, IRTBs, well-designed exhaust, increased displacement.

Fuji-Racing made 184whp in their Miata using every trick in the book, I think someone made 200ish whp with that Maruha displacement upgrade setup. BPs make ****-all for power without boost, it really isn't worth the effort and expense.

PS: if you're trying to make power N/A, buying 8.5:1 pistons isn't going to help.

[Zorix]

Thanks. I did contact the seller but have not gotten a response yet. For a higher CR, I would need to increase the bore size, correct? Where would you suggest I get pistons that have an increased CR with relief for oil squirters? I have no problem with spending upwards of $1000 on piston/rods but thats about as much as I think would be feasible. I would also like to have it in a condition that if I change my mind about boosting, I would not have to touch the block again. Also, I'm concerned about boring the block a lot due to loss of integrity. I want this engine to last. I'm also looking at somwhere around 150 hp and I would be happy. Thanks again.

[atomicEGT]

what? no, just buy different pistons for a higher CR. Wisecos are good, I've heard good things about Supertechs too. boring out the block a bit for slightly oversized pistons isn't going to hurt anything.

seriously though? rebuild it with stock parts and run a GTX turbo setup at stock wastegate pressure, you'll make like 170whp and it'll be bulletproof.

ETA: if you're dead set on going N/A (and don't think you'll want more power later), I'd build the motor like this:
-10:1 Miata pistons / stock rods
-B8 crank
-1.6 Miata clutch / lightweight flywheel
-Web 505 cams/TODA cam gears (or exhintake/Fidanzas depending on budget)
-well-designed header (I forget who makes the best for these, Genie maybe?)

should make power close to your goals and be a bit more rev-happy than a standard BP.

[Zorix]

Thanks. I was looking around but I don't know of a trustworthy seller for these pistons and there seems to be quite a few options. I've seen some 10:1 CR pistons and that seems quite high. Do I risk a problem running at that CR, especially if I decide later on to do a turbo? One of the main reasons I don't want to do a turbo yet is that I haven't found the parts to do so. I know there is a VJ11 or maybe it was a VJ20 that was designed to work with this engine, but haven't found all the parts for that yet. I also know I would need a BP26 ecu. It's a lot of work as well. The current plan is to replace the transmission with a manual G5M-R and fix the engine, next step would be boosting if I can get to that point. This is something of a learning project for me. I have a friend that has the experience in rebuilding engines but nothing Mazda or upgrading parts. I would need to come up with the upgrade plan somehow.

I guess what I am looking for is a known good seller and a Wiseco part number that would be ideal for my situation. Since it's an 83mm bore I would go for slightly oversized but possibly higher CR if it's not going to be a problem with a turbo down the road. Thank you again for clearing that up.

[atomicEGT]

you don't really *need* forged internals for your power goals. you can turbo a 10:1 motor (Miata guys do), but you have a smaller safety threshold for detonation- you'd need a good tune and I don't think a BP26 ECU would cut it at that point since it's tuned for 8.5:1.

if you want to do a turbo setup, just post a WTB here for the parts you're looking for- just be sure to come up with a plan first. VJ20 came on the BPT, but it's not ideal since it's slightly undersized. a small T3 or T25/T28 would be a better match. I recommend picking up a copy of Maximum Boost by Corky Bell, it'll help you figure out a plan for your car and the appropriate turbo.

before buying pistons, take the block to a good machine shop and have them check it out as well as talking to them about your plans for oversized pistons- they'll give you an idea of what your next step would be.

[Zorix]

For sure. I won't buy anything internal until I have the block checked. I will check out Maximum Boost for some ideas. I was looking at these http://www.flyinmiata.com/index.php?...0%20%201990-93 but it suggests removing the oil squirters and probably plugging them with something. I can understand since its ceramic coated. I just wonder how long the coating lasts.

As for turbos, is there a way to cram in an intercooler without modifying the frame or bumper? Also what makes up the GTX turbo?

I think I do want to build the engine stronger than stock that will run well as NA with the option to turbo later without going back into the block.

So I should probably limit myself to 9:1 CR and forged internals I think.

[KAinjection]

Leave the oil squirters alone. They actually help fight detonation by cooling the piston. Supposedly you gain 1-2HP from removing and plugging the squirters but IMHO the resistance to detonation they provide is more beneficial.

10:1 is not high compression these days. Maybe for an old 2 valve lump of iron it is. lol

12:1 can be used on pump gas IF you have a good tuner.


I feel you need to formulate a solid plan of what you want before advice can really be given.

Power goals of engine:???
N/A or Turbo:???

949racing has plenty of Wiseco and Supertech piston options for decent prices. If it fits the Miata 1.8L it will fit your engine.

Any piston sizes bigger than .5mm (.020") oversize will have to be forged pistons, because OE pistons dont exist in anything bigger then that unless you want stock compression (9:1)

[Zorix]

You have convinced me that turbo is the best option for this engine. I would still need to buy the BP26 ecu, correct? I know where I can get one. Can I plug it into my car as is, stock to make sure it works or will I risk damage?

[Zorix]

Well after considering all the options, I really don't have much of a choice if I want to produce some decent power. I think turbo is the way to go for me but it will have to be a two stage project. I will probably need to bore the engine anyway due to low compression right now so I don't think I will be able to run the stock internals. I will wait to get the block checked out before I commit to a bore and piston size. After reviewing the FSM again, I just realized that I was wrong about the stock CR. Somehow I thought it was 8.5:1. Would the BP26 ecu have any problems with 9:1? And would it be possible to buy and test the BP26 ecu ahead of time without any kind of turbo installed? I thought I remembered reading that I would need to buy that ecu to do any turbo application. Also would I need to change anything on the harness? Thank you.

[Zorix]

300zxrb26dett, Thanks for the tips. I only found one option at 949racing for Wiseco for a 10.5:1 CR which probably won't work for the BP26 ecu, correct?

[atomicEGT]

you can have a front-mount intercooler without modifying the gram or bumper if you size it right. you will, however, have to remove the tie-down hooks to fit the piping. a GTX setup doesn't need much in the way of an intercooler.

a basic GTX setup would be BP26 manifold, VJ20 turbo, Y or B-code VAFM, 330cc injectors, 4-wire TPS, and BP26 ECU. 9:1 compression is fine with that ECU, stock pistons and rods are reliable to at least 220whp. if you go with a VJ20, be sure to port the wastegate opening, IHI internal gates are kinda ****ty- every one I've ever used had serious boost creep issues.

yes, you can use a BP26 ECU without a turbo, and yes you will have to modify your harness. there's information about it in the ECU section of the forum I think. it's like two pins on the harness that have to be swapped or something. if you can find one, a BPC8 ECU is even better. no boost cut, ignition cut limiter, etc. they're ****ing awesome.

send Emilio a message, I'm sure he can get you the Weiscos you want if they're not listed on 949's site somewhere.

[ftjandra]

http://949racing.com/supertech-pistons-miata.aspx

I'd go with Supertech pistons as they use a different alloy that expands less. Make sure your machinist knows this and doesn't just use clearances for a 'forged' piston.

--Ferdi