Engine Rebuild Suggestions/Turbo Questions

[SteyrTMP]

Well, as you all know, I'm using an interim BP05 right now, and need to have the original rebuilt. I plan on having it bored 2mm over, and am aiming for Wiseco 8.5-8.8:1 pistons. (Why does it have two compression rates for the same pistons?) The goal is low compression, high (20+ psi) boost, while yet reliable.

Although some of the cheaper rebuild kits are tempting, I am resisting the desire and am saving up for one with good brand names.

Question: Is it necessary for aftermarket rods? Any reason not to reuse the original rods with new wrist pins and bearings?

Valvework: I'm thinking about the 1mm over valves. Same price as stock, but what's the benefit, other than better flow? Any negatives? Is it going to raise compression? Same thing with porting and polishing. What's the good, bad? I really don't want to do anything I don't have to do, but if I'm having stuff redone, I want it all done at once, along with any upgrades.

I have 310cc injectors; I am going to have them cleaned and will use those. Paid 55 bucks for those off Miata.net.

I'm hoping the crank and the cams will all be well within spec. I don't see any positive with replacing the cams, as that will raise compression, correct? I think I want to retain the stock cams, and retard timing a few degrees to reduce overlap, from what I was reading. Any suggestions?

For the turbo, I will be building another equal-length header, however this one will end up being slightly harder to do, as I need to mount the turbo in front of the engine, about level with the valve cover. Now, that is going to be putting some weight on it while being around 12" away from the exhaust manifold. Is there anything wrong with having a bracket machined to fit between the header and the turbo, and bolting onto the old AC bracket bolts? I figure that would help aleviate the weight and stress on the manifold from the turbo's weight.

Anything I'm missing? I need to come up with an intercooler, preferrably an oil cooler, I have to tap a return line into the oil pan, re-route the coolant lines, and buy new oil/coolant lines for the turbo.

Oh yeah... and I have to rotate the turbo. Currently, the exhaust and intake flanges are facing in opposite directions. I need to have them aiming in the same direction.

That's going to cause some troubles--it is equipped with an internal wastegate. I'd either have to re-make a new bracket for the original wastegate, or buy a new one. As I have to remove the stock Evo turbine manifold, I should be able to cut and grind the flange down. From there I could weld a pipe for the new wastegate and then have the downpipe on it's own, rather than both joining.

Any suggestions on good wastegates and BOV's? I want to use a manual boost controller, and I have been considering using a 1st-gen DSM BOV, and I can crush it if I want to go higher than 17-18psi.

Am I forgetting anything? Obviously there are a few more odds and ends, but mainly I want to worry about preparing the engine. I can drive N/A with low compression; I just want to get things going. I have a garage lined up, I just need to know what to have them do. Perhaps I should order the rebuild kit first, or should I have it bored first?

[mcfandango]

For 20psi power levels, you will definately want stronger rods than the stock miata ones. They are good up to ~12psi.

Valves, you can get away with upgrade just the intake side. Before you do any work to the head, get a 99 head tho. You can get a 94-97 head to flow like a 99 but you might as well start out with better. Make sure whomever does the head work knows miata engines. Its easy to do nothing or harm with porting and polishing.

You will DEFINITELY need bigger injectors than 310s to feed a high boost setup. I'd guess you would need 550s.

Cams should be ok. At 20psi you might be pushing the crank. The BP doesnt have giant journals. I have no clue what the limit of the crank is. You dont see many guys running miata engine over ~300hp on a regular basis. The miata chassis seems to be the limiting factor at ~250whp.

I think you should call Bill at Flyin Miata. He's turbo charged his Westfield now. They've also been boosting miatas for a long time. They dont charge you anything to talk and will be able to steer you right..

[KB58]

Go to http://www.rceng.com/ to accurately figure what you need for injectors and fuel. 310s are WAY too small. 300hp requires around 660-750cc injectors. And don't forget a larger fuel pump, too.

Go to http://www.turbobygarrett.com/turbobygarrett/index.html to figure out which turbo is correct. Be sure to read the Turbo Tech section.

Leave the valves, cams, and head alone. What little restriction they cause can be "fixed" by upping the boost slightly. Stock cams are good for turbos because of the small overlap. Cams do not increase compression, but they can affect it due to lob overlap. That is, aftermarket cams typically have more overlap, meaning both valves are open at some point in the cycle. This loses you boost which effectively lowers compression - but no, cams can't raise it, only removing the overlap which puts compression back to stock levels.

I recall Keith Tanner said that the transmission is the (very) weak link in the Miata drivetrain.

Regardless what you do, plan the budget to have it professionally tuned else there's a strong risk of breaking it.

Sounds like you're just getting started. I suggest rebuilding the engine now with low compression, but do a lot more reading about turbos, first. Mark Warren's book, "Street Turbocharging" is good. You have to have your roadmap layed out before spending >$6000 to do it right... and you're having a shop do it? That's going to run around $10K... just so you know.

[chetcpo]

First of all I'll say I've never owned a turbo car, but I've read some books and watched friends with turbo cars tune, blow up, rebuild, and repeat. (So forgive me if I sound over cautious) I'm sure someone with some good real world experience will chime in here and set me straight if I'm wrong.

Anyway, I can't speak for the need to replace the rods, (I think the stock ones are pretty darn good) but you should balance them. Get a good accurate digital scale and grind material off the heavier rods until they match the lightest rod. They usually have a "plug" of metal on them for this purpose.

Porting and polishing and larger valves are employed by desperate builders of naturally aspirated engines to gain more flow. (won't effect compression) You have a turbo so don't worry about that. It's expensive and IMO unnecessary for a turbo engine. The same is true of cams. Use the stockers. I would simply install new valve seals and have the head checked for trueness, maybe even planed as little as needed to get it true.

I think the key though to engine longevity in a turbo application (especially the high boost one you speak of) is good engine management and good cooling.

I would (and will when I get around to turboing my car) install a pyrometer or two (between 1&2 and 3&4) or four (one for each exhaust port would be ideal) to monitor exhaust gas temps. This can tip you off to a potentially engine destroying condition before it does any damage. The other thing you will want is a wideband O2 sensor and programmable ECU like a Megasquirt PNP. That and some tuning time on the dyno should get pretty good results.

Lastly, you may want to PM Junior if he doesn't chime in. I think that designing turbo systems and tuning them is his "thing."

[SteyrTMP]

Yeah, he and I have been talking--that's where I got the turbo. I'm using a Mitsubishi Super 16G. I'm not aiming extremely high, as in 300+... I'm aiming more towards 225-300, starting with the former.

KB, I'm not having the shop build it, just regular things I can't do myself (at least, not correctly), i.e. boring, spec-ing. It's not expensive, and I've seen some of the cars these guys work on. Another good sign--I called and asked pricing, and the guy told me to bring the head and block over and he'll give me his opinion on what I should do. He said I might not need porting and oversizing on the head, and it would just cost more.

I'll be using the MegaSquirt II, and I'll be having someone else help tune.

[mcfandango]

I'm sure someone with some good real world experience will chime in here and set me straight if I'm wrong.

Anyway, I can't speak for the need to replace the rods, (I think the stock ones are pretty darn good) but you should balance them.

Porting and polishing and larger valves are employed by desperate builders of naturally aspirated engines to gain more flow. (won't effect compression) You have a turbo so don't worry about that. It's expensive and IMO unnecessary for a turbo engine. The same is true of cams. Use the stockers. I would simply install new valve seals and have the head checked for trueness, maybe even planed as little as needed to get it true.

Like I said, the stock rods are usually ok up to ~12psi. If he really wants to run 20psi. He is going to need stronger rods.

I'm going to have to disagree on the head work. It will provide gains even in boosted setups. For a turbo it is less important than for a supercharger. However, just like too small a throttle body, restrictions hurt flow and hurt power. This is why better intercoolers provide more power. They do not have as much pressure loss thru them. Altho I do agree this is the last place to look for gains.

Honestly, the best way, and this is from someone who has a mildly built miata engine (read too much money into it), is to use the stock engine and push it to just under the limits. That way the replacement is cheap and quick when you mulch it. And you more than likely will. So far the batting average of breaking engines in FI miatas I know personally isnt that good.

[Driven5]

Go to the Flyin Miata website and check out their dyno charts and comparisons to see what they have been able to do with various setups. They even have one comparing stock head to a ported/polished head for a turbo car. This should give you an idea what kinds of things you may be looking at and what your goals may be. Also call and talk with them about your goals for the car and your personal limitations (financial/knowledge). They should be able to help point you in the right direction. Not to be a naysayer, but it looks like you're biting off a little more than you can chew right now, until you've done a lot more research and learning. A couple of other good sites to do a lot of (re)searching on are Miata.net, Miata Turbo, and Club Roadster.

[mcfandango]

Yeah, he and I have been talking--that's where I got the turbo. I'm using a Mitsubishi Super 16G. I'm not aiming extremely high, as in 300+... I'm aiming more towards 225-300, starting with the former.

250hp at the wheels is very doable with just a stock miata engine with turbo. No need for overbore or anything else. Just get everything balanced. You'll most likely end up pushing 10-12psi for that range of power.

I started out my engine at 6psi on my gt2560. I've tuned up to 10psi now (no dyno chart so I dont know the real output). I can say that I've probably gotten slower if any thing at autox events. But then again Im just as fast in a stock miata as I am in my turbo'd miata

[KB58]

250hp at the wheels is very doable with just a stock miata engine with turbo. No need for overbore or anything else. Just get everything balanced. You'll most likely end up pushing 10-12psi for that range of power.

It don't really need balancing either. Perhaps the biggest plus for forced induction cars is that they don't need to rev above factory rpm limits.

And I completely agree about driving a turbo at an autocross. The higher the boost, the slower the time.

[KB58]

I'm going to have to disagree on the head work. It will provide gains even in boosted setups.

Yes, but given the choice of turning the boost up 0.5psi to make up for a non-ported head, or spending >$1000 on head porting, I know which I'd choose.

[mcfandango]

It don't really need balancing either.

Its so cheap to get things balanced tho. If you are tearing everything apart to refresh the seals and bearings anyway. Balancing probably wont add alot of time or money to the rebuild process. My flywheel cost 30 bucks to balance (suprised how much even the new lightweight flywheel needed to be balanced).

[horizenjob]

Perhaps I should order the rebuild kit first, or should I have it bored first?

8.5-8.8:1 pistons. (Why does it have two compression rates for the same pistons?)

Generally, you would bore after getting the pistons, to get the bore to match your pistons ( you give the pistons to the person doing the boring ). The compression is variable depending on wether and how you machine the top of the pistons, and the volume of your combustion chambers.

Building engines is an entire big subject. The education process might include getting to know and spend money at a series of machine and dyno facilities, just to learn who knows their stuff and treats their customers well.

Having your own wideband O2 sensor and data logging software etc. would let you be closer to a poor man's dyno shop. Pallets of donor engines will also help.

[SteyrTMP]

The O2 sensor is on the list of things to get--gotta make sure I want to use that style of gauge for everything else as well. I don't want mixmatch.

Yes, balancing is on the list.

I'm not aiming to have the engine built for racing; I am just going to have it bored out, as if it's anything like my first car's engine, at 173k miles, it's on the edge of spec. Definately not a good recipe for boost. Furthermore, it doesn't cost me any more to have it bored out than it does having it honed (30 bucks a cylinder).

I'm not sure about the rest yet, still gathering info and parts. This is going to be a lengthy process, as I don't have 3k to throw around. I figure it's going to cost 5-700 bucks for the machining (possibly less, but I'd rather err on the safe side) It's just under 1100 bucks for the rebuild kit, including pistons and a performance oil pump. I'll also need to get bits and pieces to set up the turbo, plus stainless tubing. I'll have to have a bracket machined out. I'll need new turbo gaskets, a BOV, and a wastegate. I can see 3k pretty easily before all is said and done. Another 5-600 bucks for rods if I decide to go that far. The MegaSquirt II is around 260+ for the DIY kit.

[evotech]

While I am new to the Locost community I am very experienced in the turbo/Evo world. What evo turdo do you have. Sounds like a twin scroll reverse mount. If so I would ditch it for an cheap 16G. As far as BOV's any Evo BOV wil hold up to 25 PSI with no problem. An Evo 9 valve or JDM valve will hold alomost 28 psi. I could find you one for next to nothing. I could even sell you one for $30 or so. For simplicity sake I would stick with the internal gate, but if that is not possible the smallest Tial gate available will do the trick just fine. 20 lbs on a stock miata engine is too much. Dial it back or build the engine the right way. You are going to have to step up to 580 injectors ot there about. The real trick lick would be to use a Evo 10 engine which is now all aluminum. Just no bellhousings to mate it to anything yet. Good luck. Feel free to hit me up for an Evo parts. I have a garage full.

[Keith Tanner]

We have a turbo on our Westfield right now. We're estimating it's at around 250 at the wheels. Fast car!

If you're trying to choose between pistons and rods, put the money into rods. And engine management is the critical part of course.

Wastegate brackets are trivial for Garrett turbos, I don't know about others. I can usually make a wastegate bracket out of steel in a half hour if we need to clock a turbo differently.

The transmission does become a problem at 250hp + if it's abused. I don't think we've ever lost a transmission at FM other than two in a 350hp race car, and there were extenuating circumstances there. It's the weakest point in the drivetrain, but I wouldn't call it weak. Of course, we don't break engines often as well so maybe we're just conservative.

Turbos don't mean slow at autox. We autocross naturally aspirated and turbo Miatas regularly around here, and let's just say the turbo cars aren't exactly at a disadvantage. I haven't had the chance to autox the turbo Westie yet, but it's a whole lot faster than my Seven on our kart track.

225-300 is a pretty big range. There's a sweet spot in the 225-250 rwhp range, and above that everything gets much more expensive.

One suggestion - instead of an intercooler, consider water/methanol injection. It's amazingly effective. We're going to pull the intercooler out of the Westfield.