Built in lag?
 

Starting to gather parts for turbo install on my '93 and have a question. Knowing the rearend is a weak point and that I'm not looking for a lot of hp (I enjoy the handling of the car the most) and am looking for a little more power for hills and passing. Has anyone ever built a system for moderate hp gains but with a slower spool to minimize the stress on the rear differential? Will probably upgrade the diff. eventually but not building a track car so not expecting to subject it to that kind of abuse. Had a turbo Shadow years ago and enjoyed the feeling when the turbo kicked in and would like to get that sort of mid-range feeling again.

Differential usually blow up on launching. I've seen 220whp+ on 1.6 diff without a problem. I don't quite understand the "slower spool to minimize the stress" on the diff.

I think he means so boost will roll in when he is already rolling. Instead of something spooling up at 1500 have it spool at 4500... I could be wrong though

Maybe it'd be better to alter you're driving style just a tad, if you're worried about the diff busting then just take it easy on the launches. As long as you keep your throttle under control the turbo won't even need to spool at all. most kits i've seen kick in at around 3500 anyway

Yup, control your boost via the go pedal. Even if you have a smaller turbo that likes to spool sooner rather than later, easy launches with minimal input of throttle will work.

I use TPS based boost control. If I hooked up my VSS I could do geared/speed based.

Yes Ryan that is what I had in mind. Not worried about my driving, being a little older and experienced am a fairly capable driver but not so my son who I allow (heaven help me) to drive it some also.

I run a relatively low boost big turbo setup that does more or less what you're saying. I'm at somewhere around 250 rwhp and running between 7 and 10 psi (depending on my mood) and it's quite civil and fun. I'm only in boost when I need to be in boost.

This is what I had done in my 5L with my 80mm. No electronics required, just a big snail :D

It worked well as my trans was a weak point. Car ran good with big boost and was absolutely retarded at around 4000 RPM

Big turbos on small engines are really fun when you roll into boost. And it would defiantly help the life of the drivetrain. I wiped out my diff with a stock 1.6 :D

You can also not be aggressive with the timing down low to reduce spool time and/or run a smaller exhaust diameter.

Ok so you all understand what I am looking for, boost coming on in the upper rpm scale, so how do you control where the boost starts and how to make sure you don't run out of boost to soon (before rev. limiter). I don't think I want to wait until 4500 as that would make a small power band but 3000 to 3500 should be about right.

From what I've seen the 1.6 diff can grenade under stock power.... so you might want to just plan on swapping to a 1.8 diff. Honestly it's not that hard of a swap... and an open one can be found cheap.

Personally with a bit of effort you can roll into boost using your foot. Just don't use it like an on/off switch.

You could do a boost by gear setup or a two stage boost controller.

3k rpms is pretty low...that is where my 2560R jumps to life.

^same, On the hilly roads around here it's almost hard to stay our of boost. It's got a nice linear output though. Little throttle "little power"/heavy throttle bigger power.

most electronic boost control systems (like the megasquirt for example) have RPM vs. TPS boost curves. You can decide exactly what RPM you want what boost.

I have a T3/T4 setup on mine which originally ran 14 PSI on the 1.6L rear. It's a street/drag car and doesn't spool well till it's above 3600 RPM. Comes in nice and smooth afterward though. I tried to baby it as long as I could. Very few hard launches. Even with this, I still tore the guts out of a 1.6L rear end. You should plan on upgrading with a power adder regardless. The 1.6L rear just cant take the stress for very long.

You may be able to extend it's life some with good boost control or throttle modulation but I would say it's still on borrowed time.

Yeah I understand the rear diff is a weak link and plan on an upgrade eventually but have to build towards the final goal a little at a time. Right now I'm working on the research and making a list of what is needed to reach my goal. A mild upgrade of the suspension is the first order of business as the car is stock and I know there's better performance available there. Will then look into engine management (probably MS) upgrade then gather the needed parts for FI. Going to have to search some of the other forums then asked questions to head in the right direction for me.

Making it "lag" is not going to make it any less likely to break the diff. It will just break at 5k rpm instead of 3k rpm.

In fact, I would argue the counter-point that a larger turbo will be harder on the driveline because it will come into power all at once. In other words the derivative of the powercurve will be greater at that point.

This idea is a very common misconception. People think that big turbos make you hook up and make the car easier to drive. Ive had people tell me they wanted to go for a bigger turbo because their wife/gf will drive the car and a small turbo would be dangerous because it will spool so quickly.
This is just not true. A small turbo will spool up quickly but isnt putting down as much power. A big turbo will spool more slowly and then suddenly light up the tires and put you into a tree.

I'm not sold on needing a large turbo at all. My car is not going to be a track car just looking for a little more power for passing and climbing hills ( a fair amount of those around me). My plans are to start with engine management and maybe even a larger engine even though I like the idea of keeping the original engine in the car. I like the way a turbo car feels when driving it, the feel of the turbo boost kicking in and improving the acceleration.

This may be true. It does seem to spool hard and fast in the upper RPM range. I would imagine it would lessen the impact loading at lower RPMs but in the upper RPM range there might be more rotational torque loading on the components.

MiataTurbo.net will have answers for most anything FI. You will need to put on a flame suit for most of it though.

I am kind of on the fence with what Full Tilt said. Yes going with a bigger turbo will put down more power but it also gives you some more RPMs to play with before you get into boost, but like you said it comes on like crazy. That's why I think a boost by gear setup, or what Brain said, a TPS based boost controller would be ideal for what he is trying to do. But I mean really I think doing all this work to avoid the stress on the 1.6 drivetrain components is just too much work.

As long as you arent launching the car, do huge brake stands, brake boosting...etc it should hold up long enough for you to do your swap later on down the road. And 1.6 stuff is cheap. If it breaks throw in another one.

Agreed. I know some guys with welded 1.6s that have had no issues at all. Those cars are drift sluts as well. Due to the fact that many say it will lunch itself on stock power or last with 300whp, i would just go for it and not worry about it, regardless of how insane your setup is for boost control, if the diffs going to go its going to go. Have faith!

get a 2560 and some killer electronic boost control and you can set it up however you want.

Regardless, any 89-93 miata with a FI and/or good tires, needs a 1.8 rear diff.
Handicapping your setup to try to save a differential that apparently is made out of wood cogs does not make much sense, its most certainly going to break, so you just gotta suck it up and do it right from the beginning.

Have done some searching on MiataTurbo.net but as a beginner it's hard to wade through all the post that come up under each search, that's why I asked here first. Beside my flame-retardent suit is to small now so here's two more questions. I just aquired a AiResearch M11 turbo with .60 on the coldside and .48 on the hotside, is this good enough for a low boost set-up? And question two, the exhaust is always turning the turbo so am I right to assume that the waste opens and allows enough exhaust to by-pass so that the vacuum produced is greater than the boost produced?

when the wastegate is opened, the exhaust gasses bypass the turbine, slowing the wheel, limiting the about of boost the compressor makes.

So your saying that once the car starts and in running the engine is always under boost? Even at idle there some boost present. I had an '87 shadow turbo with a boost gauge but don't remember if it had a vacuum reading on the gauge or just boost.

no. the turbo isnt spinning fast enough to make boost. you're under the same vacuum as N/A

The throttle plate being closed at idle keeps the intake manifold in vacuum. It will be in vacuum even if the compressor is producing some pressure in the piping between the turbo and the throttle body.

Ok, that's what I thought. So any idea if the turbo I have will be good enough for low boost.

Not to start nor suggest I planning on this but---after reading many post on MTurbo and the many solutions to increasing fuel under boost has anybody tried just adding a centrally located injector(s). It seems that a simple injector driver ran off the original signal could then power them. Add a wide-band O2 sens and an adjustable fpr and you could tune whatever mixture you needed. Does this make any sense at all.

Its been done, but that is ancient technology.
A remote injector is not guaranteed to equal distribute fuel between cylinders, plus there will be issues with puddling and whatnot. The manifold is not designed to have fuel in it.
Also, you will have no provisions for tuning ignition timing, which will limit how much power you can make.

There is no excuse to do half-assed stuff like that when there are cheap and effective options like the megasquirt.

I know going with megasquirt solves all of that, was just curious if it had been tried. I know the timing issue needs to be addressed too, as to the intake issue, an exta bung welded into each intake runner would put the fuel where you want it. I have been reading on a number of the forums about megasquirt and have more questions than before. Need to do more reading then decide which unit is best for me. When I get to that point I will asked more questions and try to do this right the first time.

OK, I'm back. Having read A LOT of post on MT I've at least figured out that with all the bandaids needed to make a car safe and reliable Megasquirt is the way to go. Still need to keep cost down some but if I assemble it myself some money can be saved. From what I've read using MS in a piggyback capacity is a little less complicated, maybe. So my question is, with cost being a factor, Which MS will do the job for a low boost setup without breaking the bank? My car is not a track car ever, just want a little more power for easier driveability. Lots of hills where I live so a little more hp would be nice.

the one Brain makes.

+1 He will make one tailored to fit your setup and needs. The price is right and it is a complete solution. It's a real no Brain-er. :gag: