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Discussion Starter · #1 · (Edited)
Well, I was planning to leave my GZE bone-stock and enjoy driving it as-is, but low compression in #2 cyl means I'll need to do some substantial work on it.

...that also means I'm already thinking about "while I'm in there" mods for slight driving improvements w/o losing the current character of the car (read: I own this car specifically because I want something other than a turbo).

Looking around, it sounds like increasing boost w/ an overdrive pulley is a good, simple improvement. This thread helps highlight a few additional supporting items like a gruntbox, colder plugs, etc: tips on tuning a gze anyone ?

But given that's a thread from 2005, have there been any updates to the collective wisdom since then? A few specific questions I have:
  • Am I on the right track in thinking an overdrive pulley kit is a good, simple way to increase power?
  • Can the stock ECU "automatically" adjust fuel mixture enough without a piggyback or standalone? If not, what's the recommended "simple, but right" path?
  • Can the stock injectors live up to that fuel demand?
  • Is a gruntbox required, suggested, or a bad idea?
  • How does one connect to and tune the stock ECU, timing or fuel-map-wise?
  • Will (an otherwise stock) GZE with pulley benefit from better airflow?
  • If so, what're the key one-or-two items to focus on? Porting? Cams? Different head entirely?
  • Finally, anything else I should be considering beyond a basic refresh while I have the engine opened up? I've heard folks mention thinner headgaskets, etc...
While definitely not operating with an unlimited budget, my goal here is to do things right the first time. The goal is to get back to driving and keep it that way.

Thanks! Trying to turn some bad news about low compression into a fun project... ;)
 

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...given that's a thread from 2005, have there been any updates to the collective wisdom since then?
  • Am I on the right track in thinking an overdrive pulley kit is a good, simple way to increase power?

  • Can the stock ECU "automatically" adjust fuel mixture enough without a piggyback or standalone?

  • If not, what's the recommended "simple, but right" path?

  • Can the stock injectors live up to that fuel demand?

  • Is a gruntbox required, suggested, or a bad idea

  • How does one connect to and tune the stock ECU, timing or fuel-map-wise?

  • Porting? Cams? Different head entirely?
Not much. This car is in its twilight. Parts are no longer available. There are few of them left, and hence no business opportunity in aftermarket production. You are the pioneer now.

That is what everyone else has done, and they seem to agree with you.

No. In fact, when the SC is engaged, the ECU dead-recons the fuel based on the OE boost ratio.

The grunt box is the simple path. I won't offer an opinion on right. It does work.

I doubt it. I think that they are maxed out with the OE boost.

Given the above, I would say required

My understanding is that it cannot be done.

With a supercharger, head flow is of diminishing returns. I am not saying that it has no value, but the SC determines the volume of air and generates enough pressure to force it in. Cams are usually designed to take advantage of resonant induction, and they might make an SC engine worse, since it does not have tuned runners.
 

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My 2 cents - the early EFI systems like you'll find on a Mk I are a liability due to how crude they are. They typically have no real engine protection built in, and are essentially "flying blind" with no feedback at WOT. There's hundreds of failure modes like a dirty injector, bad sensor that can smoke your engine quickly and there's usually no real feedback something is wrong.

If you want to keep the car fairly OEM, it'd be possible to build a jumper harness between the stock engine harness and an aftermarket ECU. Then you just run some additional wires for extra sensors that will make things much safer. Yes, there's some tuning time associated with this, but think about getting wideband O2 feedback and possibly going with much more modern injectors that will make everything much nicer to drive and much more safe.

I give the same advice for Mk II's - the stock EFI system is very crude, even compared to contemporary cars (Toyota was pretty behind the times in the EFI world for new technologies through the 80's to late 90's), so jumping to something modern for a car you really like and want to keep is both a fun project and will make the car better/more reliable in the long run. Keeping the stock engine harness in place makes it really easy to revert back with minor work.
 

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As said above, the MR2SC was never popular enough to generate any real aftermarket support. So, especially all these years later, there isn't really anything available that works well off the shelf.

You can add boost with only a big pulley and the stock ECU will sort-of work for normal street driving. The ECU will run rich at the top and lean in the middle and as long as you don't push it too hard, it will mostly work. The rich top end will just show up as soot on the bumper and the lean mid-range will just feel like a stumble.

However if you do push it hard like take it to the track, you could melt the catalytic converter (I did) or cause various detonation related problems. Proper technique at the track will avoid the mid-range lean spot because you shouldn't really need to run in the middle of the RPM range at the track.

The Grunt Box or microprocessor replacement is really just a partial band-aid that works better than nothing. That was a good partial fix in the 1990's but technology has moved on. Modern aftermarket ECUs are really the proper fix. You could pay less and learn (a lot) to DIY it with something like Speeduino or MegaSquirt or you could pay more and get something professionally installed and tuned depending on the value of your time and money. There are 'plug and play' variants that will at least allow you to avoid large changes to the wiring harness.
 

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Moroccan Gold Imports
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I know people using link in other cars and it is powerful. Autotune function is apparently quite useful. I do not know anyone using it in a MK1, but I intend to purchase when my car is ready for it (88SC swap comes out of my buddy's car next weekend and will go into my 85).
 

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Discussion Starter · #13 ·
I know people using link in other cars and it is powerful. Autotune function is apparently quite useful. I do not know anyone using it in a MK1, but I intend to purchase when my car is ready for it (88SC swap comes out of my buddy's car next weekend and will go into my 85).
Are you planning to purchase the KORacing-made Link Plug-In, or are you going to wire in an off-the-shelf Link ECU yourself? Would love to follow your project as my car is an '88 SC as well!
 

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Moroccan Gold Imports
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No I will just order from KO. I am excited to get the car together. It will have a built bottom end and a ported head with cams- the works!
 
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