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Old 03-20-2012, 04:48 AM   #21
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Thanks for the further replies all. I apologise if I've annoyed anyone - that wasn't my intention. I didn't want to post one of those threads which is basically asking if I should buy a car, so wanted to ask more specific questions instead. Those questions have kind of overflowed into other questions though! I would love it if everyone said that they thought the set up was great, but obviously that won't happen as no-one can know for sure without seeing it.

My initial thought was to see if the seller's power claims could be true. It seems that that is unlikely/impossible.

This then led to the question of whether or not running this set up would cause damage. I know that this can't be answered for sure without pulling the head off, but bearing in mind I can't do that, and the rest of the set up seems to be good and running alright, I'm trying to see what the likelihood is.

I'm still new to most of this, but normally if an engine is running lean, then I guess it would be running lean throughout the rev range, as it would normally be caused by an incorrect configuration. This situation seems a bit different, as it's limited to only when the injectors reach their limit, which I guess would be when the power at the crank tries to go over about 200bhp, which is going to be a much smaller amount of time than when the power is <200bhp.

My understanding of running lean is that it causes temps to go up, and therefore causes detonation and piston expansion, which can cause scoring on the cylinder barrel. This then is why people are suggesting the compression testing (same as leakdown testing?) I think, which sounds like a good idea.

Thanks for the suggestion to see if anyone else could have a look Richy - bit of a long shot as the car is in Sussex (Loxwood), and I need to decide by Wednesday, but if anyone is in that area, any help would be really appreciated

Thanks for the well wishing, Kiwi
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Old 03-20-2012, 05:50 AM   #22
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OK, I was only asking if it's likely to be damaged? For all I know it running a bit lean when at high RPMs won't do any harm, as it will quickly be cooled again when at lower RPMs.
Dunno where you got that idea from, lean at WOT is bad period.

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No-one can test it for me, so I'm trying to figure out how to tell myself.
Why can't anyone test it for you? There will be someone local to you who would be able to advise.

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From driving it it seems to be fine - it doesn't hesitate or run badly from what I can tell. I'm hoping someone can educate me on how I would tell, or at least let me know how likely it is to have been damaged.
If it drives fine, and as you're unwilling to let anyone else come and help you you'll have to go off your gut feeling that it's OK?!?

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Your suggestion to test the compression is helpful - thanks. I've not done this before, but I've heard of it and it might be possible for me to try. Presumably compression testing would show if the barrel has been scored?
Thanks
Depending on how the results come out it could tell you anything from a blown headgasket to a bent valve to knackered piston rings.

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Which from what I understand is one of the likely results of lean running?
Lean running causes det which causes holes in pistons

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Thanks for the suggestion to see if anyone else could have a look Richy - bit of a long shot as the car is in Sussex (Loxwood), and I need to decide by Wednesday, but if anyone is in that area, any help would be really appreciated
Well don't ask that on here, it's a US forum. Ask on MX5Nutz, or on MX5OC, hell any UK forum!
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Old 03-20-2012, 05:53 AM   #23
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switch to rx7 injectors i have 2 injectors if ur interested pm me..
Wow, helpful advice and what an offer, 2 whole injectors eh? well that'll solve the OP's problem

OP ignore this tool, not only will you want double the amount of injectors he's trying to peddle, you also want to actively avoid RX7 injectors, they're an old design and a poor solution.
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Old 03-20-2012, 06:05 AM   #24
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Thanks Richy; I'm not unwilling to ask others to help, it's just the time frame is a bit difficult as I work in the evenings and the auction ends tomorrow. I'll ask on Nutz and see if anyone can help, and maybe I can sort something out.

I'd realised that I'd need 4 injectors if I were to go ahead with it, but I hadn't realised rx7 ones were to be avoided, ta!
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Old 03-20-2012, 06:30 AM   #25
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RX7 injectors will work, but the spray pattern is terrible by more modern standards. The end result is a car which is difficult to tune at idle particularly when aiming for stoich (which you want/need to pass any MOT).
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Old 03-20-2012, 11:37 AM   #26
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Which injectors are best do you think? I'm assuming 400-500cc in order to not have to up the fuel pressure. From this list: https://www.miataturbo.net/useful-saved-posts-8/diy-faq-all-your-answers-one-big-post-10821/ it seems that rx8 ones are pretty much the only choice?
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Old 03-20-2012, 01:04 PM   #27
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not only will you want double the amount of injectors he's trying to peddle, you also want to actively avoid RX7 injectors, they're an old design and a poor solution.
agree and disagree. the EV1's are old technology so there are better options but having big slow injectors are far better than fast small injectors. you dont notice the difference past 2500 rpm but at idle they are rough. i had some 680cc ev1's that idled terrible but held a solid 11.8-12.0:1 at redline. good enough for mid to high 200'swhp and [email protected] with no traction. its all about what you wanna do vs what you can afford.
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Old 03-20-2012, 02:38 PM   #28
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Originally Posted by Mellow Matt View Post
Which injectors are best do you think? I'm assuming 400-500cc in order to not have to up the fuel pressure. From this list: https://www.miataturbo.net/showthread.php?t=10821 it seems that rx8 ones are pretty much the only choice?
There are tons of choices out there... I can't help with the US/UK model cross-reference, but the MT Wiki has a great section on fuel injectors. You are looking for "high-Z" or high ohm (12-15Ω IIRC) or "saturated" fuel injectors, its all the same. You can use the low ohm/low-Z injectors, but then you have to screw with adapters and resistors... easier just to stick with the PNP high ohm units.

Before you go down the fuel injector rabbit hole, find out what that e-Manage supports!

I believe the RX8s are the Denso style and seem the be a happy medium and somewhat readily available. There are chineese eBay knockoff RX8s now, just so you know, so watch yourself.
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Old 03-20-2012, 04:27 PM   #29
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Thanks EO2K, I hadn't seen that wiki

Bit of a development - I spoke to the guy who built it again, and he said that it doesn't have a wideband o2 sensor, but that when he got it mapped the A/F ratio was 12:1 at full power measured by a bung the dyno guys put on the exhaust.

Does this indicate it wasn't running lean?

Also, if there is no wideband o2 sensor, does that mean that the eManage wouldn't have been able to properly manage the fuelling, or does the eManage just follow the instructions it's told by the map which was set up on the dyno, rather than monitoring A/F ratios whilst you're driving around and altering fueling as it sees fit?

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Old 03-20-2012, 06:49 PM   #30
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It means you either trust him or you dont... Sadly a dyno sheet isnt hard to fake up.

If i was in the position, i'd say install a wideband and i'd buy it if it meets a certain condition... 14-15.5 in cruise and 11.5-12 in boost I'm guessing the rest of the cells are tuned by "feel".
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Old 03-20-2012, 09:12 PM   #31
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Ultiamtely the car is running and running well... tested by an actual drive I presume?

That being the cae, i would say you have done due diligence and everythign is as good as you can check until you own it. If the fueling isn't right it may need a dyno tune but as I said before, factor in an innovate MTX-L gauge and sensor, it's not hard to wire in (your local exhaust shop can weld the bung in as required) and you will know.

These cars (with a turbo) are not maintenace free, drive and not do anything to them cars. If you feel you want to learn or have basic capabilities and accept the fact you WILL be doing the odd thing to it. You will be fine.

The car may turn out to have some issues but sometimes you have to accept, fate is going to throw you a curve ball and deal with it as it comes up....but I would say you have checked and asked as well as you can.

Now do you take the punt or not..
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Old 03-21-2012, 11:15 AM   #32
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Ultiamtely the car is running and running well... tested by an actual drive I presume?

That being the cae, i would say you have done due diligence and everythign is as good as you can check until you own it. If the fueling isn't right it may need a dyno tune but as I said before, factor in an innovate MTX-L gauge and sensor, it's not hard to wire in (your local exhaust shop can weld the bung in as required) and you will know.

These cars (with a turbo) are not maintenace free, drive and not do anything to them cars. If you feel you want to learn or have basic capabilities and accept the fact you WILL be doing the odd thing to it. You will be fine.

The car may turn out to have some issues but sometimes you have to accept, fate is going to throw you a curve ball and deal with it as it comes up....but I would say you have checked and asked as well as you can.

Now do you take the punt or not..
^ this.
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Old 03-21-2012, 04:07 PM   #33
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Well, the car sold for about 350 ($550) more than I was willing to pay for it bearing in mind the potential lean running, and the cost of swapping the injectors and mapping it again anyway :(

I've learnt loads in the process though, so thanks for everyone's help, and I'm going to keep an eye out for any more cars that pop up, and now I know exactly what to look for
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