Mellow Matt

Hi, I'm new to the forums, but figure this is the best place to find out what I want to know

A '96 mk1 1.8 I've looked at has a dyno chart showing it with 220bhp, but it's only fitted with 295cc Toyota Starlet injectors. AFAIK the fuel pressure has not been increased at all.

From what I've read you really need about 400cc to get 220bhp, or you need to increase the fuel pressure on 295cc injectors up to about 80psi.

So my question is, does this mean the dyno was very optimistic? And in addition, does this mean that it's likely that the engine has been running lean?

Thanks

richyvrlimited

iTrader: (1)

Doesn't matter how many forums you ask that question on you know, the answer will always be the same.

Either it's extremely lean and about to die, or there's no way in hell you're making 220bhp

Mellow Matt

Haha, ok, that's the kind of difinitive answer I like!

Presumably a quick check on the plugs would prove it though?

The fact that the car seems to run fine, and yet is pretty rapid is what's confusing me.

EO2K

iTrader: (37)

widebandO2sensorsayswhat?

Also: Welcome to the forum! Go start an intro thread and tell us about yourself and your build

richyvrlimited

iTrader: (1)

Only if you pull the plugs after shutting down when at WOT, otherwise your just reading them for the fuelling at idle.

A 180bhp mx5 feels pretty rapid. A 220bhp mx5 is VERY fast....

Seefo

iTrader: (5)

bhp is at the crank. doesn't seem nearly as far fetched. consider 180bhp on a miata is pretty much intake, exhaust, and Megasquirt.

Ben

iTrader: (33)

Dyno sheets can lie, but physics can not. Physics says that 4 x 30lb injectors at 80% duty cycle will yield ~170 hp with a BSFC appropriate for a low power turbo.

220hp will require in the range of 40lb injectors.

Ben

iTrader: (33)

Just dyno'd a built BP 11:1 1.9L, 4W head with working VICS (which made a huge difference in top end power), RB (I think) header, etc etc, MSPNP. 135 whp on our dynapack. Even if you "fudge for lie-ojet" type numbers, 180bhp is a pretty tall order.

Mellow Matt

Thanks for the replies all. The reason I ask is I'm thinking about buying this car, but I don't want to buy a car on which the engine is about to die! If I do end up getting it I'll introduce it and me

Do dynos measure at the crank rather than the wheels then? I've been here: http://www.rceng.com/technical.aspx and it reckons on about 400cc for 220bhp at the crank. Also, that figure is based on a 80% duty cycle - I guess they can actually work faster than that, just not as well?

Presumably it will only be running lean when on full boost (10psi)? If so, is it likely to have caused issues (scored barrels etc?). The car has an intercooler if that would reduce the temperature and the potential for damage?

Sorry for all the questions!

ETA: in fact, presumably it's impossible for it to actually get to 220bhp? And therefore it's not possible for it to be running particularly lean...? I don't mind if it's not as powerful as stated, I just don't want it to be unreliable.

ETA2: Forgot to reply to EO2K - I'm not sure what the wideband o2 sensor says - where would I look for this (or ask the seller to look for it...!) and what should it say? Sorry, I'm still new to this turboing lark!

Seefo

iTrader: (5)

Seems a little low considering a blue printed SM motor puts down 120-125whp. Also, considering Emilio's recent build with 10.5:1 and practically the same mods (no idea about etc. etc.)you listed had 139whp. https://www.miataturbo.net/general-miata-chat-9/95r-street-car-project-63125/

Anyways, I am not here to argue about that, I just got the feeling that the previous poster was mistaking 180whp with 180bhp.

EO2K

iTrader: (37)

A wideband o2 sensor will tell you what the air:fuel ratio is...

...but lets go back a little further. It sounds like you are looking to buy this car and it already has a turbo.

#1. What kind of engine management is the car using? IE: How is it adding fuel and retarding ignition under boost?

Best answers: Megasquirt/Adaptronic/AEM ECU with wideband o2 sensor.

Worst answer: <blank>card and AFPR with no wideband.

Where blank = voodoo, power or super. This is also known as band-aids and its bad.

AFPR or RRAFPR = Adjustable Fuel Pressure Regulator or Rising Rate Adjustable Fuel Pressure Regulator. This could be good/bad depending.

Timing control would be something like one of the MSD Miata specific Boost Timing Retard Boxes. They are not ideal, but they do work-ish.

When using the above bandaids with no wideband, you have no idea what the engine is doing under boost. It could be running pig rich or it could be running lean as hell and ready to eat a piston. This is A Bad Thing™ If the owner can't or won't tell you, I'd strongly recommend walking away.

#2. Any other question.

You need to talk to the seller and find out the answer to that first question before you move on. You don't want to buy someones disaster build and then spend weeks trying to fix/sort it out.

Mellow Matt

Thanks EO2K.

I've done some research already, so know bits and bobs. I've actually spoken to the guy who built it (who sold it to the guy selling it now).

It's got:

Garrett 2554 running 10psi
3 bar MAP sensor
52mm alloy radiator
Spec 1 intercooler (begi)
eManage Ultimate
295cc Starlet injectors

I'm not actually sure if it has a wideband o2 sensor? Although I guess one is necessary for the Emanage to know what to do?

The guy who built it said that it's got the stock fuel pump, and he thinks the fuel isn't being pumped at any higher pressure than standard.

Essentially I just want to know if it's likely to have been damaged? If I buy it I intend to upgrade the injectors, if only for piece of mind!

richyvrlimited

iTrader: (1)

No-one here is going to know whether it's been damaged. They can only speculate based on some bogus dyno printout and a vague list of parts.

The only way of knowing for sure if the engine has been damaged is to look at it/test it.

Just take along a compression tester if the compression tests come back ok you're more likely to be good than not.

Without pulling the head there's no 100% way of making sure, you have to go off gut/experience.

Where are you in the UK? There's more than likely someone local who is familiar with FI and MX5's who would be willing to look at the car with you.

Mellow Matt

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. That's why I'm asking. If the list is too vague, what more info would be needed?

No-one can test it for me, so I'm trying to figure out how to tell myself. 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.

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? Which from what I understand is one of the likely results of lean running?

Thanks

triple88a

iTrader: (2)

Stock 240 injectors run out at 6psi boost - 160-170whp at about 6k rpm and that's what about 200 at the crank?

Seefo

iTrader: (5)

You had a question and for the most part people gave you the answer, but it seems what you are really after is for everyone to tell you its ok and the engine is fine and we all think its great.

You want to know how the engine is doing? do a leakdown test. You want to know if its running lean? get the AFRs, a dyno tuned car should have a wbo2. Is it possible that its running a realistic 220bhp on 295cc, well Ben already answered that for you. So either there is something else at play which you don't know, or its not making that power.

EO2K

iTrader: (37)

Looks like GReddy still makes the e-Manage, its a piggyback controller? I don't really know much about their capabilities, but I would guess its a damn sight better than a Powercard. We have a whole section dedicated to the e-Manage, you might look there for info about widebands and the e-manage.

It sounds like we all may be confusing bhp with whp, possibly due to corrections? The RC calculator claims you can put down 200BHP @ 90%DC with a 295cc @ 43.5psi. Having said that, who knows what correction factors the guys who dynod the car were using. BHP = crank so unless this thing was on a cradle in a dyno cell (doubtful) then there was definitely some correctificating going on somewhere.

Keep in mind, if you are running 10psi boost with no manifold reference on your FPR, you are now running 33.5psi of fuel pressure and that makes your theoretical cap 175bhp @ 90%DC. Will a stock NA FPR do 1:1? I don't own an NA so I couldn't say.

I personally wouldn't run 90%DC, but according to RC, it looks like its mathematically possible. In either case, on a cold day, I could see you being VERY close to the limits of the fuel system.

But yeah, no way to tell if its broken unless you open it/scope it/compression test it.

edgar7654

switch to rx7 injectors i have 2 injectors if ur interested pm me..

mx5-kiwi

The problem with these forums is that the majority of the members are in the U.S.A.

Don't get me wrong this isn't a bad thing except for the fact that you guys have a vast access to readily available manifolds, turbos and knowledge/skillset and other goodies that are either not available in overseas locations or are about 3-4 times more expensive (at least).

So some of your answers, whilst (99% of the time) are great, they tend to have a slant or perspective that can sometimes be not quite right for non U.S members.

My advice to the OP is to decide if you like the car, weigh up the fact that the turbo is installed, check the manifolds are of decent quality. Maybe do a compression test, but then commit either way. These are the expensive parts to buy and have fitted. Sounds like the majority of the work is done here......I didn't see the ECU mentioned (you really need a good ECU).

If you decide to go for it (as i did) budget in the pruchase of an innovate LC-1 or MTX-L AFR sensor and gauge so that you can run the car KNOWING the AFR's. Then you can sleep easy or tune accordingly.

Good Luck, look forward to seeing a picture and hearing what you end up doing.

One thing I would

fastivab6tg25mr

my BP made 225whp on 370cc injectors with only bandaids and 14psi of boost @ 11.8:1 afr so i dont see how it couldnt be possible to make the same at the crank with less fuel.