9 replies to this topic

[cooperpooper]

Hello everyone, 

 

I have a 1999 JDM spec Mini. I have removed the AC system from the car and changed the SPI intake system for a custom EFI setup using a sherryberg throttle body, a single injector, and bosch coilpack all controlled by a speeduino ecu. 

 

I've been daily driving it with the current setup for about a year and am looking for my next project. I'm an engineering uni student so budget is incredibly tight... but I'm hoping to fit a turbo. 

 

My plan is to use a clone gt15 turbo (mounted between engine and bulkhead) with a self built manifold/downpipe and a small front mounted intercooler. I want to keep my boosted brake servo and current efi system. Since the engine is still the stock 1275 A+ engine with a 10.1:1 cr (according to GuessWorks), my plan would be to remove the head and increase the combustion chamber size and possibly run a thicker head gasket to lower the cr. I don't want crazy power, I was thinking something around 80-90bhp running 5-7psi? What sort of cr should I be targeting?

 

My reason for going with the gt15 instead of something like the gt17 is because I want a setup that spools up fast and is fun for around the city. But please tell me if you think a gt15 is the wrong turbo!

 

I basically just wanted to check if this is something achievable? budget is around $1000-1500CAD

 

Some other things I am unsure of:

 

For the diff, would it be necesarry to upgrade to a x-pin? or just upgrading the single pin with a stronger one? 

 

Could the stock gearbox/clutch handle this sort of power? I know the gearbox was overhauled and clutch replaced about 3 years ago by the previous owner.

 

Is it actually possible to lower the cr to a safe point by just increasing the combustion chamber size? I would love to go with a built engine with proper pistons, but budget doesn't allow.

 

I know this set up would probably end up being similar to the Jet motors kit, but I want something that I built and figured out myself and would also like to make sure the engine can handle it, as I understand the jet motors kits are intended as just bolt on with no engine mods. 

 

Let me know if there is anything else I have forgotten to consider here.

Thank you!

 

 

[Ethel]

You're not far off the stock Metro Turbo there. It had a 9.4 CR, no inter-cooler & clockwork engine management. Of course we no longer have proper petrol, but you've got plenty of other advantages over the old Metty.

 

Any improvements to the gearbox will help, but the factory turbo was pretty stock with just a bigger 1st motion shaft nose bearing over its stable mates. A 3.2 final drive, but through Metty sized wheels 'n tyres, so you should have kinder gearing.

 

...Not many turbo Min builders bother with the nose bearing and the turbo pistons, though great, were probably overkill - possibly because they had homologating the Metty Turbo Challenge in mind.

 

T3 blower & modulated boost - could be wrong but I think it was something like  only 3psi until it got into the A's asthmatic zone.

[lsto]

Just from my experience, I run a 998 turbo using a GT1544 scavenged from an old Peugeot 307HDi, running on a home made exhaust manifold and downpipe which connects to an RC40 exhaust. I initially run it with a standard head and just fitted 2 head gaskets to drop the CR. I think standard the CR was 9.6 and I think with the extra gasket I got it down to roughly 8.8. It was absolutely fine like this with no problems.
To this day I run a standard gearbox and bottom end although later this year I'm pulling the engine to replace the diff pin with a hardened one as mine has worn. I run it a 8 psi without an intercooler and it has been perfectly reliable for 3+ years as a daily. Mine comes on boost at about 2.5-3k but below that it is a bit gutless, I think that is down to the combination of the CR, 266 cam and running a HIF44 on a 998 but it wakes up after 2k. I do alot of motorway driving and my commute is 54 miles a day, the only thing I had an issue was with on long journeys at 70mph the coolant and oil got hotter than I liked, if I drove at 60 it was fine but 70 it would creep close to the red. I replaced the rad with the mini spares 4 core and fitted a 10 row oil cooler and it keeps temp perfectly now.

[Shooter63]

I must admit I've never understood why people keep fitting/recommending turbos off old diesel engines, obviously back in the day when turbo petrol engines were scarce you had very little choice, but over time various manufacturers have offered small capacity petrol turbo options in their line ups,  the picture attached is off a 1.3 Glanza, as it has cast on it, its a CT9. From the factory boost was set at about .8 bar, the engine made around 120bhp, spooled really well and if you add a MAC valve or put an adjustable boost valve in it could go to around 150+ bhp, because the car was popular you can buy hybrid versions to increase the power to higher levels. You still find O/E ones on fleabay for the equivalent of a night out, fit a rebuild kit to it and off you go, or you have the option of a Chinese copy. Seems a no brainer to me.

 

Shooter 

Attached Files

•  FB_IMG_1786781490995.jpg   32.21K   0 downloads

[Steve220]

Everything you've written is achievable if you can get the parts at a low price and you have mechanical sympathy. The diff will eve tually wear out, so a cross pin is a sensible upgrade if the engine is coming out anyway. If youre able to data log, see what the injector duty is at, as when you add boost and rpm, the quantity of fuel required goes through the roof as the afrs needed will have to cool the piston crowns, and cater for the scavenging.
Anything higher than 6psi, get an intercooler fitted.

[cooperpooper]

Thank you for the replies! Nice to hear that it sounds feasible.

 

I think I will definitely go for the cross pin diff as it's not too much more money compared to just upgrading the pin, and I have heard it can be quite catastrophic if the diff fails. Are there any other parts that need to be changed when swapping to a cross pin?

As far as cr goes, would I be able to get away with just running double head gaskets and leaving the combustion chambers as they are? I want to avoid a decompression plate as i've read they can mess with the rocker geometry. according to the cmdiy calculator, double head gasket would get me to about 9.3, would that plus an intercooler be safe to run a bit more boost than the 3psi that the metro turbo had as Ethel mentioned? 

Sidenote- would anyone know where I can find reliable figures for my 1999 jdm 1275 to put into the calculator (piston dish, combustion chamber volume, piston deck height, stroke length)??
 

 

If youre able to data log, see what the injector duty is at, as when you add boost and rpm, the quantity of fuel required goes through the roof as the afrs needed will have to cool the piston crowns, and cater for the scavenging.
Anything higher than 6psi, get an intercooler fitted.

 

This is a great point thank you Steve. I currently have a singular 66lb/hr ev14 injector which is at about 25% duty cycle under load at 3k rpm. I'm not really one to rev super high, but I think with a turbo I would definitely be pushing the injector. I could go for a larger flow one, but worried about poor idle control, and don't have a great (inexpensive) way of adding another injector like on the bagsport tb. I think i may be able to get away with just increasing fuel pressure?

 

Also I am planning to change out the speeduino for a rusefi uaefi board. Unfortunately the speeduino has no knock control, and before i go buy an external knock controller, it's basically the same money for a rusefi which would also be faster than the speeduino. Does anyone have any experience with the uaefi board?

[Steve220]

That injector is basically a 730cc ev14, to put into context, im running 2 of those and seeing 85% duty cycle at 6k rpm and 20psi of boost.

The a series is incredibly noisy, so a knock sensor is difficult to tune in.

[cooperpooper]

hm okay, changing to a 1000cc injector seems to be necessary then, although i would only be looking to run 5-7psi.

 

Steve, have you had any luck with running a knock sensor? I already have a basic bosch one, and just wired to an aux cord and amp that I can plug headphones into. Would be nice to have full knock based iginiton control though.

[lsto]

I ran a standard 998 head with twin gaskets for a while, it was absolutely fine. I think the metro run like 4psi to about 4k then the boost went up to 7psi. I believe it was done to avoid warranty claims and be a bit easier on the gearbox.
The best way to find your actual chamber volume is to measure it when you have the head off, anything else is just a guess.
For what it's worth if I was you I'd try twin head gaskets and go for about 7psi without an intercooler, or with an intercooler I'd run it up to 10 then go from there. As long as your fuelling and timing are safe you can keep developing things as time goes on while still enjoying the car.

Edited by lsto, 16 August 2026 - 03:03 PM.

[Steve220]

hm okay, changing to a 1000cc injector seems to be necessary then, although i would only be looking to run 5-7psi.

Steve, have you had any luck with running a knock sensor? I already have a basic bosch one, and just wired to an aux cord and amp that I can plug headphones into. Would be nice to have full knock based iginiton control though.

I have, but the background thresholds are high! When i had my car mapped, my tuner induced knock at low rpm and moderate load to be able to hear and log it on the haltech nsp software. From there, the threshold is set to 3dB above background noise throughout the rev range. Its more of a 'just in case' of bad fuel, hot spot on the piston etc.

My analysis on the whole thing is actually listening to the engine during dyno sessions, let it tell you what its doing, and set the timing accordingly; creep up on it, rather than put in savage timing and wind it back.. youll save your engine that way!