High Compression, Low Boost. Converting from NA to turbo.
Turbo Mini Forums

Hello.

Spent a long time reading but decided that asking the questions may actually lead to results haha .

So i'am looking to convert my NA to turbo. The car is a 998 +100 thou (1080cc) the pistons are from Australian mini sport. I have the Calver RE13OT camshaft fitted and his stage 3 998 head. The head has been skimmed to give a compression ratio of around 11:1, not including the crown to top ring gap. The bottom end is dynamically balanced and fitted with a Pre Verto clutch,lightened flywheel, rally plate and standard spring.

So very much a NA engine.

Obviously the compression ratio is far to high, so i would have to have the crown machined to give a dish. To bring the compression down to around the 9:1, in theory making the car more driveable when off boost. I am intending to fit an inter cooler to keep the charge temp lower so that a higher static compression is possible.
Is 9:1 reasonable compression?
Would dishing the pistons affect their strength?

I have been reading about cam choice on the forum, everyone seems to suggest using the standard metro camshaft.
Surely a turbo would work with any camshaft, including the camshaft i have fitted already?
The power band at the moment is around 2000-7000. I am quite a fan of the cars revvy and cammy nature. It is only used for fun so ultimate daily drivability is not so important.

From what i have read on the forum the gt15 comes recommended as does the gt17. I would be purchasing reconditioned from Ebay.
Does either of these turbos come on boost around the 2000-2500 rpm point?
I presume that you want boost ans camshaft to come together at the same time?

I am intending to have an exhaust manifold made to avoid having to cut the fire wall, and am toying with the idea of using mega squirt for the fueling side of things. i would like to fit a knock sensor as well, if this is possible.
Which version would you guys recommend for this spec?
Would i need things like twin injectors one for low speed and one that comes in at higher rpm?

At the moment i have a 3.44 final drive, with a turbo fitted would you suggest fitting something like a 3.1 or lower or sticking with the 3.44?

Sorry for this large list of questions in the one post but i have loads of questions that i cant seem to find answers for :-s. So thank you for your help in advance please correct any misconception s that i have .

9:1 compression will be ok. But be careful making the piston crowns too thin, you need the piston crowns to dissipate a lot of heat. I made some too thin and they eventually failed.

You can get a few ccs out of the pistons, but better to get a head with larger chambers.

The KC500 or MG metro cam is my favorite in a turbo car. Not sure what the cam you have in is, you want to minimise overlap to improve turbo spool.

GT17 won't fully boost til over 3500rpm on a small bore, a GT1548 is a nicely sized turbo, a GT1544 is smaller and on paper will work for a nice driveable 100bhp engine, but I've not tried one (yet).

A 3.1 is a decent diff for a 100bhp engine, It's what I used.

FI is a whole other subject, a single TB with two injectors can work ok as a wet manifold setup.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Edited by steve2016 on 9th Sep, 2016.

What turbo ? In theory the more efficient the turbo and the lower the charge temps the more boost you could run.
Are you fitting an intercooler ?

Phil.

WWW.TURBO-MINI.COM

It would be either a gt1544 or gt1548

I have a Suzuki swift ic that I was going to use or would this be too big?

no such thing as too big! basically if you can fit it in a mini its not to big.

Hello,

sorry for my lack of reply, thank you for you answers to my initial questions.

However i am of an engineering mind and wanted to know why you cant use a heavy cam. So i went away and did some reading as i wanted to know why you cannot use a camshaft with a large over lap with a turbo. As i gather it the overlap (having both inlet and exhaust valves open at the same time, which helps to create power in a higher revving naturally aspirated engine), coupled with the back pressure caused by the fitting of a turbo can cause issues. The exhaust gasses hit the turbo blades, this causes the back pressure, if the exhaust gasses are able to fill the exhaust port they will flow back into the combustion chamber causing leaning of the mixture, pinking, loss of power so on. In extreme cases the exhaust gasses are able to flow pass the inlet valve and into the inlet side which can cause even more serious problems. So to avoid these issues it is imperative to have a limited amount of valve overlap. I hope this explanation helps anyone like me understand why.

As for selecting a turbo i decided to follow a different route instead of using a Garrett it thought i would look at the turbos present on the new modern small capacity turbocharged petrol engines such as the Ford EcoBoost. There are however problems with these turbos. They are variable vane turbos, which help to give the ecoboost its linear torque curve. However these vanes are electronically controlled via the ECU, which i will not have the hardware or soft ware to operate correctly. So i began to look for Turbos present on modern small capacity cars but are not electronically controlled. This led me to the IHI38. this turbo is Fitted to the Fiat 500 Abarth. Reading on the the Fiat forums it should be similar to a T2 but is a more modern and hopefully efficient design. It has both water and oil feeds, is a compact size and the actuator is not cast to the housing all benefits.

Eventually i decided on a 3.2 final drive as fitted to the Metro Turbo, i am hoping to keep some of the rapid acceleration i am used to with the 3.44.

i have dished the pistons 3.5cc and then decided that that would be a safe maximum as i am not sure how thick the crowns are. I have also purchased a new set of rings from Calver, the gap is around the 17.5 thou mark. I am hoping that this gap will not cause a blow by issues. The rest of the cc's will be removed from the cylinder head to bring the compression ratio down to the 9:1 mark.

I am in the process of ordering the required parts for the MSX3 fuel injection. Diy Auto Tune seems to be the cheapest place. I am however struggling on how to convert the dizzy to a cam sensor. I have read the current feeds and sadly a lot of the pictures have gone so if anyone has any pictures of their own please help me out.

Equally injector size is an issue, i understand why you need a a large cc injector, due to fueling both draws on one quirt of fuel. I was thinking of a pair of 630cc at the inlet port. A second pair of 630cc injectors, fitted next to the first, and then staged later into the map. again if you have knowledge please advise.

I am going to post my fuel injection queries on the fuel injection section and see what i get :).

I thought i would throw in my own point about intercooler size. One of the many people i was talking to about turbo charging owns a twin turbo Celica track car. He informed me that the intercooler creates resistance in the inlet tract. If the cooler is larger than required for the turbo fitted the cooler stops cooling and just creates a delay to the boost pressure reaching the engine. In essence it creates lag. But obviously space is always limited in the minis engine bay so fitting an intercooler too large is unlikely to be and issue.

Perhaps it's too late but if you search inspiration in the modern world then you should look at Indycar engines. They run NA CR and very low boost levels. This also works very well with old engines like A-series that had poor VE. This allows creating a NA-feeling engine having say a 110% VE. No need for I/C under 0.3bar boost, having air temperature at 40C is perfect. This also allows using a small turbo that will deliver from low RPMs.
Forget VNT, they are VERY complicated to control. WRC engines don't use them and still have max torque from 2000 to 7000 rpm (here I'm talking about HUGE torque).
I'd possibly make new pistons to keep most of the chamber inside the piston crown. This is very thermally efficient (americans prooved that many times) and gives you freedom to shape the head part for more turbulence (as you have turbo to overcome induced backpressure). You can also stack metal and composite head gaskets to reduce CR.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

So i have decided to take a slight change in direction. I am putting all of my NA components up for sale and will be starting with a standard engine.
Please follow the link: http://www.turbominis.co.uk/forums/index.php?p=vt&tid=605311

Plus, how do i up load picture to the forum. I have created a Photo bucket for myself but when i attach photos using the link above the emoticons all that appears in the message is the http link in text, no image? help please.

once the image upload is sorted then i can go about filling up this feed

#Tried It 2

Edited by #Tried It 2 on 6th Jan, 2017.

so i thought ide post a quick update.

having decided to start from a fresh engine, i hit ebay for a scrappy engine, ended up buying 3 in a job lot. They arrive this Monday, hopefully at least one will be in good condition. So i can begin this journey to torque steer and frustrating tiny problems holding me up at every step. Built enough engine not to know that if it can go wrong it will.

I have been buying and collecting parts for this conversion over the last few months since i started the feed, but am a long way of every thing.

My intended finished spec now is as follows:

998 A+ block bored out to +60 thou. Opened up water ways around the pump and the two large coolant holes at the clutch end. Apart from the coolant the 3 coolant holes closest to the clutch, the rest will be tapped and blocked with grub screws. Creating coolant flow similar to that of a dry deck.

Omega Forged 998 +60 pistons. as these seem to be the only Omega pistons now available for the 998??

Standard 998 conrods and crank. hopefully these will be strong enough for at least 12 - 14 psi and then on upwards. Though these along with all of the bottom end will be dynamically balanced.

MED light weight Verto fly wheel fitted with the AP rally friction plate and and RTS spring plate. Following the guide on the forum.

The cylinder head i will be modifying/grinding myself from a standard casting. Based on my NA head ports and the yellow bibles guide to modifying the chambers. I will be aiming for a 9:1 CR to give me off boost drive ability while maintaining the ability to run a good quantity of boost. i would like at least 14 psi which theoretically should give me around 140 BHP. I will be using a Payen copper head gasket to begin with which will hopefully hod it together.

My turbo of choice is an IHI VL38, removed from a Fiat 500 Abarth. according to Fiat it was a 2012 car. i have read that it can produce up to 20 PSI before it becomes inefficient. It will be mounted above the clutch housing using an equal length 3 to 1 manifold, with sample tubes for the lambda sensors. the inlet manifold mill also have to be made to support the port injection, the selection of throttle body is undecided, as i will also need a idle control motor so a 50 mm butterfly with a built in idle motor would be perfect.

The intercooler is planned to be a one off to fill as much of the space behind the grill without having to alter or remove the grill. Have to keep it as incognito as possible , and naturally a Forge Motorsport recirculating valve haha.

The gear box is a standard unit fitted with a central pick up, windage tray and a 3.2 final drive.

i am planning to use a 2 core super cool, fitted in the standard location, mechanical fan removed and electric fan fitted to the wing side of the radiator. i will also be removing the mechanical water pump and replace it with a Davis Craig 80 L unit fitted to the subframe. The alternator will be dropped to sitting between the block and the sub frame and utilise a short belt. The Alternator is a 60 AMP unit from a Suzuki swift. with the extra space generated i will attempt to build ducting to the radiator. i am also intending to use a full bypass thermostat, to try and ensure the most effective coolant flow possible.

i intend to run the to and from fuel lines through the car using Teflon braided lines.

there are a few other bits and pieces but it should be a rather comprehensive build. i will have to take a bunch of photos of my growing collection of parts and of course the build once it gets going :)

cheers

#Tried It 2