BMW K1200RS - Possible supercharger conversion
Turbo Mini Forums

Hi guys,

I'm a complete novice when it comes to forced induction minis, but i do have a fair bit of experience with NA twincam 16vs.

current spec:
bmw k1200RS head
specialist components conversion
1380 block
worked rods and crank
MED cut out pistons
dog box
LSD
7.2x13 avon slicks
130BHP
approx weight 550kgs

The car feels like it can take alot more power and it actually feels a bit slow now! Options seem to be supercharger or highly strung NA route.

I understand that N/A setup would require full race head, cams, steel crank, rods, injectors, throttle bodies etc and get me 160bhp and cost £4k+. This would keep me in the same class but seems alot of cash for 30bhp.

Supercharger route i dont really have a clue what is required / possible. Can i supercharge a 1380 or does it need to be the usual 1293 / 1310? Would i need new pistons, what about CR? Could i get away without the steel bottom end if its not going to be reving as hard as the NA or does the jump in power require this? Would obviosuly need to purchase at least a supercharger, plenum, intercooler but is probably capable of 230+bhp. It would put me in the next class, but im already competitive there and would have 100bhp more...

Any advice would be very much appreciated.

Cheers,
Nick

Good questions,

yes a 1380 can be turbo'd/supercharged, the bore flex issue seems to be largely an old wives tale.

You will need to get the CR down, i would aim for 9:1 for an engine with about 12psi of boost. it is possible to machine piston dishes bigger, but obviously there is a limit, also the head chamber cak be taken out a bit too... you'll need to do some measuring and some calculations.

You will need to double check the class rules, but there will be a multiplier added to the capacity...

I seem to remember somthing about ending u in Pro mod class for hill climbing....

But I dont know the rules...

It is not currently legal to race a mini in upto 2000, but will be next year.

130 seems low for your spec. Competitive cars in the class normally have 150+. From experience over 180 in the mini needs proper balls and even better traction control.

Oh and before anybody else brings it up you really need to consider a turbo imo.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

i was planning to supercharge but the cost of doing it properly. i.e a rotrex charger has led me down the turbo route. but really depends how much your prepared to spend. that said the dyno graph from one of sc's supercharged engines is impressiv
e.

Personal I'm not a fan of 1380 setup cause it don't leave room for over bore in future

ID rather go 1293 so you got a few more bores left over if ever needed

1380s do make good power

If you haven't already bored it, I wouldn't bother going any more than 1293 on a standard block, I really don't think there is any real gain going 1380 over 1293 on a blown engine. A 1380 with an SA stroked crank on the other hand would make for a revy engine! :)

I'm biased but going down the turbo route will make it much easier play about with in the future if you want more boost, quicker spooling turbo etc..

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

Since you are already competitive in the next class, it seems you don't necessarily need 200+HP and are just looking to make your mini a bit more 'fun' to drive. A low boost supercharged set up would easily achieve that without the need for steel cranks, intercooling, or compression drops. Go for a Lysholm type or Rotrex supercharger (SC do a nice kit) as they are much more efficient than the eaton type pumps that just create massive amounts of heat.

Going that route you still have room left for future developments, i.e. Low comp pistons come rebuild time, crank up the boost, add intercooling to crank up boost even further etc. When going the N/A route you quickly hit a 160HP ceiling as you have stated with no options to further progress, furthermore revs kill engines not boost....

Only thing with the supercharger gear it will add weight, so it needs to add enough power to offset that.

If something is worth doing, it's worth doing half of.

thanks for the replies guys, very useful!

whats the regulation behind minis not being allowed in upto 2000c? Is this stated in the blue book and why are the regs changing for next year?

The car has been rolling roaded twice, 150bhp and 130bhp, but the spec should be around 130 as its just fast road setup.

180 would probably be plenty yes, but i would like the option to easily increase this as i get familiar with it. traction control is a good shout though...

The car is currently 1380, so would like to keep this block if its not going to cause major issues. I have a few spare blocks, including a 1330 with the 16v machining done, but i'm looking to keep as much of the current engine as possible.

I'm not against turbo charging, i'm just going with what ive seen done previously. anyone got any links to a turbo build? Any other pro's and cons to supercharger vs turbo? Which turbo do people recommend fitting?

Is this the regulation change you are referring to:

Proposed Regulation
(S)11.5.1. For Road-Going Series Production Cars,
the cylinder block and cylinder head must remain in
the original position and be externally identifiable as
that fitted to the original model or specified option.
Induction is free, as are exhaust systems, DELETE[[[[but must
remain in the same capacity class as the original
car or the manufacturer’s specified option for the
model and engine.]]]]

Reason: MSA does not mandate capacity
classes.
Implementation: 1st January 2014


In terms of turbo or charger, i'm no further forward. Rotrex chargers seem to be relatively well thought of but i havent seen anything regarding type, size, model of turbo. Are there any k head turbo build threads on here?

i have found the search function and doing lots of reading!

So, after lots and lots of reading. I think i'm going to go down the turbo route. Aiming for around the 200bhp mark. I've been reading about turbos but im really none the wiser or closer to making a decision. The GT28RS looks a bit overkill for what im after, the Gt17 maybe a bit small, so Gt20 or 25 about right?? Does anyone run twin scroll? I'm not interested in a peak figure but something that has decent throttle response and not too much lag!

The engine is coming out the car for a freshen up over winter and im looking to use as much of the current parts as possible. So keeping it 1380, unless there is a good reason to change. I'm going to be doing as much of it DIY as i can, so designing the manifold, plenum etc can be as custom as i need it to be.

The car is used for sprints and hill climbs, so is only run hard for 100 seconds max. I currently run a front mount radiator, so im wondering if i can do without an intercooler and run water / meth injection or a charge cooler instead?

Is 200bhp an achievable figure without significant changes to my existing setup and more a case of bolting on the new bits and pieces?! Should i be looking at getting headwork done while the engine is in bits or is this not my best use of budget?

Many thanks,
Nick

Have a look at the build threads for madmk1 and Nic. They both have huge side mounted intercoolers that work well with a rad at the front.

Even with WI, an intercooler is essential IMO.

In the 13's at last!.. Just

Getting the compression down will be a real challenge. What pistons are in there and what is the piston to deck height?

will go through those threads, thanks.

Pistons are these:




Will measure piston to deck height when ive got the block split

Looking to machine the pistons down, so that i can up the CR.

Now the engine is out and head is off, ive done some measuring and calcs.

I think the current CR comes in at 10.55, so hopefully there will be plenty material in the pistons to machine a larger dish. Anyone know what the recommended minimum thickness for pistons should be?

I'm also going to go the turbo route, GT1752, rather than supercharged.

John Kimmins built a very nice rotrex suprcharged 16v

http://www.youtube.com/watch?v=pqqau6sQ4U8

I think the graphs were on here at one point, made close to 200 and had an N/A like power band. also you run them higher CR than a turbo so might be more suitable considering your starting point.

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

www.twin-turbo.co.uk

Specialist components also do their gasket in varying thicknesses up to 6cc if that is required.

The cast omegas seem to stand plenty of dishing out though.

Yes, the SC supercharger kits are what got me thinking about forced induction. However, it appears that there is much more choice and availability in the turbo market, that can also be had for very little outlay.

MED told me there is no problem dishing out the pistons to 11cc as per the non 16v omega's, but didnt recommend going any further than that, although i suspect that is to cover themselves slightly.

I've already got the thinner 0.6mm Gasket, which can be reused and appears to be in good condition, so want to avoid having to shell out another 160+VAT if i can help it!

Edited by nky_84 on 20th Jan, 2014.

Initial manifold mockup and turbo placement:



I havent seen anyone with a manifold design as simple as this. Anyone suggest why this sort of thing isnt a good idea? I'm going to chop the downpie so that it allows space for the 4th port (not sure if i will keep the flexi or not). Also going to be extending the Weber box to create an airbox for the cold side i think....

Jimsters manifold is kind of like this, but probably shorter runners, as the turbo's down the back off the block,

Jon Kimmins's ia also like this,

both of those lumps make 250hp easily, if after 200hp, tbh you dont need to get too hung up on the design.

I made my runners as short as possible, to try to reduce lag as much as possible. Also wanted to keep things simple. As has been said 250bhp is going to be easy with a turbo, and it WILL be a handful in a 550kg mini. I had to move from 7" Avon's to 9" to get traction, and still find traction control handy when coming out of bends.

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