Roadgoing Sprint/Hillclimb Engine Choice

Tue Nov 01, 2011 10:43 pm

Hello Guys,

Hopefully this will stimulate an interesting discussion and help me with my dilema.....

Currently im working on my 318is in turning it into a Roadgoing Sprint/Hillclimb/Trackday Car.

I have several engine options i can go for and would appreciate your opinions on which might be the best option.

The regulations for the roadgoing class with respect to engines are:

-Engine must be an option for that model eg. e30 3 series so i can use a M20 if i want to but not e36 engines eg S50
- Induction is free
- Head must be original as fitted to that engine
- Internals are pretty much free

With regards to engine capacity i can either run in the 1400-1800cc class with the current m42 engine or go up to the 1800-2600cc class using an m20 engine.

Forced induction is allowed but then capacity equivalence is +40% so a turbo'd m42 would put me in the 1800-260cc class.

So i am thinking my engine options are:

-Highly tuned m42 with headwork,cams, ITBs, management etc aiming to be ~200bhp in the 1400-1800cc class which would be quite competative

or

- Turbo m42 running ~ 250bhp in the 1800-2600cc class which would also be competative

or

- M20 with cam, 6 branchmanifold, S50 throttle bodies and aftermarket managment running ~230bhp (is that realistic) in the 1800-2600cc class

I know there are many considerations and as this will be a road car it will all be a compromise.

I like the idea of the big 6 nicely tuned as it will be great on the road and up the hills but worry it might ruin the balance of the car with the extra weight. Also the turbo route or well tuned N/A m42 options will be ££££'s potentially

The fact i may have access to a decent M20 at a cheap price is also tempting. I also am not hugely into turbo'd engines and have virtually no experince with them and worry about reliability issues.

Sorry for the mammoth topic but i hope this may interest many of you and stimulate some interesting discussions....

Cheers Guys!

Wed Nov 02, 2011 2:01 am

Sell you car and by an ex race car from say the Khumo cup, it will be far cheaper and you will start with a sorted car. I expect you will be able to find a 325 on carbs or DTHB if you look around.

Wed Nov 02, 2011 2:01 am

Sell you car and by an ex race car from say the Khumo cup, it will be far cheaper and you will start with a sorted car.

Wed Nov 02, 2011 7:16 am

For sprinting I would definitely be looking at the power to weight ratios. As its all start - corner - stop.
Id probably go for this setup.

-Highly tuned m42 with headwork,cams, ITBs, management etc aiming to be ~200bhp in the 1400-1800cc class which would be quite competative

Reliable and you would get some good power and not have a havy six lump up front. Turboing gets expensive when using it for competition.
One of the guys I race with is dropping from a 2l to a 1.8 to have a better chance in his class. Making a 1.8 alloy mi16 and looking for the 250 mark.

Wed Nov 02, 2011 8:08 am

Thanks to the replies guys.

That a good point you raise about an ex Kumho Cup car but i really lke the idea of doing this projct myself and am attached to my car now. Also i aim to just pend a bit here and there as i go rather than shell out a big lump for a cup car. I will bear this in mind and keep my eyes on the look out though.

As for power-weight that was what a large concern is, although i have noticed that the average times between the two classes i run in arent too different and if anything going up a class i might actually be more competative as i will be against other bigger vehicles rather than little hatchbacks and a bloody lotus elise which i wont ever beat.

I could always build a stroker too and go up a class?

How much do you guys think i would notice the extra weight over the front if i went for an M20?

For the hillclimbs having a big torquey 6 cyclinder might be good though dont you think?

Thanks again

Wed Nov 02, 2011 9:03 am

If you are thinking of tuning the M42, do some serious research beforehand to see what is achievable without boring/stroking (which would take you into the next class). A lot of the power figures bandied around are internet myth, based on the mighty race S42 being developed from the M42. In nearly two years of searching, I've not found a single standard bore/stroke NA M42 (looking at various forum threads of builds etc) that makes anywhere even remotely close to 180 brake, and it's another huge jump from there to get 200 brake. If I'd spent half of what I've put into the M42 on a 2.5 M20, I'd have a very nice engine indeed instead of the 160 brake M42 I currently have. The weight difference isn't really that much in the scheme of things, a fibreglass bonnet would balance up the difference again. I'm sticking an M20 into mine over winter, will let you know what the lap times say next season

Wed Nov 02, 2011 4:41 pm

Hey Brian thanks for your input,

I fear you are probably right about the realistic tuning limits on the m42 as being around the 180bhp mark plus lots of money to get there. Aslo in the 1.4-1.8 class 180bhp in a car around the 1100kg mark is always going to struggle against small hatches and that pesky lotus elise

Im of the school of thought that figures dont really mean much on their own and its the drivability that counts most so i imagine a free revving and light m42 would be a joy to drive. But i wonder if it would lack the torque needed for the hillclimbs and the fact i have been offered an m20 cheap which is running 190bhp with chip and 6 branch makes m20 seems like the best option at the moment.

What are peoples experiences with tuning m20s, with a wilder cam, bit of head work, decent induction eg triple webers or thottle bodies and managment what would i realistically see in terms of power? Also having not driven a 325i what are the engines like to drvie? i imagine they arent the liveliest of engines?

Cheers guys

Wed Nov 02, 2011 8:59 pm

Brian28 wrote:In nearly two years of searching, I've not found a single standard bore/stroke NA M42 (looking at various forum threads of builds etc) that makes anywhere even remotely close to 180 brake

i think you need to look here then! http://www.bmw-rallying.co.uk/viewtopic ... 1&start=30
standard bore + stroke, 177bhp on the standard plenum. surely would piss 200 bhp with throttle bodies?

Wed Nov 02, 2011 9:19 pm

If you are serious about the M20 then I would do a search on here - loads of good threads on here, inlcuding a mighty M20 with triple webers making 230hp, but that is a 2.7 @6800ish... With a 2.5 on webers, big cam, head work etc etc, I reckon you would just about crack 200hp realistically...

Sounds like an interesting project! Build thread to come??

Wed Nov 02, 2011 10:29 pm

on a side note.. dont underestimate the benefit of a decent close ratio gearbox and a selections of diff's

Wed Nov 02, 2011 10:36 pm

Hi all im in the same bout as DR DRIFT . I dont think u can turbo or supercharge acording the to regs but they can be interprted in difrent ways. I love the idea of the 2.7 but i think that would put u into modified or rally which is lots of money in which case either m20 engine conversion stick with the m42 or go in rally with a m3 320bhp out of the box hmmm.

Wed Nov 02, 2011 11:20 pm

Wow Alan excellent find now that is interesting.....

I did find it a bit depressing to think 180bhp is not easily achievable from an m42 but i guess if that dyno is accurate 200bhp with bodies and management shoudnt be an unrealistic expectation

Ive also found a particulalry interesting engine tuning giude from metric mechanics for the m42 which makes for a lengthy yet interesting read....

http://www.metricmechanic.com/pdfs/metr ... ooklet.pdf

And, Mikey boy the thought of a 2.5 on triple webers is sexy, just for the noise if anything! would have to buy some shares in Esso though!

Wed Nov 02, 2011 11:23 pm

Oh and Brian you said you spent alot on your m42 and made only 160hp. Could you tell us the spec of that engine please?

Cheers

Thu Nov 03, 2011 3:16 pm

There is always the S14 as xSPARKYx points out... Just be prepared to be broke for the rest of your life! (I should know - I am putting one in my E30 as we speak).

But, 300hp from a normally aspirated 2.5 isn't too shabby...

I am looking to get 220hp from my 2.3 with just a few mods (DTM airbox, decent exhaust, standalone ECU...)

Thu Nov 03, 2011 4:44 pm

God yes i love the s14! what a noise!

Decisions, decisions...... given that article Alan found and the metric mechanics article a m42 with about 180-200bhp seems achievable doesnt it with standalone ecu, cam, decent induction and a bit of head work.

If that really is achievable then i think that would be the best option at present. If not i think m20 will be the way to go. The biggest shame is that the regs are so tight otherwise i could put pretty much anything in! Did someone say Cosworth YB?

Thu Nov 03, 2011 5:04 pm

i've met the chaps who built that engine in the link i put up, nice blokes so if you have any questions i'm sure they'd help. they've got a rather tasty M54 compact on the way too.
http://www.bruvsmotorworks.co.uk/

the problem with the M42 is when someone asks about tuning it the response always seems to be "put an m20 in." so very few actually do much with it and it seems to have gained a bad rep for it.

Thu Nov 03, 2011 5:19 pm

Thats another good point you raise Alan!

I have certainly all to quickly recieved the same response regarding m42 tuning when i have asked around.

As far as my limited knowledge of engine building goes i always thought any decent 16v engine is always good for 100bhp per litre so why should the m42 be any different? Afterall its a bloody F1 derived engine!

Certainly 180-200bhp in a light 318is shell with correct cam,gear and diff ratio (to fully use the powerband) would be a little beasty!

Thu Nov 03, 2011 6:07 pm

DoctorDrift wrote:Oh and Brian you said you spent alot on your m42 and made only 160hp. Could you tell us the spec of that engine please?

Cheers

Mine is similar but only 272 degree cams both inlet and exhaust.

http://www.e30zone.net/modules.php?name ... c&t=166811

Good link to the bruvsmotorsport car build, and assuming that the dyno isn't being too optimistic that's a great result

. Do sprint cars have class weight limits? I race in the same class as the M20 325s, but can run lighter. One of my reasons for swapping to a 325 engine for next season is that I can't get the 318 down to the weight limit (1013kg weight with driver post race), so can't make the most of any lighter car advantage.

Thu Nov 03, 2011 7:05 pm

Looks like I will be running with a lot of 325's next year

Are you running in a dedicated class or in calls D ?

Thu Nov 03, 2011 7:39 pm

Thanks for the link Brian, i remember browsing that thread before

nice job with the bike carbs i bet the sound was interesting

I was thinking about going for a 272 cam should i tune the m42 as i didnt want to push the power band too high up the rpms.... I cant believe that a slightly wilder cam on its own would explain why the bruv motorsport boys got another 20bhp........ I reckon a decent standalone ecu and induction would still make huge difference even with a 272 cam.

Question is, is it worth refreshing an m42 then having headwork, cams etc etc to make 200bhp if im lucky, nothing guaranteed. Or, throw the same money at an m20 which i can get cheap and doesnt need a rebuild.....

In the sprint/hillclimb series there are no weight limits par se but you have to run with the car in road trim eg, rear seats and all working electrics must remain. You can go fibreglass bonnet and boot though. Plus i have some cunning ways to get some other weight off e.g. get rid of underseal, remove industrial bumper mounts etc...

Thu Nov 03, 2011 10:23 pm

DoctorDrift wrote:Question is, is it worth refreshing an m42 then having headwork, cams etc etc to make 200bhp if im lucky, nothing guaranteed. Or, throw the same money at an m20 which i can get cheap and doesnt need a rebuild.....

well this is the crux of the matter really. as i compete in road rallying, i am limited to 4 cylinder units so my choice is easy.
i have always been a subscriber to the theory that the best approach is to fit the biggest engine possible which in your case would be a 2.7/2.8 M20.

i still think the m42 is a good little unit though, it's just 200cc too small.

Fri Nov 04, 2011 9:46 am

DoctorDrift wrote:God yes i love the s14! what a noise!

Decisions, decisions...... given that article Alan found and the metric mechanics article a m42 with about 180-200bhp seems achievable doesnt it with standalone ecu, cam, decent induction and a bit of head work.

If that really is achievable then i think that would be the best option at present. If not i think m20 will be the way to go. The biggest shame is that the regs are so tight otherwise i could put pretty much anything in! Did someone say Cosworth YB?

I'd say S14, too...It may cost a bit to start with, but you'll have a minimum of 200bhp on a standard engine with AFM...

A 2.3 can give upto 300bhp in Group A spec and the 2.5 up to 340bhp...all depends on your budget.

Next best would be a 2.7 M20 on slide throttles or perhaps carbs...
Possible to get 250bhp or so

Fri Nov 04, 2011 12:05 pm

There's a fellow on trackscotland.co.uk that uses an iS for hillclimbing.. bloody quick.

Username is Clarkyboy (same name on here) may be worth a chat?

Fri Nov 04, 2011 12:34 pm

The guy who I do some work for in Kumho's had an E30 325i on carbs and it ran rings around the E30 M3's.

DoctorDrift wrote: Question is, is it worth refreshing an m42 then having headwork, cams etc etc to make 200bhp if im lucky, nothing guaranteed. Or, throw the same money at an m20 which i can get cheap and doesnt need a rebuild.

IMO what you gain from building your M42 over putting a cheap M20 in is you know what has gone into your engine and that everything is refreshed. You could strike lucky with an M20 and be fine or you could pick up one that spends its life crapping it's self.

No matter what if you're going to be competing the most important thing is having a consistent engine that you just need to check the oil on every round.

Fri Nov 04, 2011 7:12 pm

Right guys thanks a lot for all your ideas and opinions!

After much deliberation i have decided to go for the m20 option and because i dont like to hang around i have agreed to buy the m20 which i have been offerred for £200. Its only done 100k and the seller is a genuine guy. Im picking it up tomorrow and cant wait to get started. A build thread may follow

Naturally it will get a stripdown and rebuild and then i think some lightening and balancing of the bottom end, a decent amount of head work, probably a schrick 285 cam and triple webers with ignition managment - should keep me busy over the winter!

Thanks again guys!

Fri Nov 04, 2011 8:58 pm

Good man! Lots to consider, but the M20 isn't a bad old donk...

I am pulling out my M20 very soon (for the S14 install) and have another good M20 bottom end doing nothing in my garage - both coming up for sale cheap soon for spares!!

Best of luck with the build - look forward to the thread!

Mike

Sat Nov 05, 2011 1:16 pm

Black_Potato wrote:Looks like I will be running with a lot of 325's next year
Are you running in a dedicated class or in calls D ?

Class D for me, I've heard that a couple of PBMW drivers are sticking in 325s for next season but assumed that it would be class D rather than a seperate dedicated class. Didn't think there was one? But having said that I've not been around the paddock much this season to keep up with things.

Sun Nov 06, 2011 9:48 am

Little update guys.....

I picked up my new m20B25 yesterday and stripped it before transporting it back.

It was in great condition and had come from a 100k mile car but the shells and mains were almost good as new!

Cant believe how heavy it is even the bare block is difficult to heave around on your own.

Ive had some intersting email correspondance from Fritz Bitz with regard to tuning this 6 pot beauty. They have told me not to worry about enlarging the inlet ports as the inlet charge speed will drop and looking at the standard port sizes im inclined to agree with them. They did however say using 1mm bigger inlet valves is a good idea and working the area around the valve seat
/guide area is worth 7% better flow

With regard to the bottom end i will be renew the shells and mains for good measure but i dont have any experience with crank lightening/balancing etc. As far as im aware reducing reciprocating mass as much as possible is very much worth it so the engine will love to rev. Looking at the crank the counterweights are huge and it looks in theory that a lot of material could come off them. Do any of you guys know much about bottom end tuning or anyone in the southwest who is renound for that kind of work?

I will also be trying to find the lightest flywhel i can and wondered if its worth shelling out for a nice aluminium one or just machining the current one as much as is safe?

Cheers

Sun Nov 06, 2011 9:59 am

sorry to go off topic but that 177bhp m42 will not have made that.
the rolling road matey has put it up as a front wheel drive car, so the equation that accounts for drivetrain losses will be adding power to the flywheel figure

p.s. best of luck with your build

Sun Nov 06, 2011 9:32 pm

i thought the rolling road lets the engine run down and converts the drag to the mechanical losses so it wouldn't be an issue if it was front or rear drive?
i believe the figures came from a very reputable source.

Mon Nov 07, 2011 1:03 am

the best concept we currently have may be a ported 731 head using 86mm pistons and 43.5mm valves.

see my thread.

an 86mm bore should give you 2.6l

Sat Nov 12, 2011 7:11 pm

alan1272 wrote:i thought the rolling road lets the engine run down and converts the drag to the mechanical losses so it wouldn't be an issue if it was front or rear drive?
i believe the figures came from a very reputable source.

thats the way it should be done, very easy to fudge this as one or two clicks on the hand break on coast down will elevate power figures.

any at wheel measurement thats converted to crank by any method should be taken with a pinch of salt.

Sun Nov 13, 2011 6:30 am

HairyScreech wrote: any at wheel measurement thats converted to crank by any method should be taken with a pinch of salt.

Agreed.

Sun Nov 13, 2011 10:30 am

alan1272 wrote:i thought the rolling road lets the engine run down and converts the drag to the mechanical losses so it wouldn't be an issue if it was front or rear drive?
i believe the figures came from a very reputable source.

it does however it does this through an equation, he has the equation set to fwd which will affect the result.

fairplay they may not have if they are reputable

any at wheel measurement thats converted to crank by any method should be taken with a pinch of salt.

^this

Mon Nov 14, 2011 11:31 pm

Hi guys been reading your thread, I'v just completed a m20 2.7 conv, it really is worth doing you get so much more torque over a 325i, I did the following.. lightened and bal flywheel, ETA crank, 272 cam, 3 stage cut valves, polybush all round, 3.94 LSD big brake upgrade, adj shocks all round, but the best thing I did was to fit a E36 m3 steering rack and this makes a heap of differance to the cars feel, really good in the dry... and oooohhh so much fun in the wet. If you need any help on this conversion please contact me... budget wise I think it cost me around the 2k mark with everything which inc new shells, rings , comp head gasket,block bore,new pistons, head skim ect ect. This spec build would be ideal for hill climbs ect. I did lots of them in my old 325i and it was fun.. but now... well I will let you know !
Steve.