29 replies to this topic

[benpopham]

100bhp is definitely possible from a 998.. look at the mini se7en's racers, they get around 95bhp from their spec and thats running with a restricted cam and only half a weber.

Now I know they rev to around 8/9k with that spec and almost get to 100bhp, so with a better cam and a well sorted fuelling system, I cant see why it isnt possible lower down the rev range, this engine is by no means going to be 'nice' to drive

The general rule of thumb is 100bhp per litre ...
998 = 100bhp
1275 = 130bhp

Im not saying that it completely accurate.. but gets it there abouts.

Have a look at my project thread.. Im aiming for the magic number with my 998.. but would be happy with 90 after afew more mods.

Also.. why not run FI?

[Wil_h]

bmcecosse - I have 47hp @ the wheels which is about 70hp @ the crank. I have dyno sheet around here somewhere.

mmm right what kind of compression ratio would i need to run? and what kinda psi would i need to run to reach my 100hp mark? and would 100hp @ the wheels be unrealistic for a turbo 1100?


Thanks Blake

Hold on, you wanted 100bhp at the fly a while ago. 100 atw is a lot more. For this you would definately need a turbo. But for 100bhp (fly) you'd need around 10psi, for 100 atw maybe 3 or 4psi more.

that is another option. Does a BMW head conversion make that much of a difference?

This would help, but the issue of high rpm and reliabilty are all still the same. A BMW head on an 1100 would be better on a short stroke motor.

Also.. why not run FI?

Yes if running 4 inlet ports (7-port, 8-port, BMW head, KAD head etc.) But, no, if unning siamese ports.

[miniobsessed]

Plain and simple...

Forced induction will be your best option to get 100+bhp from your 1100... But you'll find you'll have to completely strip and modify your engine to suit the pressure and power.

Actually, a 100bhp turbo 1100 will have a LOT less stress on it than an NA 100bhp 1100. A standard bottom end will easily be up to 100bhp on a turbo motor, no bother.

you dont have to rev a forced induction motor to get all the power out of it!! unlike a NA race cam'd engine, that will put serious inertial strain on the bottom end.

While you may not have to rev the nuts off a forced induction engine to get power out of it 100hp is 100hp and will cause the crank to flex just as much on each power stroke.

If I was going from a modest N/A 1100 to a 10-15psi forced monster I'd be pulling the bottom end down and making sure everything was sweet so I don't end up throwing money into a time bomb. 1100 cranks are becoming increasingly hard to find...

[Wil_h]

Plain and simple...

Forced induction will be your best option to get 100+bhp from your 1100... But you'll find you'll have to completely strip and modify your engine to suit the pressure and power.

Actually, a 100bhp turbo 1100 will have a LOT less stress on it than an NA 100bhp 1100. A standard bottom end will easily be up to 100bhp on a turbo motor, no bother.

you dont have to rev a forced induction motor to get all the power out of it!! unlike a NA race cam'd engine, that will put serious inertial strain on the bottom end.

While you may not have to rev the nuts off a forced induction engine to get power out of it 100hp is 100hp and will cause the crank to flex just as much on each power stroke.

If I was going from a modest N/A 1100 to a 10-15psi forced monster I'd be pulling the bottom end down and making sure everything was sweet so I don't end up throwing money into a time bomb. 1100 cranks are becoming increasingly hard to find...

Actually this is wrong. Turbo engines make power mid stroke where crank and conrod forces are a minimum. The maximum stress point in the stroke (TDC on exhaust stroke) will be little changed.

Most failures on turbo engines are piston related owing to the increased temperature of the burn.

[blake12345]

Wil H- Yes i want 100@ the crank from an N/A but if i was going turbo i would be aiming for this at the wheels.

benpopham - i have been following your thread and finding it very interesting. Yeh well i noticed an autocross 998cc with 90bhp (i think it was) in a mini mag recently and thought i want to give that a go and same with the mini se7en's.

Yes i know these cars rev high but thats ok, i'll just aim to do it with 5500 - 6000rpm.

I really would like this from an N/A just because it would be abit of a challenge and im not one to do things the easy way hence why i didnt go for a 1275.

I have had my gearbox rebuilt and had all the bottom end replaced and the like so i think it should be ok.

But yeh what are the best ways to keep a crank alive?

[bmcecosse]

On a standard 1098 - DON'T REV IT!! It WILL break if run over 6000 rpm for any length of time. Crank damper is essential, as is a centre strap - and a light flywheel helps. But at 6000 you will be lucky to get GENUINE 80 bhp.

[Cooperman]

It has to be said, as 'bmc...' has already intimated, that the 1098 BMC engine is quite 'an 'orrible engine' compared to the 998. It can't be revved above about 6000, has a very poor stroke to bore ratio (i.e. very under-square') yet still costs the same to modify but with poorer results. A 998 bored out to almost 1100 is a much better bet.
Whilst it is relatively easy to get 100 bhp at the flywheel with a 1275 lump, to get that from a 1098 will involve lots of extra reliability modifications, such as balanced crank, centre-main strap, custom distributor or programmble ignition, mods to acept the 12G940 head including pocketing of the block, a very 'hot' and lumpy cam and so on. It's really not going to be worth it, as a 1098 with that sort of power won't last long and will require very regular re-building. If/when it all blows up it will possibly take the gearbox with it and to pull 100 bhp it will be a cammy lump so you'll need a closer ratio gearbox and a lower ratio diff - added expense when the engine parts go down through the box.

[liirge]

Agree on that Cooperman!
most of the 1100 where used on the commercial vehicles, like vans and the like as they are economical in so much they dont rev and they are quite torquey! they also tend to start burning oil, most 1100 blocks i've come across seem to smoke a bit.

[melsmini]

1100 were built mainly for economy and torque,

if you want to go for lowdown torque and not follow the sheep with the 1275 then the 1100 engine is rather quite ideal.

but they arent very suited for all out power, but this doesnt mean it's not a worthy engine to tune, 75-80bhp imo would be a more worthwhile and easier to attain keeping reliability goal to aim for.

Edited by melsmini, 10 May 2010 - 06:37 PM.

[blake12345]

Well my aim is for at least 60hp @ the wheels and loads of torque. But i thought if i was going to do more work why not aim abit higher!

Ive heard of a few 1098's seeing 7000rpm a few times and not having any problems.

[miniobsessed]

Yeah... Had an 1100 which saw 7000rpm just about everytime I drove it. The crank is still fine It's the head gasket failure that killed it! It's still sitting in the shed and may get a rebuild one day. I saw the light and am building up a 1460cc for my own mini now

Get a good crank. Get it checked over by a professional (for cracking and wear). Get ALL the 'sharp edges' and casting marks which may shorten it's life taken care of (basically get it fully worked over) and have a little bit of mechanical sympathy for it as it's still not the strongest crank. Then put it in your motor. Aim for a gear change at about 6000rpm most of the time with the occasional squirt to 7500rpm.

If you want to go all out. Make yourself (have made) a billet crank with 2" - 2 1/8" mains and 1 3/4" big ends (to suit A+ 1275 rods - will need to be installed from the bottom of the bore) and modify your block to take it (including a set of custom steel main caps) Then fit a big blower (turbo or otherwise), race cam and big valve head... May not run under about 5000rpm but would be mad from there. Might even see 150+ at the crank...

And to everyone... I'm not having a go just a bit of fun

Edited by miniobsessed, 11 May 2010 - 09:27 AM.

[blake12345]

Well the crank has been checked ( by a professional) and balanced and the like. But yeh that sounds like a good idea. But yeh im to scared to take it above 5500rpm so 6500 or more will probably never been seen.

ANyway the reason i went with the 1098 build was that i had it sitting here and to get a 1275 i was looking at about Aus$2000 for an engine then the $4000 rebuild opposed to the $4000 that i spent on the 1098cc. Also i dont like to do what others do and every one was saying just get a 1275cc so i didnt and went the 1098.

[Cooperman]

I built a 1098 A-H Mk 1 Sprite engine for an historic rally car a while back. It had a 1275 fitted which did not comply with the regulations for a Mk.1 Sprite, but a 1098 was a period mod (Speedwell Sprite).
I bored it to +0.020", fitted flat-top pistons, a well-flowed 12G295 head with larger inlet valves, a comp ratio of 10.3:1, a 276 cam, twin 1.5" SU's on a flowed manifold, standard ratio rocker shaft, an Aldon custom-dizzy, all balanced plus an accurate build. It gave 75 bhp at the flywheel and I set him a rev limit of 6250 rpm.
With it weighing less than a Mini it went really well, especially with the SC, CR gearbox.
I don't think I would fancy going much over 80 bhp with a 1098 though. Better to bore a 998 out to its maximum which would give around 1100 and rev it to 7000 rpm.

[blake12345]

Cooperman - Thats about the kind of power my car is making now.

The reason im talking about the 1098cc is that i have already had it rebuilt less than 1000k's ago and instead of rebuilding another engine i want to just work on this one. If i didnt just spend money to get this one rebuilt i would go for a 998cc bored out to the max and the like but yeh

[Cooperman]

Cooperman - Thats about the kind of power my car is making now.

The reason im talking about the 1098cc is that i have already had it rebuilt less than 1000k's ago and instead of rebuilding another engine i want to just work on this one. If i didnt just spend money to get this one rebuilt i would go for a 998cc bored out to the max and the like but yeh

If it's already making around 75 to 80 bhp I don't think I would want to go much further with it. To get much more you are talking about a seriously 'lumpy' cam and higher ompression ratio which will mean you need to rev to over 6500+ to get it to work properly on a 1098. My Cooper 'S' has a 286 cam with offset rockers and that gives c.115 bhp at 6400 rpm and I use 7000 when driving in competition. I certainly wouldn't want to try those revs with a 1098 as I reckon the crank would snap. Also a cam always needs more revs if the engine has a lower capacity and the 970 'S' I had with a 286 used to need 7500+ to get any decent power (it never had any torque!). I did once (only once!) build a 998 rally Cooper lump with a 286, etc, and that gave 72 bhp at 6600 rpm.