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998 engine ideas.


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#1 Telejmp

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Posted 02 April 2005 - 07:56 PM

Hey,
Im looking to improve the performance of my 998 engine.
A friend of mine suggested changing the head, cam and carbourettor. Pretty obvious.. but I dont know which to go for as he never gave me any names.
He told me he used to like using a single 1.75 Su carb with the better cam and head. He claims (I am slightly unsure, as he is known for exagerating) that he once had 90 odd BHP from one of his normally aspirated 998 engines.

I have looked through the mini magazine and seen heads and cams listed as road/fast road/rally etc. but I dont know which to go for.
Obviously id like maximum power from this engine, but Id like to keep the cost down as much as possible ( I probarbly will end up spending far too much anyway, so dont be afraid to suggest expensive parts) and Id prefer not to have reliability problems.

I was thinking of trying to get hold of an MG metro camshaft? as I heard some catagory of racing mini's use or used these on 998 minis, but for the head, I have no idea. I also know ill need to buy a better exhaust/stage 1 kit.

I was also wondering about the stage 2 tuning kit from mini sport, but I think I could maybe get things like the head a lot cheaper second hand, and im still unsure about roller rockers, are they really necessary?

I read somewhere that my engine is a "high Compression" model, I know roughly what this means and im assuming I wont have problems when fitting aftermarket parts? This mini is a 89' Racing Green.


I know people will say "just put in a bigger engine" but I like being awkward and for some reason I like the idea of having a reasonably powerful 998 engine.

thanks a lot,
pEaCE
Dom

My mini is still in need of a lot of work before I even consider rebuilding my engine, so for now im just getting Ideas together, thanks again!

#2 Bungle

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Posted 02 April 2005 - 08:01 PM

My wife sarah has a 998 this is what we have done

LCB manfold ( cooper free flow is better )
single box exhaust
big valve head from ebay
twin 1 3/4 carbs from ebay

total spend £350

#3 Cir-clipalot

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Posted 02 April 2005 - 08:05 PM

get a decent stage1 kit and get it in perfect tune and youll notice a big difference for not-a-lot-a cash.

#4 Telejmp

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Posted 02 April 2005 - 08:08 PM

Bungle, are the twin carbs a big improvement?. Ive heard a few people moaning about them being a right pain to keep in tune etc.

Cir, I intend to get the stage 1 kit fitted and everything tuned before I go any further, for money reasons ill probarbly end up driving the car like that for a while anyway.

thanks guys
pEaCE
Dom

#5 Bungle

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Posted 02 April 2005 - 08:28 PM

some say they do some say they dont

but they are better than the standard small carb on a 998

we went for twins for there looks

#6 Telejmp

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Posted 02 April 2005 - 08:38 PM

yeah thats true they really do look very cool and impressive.
One of the kits that mini sport do for the 998 comes with twin carbs, I might have a look around see if I can find any performance figures using them.
pEaCE
Dom

#7 miniman5

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Posted 02 April 2005 - 08:59 PM

Hello if you lookign for some thing to make your 998 shift! then i sugest etting either a 1100 mg head, or a 998 cooper head, these have bigger valves in you see, but the ports are the same. so itle realy shift! or you could put twin carbs on or jsut fitt a bigger needle

#8 Telejmp

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Posted 02 April 2005 - 09:05 PM

miniman, would a cooper 998 head be as good as say a fast road/race head from mini spares?
pEaCE
Dom

#9 Bungle

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Posted 02 April 2005 - 09:15 PM

they would be about the same spec

just that a old cooper head might be cheaper but not unleaded .

The head we got for sarahs has mg sized valves and only cost £120 and unleaded conversion £ 50

if you buy a mini spares head it will be unleaded with new valves and guides

#10 themanlegend

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Posted 02 April 2005 - 10:04 PM

I was thinking about adding to my stage one kitted 998 but have been told that putting more strain on such a small engine isnt a good idea.

any thoughts?

TML

#11 vasi

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Posted 02 April 2005 - 11:07 PM

I'll probably get shot down by a doc for discrepancies in this but......

Better to make your own decisions and understand them when designing an engine than to listen to ten people where some are saying "get this" and the other "get that"

To make a four stroke engine perform better, there are five main areas a performance upgrade will have effect. One area for each of the four cycles; suck, squeeze, bang, blow and the last area is inertia. Some performance upgrades will cross more than one area.

1) Suck
Big improvements to be made here, standard A series engines are heavily restricted by bad casting + design. First and foremost go for a better flowing inlet manifold or better still, twin SU carbs. Next go for a modified cylinder head, larger inlet valves + port work will vastly improve gas flow properties.

2) Squeeze
Not a lot can be done, you can skim the head which will up the compression ratio but you cant go mad with this, otherwise you'll need to change the properties of your fuel ie. higher octane.

3) Bang
It is important that your engine is in correct tune ie the ignition is set correctly (so the spark sparks at the right time) and the correct fuel / air ratio is being fed by the carburetter. SO GO TO A ROLLING ROAD THAT HAVE A GOOD REP FOR SETTING UP MINIS. I cannot stress this enough.

4) Blow
The standard exhaust is completely useless, try breathing through a straw and you'll know how the engine feels. Ditch it and get either a cooper freeflow manifold or small bore LCB manifold coupled with an RC40 twinbox system.

5) Inertia
Willingness to move. The big one here is the cast iron flywheel which can be lightened and balanced, or you can buy steel lightened ones ready to swap over.

As I said before some performance upgrades cross more than one area for example cams. They affect duration (how long a valve is held open) and lift (how far open the valve moves from closed) of both inlet and exhaust valves, therefore affecting Suck and Blow.

So from the above you can deduce that the areas where you are going to see the biggest improvements in perforamance in the first instance are Suck and Blow but only if your Bang is right :)

#12 Guest_falk_*

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Posted 03 April 2005 - 09:44 AM

vasi...

you're generally right, but also with your thought about discrepancies... some additions...

blow: definitely a freeflow performes better on a small bore engine than a lcb...
the single box is the preffered option in terms of gas flow. and go for the rc40. there still is no better exhaust on the market if your also looking on the pricefactor...

suck: twin carbs are superb as they give the right mixture to all four cylinders. with the single carb setup either the outer to cylinders are running to weak or the inner ones to rich. i would recommend the twin hs2's (1.25"). absolutely necessary (and you can't get around it) is complete refurbishment of the carbs. then even your fuel consumption will go down as these carbs perform better. that way the tune-in problem disappears as well...

squeeze: try to go for a cooper head. they are available at ebay from time to time at reasonable prices. it should be 12G295 as this is the original 998 cooper head. it is leaded... why go for the cooper head? well it is not an aftermarket item so quality level should be there as a matter of fact. and it's cheaper. head must be skimmed down to match the original compression ratio of your engine.
high lift rockers: NOT on a 998 engine as they block performance! so invest your money elsewhere...

bang: rolling road is essential! and i would go for an electronic ignition...

all the above things are possible improvements without removing the engine. cam upgrades andlightened flywheels (which would make sense) need the engine taken of the engine bay...

generally i like telejmp's idea of tuning a 1000cc! engine swap is no big challenge... :cheese:

#13 Cir-clipalot

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Posted 03 April 2005 - 09:48 AM

themanlegend: something like a stg1 kit wont put too much strain on the engine, after all youre only making it more efficient.
I agree to some extent with vasi and i think thats a pretty good summary of how to tune but the workings of an engine are a lot more complicated than we tend to think. The analogy of a straw for an exhaust is a good example of this. It is not the case that the cross-sectional area of an exhaust is directly proportional to its ability to improve gas flow, things are far more complicated. Even folks with degrees in engineering and years of experience tuning a particular type of engine disagree about what produces the best results, so i dont think it would be very expedient for someone wishing to get a bit more power for a few extra quid to start off on that route, and I would suggest that asking people in similar situation what has worked for them maybe *is* a fairly reliable way of going about things.
A lot of advice about tuning given from a supposedly engineering angle seems to be from people who have just read Vizard.
Im not trying to cause offence, and like I say my very limited knowledge does agree with 99% of what vasi says, Im only saying that in terms of method its v impractical in my opinion to try to figure things out like this and if we're talking about a few quid for a few extra horses then taking advice from people whove bolted things on is a much more practical way of doing things.
I think :)
And i reiterate vasi's point 3 and what i said earlier - far too many people seem to bolt on goodies and then not bring the engine into tune (for max driveable power) for the new set up, or run it not in tune at all. Something as minor as resetting the points gap can make twice as much difference as slapping on a fat exhaust!
good luck with it anyway

#14 TimS

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Posted 03 April 2005 - 01:14 PM

the engine that you have is a good one to start with. I have spent a good few hours modifying one of the heads and managed to get good gain from it.

Really it would be good if you could give us a ball park figure of the amount of cash you have to put into this but from past experiences this is what i would do:


Have the head worked... Enlarging the ports and increasing the flow will help significantly. or get a head thats already been modified from ebay. I would personally buy a head from a minisop but instead from the modifiers them selfs. this cuts out the middle man and makes things alot cheaper!


Cam wise the best cam really to use on the road would be a Swiftune SW5 cam! have a search on the net for these and read some of the reviews(they are impressive). I would combine this with the std riockers as high lift isnt needed on a 998 so much as is alot more expenive(as the pistons will need pocketing.

Carb wise, I would stick to single, its alot cheaper and easier! The twins wont really have any advantage as an HIF 38 or 44 (44 might b a little overkill) will flow easily enough.

Dizzy. Oersonally I would change to a metro electonic ignition system as the advance curve will b alot more suited to the modified engine.

Flywheel. To get thoes 0-60 times down a little but still keepin the drivability, the verto type flywheel can be shaved for around £20 to give you that edge.

For an intake system you can use either the std metro air box(is alot better than mini) or a pancake filter. My sugestion would be to use the metro one with a k&n filter, with slight modifications to the box.

The exhaust manifold has already been mentioned, Cooper free flow is much better on a 998 than an LCB and the RC40 exhuast systems are really good for the price(MINISPARES)

#15 themanlegend

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Posted 03 April 2005 - 07:59 PM

Cir-clipalot Posted on Apr 3 2005, 09:48 AM
  themanlegend: something like a stg1 kit wont put too much strain on the engine, after all youre only making it more efficient.



Sorry but I think you misinterpretated what I said.

I was thinking about adding to my stage one kitted 998 but have been told that putting more strain on such a small engine isnt a good idea.


As in I already have a stage one on my 998, but wondered if its practical to bolt on more to what is only a 1 litre engine? Is it a waste of time as you could do the same to a 1275 engine? Would the bigger engine be more effective at coping with more power?

Basically I am confused about whether a sw5 and a g295/stage 3 head would strain my 998 too much, or is that utter *man danglies*?

Thanks

TML




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