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Disappointing 998 Performance


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#1 Minigman

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Posted 24 March 2017 - 10:29 AM

I've just fitted a 998 engine in my mini, but it's not achieved the performance I'd hoped for.

Spec is;
Std 998 bottom end with 35000 miles.
Skimmed 12G295 head with 9.8-1 compression ratio.
Kent 266 cam
Duplex timing gear.
Maniflow Cooper freeflow manifold
Somerford works replica exhaust
Weber DCD 28/36 carb with K&N filter.
3.4 final drive.

Been set up on the rolling road and achieved 49.2 BHP @ 5500rpm. Max torque (haven't got the figure at hand) was achieved at 4650rpm.

I've had issues with the carb icing and then running Rich at full throttle but now have a flexible duct tube pulling air from lower down where it's warmer.

Was hoping for nearer 55 BHP with a bit more torque for the hills.

Any suggestions?

Edited by Minigman, 24 March 2017 - 10:30 AM.


#2 cal844

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Posted 24 March 2017 - 10:30 AM

if you need more torque you need to change the cam

#3 Spider

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Posted 24 March 2017 - 10:37 AM

I'll probably have stones thrown at me for this.

 

Being somewhat simple about it, the only way to get performance out of these engines is to rev the daylights from them and even your dyno figures show this.

 

In that regard, I'd suggest for starters going to a 3.7 or even a 3.9 FD. A slightly longer duration cam may help, but don't go much more than you have.


Edited by Moke Spider, 24 March 2017 - 10:38 AM.


#4 Shifty

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Posted 24 March 2017 - 11:01 AM

I'd junk the Weber and fit a hif38 instead. Going lower than a 3.4 will make it undriveable, it will just rev its tits off.
My 1015cc lump in my elf made 68 with a similar spec, although I had an sw5 cam.

I ran a 3.4 and it was a bit revvy with that. A 3.2 would have been better.

#5 Midas Mk1

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Posted 24 March 2017 - 11:34 AM

Something not right there, my 998's (abeit 10 years ago) consistently got 53-56bhp with just a 40k high comp stg 1 spec (with longer 3.1 diff)



#6 racingbob

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Posted 24 March 2017 - 12:02 PM

depends on the rolling road some show low some show high

 

does it feel good, maybe the head needs some porting



#7 black olive

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Posted 24 March 2017 - 12:44 PM

has the head had any combustion chamber work and prting done or just a skim ?

 

I did the Vizard book stuff to a 12G202 head and with a standard cam and single HIF38 was getting 54BHP



#8 Minigman

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Posted 24 March 2017 - 01:03 PM

The head was skimmed. I didn't do any porting work.

I'm thinking it's either the carb icing at full throttle or it's just a pile of poo to start with.

May go with twin SUs no see if there is an improvement.

#9 Daz1968

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Posted 24 March 2017 - 01:13 PM

what distributor is on it, a 998 cooper std should be 55bhp, that does seem very low.

#10 Minigman

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Posted 24 March 2017 - 01:17 PM

My thoughts too. 59D with electronic 'bits' in.

#11 Icey

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Posted 24 March 2017 - 01:26 PM

May go with twin SUs no see if there is an improvement.

 

Why twins? If the HIF38 doesn't flow enough, use a 44.



#12 Minigman

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Posted 24 March 2017 - 01:31 PM

I already have some twins. Not sure the HS4 I have is good enough?

#13 whistler

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Posted 24 March 2017 - 01:48 PM

Nothing wrong with the weber unless it's not been jetted etc for a 998. I used to run one on a 997 with a 544 cam and a 4.1 diff. brilliant. Make sure you connect up the heater pipes to the inlet manifold and you won't suffer icing. I never did except when I had twin HS4s.

Currently keep a 28/36 as a spare for my 1293. 



#14 hhhh

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Posted 24 March 2017 - 03:48 PM

Something's definitely off. Are you sure the ignition and cam timing have been optimized? The 12G295 head is pretty good once skimmed (for dished pistons) but the exhaust ports are crap if you don't remove the exhaust valve guide bosses. I'm running an 1100 cam, HIF4, 12G295 modified per above and skimmed 0.100", 6% hi-lift (offset bush) forged rockers, 1-3/4" exhaust, LCB with a straight through-ish muffler and my parts guy said it goes like a stock 1275. 


Edited by hhhh, 24 March 2017 - 03:50 PM.


#15 blacktulip

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Posted 24 March 2017 - 04:40 PM

Did you pay particular attention to detail with zeroing the deck height? And time the cam in properly using a timing disc? If so,what figure did you time the cam in at? I have a very similar spec to you. I'm just running it in but I can feel it wants to go just like my old 1301cc engine did.




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