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12G202 Mods On A Budget


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#1 nzjb

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Posted 07 March 2021 - 10:51 AM

Hi,

I've just picked up a 998 which I'll be building on a budget to mild fast road specs. Ive picked up a reconditioned 12g202 but it has standard sized valves and hasn't been gas flowed at all.

I was wondering whats the best way to squeeze a little more power out of it without getting too expensive? Is it worth it to get it gas flowed with standard valve sizes?

My planned spec is:

Flat top pistons +020, around 9-10 comp ratio
Evo1 camshaft with standard rockers
Minispares electronic dizzy which matches the evo1
12g202 with minor work done
Hs4 carb
Cooper freeflow manifold and single box rc40
3.44 diff.

Hoping that I can make about 55-65hp. Does that seem achievable or will i need bigger valves and lots of gas flowing?

This is my first engine build so just keeping it simple.

Appreciate any advice for a noobie.

#2 whistler

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Posted 07 March 2021 - 11:36 AM

Have a look at what Phil does to valves for increased/more efficient flow.



#3 ads7

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Posted 07 March 2021 - 07:15 PM

Following this as I'm soon to pick up a std 1098. It's down to best bang for your budget buck.

#4 Turbo Phil

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Posted 08 March 2021 - 12:02 AM

You’d benefit going up a valve size as this allows a proper multi angle seat to be cut. A 31mm intake with a 26.5mm ex will do. With a back cut applied & the seat work done there’s a decent gain in flow.
The chambers also require some reshaping to deshroud the valves. For you application don’t go wild on the ports, blend the guide bosses away open the inlet slightly and just give the exhaust a good tidy up. You’ll be surprised at the results.

Phil.

#5 nzjb

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Posted 08 March 2021 - 07:57 AM

Following on from this I've talked to a local a series head specialist and itll be like 800 pounds to get the head done properly.

What could I expect from my spec with a standard 202. 50hp?

#6 rock1day

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Posted 08 March 2021 - 03:32 PM

I`ve had several modified heads from Peter Burgess over the last 20 + years and he has always done good work at a VERY reasonable cost.

 

My Mini 1000 with similar modifications made 40 bhp at the wheels on Aldon`s dyno in the 70`s.


Edited by rock1day, 08 March 2021 - 03:33 PM.


#7 Cooperman

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Posted 08 March 2021 - 05:02 PM

Unless the head has some basic improvement there is little point in fitting a better cam.
The key to better power from an A-series engine lies in improving the ability of the head to flow better.
With some grinding stones and an electric drill you can do a lot yourself, especially if you first read Vizard's book.
You will need the services of a machine shop for modifying for larger inlet valves, cutting the valve seats and skimming to obtain the required comp ratio.

#8 MiniMadRacer

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Posted 08 March 2021 - 06:39 PM

Just a suggestion, but cost wise would you be better off getting an exchange already flowed head from Calver or AC (if they still do them). In my opinion grinding a head yourself rarely gives the improvement you expect, its an art, and like all arts needs a lot of practice to get right. Doing a head once is probably not going to get you the results you really want or hope for. But I agree it can be fun, but you might want to practice on a scrap head first



#9 MiniMadRacer

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Posted 08 March 2021 - 06:40 PM

Sorry probably should have thrown Turbo Phil in the mix too, and no doubt many others



#10 madaboutcherry

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Posted 09 March 2021 - 11:52 AM

old efforts: 12G202 small bore with very limited budget, and a slightly higher budget | Mini Engine Stuff (wordpress.com)



#11 MiniMadRacer

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Posted 09 March 2021 - 01:10 PM

I am not sure how old that article is but he seems to think £500 was / is a bargain back then.... I know this is more than you would want ie Stage 3, but maybe you could negotiate a 202 head to Stage 1.

 

https://www.calverst...re-60-and-over/

 

Please note I am not recommendeding or not recommending the above head, I have never used any of Keiths heads and have no knowledge of them at all, I am merely using his web site as an example.



#12 mini13

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Posted 09 March 2021 - 03:27 PM

Talk to TurboPhil instead.

 

 

Following on from this I've talked to a local a series head specialist and itll be like 800 pounds to get the head done properly.

What could I expect from my spec with a standard 202. 50hp?

 



#13 rock1day

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Posted 15 March 2021 - 11:20 AM

 

Talk to TurboPhil instead.

 

 

Following on from this I've talked to a local a series head specialist and itll be like 800 pounds to get the head done properly.

What could I expect from my spec with a standard 202. 50hp?

 

Good idea but I don`t think Turbo Phil is interested in modifying small bore heads at the moment.



#14 GraemeC

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Posted 15 March 2021 - 12:30 PM

And note where the OP is based



#15 Turbo Phil

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Posted 15 March 2021 - 06:03 PM

Talk to TurboPhil instead.
 
 

Following on from this I've talked to a local a series head specialist and itll be like 800 pounds to get the head done properly.

What could I expect from my spec with a standard 202. 50hp?

Good idea but I don`t think Turbo Phil is interested in modifying small bore heads at the moment.

It’s not that I’m not interested, it’s just I’m simply to busy to take on any more work at the moment. There’s only so many hours in the day.

Phil.




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