948 tuning

Common upgrades - A-Series mods, brakes,wheels, handling, interior.

948 tuning

Postby Fentuz » Thu Jan 30, 2020 10:29 am

Good morning all,

I have a 948cc with twin HS2 on a frogeye. I am looking into “progressive” upgrade i.e. things which are consistent and can work together a progress together. I don’t want to invest immediately a large amount time and effort in 1 shot.
Ultimately, I will want an engine compliant with FIA historic reg, period 998cc but I’m giving racing a few years break. So for now, I want a fast road configuration but however is modified will have to be consistent with the final fia config (I don’t want to change/purchase things several time).

Talking with various people and reading various forum, I understand that with the 948, head upgrade is the 1st thing to do.

A good upgrade is the 12g295 head from the cooper which can be obviously be used with the 998C engine. That said, I understand that the 12g202 is now far behind a 12g295.
So is it better to go for 12g295 (expensive) and potentially do a bit of work to it??? Or get a 12g202 (cheap), swap the inlet valve for 12g295 (or a little bigger), reshape the combustion chamber to match the 12g295 design and port accordingly???

Then, the rocker, I thought 1.3:1 or 1.4:1 would be a good thing but I have been warned that the 948 with a single “let-in” camshaft bearing does not like very much increase load on the cam lobs. Great rocket ratio will increase the mechanical mechanical advantage and double springs are stiffer so all in all, it sounds like a recipe for disaster. So, before I even consider an aftermarket cam such as SW5 from swift tune, I need to understand what the real limitations are.
I know that the engine will have to come out to be to the final desired spec but for time being, I don’t want to do so, ant thing I do to is has to be doable in-situ due to lack on time.
So, if I fit a “standard” 12g295, can I fit 1.3:1 rocket with standard 948/850 single bearing camshaft? Are there aftermarket camshafts that come with the big OEM bearing and 2 smaller bearings that seat into the block bearings allowing rotational de-multiplication and therefore limited wear?
To add to my confusion, Moss list 2 types of camshaft bearing kits bhm1211 and bhm1210.
1210 seems to be of frogeye948cc but also for minis and spridgets.
1211 seems to be for any minor and mini cooper 998cc
So is it the case that there are 2 kits that fit either and then one is a better bearing material hence the £10 extra???

Vibrations, I understand than I can flush the oil, take of the sump, remove the centre block/crank bearing cap, machine it and add the strengthening strap. Fitting the damper pulley from the cooper S /minispare is supposed to be better than the 1275cc.


Block… there a 2 ways really:
Using the 948 block, bore it out to take the minicooper pistons and con rods, redo the bearing, drill/bore out the camshaft housing to take the 3 bearing camshaft. Swap the oil point to the 1275cc style.

Using a 1098 block, fit the minicooper pistons and con rods, the 948cc crank etc. Issue with that is that the engine block has a 1098cc ID and a technical file will be required to prove that it is a compliant 998cc @ scrutineering.


Clutch, I saw in and old US owner manual that a 9 spring clutch is better for motorsport compare to the std 6 spring version. I believe the triumph Herald 948/1200 and spitfire Mk1 were fitted with 9 spring clutch to the same diameter and spline design as the frogeye but I such for a supplier, the only things I can find are 6 springs version.
Where can you source 9 spring clutch?
Alternatively, if it were a nightmare, would it not be simpler to fit a lightweight 1098 flywheel and 1098 clutch kit?

Thanks
G
Fentuz
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Re: 948 tuning

Postby Plin » Sun Feb 02, 2020 12:50 am

:D Welcome to the forum Fentuz - afraid I know nothing about your queries but wanted to welcome you to the forum. Hopefully someone will pop along and offer their advice but until then enjoy our friendly forum!

(P.s. Would love to see a photo of your Frogeye, especially any of it racing!)
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Re: 948 tuning

Postby Fentuz » Sun Feb 02, 2020 7:37 am

Hi,
I raced an elise
Image

And the frogeye is a long term project
Image
Fentuz
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Re: 948 tuning

Postby Plin » Sun Feb 02, 2020 5:17 pm

Thanks for posting the photos of your lovely cars. :drive: No doubt great fun racing your Elise?!
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