MK3 Spitfire carb upgrade

[Piglet]

Any suggestions? I'm looking for a bit more power out of the old girl. I intend to fit a stainless twin exhaust with manifold as well. Are there any 'plug and play' carbs that would give me, say, 20-30 more bhp?

Alex

[Pete Lewis]

i fear as soon as you start to mess with carbs from the std you end up with a headache 

of what needles what springs , you dont get more power by going BIG  it doesnt work and you have a perpetual headache

there are lots of specs about for going HS4   4-2-1 , silly pancakes all will end up in tears and empty wallet .

these make it sound quicker but in reality its often worse.

you must do a lot of homework before you jump 

pete

 

Edited February 10 by Pete Lewis

[johny]

I see theres a used supercharger kit going on ebay that would probably help😁

[DanMi]

to get 20-30 more bhp would requiree a full engine rebuild with gas flowed head, high lift cam etc. New carbs and exhaust might give 5bhp. The twin exhaust will probably be more of a placebo as the louder note will make you think it is faster

[Iain T]

13 hours ago, Piglet said:

Are there any 'plug and play' carbs that would give me, say, 20-30 more bhp?

For normal driving it's not bhp you need it's torque. Perhaps look at a camshaft spec and talk to Newman Cams as they are very helpful or Chris Witor. However you will open Pandora's box then look at distributor/electronic and the nightmare of carburetor needles/damper oil/spring rate. I know this as I've been through the pain. First off check your cylinder compressions are equal and correct or it's all a waste of money. 

Iain 

Edited February 10 by Iain T

[Steve P]

Aren`t MK 3`s supposed to be liveliest of the range?.

I had an FH 1300 engine in my Herald for a while with twin HS4 carbs and a 4 into 1 manifold and Vitesse exhaust, coupled with a 3:63 diff and single rail O/D gearbox it was a great drive.

As Pete said just throwing carbs at it often ends up with more grief for no gain. I would start by getting the best out of what you have by a proper tune up first.

Surprising how much can be gained by a decent tune up.

Steve

Edited February 10 by Steve P

[Nigel Clark]

The 1300cc Spit Mk3 really won't see any benefit from bigger carbs, unless you go for an upgraded cylinder head and hotter camshaft.

As Pete has pointed out, simply fitting bigger carbs will probably cause difficulty in setting up. For 20-30 extra bhp, the engine will need a full rebuild, with aforementioned cylinder head and cam modifications. Bigger carbs alone won't won't achieve anything like that kind of increase in power.

Nigel

[Josef]

Have you got an FD prefix engine number? It should make 75BHP in standard tune, and it’s a nice revvy engine, mine certainly feels fast! Would be worth checking the carbs, dizzy etc for wear, and perhaps measuring the cam lift to make sure it does have the expected Mk3 cam fitted. Plus a good tune up, best thing I’ve ever learned for making the engine more performant is doing the timing by feel and road test!

[Iain T]

42 minutes ago, Josef said:

, best thing I’ve ever learned for making the engine more performant is doing the timing by feel and road test!

Yes the WSM is a starting point only. Keep using if possible the same grade of fuel and listen and test. 

Iain 

[Piglet]

Thanks everyone. I had a sneaky feeling it might be a bit more complex than just carbs.

Yes it's the 75bhp revvy little motor and certainly isn't slow but a bit more pep is always nice to have! I think I'll leave it as is for now, hot cams etc means tearing the engine down and I don't want to start doing that!

Alex

[Pete Lewis]

you could try advancing  by turn the dizzy to the best idle and back it off a touch  the best is too far advanced

if it pinks on 97+ fuel then retard a little to stop it .

might just improve the punch by optimising the timing 

Pete

[Piglet]

Thanks Pete

Certainly worth a try.

Alex