23 replies to this topic

[wtrdave]

Hi guys,

I have a 1275 carbed engine with a stage 1 kit.. So I want more power but on a budget if possible.. I have about £500 to spend on the engine (can do more if needed). What would be best to start it off?

Cheers,
Dave

[Noah]

A service and a rolling road session.

[Cooperman]

Think about what is needed to improve performance of a clasic car.
The objective is to get more fuel/air mixture in, burn it as effectively as possible, then exhaust it at the best exhaust velocity.
With the BMC A-series engine, the biggest limiting factor is the cylinder head. the valves are partly shrouded by the combustion chamber walls, so a better breathing head is the basic key to extracting more useable power.
Once the head is capable of 'flowing' more mixture you need to be able to get the mixture in, so a correct size carburettor is needed with a smooth alloy inlet manifold.
The exhaust needs to be either a 3-into-1 tubular manifold or an LCB manifold. The LCB is best with high revving engines, whilst the 3-into-1 is best with lower revving engines.
For around £500 you might just be able to find a gas-flowed head with 35.6 mm inlet valves and 29.5 mm exhausts. Once you have this, by careful measurement and calculation establish wht the compression ratio would be the head fitted 'as is', then have it skimmed to get the combustion chamber volume correct if it is not as you want it. Ideal compression ratio is about 10:1.
Once that is all done you will need to get the mixture and ignition settings optimised on a rolling road or done 'buy eye and ear' by someone who knows how to do this.

[wtrdave]

Have already given it a service and rolling road will be done

[crock]

I am assuming your car already has an electronic (no points) dizzy?

[Ethel]

Don't waste money on a rolling road if you are going to modify it further. A cylinder head is definitely the next move, but don't overlook the free performance enhancers like junking unnecessary weight and having the brakes & suspension working properly. You can improve the head a lot while retaining the original valves, but finding a 2nd hand one that's been well modified is likely to be the most cost effective.

[wtrdave]

If I update the head will I need to add other things? I've already upgraded the brakes and suspension..

Dave

[Bungle]

buy your self a copy of David Visards yellow bible , there are lots of little free mods you can do at home

[ACDodd]

What mini do you have and what spec is the 1275 you already have? How many miles has it done?

AC

[mini-luke]

You can bolt all the go faster bits in the world on an engine with valves rattling in the guides and oval bores it won't solve the cause of the lack of power (not aimed at the OP personally)

[scott_65_cooper_s]

Agree with Ethel above. There's a lot of mileage in saving weight and so many ways to do it for free.... All depends how you like your creature comforts.

[Big_Adam]

buy your self a copy of David Visards yellow bible , there are lots of little free mods you can do at home

What he says, its a good "I shouldn't have eaten that week old take out" toilet book.

[Bungle]

i'm not sure how absorbent the pages are

[wtrdave]

What mini do you have and what spec is the 1275 you already have? How many miles has it done?

AC

Its a 93 mayfair 1275, carbed stage 1. 70k miles on the clock.

buy your self a copy of David Visards yellow bible , there are lots of little free mods you can do at home

Just ordered a copy :)

You can bolt all the go faster bits in the world on an engine with valves rattling in the guides and oval bores it won't solve the cause of the lack of power (not aimed at the OP personally)

I don't want to just bolt things on, I want to do things right and the best way of doing them, also I want to learn how to upgrade the engine and how all the parts work.

Dave

[ACDodd]

Your in luck sprites respond well to tuning. The only thing that concerns me is the mileage. 70k is a bit high. See below for the results of a home brewed enhancements as tested by myself. This still tops my table in terms of bolts on improvements. Please note this engine had only covered 40k at the time these mods were fitted and tested. I would budget for a full overhaul at the same time as your upgrades.

Ac



Another surprise of the day was this modified 90's sprite, these were the most detuned of the factory 1275's with only 52bhp, well for this owner something had to be done;

This one has covered around 40K miles miles. The engine features a stock A+ 1275 bottom end inc stock sprite cam. It uses customer home modified head (35.7 x 29.4 valves),appox 10:1 CR. It uses 1.5 roller tip rockers. Fueling is via a Single HIF44 SU carb, cone filter, Custom ACDodd needle, Ignition utilized an ACDodd Custom curved Lucas 65DM4 electronic dizzy, the usual freeflow intake and exhaust system. Fuel unknown.

Produced figures of 82.5hp@ 5500rpm (flywheel), and 89.3lbft @ 4500rpm. This is very very good output considering the very mild cam used. Good news for those with sprites, as this lot is all bolt on with out the need to remove the engine to get this huge power!

Here are the exact figures if anybody want to plot them, runs taken in 3rth gear, power at wheels was 76.5bhp peak.
Correction factor 0.98672 today, DIN 70020

Rpm Power Torque
1000
1500 21.48 75.21
2000 30.88 81.08
2500 40.27 84.61
3000 49.34 86.37
3500 58.06 87.13
4000 66.79 87.69
4500 76.52 89.31
5000 80.55 84.61
5500 82.56 78.84

AC

Edited by ACDodd, 05 March 2013 - 07:18 PM.