36 replies to this topic

[Burgerdale]

Hi everyone, sorry for asking the same questions that have been done to death.
Can find a clear answer for my spec.
Anyway, I building a new block after problems with my old one and whilst I'm at it I might as well do it right.
My spec bar the cam/compression ratio:
A series block (austin 1300 block, hole above centre main)
+60 county pistons
Wedged and balanced crank
Vernier duplex timing
Sccr gearset
Helical drops
X-pin diff
3.7fdr (can't remember the exact ratio)
36mm in 29out Rim flo valve
Heads flowed and ported, etc. Nice bit of work.
1.5 forged rockers
Manifold st2 exhaust manifold
Weber 45 (will jet to spec)
5"inlet manifold
10" wheels

I had a 286 cam in it but I didn't enjoy the experience. Not sure if it was to cam timing being off but it really didn't like setting off up the steep hill near me and unless I was bang on the power band at all times it would bog down.

I'm now thinking of fitting a cam that would suit the fact a have to drive through a town centre to get anywhere.
I'm thinking 266 but I want to make sure I match it to the spec to get the most from it and that best suits the environment I'll be driving it.
I'd ideally like it to be quick off the mark as opposed to a massive top speed.
Traffic light races will be the closest it'll see to a track/racing.

So when I've decided on the cam, I'll need to match the compression ratio.
What would a good ratio be for say a 266 or an sw8? Or whatever cam is best for the set up/use?
Finally, what bore exhaust?
I had a 1, 7/8" with a 2,1/4" tip before and it had too much back pressure. I could feel it from 6 foot away.
I was thinking a full 1,3/4 manifold twin box. Side or centre. With the little extra length of a side exit help?

[gazza82]

Not worth going to +60 unless it needs a rebore snd already at +40. County pistons? There are better probably.

AC says 9.75:1 cr for 266 cam which should be nice in traffic. You'll need to calculate that once you know all the dimensions.

Weber probably won't ... HIF44 might be beter.

Crank work might not be necessary for road use.

[KernowCooper]

I have a 276 in mine with 10.2 CR and it pulls really well and is more than up to the job of town work with that diff ratio, I also have a Maniflow side exit system of 1 3/4 on mine and a side exit single silencer.

Edited by KernowCooper, 10 October 2015 - 03:48 PM.

[carbon]

Standing start on a steep hill with SCCR will be pretty tough on the clutch unless you have a really low final drive. First gear with SCCR clubman set is about 2.58:1, compared to A+ which is 3.64:1 first gear ratio.

So with FD= 3.76 and SCCR 2.58 first gear your overall first gear ratio is about 9.7:1

This is very similar to using really tall 2.75 FD with 3.64 A+ first gear = 10.0:1

 

With the cam selection are you planning to keep using the 1.5 rockers? If so and you're looking for reasonable amount of low end grunt then I would recommend the MD266 cam. I have the MD266 in a 1293 and a 1330 and works well in both, but works much better at mid and high end if you use 1.3 ratio rockers. I have yet to try fitting a set of 1.5 rockers. The 1293 is running 9.75:1 compression but needs Shell 99 octane to run sweetly.

 

For exhaust I would be very surprised if you need anything larger than 1.75 bore. I am running this size with twin box RC40 side exit - yes I also can feel the exhaust pulses when standing 6 foot away from the tailpipe, but that's it doing its job properly and getting the gas out...

Edited by carbon, 10 October 2015 - 05:01 PM.

[Sheikh Pip]

I'd say you had a setup problem originally! Did you have it Rolling Roaded?

[Cooperman]

Is that block not the one which doesn't like high revs?

Spending a lot on the - build you need to ensure that you have a good block.

The A+ block is much stronger, as is the A+ crank and the A+ rods are stronger and lighter.

For pistons use the 21253 as they are excellent.

Is the car for competition of for road use? If it is for the road you need to look at an engine with high mid-range torque, so forget the high-power spec and go for a MK.1 Cooper/Cooper 'S' gear ratios, 266 cam, HIF44 carb, 10:1 C.R., Aldon 'Yellow' dizzy and a well-gas-flowed head. With a lighter flywheel and a 3.44:1 FDR it will be a superb road engine.

Always re-bore to the next size up unless building a competition engine as the gain from 1275 to 1330 cc is only a nominal 4 bhp.

What is important is the build quality. I built a 1330 engine for an endurance rally Mini a few years ago. The engine had to be standard, so I 'blueprinted' it by careful assembly, super accurate cam timing, cleaning the 'flash and lumps from the inlet manifold and the combustion chambers, slimming down the valve guide bosses and shortening the guides slightly. The flywheel was slightly lightened and the cam was MG Metro. The head was also MG Metro with the 35.6/29.5 valves. FDR was 3.44:1.

It gave a genuine 84 bhp at a comfortable 5700 rpm, but the torque was super and it really did go well. It was also very 'friendly' to drive in all conditions.

[Burgerdale]

It needs a rebore and I already had the pistons so it's just cost effective for me. They've not had bad reviews though, a lot of triumph guys use them too.

[carbon]

Are these County pistons the same as 21253 type, and do you know the dish size?

 

The compression height of the 21253 is quite a bit higher than the old 1300 type pistons, but if your 1300 block has not previously been decked you should be OK and with luck the 21253 will end up with crown about 5 - 10 thou beneath the deck face.

[Burgerdale]

Think it is the block that doesn't like high revs. It's a spare block that I had so I'm trying to use the parts that I've got available. Same with the pistons and reboring to fit them instead of buying more.
I've also a 1293 genuine gt block, I know it's the same bar maybe the hole above the centre main. Just trying to avoid using it as it's destined for the gt build.
The rockers and everything else is what I already had. Not got the funds to replacing everything again now.
It was 1380 before, just built and was running it in. However it was second jand although all new and never run. I made the error of not checking all the builders work. Took a piston out to check the shells and rings and it was all new. Assumed (wrongly)the rest was OK. Gudgeon pin must've moved and has scored a bore badly.

So the parts I've to play with are as above.
Unless I can get hold of a cheap bare a+ block.
Trying to minimise costs thought I'd stretch to a cam and exhaust.

[Burgerdale]

I'll check the pistons in the morning and be able to get the details.
I've standard rockers or 1.5s
Weber 45 or hif.
286 or ??? Cam
1, 7/8 exhaust or ????
I'll calculate the compression and get the block/head skimmed to suit.

[carbon]

Suggestions for cost-effective rebuild:

- stick with the 1.75 bore exhaust, going larger won't improve low-mid range power

- Weber 45 likely to be overkill for fast road, HIF44 is a better bet on decent manifold and with large K&N

- Cam for fast road motor could be MD266 with 1.3 or 1.5 rockers, or MD276 with std or 1.3 ratio rockers

- You need to decide what octane fuel you are going to use before setting CR

 

1275GT blocks are essentially the same as the Austin/Morris 1300 blocks. Unless you're planning to run this engine at 7000rpm for extended periods then I would not be too concerned about the hole above the centre main bearing.

[carbon]

Very old rule of thumb, divide octane number by 10 to get idea of suitable CR

- so with standard unleaded 95 octane use CR about 9.5:1

- or use Shell 99-octane and set CR to about 9.9:1

 

Other makes of fuel also available (sometimes).

[Burgerdale]

Thanks carbon,
Thought the gt block was the same, barring maybe not having the hole.
Not really going to be caning it at 7k around a track. Ill just be terrorising the local area and some shows. Convoying to shows barely gets us above 60 down the a1.
I've got a weber and a hif,so can fit either. I'd need to re-jet the weber and change the choke size etc to use that.
I live near a shell so I always use the v power or whatever silly name it has this year.
Thanks for the advice everyone.

[Burgerdale]

Thanks for the advice everyone. Sourced myself a good a+ block. Bores are actually in better condition that the other blocks I've got.

[Burgerdale]

Latest update.
I've just check the county pistons I have. Turns out they're midget spec with an 8.8:1 Compression ratio.

So back to the drawing board and hand deeper into the wallet.

Which now opens more questions for me.
If I've got a lightened and balanced crank, Lightened fly and genrally spent some money on the engine. What's a wise balance to strike? Do I want to use higher revs that I'm assuming that allows. Do I want to push the power up the revs? As said before I don't want to go too much to keep a fast response setting off.
What pistons to I go for and what size?
Is there any point boring the cylinders out? The new block I've got is spot on, the bores are smooth and it's still 1275.
If I'm brutally honest i just want mine to beat my mates at traffic light races and have enough to almost keep up with him. He's got a decent spec though. 1330, 286, mega jolt, weber 45 and ultralight flywheel.
I don't expect to have the best of both worlds of ultimate be quicker but enough to annoy him when we're having some pub banter.