6 replies to this topic

[tom130691]

Hi All, 

I had a badly knocking engine about 4 years ago, (1275 A+)  I pulled it apart and had spun the rod/crank shells. I then purchased a bottom end of another 1275 engine just incase, 

Ive finally found some motivation to put the car back together the parts from the spare engine are in better nick but are more performance orintated, 

so far I have
 

Twin HS4's (red springs no4 needles)

Kent 286 cam
21963(cooper?) Pistons which I believe to be higer compression 10:1

so im starting to feel that dropping a stock head back on top is going to be abit of a restriction, I started to look at stage 3 cyclinder heads but there is varying CC option with people like MED, 

And id assume bigger isnt always better due to the CR factor particularly with the cam i have?  what have you guys run with this cam any recomendations?


Car is only a toy not a daily driver so I dont need it to be sensible

Edited by tom130691, 12 December 2018 - 04:44 PM.

[nicklouse]

first work out your swept volume. the decide on the required CR for the Cam and fuel then you will know what CC you need in the head.

 

now it is not quite that simple as the position of the piston at TDC needs some thought as well. the piston was always brought to be flush with the block surface (no idea if thoughts have changed on that) and don't forget to include the head gasket of choice`s thickness and the space above the top ring into the swept volume.

[GraemeC]

C’mon Nick - head gasket & space above top ring are not part of swept volume.

[nicklouse]

C’mon Nick - head gasket & space above top ring are not part of swept volume.

brain half on work and here! better recheck the Brake system DWGs

[nicklouse]

phew DWGs are OK so only got things arseovertit here

[Cooperman]

With the 286 cam there is a need for a very well-flowed head with at least 35.6 mm inlet valves. A fairly high CR is necessary.

The 286 requires an engine able to really rev, as peak power will come at around 6400 rpm. With those revs the 21253 piston is not ideal, although they can be OK so long as the CR is kept below about 10.2:1.

A 286 is not really suitable for a road car as you need a low ratio final drive ratio and a close ratio gearbox in order to keep the engine 'on the cam' and to avoid too much clutch-slipping to pull away. It is a great rally or sprint cam which is also capable of limited road use. The engine needs to be running at between 4500 rpm and 6700 rpm for best performance and if you don't use those revs most of the time, then you are 'over-cammed' (a common problem).

I have a 286 in my rally 'S' and run a 3.9:1 FDR with a SC CR gearbox. I use fully balanced Karl Schmidt pistons with a light flywheel, twin H4 carbs, an Aldon 'Custom' distributor and an LCB ex. manifold. The static CR is 11.1:1 and the 11-stud head is fully-flowed with 35.6/30.5 valves. It has 1.5:1 roller-tip rockers. It is very 'cammy' but great in competition.

[tom130691]

With the 286 cam there is a need for a very well-flowed head with at least 35.6 mm inlet valves. A fairly high CR is necessary.

The 286 requires an engine able to really rev, as peak power will come at around 6400 rpm. With those revs the 21253 piston is not ideal, although they can be OK so long as the CR is kept below about 10.2:1.

A 286 is not really suitable for a road car as you need a low ratio final drive ratio and a close ratio gearbox in order to keep the engine 'on the cam' and to avoid too much clutch-slipping to pull away. It is a great rally or sprint cam which is also capable of limited road use. The engine needs to be running at between 4500 rpm and 6700 rpm for best performance and if you don't use those revs most of the time, then you are 'over-cammed' (a common problem).

I have a 286 in my rally 'S' and run a 3.9:1 FDR with a SC CR gearbox. I use fully balanced Karl Schmidt pistons with a light flywheel, twin H4 carbs, an Aldon 'Custom' distributor and an LCB ex. manifold. The static CR is 11.1:1 and the 11-stud head is fully-flowed with 35.6/30.5 valves. It has 1.5:1 roller-tip rockers. It is very 'cammy' but great in competition.

Ive read its abit lairy for the road but hey ho thats all ive got worth putting in, (std cam would need a regrind) Ive done 4000 miles in the last 7 years It can get away with being abit of a PIA,  
Im not chasing BHP numbers (only had 53 last time it actually ran) , my daily has 3 times the power and thats shortly going to get another 100 on top, so the mini will be pulled out of the garage for a laugh every now and then.

 

Not sure what Final drive numbers I have anymore,  I know one box has a shortish one as I chose that and sold an eco longer FDR when I had it rebuilt, the other box I have, I dont have history on, any easy way to check these? (they arnt mounted to a block)  (the spare engine did have straight cut drop gears too not sure if these are likely to play with the ratios at all?)

LCB is on the shopping list after the previous was left outside and is looking terrible  for it, toying with the idea of a flywheel but will avoid it if I can, Was planning to avoid the rocker arms at risk of making the inherent drawbacks of this cam worse.

https://jscalc.io/ca...NEglVkKLQir11T  been using this to play with compression ratio's  so far I know my current head has stock valves and 21cc  pistons are dished to 8cc

Need to get the block back from SMMC on friday with its new cam shells before I can get deck hieghts but i think im somewhere around the 10-10.2 range at the moment, 

Edited by tom130691, 11 December 2018 - 07:10 PM.