Stroker S Engine, Which Pistons?

[MkI-Speedwell]

I am building a 1275 S engine with a stock bore, and 18cc S Head. 84 mm. Stroker Crank. Pistons with a stock bore are hard enough to find, but I need a dish to bring down the compression. Willing to overbore in order to find a piston. Already considered a custom head gasket.
Really would like to keep this crank. What are others doing short of custom made pistons?

Appreciate your thoughts.

[iain1967s]

Would a decompression plate bring you back to the standard S spec of ~24cc ?

Usually used by the turbo boys, available on 3cc and 6cc sizes, with a regular head gasket on each side.
https://www.jonspeed.co.uk/decompressio ... -steel-6cc

[251 ENG]

Why do you want to use this odd combination of parts ?

[MrNoo]

18cc head is probably an old race head. As above a very odd assortment of bits, stroked cranks normally go with large overbores to produce low revving high displacement engines, so you'd be looking at going 73.5 or similar. Cannot see what the benefit would be using a long throw crank in a std bore block.
But I know how you feel re an S block, have one here on Std bores and want to run an Arden 8 port large valve head, it'll need to be opened out for valve clearance, guess it can always be sleeved down at a later date.

[CooperTune]

I have a Cooper S block that we line bored, bored .060 ( after having been run at std, .020, .040 ) squared and zero decked in the
mid 70s. It was revved to the low 9000s and crank magnafluxed, bearings and rings twice a year the two years I ran National SCCA
Solo 2. When I went Vintage racing I stripped the engine placing the block under the work bench. For the mini 50 Can Am at Mid Ohio
I wanted something special for the 500 +- trip out. Located 73 mm pistons bored the block and built it up. Even with a std 940 uncut
head compression was out of sight. I ran the figures over and over then ordered a Cometic custom gasket ( roughly $250 ) and put it
together. With my custom gear box I was able to drive out and back running 70 mph at 3000 RPM. And yes I did check out 4000 rpm
a few times which is around 96 mph on GPS. This has been a daily and only transportation until about a year ago. I have taken over
care of my 98 year old father and needed something he could get in and out of for appointments. The gasket is not a bad option.
Steve (CTR)

[Spider]

Plates and Gaskets will work and get the CR down, but I find that a lot of squish is lost by doing this and the engines don't go nearly as well as they should.

[MkI-Speedwell]

I'm a total noobie in building a stroker.

MED has these pistons: https://www.med-engineering.co.uk/engin ... tons-short

11cc dish.

[wantafaster1]

You should work out which cam you want to use, you can then estimate the compression and after that calculate the required dish to suit the cylinder head

[850man]

Machine the roof of the chamber to increase the cc. We do it with our supercharged engines rather than decompression plates & extra gaskets, that's what the amatures do. Increase the dish in the top of the piston as well, if required.

[IanD1965]

I’m having a Hillclimb engine built with a 84mm crank and +20” Cosworth forged pistons.
With the right head it produces the same figures as a 1380. Time will tell.
Ian

[mk1]

I’m having a Hillclimb engine built with a 84mm crank and +20” Cosworth forged pistons.
With the right head it produces the same figures as a 1380. Time will tell.
Ian

Hum, It's not a route I have ever come across to that sort of power. Who suggested that a long stroke 1330 engine would make similar power to a well developed 1380? You are 50cc down on capacity before you start.

Usually the biggest weakness of the 1300 is the poor bore to stroke ratio, this has always been known as the roughest engine in the large bore range. By building an engine with an even longer stroke than standard & comparatively small pistons you will be aggravating this factor.

Usually getting an A series to rev is the key to making decent power, with such a poor bore to stroke ratio an engine like that is never going to rev freely.

It will be very interesting to see how your engine actually performs.

[MrNoo]

Yes, I would be after a short stroke crank and as large a bore as is safe, with modern steel rods and cranks seriously high rpm is now within reach with reliability and heads are available that enable it to all breathe and take advantage or the high rpm. Over square engine or as close to as is ideal for decent hp

[mk1]

I ran a short stroke 1299 for a while, well until my good mate Rich ran it into the ground at Donnington. It was a sweet engine & made decent power. Was a pretty cheap build too compared to a lot of other combinations.

[IanD1965]

I have taken the advice from the engine builder . He seems to know his stuff and is well respected. I don’t think he’d build it if he didn’t think it would work. I did initially ask him about a 1380 Hillclimb lump and he said they are getting the same power from 1293. All to do with the pistons and head. Nothing new.
What I want is a good strong reliable lump that is going to last, not really interested in the bhp , more in the torque and how it pulls out of corners etc.
My previous mini lump was 74 mm x 84 mm and put out 138 @7k and had 110 ib/ft @ 5k
I didn’t want to go too extreme this time.
+ 20” is enough.

[Supersonic]

I had a 1299cc (76.2 Gordon Allen crank) 8-port cylinder head and 40mm Webbers and it produced 145 BPH at 8k RPM. I also had the same setup in a 1480cc (86mm Gordon Allen crank) and it produced 156 BHP at 7k RPM.

The big engine was much easier to drive and better in the wet

Alan

[IanD1965]

This is for a Hillclimb car , different characteristics to a full race screamer.
Just wanted plenty of meat between the bores , with a decent gasket should prove reliable. Should go well in a lightweight fibreglass Jem.
I’ll let you know how I get on .
Ian