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+--- Thread: Austin 850 performance conversion (/showthread.php?tid=468)
Austin 850 performance conversion - abri - 07-05-2016
My idea with this thread is to keep track of and show you guys a little project I've been wanting to do for a few years. I quite like subtle performance upgrades using parts that were around when the cars were built. This particular one was assembled at Blackheath somewhere in the second half of 1962. It still has its original interior, which was my main reason for buying it. I use it as may daily driver and so far it's been going very well. It as 35k miles on the clock, but the speedo cable has been replaced so there's no way to say for sure how fresh the motor is. The gearbox is not as good as some later 850s I've owned, but that could also be a result of slightly older technology. I have some reading up to do.
So my idea with the performance conversion is essentially to fit a 12G202 cylinder head as was used on the standard SA 998 motors as well as the 997 Cooper and a couple of other BMC small bore A series models. Together with this head I'm planning to fit a 3-1 Cooper exhaust manifold and a set of twin H1 SU carbs on (what I think is) a Sprite manifold. This thread will be somewhat technical because I'm going to go through all the calculations that goes into getting the compression ratio that's desired. We often see people put together engines without much regard for measurements and end up with extremely high compression which then has to be compensated for by having special gaskets made etc. I'm going to do the maths and take the measurements to do it right and I'd welcome input from more knowledgeable people on here when I'm making mistakes...I assume I will, because this will be my first attempt at this type of modification.
So far I've collected a decent looking head which I've measured and appears to be standard, complete with valves, the right exhaust manifold, the small bore "performance" head gasket that Minispares sells, and the set of H1 carbs on a manifold. I've done most of the research into what measurements to take. The next steps are, doing the measurements on my engine and head to make sure I get the correct amount skimmed off the head. Also, I need to strip the set of carbs to have a proper look at what's needed and order a rebuild kit from Burlen Fuel Systems and do a rebuild. At the moment I'm trying to figure out what needles to try in this setup and have asked for some advice. This needs to be done before I can place the order.
To start with, here is the car in question
![[Image: 27497057194_620b4fd9bf_k.jpg]](https://c3.staticflickr.com/8/7288/27497057194_620b4fd9bf_k.jpg)
So, to work out whether this plan will work there are a number of measurements to do and keep in mind and some mathematics. As I've mentioned, I've had some help and done some research to get the most important numbers right. Some are up for debate, like the intended compression ratio but more on that later.
To start with, what is compression ratio? Here people talk about a swept volume and an unswept volume. The swept volume is the volume of the cylinder (above the piston) from bottom dead center to top dead center, in other words the volume that the piston "sweeps" on its way up. The unswept volume is everything above the piston at top dead center. The compression ratio is the sum of the swept & unswept volumes divided by the unswept volume.
The swept volume is the easy part:
Volume of the swept cylinder (1/2 the bore squared x PI) x stroke. If you're using millimeters for the bore and stroke then divide the result by 1000 to convert from cubic millimeters to cubic centimeters
For my car, which is an unmodified 848cc, the bore is 62.94mm and the stroke 68.26mm. This means the swept volume is 212.463cm
The unswept volume is made up of the following:
1) The ring land volume which is the tiny area around the piston crown above the top compression ring up to the level of the crown
2) The dish in the piston
3) The cylinder volume from the height of the piston crown to the top of the block
4) The volume provided by the compressed gasket between the head and block
5) The volume in the combustion chamber in the head (with the plug in place)
So my job is to collect data on all these measurements, put them in a calculator and work out how I can go about getting the desired compression ratio with a head that did not come standard on an 848cc motor.
The values I have so far are:
1) Ring land volume - using someone else's figures = 0.6 cc
2) Dish in the piston, using a figure measured by a friend of mine on a standard 848cc piston as follows (note the piston in the photo is not the actual piston. Just to show the example. The figure I'm using for dish = 1 cc
![[Image: 28077227006_821d8c3a63_k.jpg]](https://c7.staticflickr.com/8/7475/28077227006_821d8c3a63_k.jpg)
3) Cylinder volume from the crown to the top of the block = area x measured height (in other words 1/2 bore squared x PI x measured height). For this measurement the head obviously has to be off the block so one can take measurement. I haven't done this on my engine because I use my car as a daily driver. I've taken the measurement on another standard 848cc engine. I'm hoping this will be close enough. In fact if anyone thinks this is a mistake and I should rather take the measurement on the actual motor, I'll have to do that. For the time being, here are some measurement pics
![[Image: 28144292242_2d635a51e9_k.jpg]](https://c3.staticflickr.com/9/8601/28144292242_2d635a51e9_k.jpg)
![[Image: 27496583554_68d94029cb_k.jpg]](https://c3.staticflickr.com/8/7452/27496583554_68d94029cb_k.jpg)
This measurement was 0.017" which is 0.4318 mm. Using the formula above, the volume above the crown up to the top of the block is 1.354 cc
4) Gasket compressed volume, this is an easy one. The small bore performance head gasket from Minispares actually says what its compressed volume is when torqued down = 2.8cc
So far, if we add up 1) to 4) we get 5.754 cc. This is everything unswept underneath the head.
The next update will deal with 5) the combustion chamber volume and how the choice of head influences the calculation
Please point out errors when you see them and give advice where I'm going wrong.
RE: Austin 850 performance conversion - Vinay-RS - 07-05-2016
This build is going to be cool. Looking forward to seeing it unfold
RE: Austin 850 performance conversion - Willy - 07-06-2016
Following this one. Looks like a nice car Abri
RE: Austin 850 performance conversion - Cooper1275 - 07-06-2016
Hi Abri,
Really looking forward to following this thread.
Always good to see someone on the forum attempt something technical and so demystify it all a bit for the rest of us in the process.
As a 'non-technical' person I always tend to think a good engine build or performance upgrade is Voodoo/Magic but in reality it need just needs a practical and methodical approach I guess.
RE: Austin 850 performance conversion - Jared Mk3 - 07-06-2016
Keen to see your progress.
RE: Austin 850 performance conversion - abri - 07-06-2016
(07-06-2016, 01:25 PM)Cooper1275 Wrote: Always good to see someone on the forum attempt something technical and so demystify it all a bit for the rest of us in the process.
As a 'non-technical' person I always tend to think a good engine build or performance upgrade is Voodoo/Magic but in reality it need just needs a practical and methodical approach I guess.
We're pretty much in the same boat there, so I hope I can achieve my goal of writing it up nicely. Once I found out how it works, its actually very straightforward and common sense. I've also had help from other forums where people explained it to me. The magic of the interweb
RE: Austin 850 performance conversion - Dion - 07-06-2016
Looking forward to this, nice to see something completely different.
RE: Austin 850 performance conversion - Francois - 07-06-2016
Following this one for sure.
RE: Austin 850 performance conversion - askalbert - 07-08-2016
Some books that may be fun to read are "Tuning the (Classic) Mini" and "More Mini Tuning" by Clive Trickey. as well as "The Wild Card" - History of Vortz Racing. (Need one of these myself.)
Clive Trickey because he was there at the start with 850 racing and illustrates well what can be done with standard parts on a budget.
Vortz because Nick Vorotsos (Vortz) did a lot with the smaller capacity engines, some is outlined by "Jaydee" on the Mini Forum in this link:
http://www.theminiforum.co.uk/forums/topic/287121-vortz-racing-cars/
I'm keen on this thread as well as I have a '61 shell which eventually (watch the grass grow) is intended to head a similar route. Lovely car there.
http://www.theminiforum.co.uk/forums/topic/283537-clive-trickeys-race-mini-ktr-223e/
Some Clive Trickey books in Johannesburg - Chapter1 Books:
Tunini A Mini
http://www.abebooks.com/servlet/BookDetailsPL?bi=15157016224
Building and Racing 850
http://www.abebooks.com/servlet/BookDetailsPL?bi=15703212743
Modifying Cylinder Heads
http://www.abebooks.com/servlet/BookDetailsPL?bi=15426200499
RE: Austin 850 performance conversion - abri - 07-11-2016
Thanks for the comments and help so far. I've done a little update in the main thread for anyone who's interested.