Cross flow questions
Discussion
Hi
Just rebuilding the engine from my Vixen S2. The original owner had a strangely 'functional' approach to using the car for his 53 years, he didn’t exactly lavish cash on it, but used it actively for 49 of those 53 years!
He had a 'gold seal' type rebuild, of the dodgy type, after holing the sump on a gate bracket. On inspection the rebuild has 681 heads (semi chambered) but 711M pistons with large chambers and valve cut outs. The resulting compression ratio calculates at 7.6:1. Low performance…
I hear I need 1300 pre 711M pistons and possibly Kent 234 cam.
Questions. Semi chambered head measures 10mL volume. Anyone have better number?
Volume of piston chamber in 1600 and 1300 pre-711M pistons?
Where to buy pistons?
Cam, Kent do several series, the 224/234, etc. then an A2 and another fast road cam, I forget the number. The A2 seems to have longer duration lower lift than the 234. Why so many cams? Is the 234 old school and the others newer profiles?
Anyone got any bits they want to sell?
Lots of questions!
Thx
Nic
Just rebuilding the engine from my Vixen S2. The original owner had a strangely 'functional' approach to using the car for his 53 years, he didn’t exactly lavish cash on it, but used it actively for 49 of those 53 years!
He had a 'gold seal' type rebuild, of the dodgy type, after holing the sump on a gate bracket. On inspection the rebuild has 681 heads (semi chambered) but 711M pistons with large chambers and valve cut outs. The resulting compression ratio calculates at 7.6:1. Low performance…
I hear I need 1300 pre 711M pistons and possibly Kent 234 cam.
Questions. Semi chambered head measures 10mL volume. Anyone have better number?
Volume of piston chamber in 1600 and 1300 pre-711M pistons?
Where to buy pistons?
Cam, Kent do several series, the 224/234, etc. then an A2 and another fast road cam, I forget the number. The A2 seems to have longer duration lower lift than the 234. Why so many cams? Is the 234 old school and the others newer profiles?
Anyone got any bits they want to sell?
Lots of questions!
Thx
Nic
Nic,
From what you've said you seem to have a pretty good handle on this.
FWIW, the A2 profile cam is the old school & the Kent 234 more current. The A2 being is an old Cosworth profile being one step above Ford GT profile - fast road you may say. Cosworth produced up to A6 which was aimed at full race. The A2 is long duration but also low lift so you shouldn't need to worry about valves hitting pistons. The 234 will almost certainly have a higher lift and may need deeper pockets in the piston. The advantage in shorter duration & higher lift is mainly using less fuel. The A2 will consume and exhume unburnt fuel so not as efficient. FWIW I run the A2 cam and has a good spread of power from low down, but you will probably get more top end power from a Kent 234.
Pistons are available from Burton Power. Multiple brands of both cast and forged - all subject to how deep your pockets are and what you intend to use the car for. The Accralite forged will cope with more heat than cast which are known to melt under high revs if using poor fuel or timing/mixture not setup correctly (yes it happened to me). But they do cost 3 x as much £'s. All the relevant info is on the Burton site and they're pretty knowledgable if you call them for clarification.
My engine is a 711M with flat head so don't have any knowledge of your semi-chambered head.
Moto
From what you've said you seem to have a pretty good handle on this.
FWIW, the A2 profile cam is the old school & the Kent 234 more current. The A2 being is an old Cosworth profile being one step above Ford GT profile - fast road you may say. Cosworth produced up to A6 which was aimed at full race. The A2 is long duration but also low lift so you shouldn't need to worry about valves hitting pistons. The 234 will almost certainly have a higher lift and may need deeper pockets in the piston. The advantage in shorter duration & higher lift is mainly using less fuel. The A2 will consume and exhume unburnt fuel so not as efficient. FWIW I run the A2 cam and has a good spread of power from low down, but you will probably get more top end power from a Kent 234.
Pistons are available from Burton Power. Multiple brands of both cast and forged - all subject to how deep your pockets are and what you intend to use the car for. The Accralite forged will cope with more heat than cast which are known to melt under high revs if using poor fuel or timing/mixture not setup correctly (yes it happened to me). But they do cost 3 x as much £'s. All the relevant info is on the Burton site and they're pretty knowledgable if you call them for clarification.
My engine is a 711M with flat head so don't have any knowledge of your semi-chambered head.
Moto
Thanks Moto.
Found out the following, for the record.
Semi chambered head = 9cc
711M 1300 piston chamber = 36cc
711 1600 piston chamber = 44cc
The piston clearance to the top of the block is around 40 thou. Gasket varies but mine was 55 thou. The combined volume of these is 13cc.
I still don’t have the chamber sizes for the pre 771M if anyone has them?
Next question, why are Burton head gaskets £200? I can get them for £25 elsewhere?
Thanks
Nic
Found out the following, for the record.
Semi chambered head = 9cc
711M 1300 piston chamber = 36cc
711 1600 piston chamber = 44cc
The piston clearance to the top of the block is around 40 thou. Gasket varies but mine was 55 thou. The combined volume of these is 13cc.
I still don’t have the chamber sizes for the pre 771M if anyone has them?
Next question, why are Burton head gaskets £200? I can get them for £25 elsewhere?
Thanks
Nic
that's AJP8 money!NicBowman said:
Thanks Moto.
Next question, why are Burton head gaskets £200? I can get them for £25 elsewhere?
Thanks
Nic
You're probably comparing apples with oranges. A standard gasket set including head gasket from Burtons is £20Next question, why are Burton head gaskets £200? I can get them for £25 elsewhere?
Thanks
Nic
https://www.burtonpower.com/top-end-gasket-set-for...
You're probably looking at the Cometic head gaskets which are £100 - £200. They are BIG money that may be worth spending if you're running a race spec engine.
Moto
Additionally, I *think* that the "A-series" cams go straight in whereas Kent 224, 234, etc. will need valve pockets machined into the piston crowns. That's why many swap to 1300 pistons in a 1600 to recover the compression lost from having the pockets (1300 pistons have a smaller combustion chamber).
Also, I seem to remember that the 711 heads are flat as the combustion chamber in the piston crown so having both (681 head and 711 pistons) does lead to a low compression.
Also, I seem to remember that the 711 heads are flat as the combustion chamber in the piston crown so having both (681 head and 711 pistons) does lead to a low compression.
get yourselves a 711block and a matching head and start from there.
the 691block was not as strong as the 711, the semi-chambered head doesnot match with the actualy available parts (like pistons).
more x-flow expertise here:
http://www.turbosport.co.uk/forumdisplay.php?f=179...
https://www.locostbuilders.co.uk/forum/
the 691block was not as strong as the 711, the semi-chambered head doesnot match with the actualy available parts (like pistons).
more x-flow expertise here:
http://www.turbosport.co.uk/forumdisplay.php?f=179...
https://www.locostbuilders.co.uk/forum/
Hi. Thanks all. My engine was a right mix up. 681 block and head, but later crank, conn rods and pistons. Non GT cam. So, cr@p, I think is the word. The last owner wondered why his Sierra was faster.
Trying to optimise performance vs cost, spending big money is easy, getting best value takes an eye for a lucky deal!
Going for 681 block, flat heads, 234 cam, 1300 standard (but pocketed) pistons. Should give 10:1 compression ratio. Still need a head, so state of tune will depend on what comes up. Open to offers if you have one!
Thx.
Trying to optimise performance vs cost, spending big money is easy, getting best value takes an eye for a lucky deal!
Going for 681 block, flat heads, 234 cam, 1300 standard (but pocketed) pistons. Should give 10:1 compression ratio. Still need a head, so state of tune will depend on what comes up. Open to offers if you have one!
Thx.
Hi. Thanks all. My engine was a right mix up. 681 block and head, but later crank, conn rods and pistons. Non GT cam. So, cr@p, I think is the word. The last owner wondered why his Sierra was faster.
Trying to optimise performance vs cost, spending big money is easy, getting best value takes an eye for a lucky deal!
Going for 681 block, flat heads, 234 cam, 1300 standard (but pocketed) pistons. Should give 10:1 compression ratio. Still need a head, so state of tune will depend on what comes up. Open to offers if you have one!
Thx.
Trying to optimise performance vs cost, spending big money is easy, getting best value takes an eye for a lucky deal!
Going for 681 block, flat heads, 234 cam, 1300 standard (but pocketed) pistons. Should give 10:1 compression ratio. Still need a head, so state of tune will depend on what comes up. Open to offers if you have one!
Thx.
TwinKam said:
This.
Trouble is, anything Blue Oval of that era is now 'worth' stupid money.
Oh the ones we threw away....
Use what you have...Trouble is, anything Blue Oval of that era is now 'worth' stupid money.
Oh the ones we threw away....
Yes a 711M block is better in terms of main bearing journals and cam follower area and you can bore them 90 thou with more certainty however..
Nowt wrong with using what you have if you are not boring the block out to its max tolerance and you are not trying to go stupid with heads cam and carbs.
A 681 will make a good 120hp engine and last just as long as any other crossflow block !
Horses for courses
It's true that everything 'Crossflow' is getting expensive. It's unlikely to find any 711M 1600 engine for less than £1,000 and even then it'll be in need of full refurbishment / rebuild with lots of new & expensive parts to purchase if you're wanting a few more horses than standard.
This engine is currently on Race Cars Direct which to me seems like a very good buy
https://racecarsdirect.com/Advert/Details/133767/c...
Another reason to start a build with a 711M block is that the choice of aftermarket parts for these is much better / wider.
Moto
This engine is currently on Race Cars Direct which to me seems like a very good buy
https://racecarsdirect.com/Advert/Details/133767/c...
Another reason to start a build with a 711M block is that the choice of aftermarket parts for these is much better / wider.
Moto
Moto said:
It's true that everything 'Crossflow' is getting expensive. It's unlikely to find any 711M 1600 engine for less than £1,000 and even then it'll be in need of full refurbishment / rebuild with lots of new & expensive parts to purchase if you're wanting a few more horses than standard.
This engine is currently on Race Cars Direct which to me seems like a very good buy
https://racecarsdirect.com/Advert/Details/133767/c...
Another reason to start a build with a 711M block is that the choice of aftermarket parts for these is much better / wider.
Moto
…same price as just a few parts on eBay…This engine is currently on Race Cars Direct which to me seems like a very good buy
https://racecarsdirect.com/Advert/Details/133767/c...
Another reason to start a build with a 711M block is that the choice of aftermarket parts for these is much better / wider.
Moto
https://www.ebay.co.uk/itm/144920556896?mkcid=16&a...
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