X-Flow downdraught heads

[stoppodriver]

Hello ,
I'm new on this forum , I only found it by accident as i " googled " Downdraught head . There was a mention in one of the other threads , under Flow benches - but I didn't want to hijack someone elses thread . I will shortly be building a 1700 cross flow for racing ( short circuit ovals - in the UK ) and was wondering if the downdraught head was an advantage ( or is it only on the pre-crossflow ) we're only allowed to use sidedraught carbs . I've only read about this type of head - haven't seen any in use , presumeably they used downdraught carbs (?) . Any info would be welcome , or links to sites etc . Also if anyone has any experience with race X-Flows , i'd like to hear from them , Having watched some of the other cars racing , which have alot of a HP , I get the impression that an engine with more torque at lower rpm could be quite competitive .

Regards

AL.

[graham bahr]

i dont think its possible to downdraft a x/flow head as the ports would be trying to come through the push rod holes, its possible on a pre x/flow because the inlet ports are on the other side of the head.

you might also find these refered to as MAE heads which stood for Modified Anglia Engine

downdrafted pre x/flows used down draft side draft carbs and fuel injection, although called downdraght the ports were not vertical but actually exited the head at an angle of about 60 degrees, so either sort of carb needed a curved inlet manifold, but whichever way you curved the manifold you got a power gain because the curve in the inlet manifold is far gentler than the one in the heads origonal inlet port.

ultimate engines used throttle bodies and mechanical style fuel injection and could give power outputs of approaching 130bhp per litre, on a 1000cc engines reving to 10,000rpm

the inlet ports on these heads are probably too small though to flow anything like enough air to produce such a high specific output per litre on a 1700 bottom end, but i would like to have a go at trying it,

[GORDON STREETER]

I have tried various combinations of cylinder heads over the years, and although in their day they were a good step forward things moved on when the crossflow design came in. Graham is correct in what he said regards the CF and pre CF heads. Although there was a few downdraft heads actually cast, most were modified standard heads milled out and tubes either brazed or bonded in. In the single seater race cars the engine was cantered over so they could get a straight inlet tract. Although it is possible to get up to 190BHP from a 1700 crossflow on carbs it will cost a fortune to build to make that sort of power and be reliable.
Unless you have to use that type of engine you can get more power and a lot cheaper from a more modern unit !

[stoppodriver]

Firstly , I apologise for asking a stupid question . We can only use pre cross flow , cross flow or Pinto ( I don't want to use the Pinto , because I've probably got the heaviest car on the grid and could do without the extra weight up front ) . I did read on another forum about Clubman racing , that a chap got 185bhp from a 1700 crossflow using a 1300 head and relatively small exhaust primaries - He was using most of the parts i'm going to , which will be Datsun 180 crank , Ford 1.8 diesel rods , Alfa 155 pistons , not sure what cam yet . Probably Dellortos's ( were allowed 40's to 50's but choked to 36 - is there still any benefit from using the larger carbs ? ) I've no experience with sidedraughts , but was led to believe by people who've used both , that the Dellorto's were better (?) . It will be dry sumped . A few of the other cars are all steel and rev to 9,500+ , but i don't think that's nessesary , i'd like to see it deliver good power but be able to pull well from about 4500 to 8000 ish . Many thanks .

Regards

AL.

[graham bahr]

if you are allowed a maxium choke size of 36 mm then use 45mm carbs, 36 chokes are too big to be effective in 40mm carbs because it will be the butterflies and aux vents that are restricting the airflow through the carb once you reach a choke size of 34mm, your not really going to see the benifit of going bigger than 45mm on carbs if your limited to a 36mm choke.

for your purposes there will be very little to choise between webers and dellortos, dellortos are a newer design and the jets go up in smaller steps so are a bit nicer on some road cars because they can be jetted slighly closer to what the engine idealy wants, but for race use with realitively rich mixtures ther isnt really anything to choose, (BL A series engines do slightly prefer webers but that because the A series likes a bigger fuel droplet size, which in most cases would be a dissadvantage) so i would just buy which ever carbs i can get the best deal on or that my rolling road man has best stock of jets etc for.

with regards to x/flow heads it doesnt matter what size engine it origonally comes from they can all be modified to the same spec, so that fact that guy started with a 1300 head is a bit of a red herring.

Andy Pipe had a geniune 171bhp from a 1600cc x/f using a kent 254 and "normal" x/f well tried and tested tuning practiscs so given the same spec and 1700cc that would be a tad over 180bhp so there isnt any need to reinvent the wheel with this engine

[stoppodriver]

Thanks for that , the only reason i'm using the datsun crank etc is to keep the cost down - i'm getting the machine work done ( inc flywheel ) at a much reduced cost in exchange for supplying some parts he couldn't get hold of . I don't want to waste any money trying something that might not work , but on the other hand there tends to be a " monkey see- monkey do " approach where people put huge carbs etc on to little or no advantage , i just want what works the best at a reasonable cost . RegardsAL.

[ian.stewart]

Have you looked at the Ally American Head, that is meant to be significantly better flowing than the Ford item, The use of diesel rods is well documented---- BUT I assume the object of the Datsun crank is to be strong and be able to Rev, By the time you have reduced the weight of the rod to use the revs to your benefit, it would probably finacially better to get a set of H beams in the first place

[GORDON STREETER]

http://www.flickr.com/photos/16345037@N03/2279860027/

Here's one I prepared earlier !

[GORDON STREETER]

I would certainly plug for the crossflow option. Although I have got very good power out of the pre-crossflow engines I had to use a specially made inlet manifold, and ruined several castings getting the head combustion chamber correct (more difficult on a smaller cc engine) The crossflow head is much easier to work on /more available and ultimately will give more power. The 1489cc engine I run has a normal crossflow head but I have another engine that started off pre-crossflow that I modified with a crossflow head with combustion chambers , still using the original flat top pistons. Although they are both the same cc /all steel /dry sumped /gear driven, the former engine gives about 10 more HP.

[stoppodriver]

Thanks for the replies / comments . Not allowed alloy heads unfortunately - as for the Rods / crank , I was led to believe the diesel rods would rev to 8500+ OK and that the Datsun crank would cope ( or do you think the weight of the rods would be a problem ? ) RegardsAL.

[GORDON STREETER]

I personally can't comment on diesel rods as I have never used them. I always use the best parts available as its sods law the weakest part will possibly break and then you have to start again costing loads more money.
However revs are the killer and if you can produce an engine with good torque the weight of the rods shouldn't present a problem to 8500. I wish you well with it !