xflow sounds like subaru?

[ashaughnessy]

I've recently (within the past couple of weeks) had a new exhaust (4-1 side exit race to replace 4-2-1 rear exit) and new carbs (45DCOE to replace 40DCOE) and I'm just getting used to the new noise. It sounds a little like a subaru. It sounds like either the valve clearances are wrong or the throttle balance is out, and that one or two cylinders aren't either sucking, firing or blowing as well as the others. However, it's just come back from the engine builder and I've rechecked both those things myself so everything should be OK.

So the question is - how does your crossflow sound? It used to sound smoother with the old setup. I'm not sure if my ears are being too sensitive. It sounds OK once you get above about 3500 to 4000 revs. It pulls cleanly. I've also checked the plugs for fouling but they seem OK. Haven't checked the distributor yet though. I did adjust the valve clearances *slightly* and also adjusted the throttle balancing screw *slightly* and I think it perhaps sounds a little better after that.

Anthony

[Tim_H]

you'll possibly get a different noise from the exhaust, if all the primaries are equal length. Your 4-2-1 won't have had that, probably, and some exhaust from 1 cylinder will have met another's exhaust on the old system.

 

4-1 with equal length is designed to eliminate that.

 

How's the power?

 

With the all the extra breathing it's now got, it should be a lot more livelier at the top end. You could probably make good use of a peaky cam now, esp if you match it to a big valve head (that I expect you've already got)

 

Tim (L7 EVN)

[ashaughnessy]

Power is good - rolling road print out says 150 bhp (actually, 149 point something, but I'm saying 150 :-) with a nice smooth torque curve. Runs very well and pulls extremely well from low revs, better than it ever used to. Just sounds different. Your point about the length of the primaries is interesting. It's the caterham standard 4-1 side exit. I haven't measured the lengths so I don't know if they're the same but this would be an interesting explanation. I'll probably check the valve clearances and throttle balance a second time, just to make sure.

 

Anthony

[DaveMorris]

Anthony,

Standard Caterham exhaust does NOT have 4 equal length primaries. Numbers 1,2 and 3 are prety close but number 4 tends to be quite a lot shorter. I have the measurements of them somewhere (but can't lay my hands on it at teh moment).

Having said that it's better that the 4-2-1 rear exit system.

I think (but may be wrong) that the simplest way to get 4 equal primaries to exit a Caterham engine bay (esp a dry sumped one) is as per the Norman Verona method - i.e out thru the lhs of the bonnet.

 

What cam are you running ? This will definitely make a difference to how the engine sounds and at what rev range it starts to sound more "turbine like" (if ever you could use that expression to describe the noise a x-flow makes).

 

I've recently run a 244 and am (just for a short period) running an A6 cam - and there's LOTS of difference in sound.

 

Dave

[alan c]

All of the above sounds intersting. I have 4 into 1 exhaust, 45's and a 244 cam and I didn't think I was getting anywhere near 150bhp but I need to go and get it tested to see exactly.

It sounds a bit rough until about 3000 rpm and then is fairly smooth up to 6000 where I have my red line set.

Anyone got any ideas on the next upgrade from this or is it an expensive all steel job with more revs?

[ashaughnessy]

OK, sounds like it isn't a problem, just a different sound.

 

Alan, you won't be getting 150 bhp if your redline is at 6000. My peak power is at about 6800. I had a fair bit of work done to get me an extra thousand safe revs though. The power comes from the breathing and the revs. You've got the right carbs, exhaust and cam but you'd have to know what's been done to your cylinder head (porting, valve sizes, etc) and what your safe rev limit is. I don't have steel internals (except forged pistons) but did have strengthening done on top of the standard supersprint spec.

 

I've also heard the forged pistons are worth up to 8bhp on their own but presumably that's at high revs.

 

Anthony

[Normans_Ghost]

As far as I know and according to Roger King the primaries should be 28" in length. Also, on Ford engines 4-1 is best. I had one made which was 4-2-1 and I lost a lot of power (not sure if it was BHP or Torque or both) but the engine went "flat". The new manifold (Powerspeed) has 28" primaries and 4-1 collector. I cant remember the diamater but it's large, maybe too large.

 

Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here

You and your seven to The French Blatting Company Limited

[alan c]

Anthony

At some point I am going to have to take it apart to see whats inside. As you will gather I have 'inherited' the spec as is. Mine also has a dry sump as well but I do not suppose that makes much difference. Intersting that you can get to 6800 with the limited work you have done.

What does 150 bhp translate to at the wheels any idea?

Have you got a dyno print out and who did the work for you?

I am thinking about doing something on the engine front next winter.

Alan

[ashaughnessy]

I don't know what the at-the-wheels power figure is. I can't find the print-out !!! Don't know what I've done with it. The work was done by Dave Brooks in Crewe, at http://www.davebrooks-engines.co.uk

 

I'm not sure about "limited work" - it cost me a fortune :-) A lot of it was specifically to raise the rev limit to get the most out of the extra breathing he put in. The end result is more power all the way through the rev range, which is really nice, thanks to good setup.

 

Anthony