47 replies to this topic

[nicklouse]

Just in case you did not find the doting section here is all the info you need.

[Allrounder]

[quote name="mini-geek" post="3453527" timestamp="1488146800"]

The guy is very experienced I have no doubt over his diagnosis.

But what else could it be.. it's a popping crackling noise at high RPM and the power dips off as it happens.. it runs fuel injection it has fuel it has spark so the only thing missing is compression..

Ive no doubt of the guys experience. But fuel pressure is a good shout and easy to check. Also have they checked the trigger wheel/crank sensor setup, especially the the air gap!Coil unit breaking down under high load! Fault with the software!

What was the lambda showing when this popping cracking was happpng.

[Swift_General]

I would seriously doubt you're getting valve float from 5K rpm with VS2s unless there is some manufacturing defect which would be very unusual.

I would be looking elsewhere for the problem.

Edited by Swift_General, 27 February 2017 - 10:41 AM.

[mini-geek]

I've asked the question to the mapper, I have already asked but we had assumed that valve spring compression or the lack of was the issue..

Problem is it's it's now in pieces so checking others is difficult..

Fuel pressure is possible and we have discussed that it's close to its limit for supply but he has said it isn't that and you'd notice that by it leaning out as far as I'm aware that doesn't happen..

CPS well that would show on the computer as you'd get an inconsistent rpm reading

[Northernpower]

I fully understand your frustration, been there done it. I assume you checked the obvious, correct plug gaps and plugs not breaking down? Its still does happen; too wide a gap is as bad as too small a gap. I'd still look for a non mechanical problem. There are very few double valve springs that won't cope with the revs you're talking about even with a real lairy cam in. You may be getting good fuel pressure but again I'd go back to basics and look at things like fuel tank vents etc.

Edited by Northernpower, 27 February 2017 - 12:06 PM.

[mini-geek]

I've got some minispares AEA526 springs anyway from a previous build so going to chuck them.. just to rule out that

Could it be anything mechanical?

Can I rule out detonation?

I seem to remember I had the issue but not as bad when I was running carb and mega jolt on the same engine with different cam but that was a long time ago and I honestly can't remember..

Edit-- didn't see the post above before posting that..

Edited by mini-geek, 27 February 2017 - 12:11 PM.

[Northernpower]

If you get it back together and its still there and you want to try something different I use a rolling road near Harrogate for mine and he has quite a lot of experience with the SC setup in all different guises. I'm not saying for one moment you're guy doesn't know what he's doing but sometimes a fresh pair of eyes on a problem helps.

[Orange-Phantom]

If you are using the correct valve springs for the cam, for which the VS2 are the correct spring, then if I was a gambling man, I'd put a sizeable bet down and say it's not your springs. 

 

Furthermore if you use springs that are too high in poundage for the cam you can cream cracker your cam and followers.

 

When I stripped my engine recently I found they had used valve springs rated far too high for the cam, end result, cream crackered cam and followers!

 

I've now got a matched set of springs for the new cam.

[mini-geek]

Ok I've now confirmed with him that it's nothing todo with fuel or spark it's got to be mechanical.. it's also not detonation..

So if it's not valve float what causes a cracking noise and drop of power at 5000 rpm that is most noticeable at 6000rpm onward what can it be?

Edited by mini-geek, 27 February 2017 - 05:19 PM.

[carbon]

If you are sure it's mechanical then it would be worth double-checking all of the component tolerances in the build such as piston crown height below block deck & head gasket thickness (just in case your pistons are hitting the head at high rpm).

[mini-geek]

I will double check that but there are no marks on the piston plus the piston is a few thou below the block at TDC

[Allrounder]

Wouldn't happen to have any footage of it on the r/r when it's playing up??

[mini-geek]

Sadly not it just sounds like a cracking noise

[Orange-Phantom]

It's not something daft like a soft rev limiter kicking in?

[mini-geek]

No it's nothing like that!