HI JOSS, Will take a deep Breath next time, there are to many very informative post to waste time on BC thanks

Location: Tinopai NZ

Hopefully all Forum users have now viewed the excellent video and have an understanding. It is certainly a painless way to learn compared with books.

For the more curious, in the sv frames at 1.50 the flame front seems to reverse unlike the other shots. Presumably this is due the squish effect of a typical sv head

To complete the picture it is perhaps appropriate to point out that normally a thin layer of static molecules remain adjacent to the metal surfaces and act as an insulator. The pressure waves from persistent detonation strip these way and hence holes burn thru piston crowns etc. The risk is greatest at high power (when often the tell tale noise is obscured by the general din.)

Location: Auckland, NZ

This thread seems to be getting nasty and personal.

The subject is one on which I can't contribute anything useful, but I'm interested to read everyone's opinion, as I have a Speedex head on a car that hasn't yet hit the road.

By all means point out errors in other people's statements, but lay off the personal abuse and insults!

Location: Herefordshire, with an "E", not a "T".

Yes, Martin and Dave are right - let's discuss the ideas and not the personalities. This thread is about tuning heads - let's tune ours to be tolerant of others views.

Disappointed Dave

Martin. I agree. This is supposed to be the Friends Forum. It seems to me that Bob might be poking a stick at his protagonists, and in that regard he's winning hands down!
In the interest of learning and increasing our scope of knowledge we should laud those that make contributions, not ridicule. Age is supposed to mellow us.

Location: New Zealand

Hi Folks,

I have just taken delivery of a Replica Whatmough Hewitt head,which I have been led to believe has better breathing than most other heads.

I am about to polish out the casting marks on the chambers then give it a whirl on my type 65

I have been hitting a brick wall at 5000rpm the engine pulls like a train then seems to run out of puff.

Pigsty trials cam and followers/80 thou bore / alan crank and rods, 1 1/4 downdraft SU on standard manifold / light flywheel and coverplate.

I will let you know how I get on.

Regards Richard

Location: Cornwall

This is all ok, but I think burn pattern is not the most important thing, anyway.
I agree you have to burn the fuel/air mix efficiently, but it's all a waste of time if the cylinder isn't full of the stuff. So, for me, I'd go for improving volumetric efficiency, any day. If it can't breathe, it won't rev. If it won't Rev, you won't get power, at least not in a 750cc engine.

Richard, two questions. What head were you using, and what axle ratio have you. And a supplementary question will it Rev higher than that in third gear?

Hi Alan,
I am running a standard Nippy Head at the moment.
I can hit the same revs in all gears. cars has the correct low axle ratio and close ratio gearbox.
I have tried a VW distributor and found it to be no better than a good manual advance one.
I have also tried different exhaust systems.
I am sure that the engine is running out of breathing hence the Whatmough Hewitt cylinder head.

I have had more revs with a ruby head on the same engine but it oils up the plugs.

Regards Richard

If it revs to 5k in top on 5.625 axle, that's about 70mph which I guess is about right for a nippy. However you are really getting into the zone where bolt on go faster bits aren't enough, and you'll need to give some serious thought to port shapes, manifolding etc to get it to go faster. Frankly, an engine that won't tolerate a 37 head is not the right place to start tuning and I'd be inclined to fix that before anything else. Another thing, it's surprising it pulls the same revs in all gears. If it does 5k in top I'd expect it to go off the clock in 1st, 2nd and 3rd. Are you sure you don't have valve bounce?

Richard,
Is the ignition coil limiting your revs? Have you tried a different/new one?
Dave.

Location: Sheffield

Hi,
I am running 12v with a new coil fitted last year.
I have no sign of any missfiring and my electric revcounter holds steady.

Double valve springs fitted so no valve bounce.

I have just finished die grinding the Whatmough Head to give valve clearance at 8mm lift with no gasket fitted, I have also balanced the chamber volumes.

So apart from finding a set of long reach plugs I am ready to swap the heads over.

Location: Cornwall

Just be a bit careful with long reach plugs. On the Whatmough head I used the valve would hit the bottom of a 3/4in reach plug. You might find you need some spacers to lift them up a little bit.

Hi Richard

I realise I am encroaching on sacred territory, but is that the Pigsty cam documented on the old Speedex site? 22 40 54 13? And if so is it run in that form or retarded? If the former the inlet closing seems conservative for high power at 5000 rpm, altho would not prevent revving at light load. Or is it some more recent version?

Location: Auckland, NZ

Is your rev counter accurate?
Is your can timed correctly?

A friend of mine has a Pigsty trials cam in his Ulster rep trials car, 1 1/4 semi DD SU, proper Ulster exhaust manifold. I know from personal experience that it will rev past 6000rpm (the rev counter only goes to 6k). However, it does not have great low down torque and is quite easy to bog down with it coming "off cam" at anything under 1500rpm.

Hi All,
I have just put another modified block with new slipper pistons valves guides springs,
fitted a pigsty race cam
and new shell bearings under the whatmough head, also a lighter flywheel clutch assy.
my tickover is a tad lumpy as expected, car pulls really well and will hit over 5000rpm on light throttle I just need to run it in a bit more. before I really thrash it.
engine sounds sweet and will pull from 2000 RPM,

Location: Cornwall