I don't understand all these deleted posts, as far as I could see Multivalve started a perfectly reasonable thread and then it was deleted yet again, can't understand it!

Quote:


I don't agree.
Being as no-one even volunteered to identify the head (an IMP) it just shows the attitude here.
Am I here to sell IMP heads??
Decent head specialists don't grow on trees any more, they're either dead or retiring these days.

Out of technical interest the IMP head resembles the Jag XJ40 head in astonishing ways.....

FYI:- Andy Chesman also started in motorsport by modifying Imp heads.....

This is a Chesman head I'm doing atm ...flow figures below

I don't suppose any of you care about Chesman and his racing Jag stuff... 

covkid wrote on 01.02.2010 at 19:00:16:


So if Mr Coventry can do better...come and prove it...

Chesman's head before and after modification...

Prove to me you can get 128bhp from 998cc and we'll talk about it...

I don't know why I bother.
You don't get it do you??

What is eating you?
Jealousy, stupidity, ignorance?

You can choose to remain stupid, but it's your choice.

Working on many different engines you can learn useful things.
Chesman made modified imps for a living, that made him one of the best V12 Jaguar engine specialists around.
(those engines have almost identical problems)

The Imp engine was a Coventry climax (or you forgot your Coventry sense of pride now??)
It was a slant 4.
Your Jaguar AJ6 is a slant 6.

Now look at both.
They are very similar, in fact that Jaguar engine had very similar design teams.
Also unsuprisingly you can get 30% more flow from a Jaguar head also.

Of course you can carry on being stupid and ignorant.

It's your choice after all, but intelligent people never stop learning..

Go on, you KNOW you can do it, just once....

LEARN SOMETHING!
(instead of prancing arrogantly around in your Jaguar blinkered world)

There are 2, AJ6 heads, with some minor variations introduced down the line.
They both have different problems.

The early head has 2 cam follower variants.
Small and large. The larger cam follower is used in all later heads.
The X300 introduced the "AJ16" head which is supposed to be a major improvement.

In all my tests, the AJ6 head performed far better than the AJ16 head, as the ports have been made far too large on the AJ16.
This sounds counter intuitive, because popular hearsay and logic says the later head is better.
This is not so.

In most of my work on cylinder head modification it's a primary rule to keep ports as small as possible in order to keep the port velocity up.
On the AJ6 head I was able to get a flow improvement of up to 30% doing modifications to the ports and seats alone, and this was especially noticeable when done to the EXHAUST tract.

Again the primary response to all my posts on this forum has been trashy, negative, childish, and mostly downright rude, as well as contradicting all my work showing there are major improvements that can be made to 4V engines such as the Jaguar.

That REALLY "gets up my nose", as you can see.

Now back to the subject:-
On an early XJS I modified in Strasbourg, the engine had such a major improvement to driveability that the 0-100km/h time was reduced by more than 1.3secs on an otherwise standard engine (which had in fact done more than 220,000kms), such are these units robust.
There are major improvements made to the fuel consumption doing this, and no down sides. This kind of work removes the characteristic kink in the torque curve, for which the AJ6 is well known and gives a major improvement in torque from 1500-3500rpm.

I must admit I was very suprised by such a result as I expected to see a large increase in power from 4500rpm on.
This doesn't happen because the other engine ancilliaries have been poorly designed, eg. the inlet tract being made TOO LONG and the exhaust manifold TOO SHORT.
This was a poor compromise adopted by the factory to get round production spread and tolerances.

There are also severe mismatches between the inlet manifold and head, which result in the symptoms you describe....poor fuel economy when cold and poor torque curve.

I could say more, but I have no doubt someone will come along and edit this post as well.

I hope this answers your question.

"Decent head specialists don't grow on trees any more, they're either dead or retiring these days".
In many ways head specialists are not needed anymore, manufactuers get their engines pretty well spot on for their intended use, and if you want more power just fit a turbo or supercharger which is the choice of Jaguar and many other manufacturers. As for inlet tract velocity that is a bit of a non starter, inlet tract turbulence and resonance are far more important since the peak velocity is only achieved for a few degrees in every 720 degrees of the 4 stroke cycle.
Cheers

I think that there's a difference between a genuine discussing about engine tuning and Multivalve's attempts to sell us his wares.

Add to that a generally aggressive, insulting and disruptive manner and you have a right royal pain in the arse.