Thoughts on this head/chamber work?
Discussion
227bhp said:
Jhonno said:
??
I'm not trying to create any sort of guessing game, I'm currently building my own AJP (N/A), which I was going to get headwork done on it, and came across this, and wondered the benefits if any for such drastic chamber modification. The most powerful 4.5 AJP I know of, had some chamber work, but no images of what was done.
Yet you have, you could have bundled all that into a properly worded question in the first place so instead of everyone asking questions, they could have been answering yours.I'm not trying to create any sort of guessing game, I'm currently building my own AJP (N/A), which I was going to get headwork done on it, and came across this, and wondered the benefits if any for such drastic chamber modification. The most powerful 4.5 AJP I know of, had some chamber work, but no images of what was done.
It shouldn't be a case of pulling teeth or playing some kind of game of bloody hangman, if you want someones help then give them all the help or tools they need from the start. You wouldn't equip your gardener with a pair of scissors and then give him a lawn mower 2 years later would you?
Anyhow, less fratching, you see the issue, so hastily moving on
The phrase you need for your research is 'Chamber pressure recovery', that is what they are hoping to achieve there. It isn't new by any means, Saab used it decades ago:
As you can see they've cleverly designed a hole for the exhaust mouse to get through too.
And they may have got the idea (as did others) from motorbike engines which used it in the 80s, maybe even earlier:
I get the feeling it's more of a 4 valve thing which 2v head workers have adopted, basically what these shapes do is encourage the air to keep some of its speed, another useful term is 'Cloverleaf combustion chamber'.
The first point is that a well designed smooth chamber which pushes the mixture towards the centre and has no corners for it to hide in is what we want for good overall efficiency.
Second advantage is explained like this; when you squeeze air as it is travelling through a pipe it speeds up (more velocity), open it out into a larger area and is loses velocity and slows down.
When the air has been squeezed through the gap between the valve and the seat it's travelling very fast and it will tug the air behind along with it. If you can imagine a train of 50 people holding hands running through the streets, the first 30 could be pulling, the last 20 could be pulled along by them, like it or not.
So when the air enters the chamber after the valve the pressure drops, it relaxes and slows down. It goes where it wants, tumbling outwards and it doesn't draw so hard on the stream behind it. If we carry on the 45' valve seat angle as best we can it will help the air carry velocity and also help it tumble inwards towards the centre - just where we want it.
On the exhaust side you are preparing the air at the right angle so it vanishes down the exhaust port as quick as it can.
In the inlet port the sharp corner opposite the valve guide is known as the 'short side radius' or SSR, this is the busiest part of the port. When the piston drops the valve opens and air rushes over this at high velocity as it is the shortest route from A to B, it's a very important part of the port. What you need here is a large radius, if it's too small or sharp the air will leave it, whirl around and lose velocity or skip off and try to get through the opposite side of the valve by the longside. What (hopefully!) they are attempting by the welding in there is making that radius bigger so the air clings to it, they have also widened it because that is where a lot of it is flowing.
You cannot tell air where to go, you can however cajole, manipulate and help it on its way.
The flow bench is only a tool or a guide to measure. It does not necessarily follow that a gain in CFM equates to a gain in bhp, those mods might not even show much of an improvement in overall port airflow, but will on the dyno and vice-versa because more of the valve opening area is being utilised. You can measure which parts of the valve circumference are flowing more or less air too, but that's a different story.
As has been previously outlined, it needs a proper back to back Dyno test to see, pretty rare anyone gives you a pictorial guide of how to do something and shows you the results for free though....
Anyhow, less fratching, you see the issue, so hastily moving on
The phrase you need for your research is 'Chamber pressure recovery', that is what they are hoping to achieve there. It isn't new by any means, Saab used it decades ago:
As you can see they've cleverly designed a hole for the exhaust mouse to get through too.
And they may have got the idea (as did others) from motorbike engines which used it in the 80s, maybe even earlier:
I get the feeling it's more of a 4 valve thing which 2v head workers have adopted, basically what these shapes do is encourage the air to keep some of its speed, another useful term is 'Cloverleaf combustion chamber'.
The first point is that a well designed smooth chamber which pushes the mixture towards the centre and has no corners for it to hide in is what we want for good overall efficiency.
Second advantage is explained like this; when you squeeze air as it is travelling through a pipe it speeds up (more velocity), open it out into a larger area and is loses velocity and slows down.
When the air has been squeezed through the gap between the valve and the seat it's travelling very fast and it will tug the air behind along with it. If you can imagine a train of 50 people holding hands running through the streets, the first 30 could be pulling, the last 20 could be pulled along by them, like it or not.
So when the air enters the chamber after the valve the pressure drops, it relaxes and slows down. It goes where it wants, tumbling outwards and it doesn't draw so hard on the stream behind it. If we carry on the 45' valve seat angle as best we can it will help the air carry velocity and also help it tumble inwards towards the centre - just where we want it.
On the exhaust side you are preparing the air at the right angle so it vanishes down the exhaust port as quick as it can.
In the inlet port the sharp corner opposite the valve guide is known as the 'short side radius' or SSR, this is the busiest part of the port. When the piston drops the valve opens and air rushes over this at high velocity as it is the shortest route from A to B, it's a very important part of the port. What you need here is a large radius, if it's too small or sharp the air will leave it, whirl around and lose velocity or skip off and try to get through the opposite side of the valve by the longside. What (hopefully!) they are attempting by the welding in there is making that radius bigger so the air clings to it, they have also widened it because that is where a lot of it is flowing.
You cannot tell air where to go, you can however cajole, manipulate and help it on its way.
The flow bench is only a tool or a guide to measure. It does not necessarily follow that a gain in CFM equates to a gain in bhp, those mods might not even show much of an improvement in overall port airflow, but will on the dyno and vice-versa because more of the valve opening area is being utilised. You can measure which parts of the valve circumference are flowing more or less air too, but that's a different story.
As has been previously outlined, it needs a proper back to back Dyno test to see, pretty rare anyone gives you a pictorial guide of how to do something and shows you the results for free though....
Edited by 227bhp on Tuesday 15th August 10:50
This will be the turbo ajp being done by ICE at Silverstone, it's a project started about 10 years ago by the now defunct Autocraft, later RND? At least they were doing a similar project that never got finished. Looks like it could be another 10 years before it's finished again but if it's a job fitted in amongst other things that means they're generally busy, which is a good thing generally? There's a whole facebook page devoted to it but updates are few and far between.
Edited by spitfire4v8 on Tuesday 15th August 16:13
spitfire4v8 said:
This will be the turbo ajp being done by ICE at Silverstone, it's a project started about 10 years ago by the now defunct Autocraft, later RND? At least they were doing a similar project that never got finished. Looks like it could be another 10 years before it's finished again but if it's a job fitted in amongst other things that means they're generally busy, which is a good thing generally? There's a whole facebook page devoted to it but updates are few and far between.
Yes, that is the one Joolz.. They seem to have been doing some recent work on it again.. I think it is a side project to help the owner out, hence the pace.Edited by spitfire4v8 on Tuesday 15th August 16:13
I mapped the wilder 3.8 sp6 on the ICE engine dyno when we were running them in the the t350 racer, made decent power but I found more from my own 3.6 later on but at the time it was the best sp6 I'd mapped.
They do a lot of big american stuff so presumably they're borrowing lessons learned from that side of the business for the ajp8. Wish they'd get it finished though. Does Campbell still own the car (think the owner was called campbell anyway?)
They do a lot of big american stuff so presumably they're borrowing lessons learned from that side of the business for the ajp8. Wish they'd get it finished though. Does Campbell still own the car (think the owner was called campbell anyway?)
spitfire4v8 said:
I mapped the wilder 3.8 sp6 on the ICE engine dyno when we were running them in the the t350 racer, made decent power but I found more from my own 3.6 later on but at the time it was the best sp6 I'd mapped.
They do a lot of big american stuff so presumably they're borrowing lessons learned from that side of the business for the ajp8. Wish they'd get it finished though. Does Campbell still own the car (think the owner was called campbell anyway?)
Interesting..They do a lot of big american stuff so presumably they're borrowing lessons learned from that side of the business for the ajp8. Wish they'd get it finished though. Does Campbell still own the car (think the owner was called campbell anyway?)
I am guessing they are applying things across yes. I don't think it changed owners, just builder. He is a friend of ICE either way, which is why they picked up the mantle on it.
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff