Janspeed manifolds - Worth the money?

[talkingcars]

As part of my maestro project I'm planning to do a night school course in welding, once the body's sorted I'm fancing knocking togeather a manifold............

[dave23572]

Just a thought.

If anyone knows a firm that is capable of making some custom manifolds to meet Fred68's specifications, I was wondering, if we got enough people together willing to buy one, then a batch could be made which would get the unit cost down to something possibly affordable.

I don't know anyone, but even if there was, I guess they would need some time to design and develop it, plus also I guess the designer/manufacturer would need a loan ZS180 car to develop around and do trial fitments and testing etc.

I guess this idea is pie in the sky...

[Fred68]

Manifold and exhaust design is extremely complex. In reality, to get optimum torque from any engine requires a custom designed system. A optimised manifold can help the cylinders fill with the next air charge. Now obviously anyone building systems for open market would need to compromise the system. Manifold primary and secondary length is dictated by many factors. The size of the pipes is very important. Too larger and gas speed will be slow. Too small and although gas speed will be high, back pressure will increase.
Primary length is dictated by many factors. Things like bore diameter and stroke, rod length and valve open/ overlap period are all important. To make things more complex. The optimum primary length is only beneficial at certain points in the rev range. The trick is to get benefits in key points in the rev range at the same time, not causing massive losses elsewhere in the rev range.
This is where secondary length helps. The secondaries can be optimised to lift low points in the rev range.
If all the science is removed from the design. The very best option is remove anything in the manifold and system that causes a restriction to gas flow.
This is why manifolds like the JS manifold work. It's not adding power to the engine, but it doesn't rob to much ether.

Years ago, I made several manifolds with slightly different primary lengths. The theory was to spread a smaller power increase over a wider rev range. It worked too but I found with this method, carburettor calibration almost impossible. Mostly because anything done to the exhaust is reflected in the intake.

[dave23572]

Very interesting and a shame such a manifold was never developed.

[top_man_eldo]

Interesting reading, the fella I was talking to who was designing and building his own manifolds for the 180 was "2bellys" on .org forums. I'll give him a PM to see how he's getting on as it was around 8 months ago that he mentioned this.

[Fred68]

Originally Posted by dave23572

Very interesting and a shame such a manifold was never developed.

The only way such a manifold would come to fruition would be if sold as a complete kit. This would come with heads, cams, ECU, air filter/cold intake and the manifolds and system. Going to this extreme would add lots of power over standard but the cost to many would be prohibitive.
As a DIY build, a well made manifold with longer primaries would be a viable alternative to the JS manifold.

[easytime]

'It's not adding power to the engine, but it doesn't rob to much ether.'

What you have just said is that the JS rob power?

[Mark S]

a diy build mani would not come cheap, if you count up the bends in a custom set of mani's which have 24" primaries (and you are talking about 30" here!!!) on a kv6, and multiply that number by £15, which is the typical cost for a mandrel bent piece of steel, perhaps more for stainless??? you will easily exceed the cost of the janspeeds, this is before you've had the header plates laser cut and attempted welding it together!!!
To add to this, you will be ordering bends which are not off the shelf - as in, not a 15, 30, 45 degree bend etc.

[Fred68]

Originally Posted by easytime

'It's not adding power to the engine, but it doesn't rob to much ether.'

What you have just said is that the JS rob power?

Pretty much anything that is bolted to the exhaust or inlet ports of an engine will loose torque.
A correctly designed manifold will or can cause a vacuum in the exhaust port. This vacuum will draw extra air into the cylinder via inlet valve. This does add torque over and above that, that is generated by open ports.
This extraction only works for a set design of manifold. Any other type of compromised designed does in fact loose torque, when compared to open ports.
The JS manifold is much better in terms of flow over the standard manifold. This is why there is a torque gain.
It's not the last word in extraction manifolds for the KV6 though.

[redzed]

heres a very bad quality vid of the sound of my zs with janspeeds. http://s1363.photobucket.com/user/ia...250d5.mp4.html

all i have is a induction kit and janspeeds (not been remapped and is on standard cams) and its rolling roaded at 175bhp @ the wheels (190-210bhp at fly depending on how its guessed ;-) ), which is not a bad amount of power