tubular exhaust mani for a gutsy 16v...suggestions?

AS the title says folks, I'm thinking about an exhaust mani for my valver engine . I have a Supersprint one for the mk1 , but I think it's built more for ease of manufacture than best spread of power . Without commisioning one from the likes of Tony Law , what else is out there for a 16v mk1?

 

There isn't a really good one Tris. .though I've used the Ashley conversion 4-1 manifold @ 190hp.

 

Ashley on mine also. I cut the collector up, cleaned up the inside of the manufacture and re welded it. It was quite poor inside
Jon

 

Jason ... think that mine is an Ashley ?

 

I think it is Andrew yes.

 

Ashley here too, like Jon mine's been cut apart and re-welded to clean up inside the collector.

I added in an o2 bung and had it silver ceramic coated.



It's holding up well after 2 seasons of racing and it's made 182HP at the wheels on the last Dyno tune.

 

That looks pretty good Peter!

 

You guys don't rate 4 2 1s then? For road car use.

 

Tristan, at what operating engine speed do you expect to achieve maximum torque?
Also at what engine loads are you likely to use the engine?

 

Tbh Ed I'm not 100% sure . I suppose I'd like it to have reasonable pull from 3500 to 7000.
Its a fun road car after all. Not a racer .

 

Pull from 3500-7000rpm eh?

If it is a road car you are likely to have the occasional moments where you will be at WOT between 4-6k and sometimes be at mid part load at say 2-3.5k. You actually want a fast responding engine vs an all screaming top end unit.

Let us describe what happens in a typical pull from 3500-7000rpm from an acceleration perspective.

Torque 3.5-5krpm loads to WOT

For a road car, a 4-2-1 exhaust would be preferred to provide strong scavenging in the 3-5k area at various loads, providing this is matched to the chosen induction length and cam choice. There are two of the off the shelf solutions. The Supersprint Tri-Y, with modifications to the collector or a OE ABF Euro 4-2-1 system, with a custom downpipe for the mk1. Gurdip's NASP ABF used this system and it was discovered the collector could have been improved on leading to more scavenging at higher speeds. The WOT torque as you know from the shared dyno plots was not a problem, with a plateau between 4-5.5k. On my own ABF road/track car as well as others who I have shared the idea with, a OEM 421 tubular manifold is used, in my case maximum torque is generated with a plateau from 3.8krpm to 5.5krpm. Throttle response anywhere on JENVEE is pretty instant. I have also seen and tuned applications with ITBs etc that rev to 8000rpm with the OE tubular header.
For an engine that can achieve maximum torque say at 5-7k and so on then you are looking at commissioning a custom header.

After 5.5krpm to 7.5krpm

Based on your cam and CR, between 5.5 and 7.5krpm, engine VE drops and frictions starts to increase, so torque starts to drop off. However if you can still achieve near 90-85% of your maximum torque at the peak power rpm and about 75-70% at your redline, the vehicle, if it is light will still accelerate albeit slower than at the torque max.

If that decribes what you are after then feel free to fit the Supersprint manifold. Do wrap the manifold and the steering column gaiter though!

 

Like the silver Ashley, makes mine look like a right old pile of scrap!
Agree every race/rally car I have has a lambda boss welded in.
You would, wouldn't you...
Jon

 

Would you notice the difference between a 4-2-1 and a 4-1 on the road?

 

My opinion, no.
Jon

 

Yes. Providing the calibration is optimised and both engines were the same spec, the launch torque is also greater on the 4-2-1 system.

 

But would you notice 5ftlb in 140? On the road.
And that assumes you went to the trouble and expense of a back to back optimisation for a road car.
I can think of better VFM engine tests
Again, IMHO
Jon

 

That is only one condition, suggesting 140 (mph?), top gear and near 6-7krpm gearing dependant.
Header scavenging, all other parameters being equal, can be worth 15lbft at certain loads/engine speeds, usually in the normal driving range sub 1500rpm to 3krpm with the engine map optimised to take advantage. I have personally worked on such experiments systems in a OEM environment.

 

In my very non OEM development days playing racers with mini's I used to exclusively run 3:1 systems on 300+ full race cams, per the tuning bibles.
At clubman level, won a bit.
Went back to LCB's (mini 4:2:1) (quarter the price, more robust) and the engines still collected pots.
Two best things about clubgti is the proper tech input from pro's and the VFM experience based input from 'clubman'.
Long may the discussion continue
Jon
If you've got 500-1000 for a manifold and related setup, let us know how you get on.

 

I also have Vizard's A series Bible and have played with a 1293cc, omega dished pistons, a Piper 286 cam, with LCB and split Webers . Shame in those days I did not have a dyno but, I am sure it would only prove what was in his book.

 

i posted a delta graph somewhere with my ibiza valver engine going from an off the shelf tubular 4-1 milltek manifold to a properly designed simpson long 4-2-1. cannot find it presently but it was well worth doing.....

edit
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