4-2-1 exhaust

[Shaun_E]

OK having sorted out the damper situation, my next choice is "Which exhaust system?".

On Dave Andrew's recommendation I need to replace my 4-1 (Caterham competition unit) with a 4-2-1 system.

Options are:

1) Have my system modified - but are the primaries big enough?

2) Buy the Caterham VHPD unit - how much and is it stainless?

3) Get a 3rd party system - EBD, H&S, Powerspeed, etc.

This is to go on a 200bhp+ K series.

If I get a 3rd party system, I'll get a Raceco silencer.

Your thoughts please gentlemen.

 

 

Yellow SL #32

[Jason Plato]

dont bother - the 4-1is fine on power outputs upto and over 245 bhp with a good condition caterham std silencer .

 

There may be small gains to be had by changing 4-1 > 4-2-1 but I think you realy need to ask yourself if its diminishing returns . Unless you have stacks of cash to get rid off 😬

 

Dave

[KevSull Too]

If yer flogging the 4-1 can I have first refusal...?

 

😬You laugh at me because I'm different, I laugh at you because you're all the same. 😬

 

[martinwhitcher]

agree with Dave J, unless it's the 4-1 under bonnet system , I have a Powerspeed which is FAB

 

Martin

 

MW 51 CAT

Superlight No.171

now known as:Superlight DVA 207

 

Edited by - Martin Whitcher on 29 Sep 2005 13:22:40

[Shaun_E]

Oh how I wish I had stacks of money to get rid of - sadly not. I just wanted to make sure that I wouldn't be wasting my hard-earned on a 200bhp engine only to strangle it with the exhaust. Sounds like I'll be OK with what I've got - it's the Caterham unit with the 4 separate primaries exiting the bodywork. I'll probably need to get a bigger silencer at some point to keep the noise down as I currently have the 5" that is not repackable.

 

Yellow SL #32

[Jimchap]

Just asked CC about exhaust options and costs for a 140 SV Roadsport and recieved the folowing from Simon Lambert

 

"There are two competition options available for your car which are as follows.

 

VHPD system - used on the 165 bhp VVC model SV

4-2-1 system , no cat, -595 pounds + VAT

4-1 system, with cat, 810 pounds + VAT

 

R500 system - used on R33/R400/R55 model SVs

4-1 big bore, repackable large diameter silencer, polished system, no cat - 810 pounds + VAT

4-1 big bore, repackable large diameter silencer,polished system,with cat- 1043 pounds + VAT

 

If you go for the cat option, this is in lieu of the straight through collector that you get when you don't have it. This can be purchased as well (or visa versa) - it is a straight swop.

 

In both cases fitting including cutting the new hole in the side panel is about 3hrs at 54 pounds /hr + VAT"

 

[David M]

The Powerspeed 4-2-1 was part of a bulk buy recently with a stream of very happy BC customers, especially since completing a before and after run on Dave Walkers rolling road, +4Bhp and 10% increase in Torque with a lovely graph showing the two runs....... If you get Dave to fit it, he'll do a really tidy job when it comes to the hole cutting part...... they also made me up a 4-1 section to allow me to connect my old Caterham exhaust with silencer for when the first MOT comes around......

 

David

 

GF04RCE.... every day is a Caterham day!!!! He heee!!... pictures here. Problem is every day seems to be a GT4 day too...!!!

[oilyhands]

My suggestion was to convert to a 4-2-1 rather than buy a new one. Back to back tests on DWs rolling road on Mike Bees engine showed a siginificant increase in torque in the mid range between a long 4-1 and long 4-2-1 so it comes down to cost benefit. The costs of converting are a lot lower than buying a new manifold and probably well worthwhile.

 

Oily

 

Edited by - oilyhands on 29 Sep 2005 20:03:49

[Shaun_E]

The primaries on my system are only 1.5" - will that make a difference? The recommended primary diameter is 1.75". The collector and rest of the system is only 2".

It might be cheaper to sell my system and buy a correctly sized one. The Caterham VHPD system is £595 + VAt including silencer and I will more than likely need a bigger silencer than my current 5" to meet track day noise regulations.

 

Yellow SL #32

[david nelson]

I have a 4-1 race exhaust and looked at this in great detail. I came to the conclusion that it would make little effect overal. There have been some big HP k's run on the 4-1 system.

 

what is the ideal primary lenght and diameter? seconderys what lenght and the can you get a long enough can to kill the noise?

 

I get the impresion that no real R&D has been done on this, and would cost far to much.

 

 

David

[oilyhands]

Gawsh.. there is no argument about peak power and 4-1 systems, that is hardly surprising since 4-1 systems generally favour the peak power figure at the expense of torque in the mid range. 4-2-1 systems conversely favour mid range torque over peak power. Research *has* been done , this clearly shows that the area under the torque curve is larger with a long 4-2-1, in one example a 6% improvement in mid range torque for a 1% decrease in peak power.

 

In practice a well designed 4-1 will give very good results, but the chances are a good 4-2-1 will give better mod range torque.

 

Oily

[Mike Bees]

As Oily says, we got some very worthwhile mid-range gains in torque on my 1.7K by converting the stock long 4-1 Caterham system to a 4-2-1 (using the 4-1 primaries and adding a 2-1 section on the back of it). The only downside to this is that you end up with a rather short silencer.

 

1.5" primaries were not holding my engine back - it made 239bhp in the spec. it was in at that time on the stock long 4-1. Changing the primaries to 1.75" made no measurable difference.

 

Mike

[Jason Plato]

When I had my 1600K , I changed from Caterham 4-1 > Caterham 4-2-1 , there was a slight improvement in midrange torque (4lb ish) , but the biggest change was by altering the intake trumpets , I went from 90 mm > 140 mm - this moved the whole curve with no loss of top end power . There would no doubt be bigger gains if I like Mike Bees were able to spend significant amounts of time testing variable lengths of exhaust against my specific engine - Mike put in lots of hours on this , no doubt DVA has also done loads - I have also made up an adjustable primary system for testing some time .

 

My original point was that changing the system will be an upgrade cost of £300 for a Caterham system (sell the 4-1 for £400) plus a remap - this could be viewed as deminishing returns unless you are tuned the hilt already and seeking the last 3% .

 

If you are going to change the exhaust and get a remap then I would strongly suggest you try using longer trumpets - if you can withstand the noise and cutting a hole in the bonet . There are good gains to be had here

 

David N - loads of R&D has been done - you just havent spoken to the right people

 

Dave

 

 

[david nelson]

My understanding was that Mike changed to a milder inlet cam at the same time as making changes to his exhaust, and this might have been a contributing factor to the shift in torque.

 

When I looked into what dimentions should be used i got the following:

 

Primaries: 1.75" diameter, 27" long.

Secondaries: 2" diameter, 11" long.

Main outlet: 2.5"

 

31 inch primaries of 1.5 inch diameter

12 inch secondaries of 1.75 inch diamter.

 

 

As can be seen the is some veriation.

 

 

David

 

[Jason Plato]

Each engine will have different optimal lengths depending on total spec .

 

I'm sure Mike will correct ......but he did the tests on the exhausts during one session at emerald using one cam . I have overlays of maybe 6 or 8 different variations he tried all good research

[Rob Walker]

If you are to buy a 421 system the Caterham VHPD ( LEFT HAND DRIVE) full system gives very good results. The primaries were reshaped to clear the steering colum on LHD cars and this also gives extra clearance around the starter motor. 233BHP and 162lbs torque out of my 1.8K at 7800rpm and very good low down torque

 

The other point to consider is that the hole in your side skin will fit this system.