Exhaust Options On A Gti-6 Engined 205

[Batfink 201]

I've been trawling through old threads reading on what people have done exhaust wise to their gti-6 powered 205's

Seems most are happy with the standard system with the downpipe cut down to fit.

so getting my brain in gear that is a 2.5" to 2" in the downpipe, then a 2" system.

 

Its generally regarded that a 2" system is good for around 190-200bhp, but then can start to restrict top end.

Maxi I think ran his 216bhp gti-6 engine on this though.

Has anyone done a back to back test with a standard and wider 2.25" or 2.5" system to see if there were any benefits in top end, or losses in mid range?

Obviously the more standard parts that can be used, the cheaper everything gets, but its a track car and I only really care about gains at the top of the powerband so dont want to loose out there.

 

I'm now thinking I shouldnt have cleared all the 8v magnex exhaust parts I had kicking around

 

opinions welcome...

 

Kev

[brumster 135 1 Cars]

Can't offer anything much more than I ran a 2.25" on my previous 1900 mi16, upon recommendation, but with no RR results I can't put a figure to it. It would have been somewhere between 180 and 200bhp according to general opinion on the cams. I'm now up to 2.5" on the new Longman lump (specced to ~250bhp), I could probably have stayed with 2.25" but I needed a new system anyway so we thought we'd play it safe! Seems to work fine but again no firm figures or results. I know 2" was given the thumbs down by both Andy Baker and Longman, so I guess the limit for a 2" system does lie somewhere around the 200bhp mark.... not sure of the technicalities of it, but the advice I've received seems to echo what you've been told.

[Retro Pug 0 1 Cars]

I'm looking at this now and I think I'm going to get a 2.5" system as I plan further mods - bodies, management etc.

Edited October 22, 2009 by Retro Pug

[Tom Fenton 1,526]

Not really that relevant, but a 2.5" downpipe and 2" Magnex twin box is good for 88dB and 195bhp on my 1600 turbo.

[Batfink 201]

my spec is going to be the xu7 engine, on cams, throttlebodies, gti6 head and manifold, dry sump etc so i think between 180-190 realistic but might get towards 200bhp max so i'm right in the borderzone on what to do really.

[Batfink 201]

Not really that relevant, but a 2.5" downpipe and 2" Magnex twin box is good for 88dB and 195bhp on my 1600 turbo.

 

still relevant surely with it being in the same power range?

[DrSarty 90 1 Cars]

Well that Maniflow 4-2-1 with the rest of the 2.25" system you sold me a long time ago Kev is still going strong.

 

Some people don't rate 'Powerflow' but that's what either the middle or rear box say on them, and they've stood 2 engines now, up to ~230BHP.

 

I'd say 2.25" to be safe.

[Tom Fenton 1,526]

still relevant surely with it being in the same power range?

 

Maybe, obviously a turbo is a different beast altogether, but at the end of the day what makes power is airflow, so for a similar power you will be flowing a similar amount of air/gas.

[andyjstone 5]

I've got a custom 2.5" mild steel jobbie that Miles sorted out, connects straight on to the manifold so its 2.5" all the way and seems to work fine.

 

Before that I had some 3" Scorpion thing that was on it when I got it, but once I put the GTI6 in it rattled to bugger and really wound me up.

[Miles 331 1 Cars]

I do what Andy's got on his with custon exhaust now, But having never done a back to back it's hard to tell for sure, I;ve got the same on my 306 from the D/P flange for the time being until I get my small fuel tank then it's having a 4-2 manifold & system, but again the engine spec is changing

 

Off topic, but give me a call about the clip, Emails down at the moment

Edited October 22, 2009 by Miles

[DrSarty 90 1 Cars]

flange

 

....

[Cameron 16]

You should be ok with a 2.25" system, I have a 2.5" on mine but its overkill at the moment as I'm on standard plenum and 183bhp. I'm pretty confident it will show benefits over 2.25" on an engine that has had a lot more work and is in the 220-250bhp range.

 

If anyone with a high power RS engine is interested in a back-to-back test, I can lend my exhaust (ready to fit std manifold) on an RR session, would be interesting to see the difference.

[DrSarty 90 1 Cars]

Slightly off-topic as it concerns Mi engines, but Dan Taylor and I are 98% sure we can modify a GTI6 exhaust manifold to suit an S16* (XU10) head and maybe an Mi16 (XU9) head too.

 

We should be able to run quite a decent back-to-back on the Mi engine as well then: Maniflow 4-2-1 vs Mi16 reangled vs GTI6 mutation.

 

Be interesting to see how all the different manifolds work in different applications.

 

Good luck with your tests Kev.

 

 

 

*Note: It's often been commented that the standard OE S16 cast iron manifold is cack, so I'm quite excited to see how the '6 mutation works on it, as it's a lovely piece of work.

[petert 554]

Slightly off-topic as it concerns Mi engines, but Dan Taylor and I are 98% sure we can modify a GTI6 exhaust manifold to suit an S16* (XU10) head and maybe an Mi16 (XU9) head too.

 

Only if you make a super duper wedge plate like this one:

 

http://www.taylor-eng.com/conversion/conversion_parts.htm

[DrSarty 90 1 Cars]

(Sorry again Kev)

I was pretty sure somebody else would've done this; could've guessed it'd be you Pete.

 

How much are those kits please (GTI6 exh fanimold to Mi head and S16 head - as I know XU9 is 9 hole and XU10 is 10 hole) please?

[maxi 36 1 Cars]

Slightly off-topic as it concerns Mi engines, but Dan Taylor and I are 98% sure we can modify a GTI6 exhaust manifold to suit an S16* (XU10) head and maybe an Mi16 (XU9) head too.

 

We should be able to run quite a decent back-to-back on the Mi engine as well then: Maniflow 4-2-1 vs Mi16 reangled vs GTI6 mutation.

 

Be interesting to see how all the different manifolds work in different applications.

 

Good luck with your tests Kev.

 

 

 

*Note: It's often been commented that the standard OE S16 cast iron manifold is cack, so I'm quite excited to see how the '6 mutation works on it, as it's a lovely piece of work.

 

 

Get with the times Rich, I did it years ago. I had an S16 stroked and overbored bottom end with a XU9J4 (early Mi) head. I mated to this a gti6 exhasut manifold. It was a LOT of work. I used a QEP spacer plate to give me enough room and material to blend the ports. Hours and hours with the mig and die grinder. Then it was engine in out, in out to get the manifold to fit (first gti6 manifold I had modified to clear bulkhead). So im not suprised Dan thinks he can do it as he knows I did it a long time ago........

 

Just for the record. A std BOSAL system for a later GTi with no silly split in the downpipe will see you safe to 220BHP, I have proved this personally, not something I read on the net. I now run 241BHP and still run a std GTi6 exhaust manifold and std Bosal downpipe mated to a 2.5" system that I made from scratch.

 

Maxi

[maxi 36 1 Cars]

Also, Nick Watling who used to work for QEP, now runs and owns AMS in the same building, modified a GTi6 exhaust manifold years ago to fit an S16 head. It was for revlas car, which is now owned by wildejon. So both have been done before by people dan knows.

 

A point also worth noting, I am now being restricted by a GTi6 manifold @ 241BHP.

 

Maxi

[DrSarty 90 1 Cars]

Sorry for the double posts (internet issues).

 

All right Ad, keep your Alan's on!

 

Dan made the suggestion of how to do the work, and he did say it would be a ball ache.

 

It's not anyone trying to nick anyone's idea (and I know you didn't say that) and I'm obviously behind the programme here. It's just that I wasn't getting the impression from Dan that it had been done before. Thanks for the history lesson.

 

JRG put the idea in my head and Dan and I just casually discussed it. I'm in two minds now as to whether that conversion is really worth it.

 

241bhp is a lot of horses through it so that's pretty good and safe for typical 200bhp conversions. Your description is very valuable, and I feel that perhaps PeterT's kit is a better starting point with just some finer grinding and shaping to suit.

 

Kev>

So what does this mean you're going to start with, because I'd say the GTI6 std exh manifold should be well suited?

Edited October 24, 2009 by DrSarty

[Batfink 201]

Sorry for the double posts (internet issues).

 

All right Ad, keep your Alan's on!

 

Dan made the suggestion of how to do the work, and he did say it would be a ball ache.

 

It's not anyone trying to nick anyone's idea (and I know you didn't say that) and I'm obviously behind the programme here. It's just that I wasn't getting the impression from Dan that it had been done before. Thanks for the history lesson.

 

JRG put the idea in my head and Dan and I just casually discussed it. I'm in two minds now as to whether that conversion is really worth it.

 

241bhp is a lot of horses through it so that's pretty good and safe for typical 200bhp conversions. Your description is very valuable, and I feel that perhaps PeterT's kit is a better starting point with just some finer grinding and shaping to suit.

 

Kev>

So what does this mean you're going to start with, because I'd say the GTI6 std exh manifold should be well suited?

 

I was certainly planning to use the gti-6 exhaust manifold as it only cost £50 and my engine will produce less power than a tuned 2.0

I think I will try a 2" system and then take Camerons offer up to do a comparison on a rolling road as the differences should be very apparent if the 2" restricts top end in any way. I'll try to make a straight through system, but will see what parts I can get my hands on. In some ways I feel I am now making a lot of compromises to get the car built cheaper and therefore quicker, but it could turn out to be some useful research.

[petert 554]

As Maxi said, they're heaps of work. I start with a 25x75mm slab of aluminium. Even after a session on the CNC mill, there's still plenty of hand blending to do. Even then, the angle is still too steep on the transistion from Mi16 to GTi6. The 1.625" primaries are too restrictive. You really need 1.75" if you're making peak power at 7500+. I think you're better off making custom 4-1 pipes.

 

As a rough guide for pipe size:

2.0" <180hp

2.25" <220hp

2.5" >220hp

 

Here's some pics:

http://forum.205gtidrivers.com/index.php?showtopic=105799

Edited October 24, 2009 by petert

[maxi 36 1 Cars]

Exactly! The angle required to blend the flange to the pipes is ridiculous and even to a simpleton like me was obviously going to be no good for flow, I carried on though as I wanted to prove to myself I could do it.

 

Rich, I wasnt getting arsey!

 

Maxi

[Cameron 16]

The aftermarket Mi16 4-2-1 manifolds are no better though, they still use an oval port rather than a twin port, so you'll still have issues with poor flow out of the head. The only manifold I've seen that does it properly is a BTB one made for the 406 BTCC, but as you can imagine they were expensive.

[DrSarty 90 1 Cars]

Apologies to all. I've learnt the hard way again.

 

It proves again what a resource this forum is. That was useful info from Pete (especially with the link) and from Maxi. Had I researched here first I would've been better prepared.

 

So Kev, I would be tempted to spend once and get it right, and get a custom manifold and system to suit the GTI6 style head.

 

Do Maniflow do an off the shelf version for the GTI6 style (XU7JP4, XU10J4R & RS) heads?

 

You have PM BTW.

Edited October 24, 2009 by DrSarty

[maxi 36 1 Cars]

Apologies to all. I've learnt the hard way again.

 

It proves again what a resource this forum is. That was useful into from Pete (especially with the link) and from Maxi. Had I researched here first I would've been better prepared.

 

So Kev, I would be tempted to spend once and get it right, and get a custom manifold and system to suit the GTI6 style head.

 

Do Maniflow do an off the shelf version for the GTI6 style (XU7JP4, XU10J4R & RS) heads?

 

You have PM BTW.

 

AFAIK (am I in the cool gang now I use forum abreviations?) all Maniflow manifolds are custom fit for this application after my phone conversation with them. I could be very wrong though.

 

Maxi

[taylorspug 7]

For the record I didnt know Nick had done a '6 manifold onto an S16 before, and i was going to do it completely different to how Maxi had done it in the past, and without a spacer plate. So im not copying anyones ideas... My plan would have also addressed some of the problems with the ramp angle too. No matter anyway, im not exactly hanging out to do one, as it is still alot of work.

Edited October 24, 2009 by taylorspug