Gti6 Manifold, Anyone Using An Uprated Item?

[maxi 36 1 Cars]

Right, had my car mapped and its under power. The only thing I think it can be is the std gti6 manifold holding it back. Has anyone ever used an aftermarket manifold for this engine??? I spoken to a few people and the longmans item seems the way to go. Just to recap its a gti6 (block and head, not much else) engine in a 205.

 

Matt of pug1off was recently telling me he was having similar problems with an almost identical engine and he was stuck at the same power as I am. He too thinks the solution is the manifold but didnt really have any answers after that.

 

 

Maxi

[maxi 36 1 Cars]

Just to add, I am talking about the exhaust manifold. The engine should have been around the 250-260bhp mark.

 

Maxi

[Toddy 7]

Maybe worth giving James Lumley a PM as iirc he has a 270bhp engine?

 

You could also try maniflow, Tony Law exhausts or Torque Technique.

[dale205mills 39 7 Cars]

This is a very interesting post you have started maxi, I allways thought the standerd gti6 exhaust manifold was very free flowing and I will be very interested is seeing your findings with useing a aftermarket manifold

[Miles 331 1 Cars]

Watch the Maniflow (longman) ones as the std one they do or did as I haven;t seen one for a while was un-equal lengthand lost some torque over the std one, They might have re-designed it now so worth asking or looking at, I know when I finally get around to having mine mapped I know what sort of power it should make again using the std 6 manifold so I can see a ex-works type of design being made up for me

[Alastairh 47]

But how does this relate to the 306 boys running there bolt on SC kits running 250+ brake?

 

Al

[Miles 331 1 Cars]

Thats a very good point, But as I was saying to someone today I can;t see the point of S/C or T/C unless your looking at 280bhp + as you can get less without going down that route.

Have a look at Dixon's manifold as the same idea will translate but would be nice to do a back to back

[GTI6BOY 29]

straight will always be better than the std one due to less friction.

 

Longmans would not have taken the time to design one if they were not better.

 

We have a maniflow mani (longmans one) and you defo notice the increase in torque

[Sandy 189]

Dixon's manifold is quite different to the Longmans ones. We designed it to suit the cams (which in turn the head has been worked to suit etc etc) to produce substantial mid range and I'm not sure it will produce a significant increase in peak power if that's what you're seeking. Can you give us any initial graphs and specs to go on at all?

[maxi 36 1 Cars]

I will scan the graph in later.

 

Big cc GTi6 with a diesel crank

steel rods

overbored to 87mm with forged pistons

larger inlet valves

45mm Throttle Bodies

CR 12.6:1

Catcams (cant find the invoice so I cant remeber which ones) with the correct solid lifter setup

 

And various other little bits and bobs. Dont get me wrong, the thing goes like a bastard and was trying to climb out of the rollers at 5000RPM onwards when chris was mapping it.......

 

The only other option I can see is that it needs to rev further. It makes max power at the rev limiter (8000RPM) but I didnt want to go any higher as I was concerned with reliability issues.

 

Maxi

[petert 554]

Have you compared the pipe OD and lengths of the GTi6 manifold to the power/torque PRM ranges you're trying to achieve? I seem to recall they were designed for around 7000. I used to have a link to a good 4 cyl. calculator but have lost it. It was on a motorbike site.

 

edit:

found it. Try entering your specs. into this:

 

http://www.mez.co.uk/mezporting/exhaust_length.html

Edited July 21, 2008 by petert

[Dj_mini 7]

I will scan the graph in later.

 

Big cc GTi6 with a diesel crank

steel rods

overbored to 87mm with forged pistons

larger inlet valves

45mm Throttle Bodies

CR 12.6:1

Catcams (cant find the invoice so I cant remeber which ones) with the correct solid lifter setup

 

And various other little bits and bobs. Dont get me wrong, the thing goes like a bastard and was trying to climb out of the rollers at 5000RPM onwards when chris was mapping it.......

 

The only other option I can see is that it needs to rev further. It makes max power at the rev limiter (8000RPM) but I didnt want to go any higher as I was concerned with reliability issues.

 

Maxi

 

Could the 45's be holding it back?

[welshpug 1,627]

inlet tract Length?

 

I just read through Black_mi16's project thread and though I cant remember his cam choice or compression ratio he used a gti16 manifold which is quite similar to the gti6 one with good results (circa 250 ATW)

 

sounds like one hell of an engine whatever the peak figures!

[B1ack_Mi16 67]

inlet tract Length?

 

I just read through Black_mi16's project thread and though I cant remember his cam choice or compression ratio he used a gti16 manifold which is quite similar to the gti6 one with good results (circa 250 ATW)

 

sounds like one hell of an engine whatever the peak figures!

 

True, but the Gti16 one has slightly bigger inner diameter of the runners compared to the gti6, however the gti6 one has nicer and smoother transactions in the first 10cm from the head flange, and also gti6 has a better collector.

 

I have both a gti6 and gti16 one in my garage at the moment the inner diameter of the gti16 is 38mm as far as I can remember.

 

I guess the gti6 is like 34 - 36mm somewhere.

[Alastairh 47]

How did you go about the bulkhead clearance with this conversion?

 

I presume you've re angled the manifold? I know its a weak idea, but just trying to think of possible reasons why it would be strangled in your place say over 306's boys Supers.

 

Maybe its too much of a beast and peak power is beyond 8k which your not happy to take?

 

Al

Edited July 22, 2008 by Alastairh

[Sandy 189]

It's probably down to a combination of factors. To get the sort of results you want, everything has to work together. When Colin built Ian's 2.0 16v last year, it made 234bhp/174lbft, not bad except we were expecting 250bhp odd from the cam/exhaust combo John Read had given us. We got the distinct impression at the time that something on our side of things might be holding it back a bit, perhaps the head, which I'd had done originally for a 1.8. I had it apart recently after a cambelt and stray bolt "incident" and implemented a few subtle alterations to the inlet ports and TBs, from what I've learnt since it first went together. It came alive then with 266bhp and 186lbft! I think the mid range could have been improved further with more time spent on the inlet tuned length, but time of course always runs out at some stage.

 

I've raked up your figures from an old thread and plotted them against Ian's to get an idea....

 

Looking at that your torque seems to be tailing off from around 6000rpm, so I very much doubt there's a hidden second wind beyond the limiter. I asked for the detail because it'll take detailed and interactive improvements to realise the sort of substantial gain you want.

[TT205 42]

Looking at that your torque seems to be tailing off from around 6000rpm, so I very much doubt there's a hidden second wind beyond the limiter. I asked for the detail because it'll take detailed and interactive improvements to realise the sort of substantial gain you want.

 

Isn't it a bit peculiar that both traces are absolutely identical up to 6K and then Maxi's falls away - would you not have expected Maxi's entire curve to be 'skewed' to the left if it runs out of puff sooner

 

Was rpm measurement on Maxi's accurate?

Edited July 23, 2008 by TT205

[maxi 36 1 Cars]

Hang on guys, Sandy has the graph for the old engine, not the present one which I am running! Trying to get the new graph scanned in although im having a few technical issues (the f***ing scanner wont work!)

 

Sandy: I couldnt agree with you more that I think its a combination of things that are restricting power. It might be worth pointing out that the engine is also down on torqur to 170Ibft compared to the old one (2.1 mi/s16) which made 174Ibft.

 

Al: Yes mate, I always reangle the manifolds, that is THE way to do it as far as im concerned, got a little jig for getting them perfect everytime. As for the SC 306 boys, I was under the impression with forced induction, its easier to make power Ie: limiting factors will be much more apparent on a NA engine.

 

Maxi

[Sandy 189]

Forced induction generally masks the inefficiencies.

If you can rip the figures, I can graph them for you.

 

Isn't it a bit peculiar that both traces are absolutely identical up to 6K and then Maxi's falls away - would you not have expected Maxi's entire curve to be 'skewed' to the left if it runs out of puff sooner

 

Was rpm measurement on Maxi's accurate?

Not necessarily an issue of accuracy, it's really very common in my experience, for tuned XU 16v engines to make apparently tepid mid range; which is invariably mostly down to using the Jenvey/Longmans inlet manifold which limits inlet length to about 330mm in the 205 and the sweet spot is usually well beyond that. Changing the inlet design on Mos's 2.1 instantly added more 40bhp at 4500rpm and around 20lbft across the rev range literally overnight. Exhaust manifold and system design is a major factor too and having one that's tuned to work with the cams is how the honey really starts to flow. The traditional accepted wisdom of power "see-sawing" from mid range to top end only really relates to engines that haven't been holistically developed to the full. The trouble is, few people have the time, money, resources etc required to achieve that.

Edited July 23, 2008 by Sandy

[fletch 0]

Adam,

 

Chris Bowen on the Gti-6 forum has an N/A Touring Car engined 6 with a Maniflow manifold, I *think* the BTCC 306s all used maniflow manifolds (although not necessarilly the same design as Chris')

 

Might be worth speaking to him?

[GTI6BOY 29]

They were used on them yes and chris does have one so they must be better than standard?

[Miles 331 1 Cars]

I will be getting a manifold made up for a customer early next year for a similar spec engine bar a 2.1 version, It won;t be Maniflow making it either but my man so it will be intresting to see what it does on the dyno.

A way off I know but handy referance

[Sam 4]

Adam,

 

Chris Bowen on the Gti-6 forum has an N/A Touring Car engined 6 with a Maniflow manifold, I *think* the BTCC 306s all used maniflow manifolds (although not necessarilly the same design as Chris')

 

Might be worth speaking to him?

 

Tony from Touring Car Spares had a BTCC 406 manifold down there when I was there last but that was about a year and a half ago now. Looked prety beefy to say the least. He only wanted 100 for it and it looked a bit special! Needed a collector though.