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MG MGF Technical - Custom made 4-2-1 exhaust manifold + flex pipe

Hi,

I was wondering how much it would cost to get a 2.5" 4-2-1 exhaust manifold and a 2.5" flex pipe to the exhaust in UK.

I know QED does 4-2-1 systems, but I remember Rob saying that it will be quite expensive.

I got a quote locally from a reputable performance car shop, and gave me a quote for both mild steel and stainless steel one. 360 pounds for the stainless and about 300 pounds for the mild steel. [that's both the manifold and the flexi pipe]

The price doesn't look too bad to me. Well I am sure Rob can afford this... [I know I can't...]

Looks like I need to save up a lot of money for next holiday. This will be a nice mod with Rob's exhaust on my car!

Will 2.5" pipes fit in the car though.... hmmm
:-)


Hanah Kim

One question, what sort of power benefit would I get from this upgarde?
Hanah Kim

300-360 quid is in the same ball park as equivalent systems here in the UK.

Not sure that 2.5" is the ideal diameter - maybe 1 5/8" ;o) 2.5" will give plenty of top end power, the smaller diameter will not rob too much of this top end, but will benefit torque.

Hanah, as usual, the exact gain of power will depend on the state of tune of your engine - maybe something in the same ball park as a performance exhaust - say 5 bhp - but coupled with a really impressive gain in torque (10% as opposed to 5% gain with an exhaust).
Rob Bell

PS Wish I could afford it - too much to do on the new house!!! :o(
Rob Bell

Hi Rob! Good to hear from you. I knew you would check out this thread.

I thought it would cost considerably more in UK, but seems to be priced similar. It's quite a lot of money really...

Does that include both manifold + flexi pipe to cat?

I really do not understand how the system works, so I will ask you a few questions. And yes I have checked previous threads in the archive already.

1. Why would smaller diameter provide more torque in the mid range?

2. On an old thread, it mentions that keeping the secondary pipe long is important. Shortening this will lose the benefits. I don't know what this 'secondary pipe' they were talking about.

3. Is there anything else that I should look out for (that's if I decide to go for it at the end of the year), to get it custom made? I already asked the quote for 4-2-1. But... anything else?


>>as usual, the exact gain of power will depend on the state of tune of your engine

Rob does this mean that without engine tuning (ie. porting / cams / big valves etc.), the benefit won't be that great?


Torque benefit sounds great though... so installing your TT exhaust will improve torque as well? (I was pretty much expecting only nice sound from back of the car!)

Yeah, it's all about the priorities.. 350 pounds is big money.. whoever looks at it. I will probably miss this upgrade as it costs too much (350 pounds, is what I have in the bank account! Ouch... )

Hope your new house decoration / renovation is coming well! My dad renovated the current house.... it costed as much as the house itself cost us. :-D It's a dental clinic downstairs, and home upstairs.

Thanks Rob!
Hanah Kim

Good questions as usual Hanah :o)

>>1. Why would smaller diameter provide more torque in the mid range?<<

Complicated, and I do not profess to have the answers, but there are issues to do with back pressure on the combustion process (valve timing and overlap - there's stuff on this discussed in the archive) and timing the pressure pulses to aid exhaust gas extraction.

Basically, bigger doesn't mean better.

>>2. On an old thread, it mentions that keeping the secondary pipe long is important. Shortening this will lose the benefits. I don't know what this 'secondary pipe' they were talking about.<<

On a 4-2-1 exhaust manifold, there are four pipes from the exhaust ports from the cylinder head - these are the first pipes in the system, and hence primaries. These pair off into 2 pipes (the second set of pipes in the system, hence secondaries). I guess you could then refer the single exhaust pipe then to be the 'tertiary'.

>>3. Is there anything else that I should look out for (that's if I decide to go for it at the end of the year), to get it custom made? I already asked the quote for 4-2-1. But... anything else? <<

There are ideal lengths for primary and secondary pipes - but I do not have access to this information. The EBD and QED systems are known to be good, so knowing the lengths of these would be helpful for your fabricator.

And you WILL need a flexible union in the system to prevent fracturing of your nice new manifold. The question is where to put it without compromising your design.

>>as usual, the exact gain of power will depend on the state of tune of your engine
Rob does this mean that without engine tuning (ie. porting / cams / big valves etc.), the benefit won't be that great?<<

Exactly, there is a %age benefit to be had: so the more powerful the engine, the greater the gain (plus a higher flowing engine will need better exhaust gas extraction, so the benefits of a better manifold stand to reason).

>>Torque benefit sounds great though... so installing your TT exhaust will improve torque as well? (I was pretty much expecting only nice sound from back of the car!)<<

The TT was the joint best system (with the MSD) for torque gain: 5 lb.ft of torque, nice and low down in the rev range :o)
Rob Bell

Rob, as usual my kudos for your knowledge and prompt help/response. :-D

Maybe for untouched engines like mine, should consider some other works to improve the engine rather than spending heaps of money on manifold..? ie. porting?

But then I do not want to touch the internals of the engine as of yet. Want to keep it as stock on that. Just want to do 'clip ons' really...

I am still daydreaming, but having more torque would be more beneficial (IMO) than having more power output for cars like F which lacks 'torque' (especially VVC)

It was just an interesting part that I had to go across... all the Max Power (no there is no Max Power magazine here, but read a few mags) type of cars seem to have awesome extractors.. ;-) No, didn't mean that I want to join their brigade.. no way!

More torque with TT! I can't wait..

Did I tell you I returned my Superchip? I didn't want to risk my engine... I felt more torque, but didn't think it was worth the money at the end.

Anyway thanks Rob!! Will let you know when the exhaust arrives!

Hanah Kim

Head portiing versus manifolds - tricky. One problem area here is the lack of a decent replacement chip for the VVC MEMS. Too much head porting, and your engine will readily exceed the MEMS mapping, and it'll run like a dog.

The changes in the manifolds will not be too excessive for the MEMS to cope with, and will cost less to have made and to fit. (MUCH easier to fit a new exhaust manifold than to take the cylinder head off, with all that entails regarding cam timing, gasket replacement and bleeding the cooling system.)

I know that the manifold route can be made to work very well with the standard MEMS, as I had the great fortune to drive the Janspeed fettled ZR160 (a VVC engine, as you know). With a new induction system (the latest ITG Maxogen) and a 4-2-1 manifold, sports cat and exhaust, power was up 20 bhp and torque a useful 10 Nm over standard.

Obviously not an F - but I can't see any reasobn why these improvements could not be translated to our cars. :o)
Rob Bell

Thanks Rob.

Update on exhaust: I emailed Parcel Force to track it down for me. Just left UK today. *arse to them!* :-(
Looks like an after exam job.


On to manifold again...

I found this info on Dave Andrew's site.

Rolling road tests have shown that the best configuration for the 1.6/1.8K series is a 4-2-1 manifold with 30-32 inch primaries of 1.5inch diamter and 10-12 inch secondaries of 1.75 inch diameter culminating in a 2.25 inch system, this setup brings large gains in the low and mid range torque without affecting top end power. Long 4-1 manifolds can give a small improvement at the top end at the expense of torque lower down. One Caterham owner who changed from the short 4-1 standard Caterham manifold to a long 4-2-1 custom made manifold saw an increase of 30ft/lb at one point in the rev range and an increase of 20BHP on the peak power figure, this was on an engine with modifed VVC head, DTH bodies, 835 cams and M3D engine management, the improvement made was solely down to the manifold.

Rather interesting.... I now have enough information to get my custom one.... maybe for my next Christmas present! :-D




Hanah Kim

Sorry to hear about the delayed departure of the exhaust Hanah - but at least it should be with you soon.

I think I'd seen DVA's comments on manifolds before, but thanks for posting the details :o) Very useful for anyone wanting to make their own system :o)
Rob Bell

Thanks to your description, I know what the hell they are talking about! :-D (all those primaries, etc.. etc..) A real help!

And please email me with your account details / address.... I was waiting for it, but it never came..?
Hanah Kim

Yimmy was concerned about putting that info in an e-mail (security).

Can you e-mail us you phone number, and we'll give you the details that way :o)
Rob Bell

Hi Rob,

congrats on the new house! I´m the same boat. About to get married (October) and finding a nice appartment a couple of weeks from marriage is giving me some serious headaches at the moment.

About the exhaust manifold. I noticed B&G do a nice 4-2 manifold. Any experience?

BTW, still no answer on the power gain from the double flexi from the Racing syndicate. Guess we´ll have to buy one to find out.

cheers,
David.
DAvid @ work

Hi David,

thanks - and congratulations to you too! :o) All the best for October!

I wasn't aware that B&G were retailing a 4-2-1 manifold - I'll check that out. Chances are though that it won't have the flexipipe section... we'll see.

Shame that Racing Syndicate haven't got back: indeed it does look as though we'll have to test one for ourselves... :o/
Rob Bell

Rob,

I read it in their new catalogue -swapped it with with Eric, he now has my racin syndicate design booklet- which next to plenty of MS stuff (a shame) includes engine and brake tuning stuff too. I didn´t see the flexi though, just the exhaust manifold 4-2, in nice polish stanless steel. Can´t remember a price. If you´d search their online shop you should find a price, but not a picture!
Hmmm...the R-S-D flexi might be my next mod.

cheers,
David.

Hanah, I didn´t forget you, I´m just realy busy at the moment.

David

Emailed you Rob!

And David yes.. thank you! :-)
Hanah Kim

This thread was discussed between 09/09/2002 and 12/09/2002

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