45 or 50mm exhaust

Bitza · 15-12-2019, 02:18 PM

Hi all, has anyone out there experience of tuned 1078 2v exhausts? While I understand that using a standard M1000s 40mm exhaust will be over-restrictive, so going to 45mm dia (+25%) is a no brainer, but its been suggested to me that 50mm (+50%) would be better for max power. As my bike is primarily a road bike I was wondering if 45 might be better for mid-range, even if there was a loss around max revs/power. All thoughts welcome Bitza.

stopintime · 15-12-2019, 02:44 PM

My highly tuned 839cc at 99bhp exhales well enough through 45mm....

Nickj · 15-12-2019, 03:55 PM

Quote:

Originally Posted by stopintime

My highly tuned 839cc at 99bhp exhales well enough through 45mm....

More detail

stopintime · 15-12-2019, 07:11 PM

Quote:

Originally Posted by Nickj

More detail

Open air box, high flow filter, port & polish, 900ie cams, larger 44 inlet / stock 38 exhaust valves, pistal HC (11:1) pistons, Carrillo rods, lightened and balanced crank, flywheel, Termignoni, dyno work.

Very close to a pure race tune. Probably missing larger exhaust valves and tiny bit of added compression to exceed 100 bhp. Would be useless as a street bike.....

Bitza · 16-12-2019, 02:22 PM

The book is called "Four-stroke performance tuning" IBSN 97818442531142 printed by Haynes I believe, but I simply used an on-line calculator using a formula from the book. Due to the endless variables referred to above, I can only take the results as a guide to what the actual situation in my case is likely to be. I find that you can often make pretty sound decisions if you understand the general "tendencies" of a particular situation and have some concept of what magnitude of change will make a "significant" difference. Even where you don't actually know all the science/engineering of the subject.

Having spouted all this I just wish that I had realised how restricting the standard 40mm headers were when I had the 944cc engine in the bike, I might have even saved myself the heartache of replacing it with a 1078 lump?! Bitza.

Mossleymonster · 17-12-2019, 09:41 PM

Quote:

Originally Posted by stopintime

Open air box, high flow filter, port & polish, 900ie cams, larger 44 inlet / stock 38 exhaust valves, pistal HC (11:1) pistons, Carrillo rods, lightened and balanced crank, flywheel, Termignoni, dyno work.

Very close to a pure race tune. Probably missing larger exhaust valves and tiny bit of added compression to exceed 100 bhp. Would be useless as a street bike.....

Just out of interest, what is the balance factor? ie stock and your alterations.

stopintime · 18-12-2019, 07:14 AM

Quote:

Originally Posted by Mossleymonster

Just out of interest, what is the balance factor? ie stock and your alterations.

Balance factor?

Darren69 · 15-12-2019, 02:54 PM

Whilst I've no experience of your situation exactly, I would say that its probably best to over size your exhaust. It certainly wouldn't be a bad idea to make it 50mm instead of 45mm but as I understand 45mm is the way to go for the 2v 900 at least with a spaghetti header. I'm currentlu running a 916 testabassa S4 motor stock with 45 headers and mid section into hi level 50mm link pipes with probably about a 10% increase in mid and top end. I think stock is 40mm all through. So restricted. But with a 2v you can teally feel it (head flow restriction).

Bitza · 15-12-2019, 04:19 PM

Have just found an exhaust calculator on-line, based on the formula from A.Graham Bell's book. Having fed in the capacity and cam(Vee-Two 300) details, it tells me that a 45mm dia header would be optimum at around 6000rpm and therefore I guess becoming progressively more restrictive as revs rise. A 50mm dia is optimum at around 7750rpm. On which basis I conclude that the advice to use 50mm is sound.

Thanks for the feedback people have given, but don't let this post stop anyone from saying their piece. Bitza

350TSS · 15-12-2019, 05:26 PM

Can you share more details from the book, sounds(?) interesting, how does it calculate the degree of back pressure, open pipe vs a standard restricted exhaust?, megaphone vs an open pipe vs a reverse cone megaphone?

Kato · 17-12-2019, 09:16 PM

http://www.ukmonster.co.uk/monster/s...ghlight=stroke

Read the whole thread

Kato · 17-12-2019, 09:23 PM

50mm primaries on a 2 valve will kill mid range power & torque

Kato · 20-12-2019, 02:19 PM

Bitza hey mate yep definitely around although currently in Kampala with S**T internet access

The secret for you will be keeping the gas speed as hight as possible out of the heads.

All the power on a 2v is made in the head, it is a rubbish design made to work with the legendary valve train
Until you spend huge wads of cash on some very seriously modified heads don't go bigger than 45mm on the primary tubes in fact 43mm would be better but that will involve a custom made header get a decent 45mm system and have it ceramic coated, this will reduce heat loss by around 20% will keep gas speed up and you can pretty much do what you like with the end cans

Bitza · 22-12-2019, 04:43 PM

Thanks for everyone's help on this one its been really helpful. I'll post an update after its been on a dyno to set up the ecu. Bitza

jerry · 23-12-2019, 06:14 AM

Kato what u doing in Kampala ,, ??? engineering ??

15-12-2019, 02:18 PM	#1
Bitza Bronze Member Join Date: Jul 2006 Location: Poole Bike: M900ie Posts: 470	45 or 50mm exhaust Hi all, has anyone out there experience of tuned 1078 2v exhausts? While I understand that using a standard M1000s 40mm exhaust will be over-restrictive, so going to 45mm dia (+25%) is a no brainer, but its been suggested to me that 50mm (+50%) would be better for max power. As my bike is primarily a road bike I was wondering if 45 might be better for mid-range, even if there was a loss around max revs/power. All thoughts welcome Bitza. __________________ Bitza

16-12-2019, 02:22 PM	#5
Bitza Bronze Member Join Date: Jul 2006 Location: Poole Bike: M900ie Posts: 470	The book is called "Four-stroke performance tuning" IBSN 97818442531142 printed by Haynes I believe, but I simply used an on-line calculator using a formula from the book. Due to the endless variables referred to above, I can only take the results as a guide to what the actual situation in my case is likely to be. I find that you can often make pretty sound decisions if you understand the general "tendencies" of a particular situation and have some concept of what magnitude of change will make a "significant" difference. Even where you don't actually know all the science/engineering of the subject. Having spouted all this I just wish that I had realised how restricting the standard 40mm headers were when I had the 944cc engine in the bike, I might have even saved myself the heartache of replacing it with a 1078 lump?! Bitza. __________________ Bitza

15-12-2019, 02:54 PM	#8
Darren69 Transmaniacon MOC Join Date: Sep 2013 Location: Sutton In Ashfield Bike: Multiple Monsters Posts: 6,023	Whilst I've no experience of your situation exactly, I would say that its probably best to over size your exhaust. It certainly wouldn't be a bad idea to make it 50mm instead of 45mm but as I understand 45mm is the way to go for the 2v 900 at least with a spaghetti header. I'm currentlu running a 916 testabassa S4 motor stock with 45 headers and mid section into hi level 50mm link pipes with probably about a 10% increase in mid and top end. I think stock is 40mm all through. So restricted. But with a 2v you can teally feel it (head flow restriction). __________________ Roast Beef Monster! Termignoni and Bucci - Italian for pipe and slippers! S4 Fogarty, S4R 07T, 748, Series 1 Mirage

15-12-2019, 04:19 PM	#9
Bitza Bronze Member Join Date: Jul 2006 Location: Poole Bike: M900ie Posts: 470	Have just found an exhaust calculator on-line, based on the formula from A.Graham Bell's book. Having fed in the capacity and cam(Vee-Two 300) details, it tells me that a 45mm dia header would be optimum at around 6000rpm and therefore I guess becoming progressively more restrictive as revs rise. A 50mm dia is optimum at around 7750rpm. On which basis I conclude that the advice to use 50mm is sound. Thanks for the feedback people have given, but don't let this post stop anyone from saying their piece. Bitza __________________ Bitza

17-12-2019, 09:16 PM	#11
Kato Dismantled Join Date: Feb 2006 Location: East Molesey Bike: Multiple Monsters Posts: 2,223	http://www.ukmonster.co.uk/monster/s...ghlight=stroke Read the whole thread __________________ "Political correctness is just intellectual colonialism and psychological fascism for the creation of thought crime"

15-12-2019, 02:44 PM	#2
stopintime Registered User Join Date: Dec 2010 Location: Oslo Bike: S2r Posts: 426	My highly tuned 839cc at 99bhp exhales well enough through 45mm....

15-12-2019, 05:26 PM	#10
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,419	Can you share more details from the book, sounds(?) interesting, how does it calculate the degree of back pressure, open pipe vs a standard restricted exhaust?, megaphone vs an open pipe vs a reverse cone megaphone?

17-12-2019, 09:23 PM	#12
Kato Dismantled Join Date: Feb 2006 Location: East Molesey Bike: Multiple Monsters Posts: 2,223	50mm primaries on a 2 valve will kill mid range power & torque __________________ "Political correctness is just intellectual colonialism and psychological fascism for the creation of thought crime"

20-12-2019, 02:19 PM	#13
Kato Dismantled Join Date: Feb 2006 Location: East Molesey Bike: Multiple Monsters Posts: 2,223	Bitza hey mate yep definitely around although currently in Kampala with S**T internet access The secret for you will be keeping the gas speed as hight as possible out of the heads. All the power on a 2v is made in the head, it is a rubbish design made to work with the legendary valve train Until you spend huge wads of cash on some very seriously modified heads don't go bigger than 45mm on the primary tubes in fact 43mm would be better but that will involve a custom made header get a decent 45mm system and have it ceramic coated, this will reduce heat loss by around 20% will keep gas speed up and you can pretty much do what you like with the end cans __________________ "Political correctness is just intellectual colonialism and psychological fascism for the creation of thought crime"

22-12-2019, 04:43 PM	#14
Bitza Bronze Member Join Date: Jul 2006 Location: Poole Bike: M900ie Posts: 470	Thanks for everyone's help on this one its been really helpful. I'll post an update after its been on a dyno to set up the ecu. Bitza __________________ Bitza

23-12-2019, 06:14 AM	#15
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,822	Kato what u doing in Kampala ,, ??? engineering ?? __________________ MONSTERMAN