# 90mm vs 102mm - Power/Performance?



## ISR36 (May 6, 2015)

Hi,

I've had a good search, and it seems most threads are in regards to noise.. however:

I'm interested to know what the performance difference is between the two? I'm looking at no more than stage 4.25 (so around 670hp based on the figures Litchfield are reporting now!), so interested to know how much difference a 90 vs 102mm would make, and whether at this power level, I'd see any improvement with the 102mm.

Thanks!


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## twobadmice (Jul 2, 2013)

I have a 102 which flows very nicely. I think it depends on the level of tune you have. If you have higher tune you need to pass more gases therefore a larger bore.
The 102 sounds throatier and if you upgrade from 4.25 you will not have to change your exhaust.
This is just my humble opinion Im sure someone will happily share the science on this.


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## Donga (Mar 3, 2013)

Would have thought a 90mm would be louder but depends on downpipes/exhaust. I'd go for 90mm if you know you are definitely not be going any higher than 700bhp, if you may have more in the future, save yourself some money and get a 102mm.


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## Mrw (Aug 22, 2012)

People have made 1000 bhp on a 90mm system, I run 900 with no problem as well .


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## Donga (Mar 3, 2013)

Mrw said:


> People have made 1000 bhp on a 90mm system, I run 900 with no problem as well .


Ah ok! In essence, a 90mm is plentey! Just more noise :chuckle:


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## gtrmackem (Apr 12, 2014)

ISR36 said:


> Hi,
> 
> I've had a good search, and it seems most threads are in regards to noise.. however:
> 
> ...


I had the Litchfield 4:25 with standard 76mm Milltek exhaust. Wasn't planning on any more power. Car made 662 bhp 602 Ibf.ft on their Dyno. Bloody loud though :chuckle:


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## Donga (Mar 3, 2013)

gtrmackem said:


> I had the Litchfield 4:25 with standard 76mm Milltek exhaust. Wasn't planning on any more power. Car made 662 bhp 602 Ibf.ft on their Dyno. Bloody loud though :chuckle:


Its a good alarm for the neighbours early morning


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## gtrmackem (Apr 12, 2014)

Donga said:


> Its a good alarm for the neighbours early morning


Yeah, revs to just over 2000 rpm as well from cold.. Funny think is both neighbours are moving... :chuckle:


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## Donga (Mar 3, 2013)

gtrmackem said:


> Yeah, revs to just over 2000 rpm as well from cold.. Funny think is both neighbours are moving... :chuckle:


Seems like a rather easy way to get rid of my neighbours too... :chuckle: decat


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## ISR36 (May 6, 2015)

gtrmackem said:


> I had the Litchfield 4:25 with standard 76mm Milltek exhaust. Wasn't planning on any more power. Car made 662 bhp 602 Ibf.ft on their Dyno. Bloody loud though :chuckle:


My old GTR had the same as yourself, although my 76mm was a Milltek Race Plus - I can't even begin to describe how loud this thing was, but it was fun (in an immature way!).

I'm looking for noise again, but maybe not quite as much as the 76mm Race Plus..


So, from the sounds of it, having a 76, 90 or 102mm won't make a blind bit of difference to the power I'm looking at!

Never say never and all that, but I really can't see myself going above 662hp (for example), especially considering this car won't be used all that much for tracks.


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## gtrmackem (Apr 12, 2014)

ISR36 said:


> My old GTR had the same as yourself, although my 76mm was a Milltek Race Plus - I can't even begin to describe how loud this thing was, but it was fun (in an immature way!).
> 
> I'm looking for noise again, but maybe not quite as much as the 76mm Race Pro
> 
> ...


Yeah I'm the same really, wasn't looking at tracking it much. Maybe the Nurburgring one day, as for power gains, if your stopping at stage 4:25 then don't think it makes any difference with what size exhaust you use. I'm running a non-resonated y-pipe as well, so that doesn't really help with the decibels..:GrowUp: but I do love the sound it makes...:chuckle:


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## Donga (Mar 3, 2013)

ISR36 said:


> My old GTR had the same as yourself, although my 76mm was a Milltek Race Plus - I can't even begin to describe how loud this thing was, but it was fun (in an immature way!).
> 
> I'm looking for noise again, but maybe not quite as much as the 76mm Race Plus..
> 
> ...




Go for 76mm Milltek Race Plus again . Do it properly or dont do it at all :chuckle:


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## Tariq (Mar 24, 2008)

Donga said:


> Its a good alarm for the neighbors early morning



Not if you need to pop out around 3am in the winter with a frosted up wind screen.

i get it of my drive as soon as its fired up.


T


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## scoooby slayer (Jun 13, 2009)

The larger exhaust will make abit more power, I'm sure JP picked up 7 hp and a chunk more torque at stage 4 with 102mm


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## boyknacker (Apr 7, 2014)

I went from 90mm Miltek to 102mm SVM. Much more torque better sound as the 90 mm was too quiet for a car like this


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## borat52 (Jan 29, 2006)

I made 750bhp at stage 4.5 on the Litchfield with a 76mm GTC stainless exhaust and Forge intercooler (original style). I'm far from convinced on big claims for bhp increases for either exhaust diameter or intercooler type. Intercooler for sure can help with lowering temps for sustained high output conditions but for a power run, negligable.


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## ISR36 (May 6, 2015)

Hmm, I'm still in a predicament of what to do. 

Logically, there must be an improvement of the 90/102mm over the 76mm, of increased flow etc. 

I've spoken with Iain, who understandably rates his own 102mm over competitors, and having seen the quality of work at Litchfield, I'm not in any position to question him - howver, would anyone be able to advise how much difference there is between them? If you've been fortunate enough to have seen/tried both.


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## DonnyMac (Jun 21, 2012)

Donga said:


> Go for 76mm Milltek Race Plus again . Do it properly or dont do it at all :chuckle:


I have this on mine - whahahaha - It is embarrassingly loud, my neighbours think the car is broken :chuckle:


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## ACspeedtech (Aug 25, 2011)

A well designed 90mm will flow 800-850 before becoming an issue at all.


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## Callum66 (Apr 5, 2014)

Is there a difference in the quality of fit on a 90mm system over a 102? I don't mean in build quality but how it fits in comparison with the OE system. I like the idea of a 102 for flow but will never go beyond a 4.25 tune and would prefer not to have a system which is prone to hitting bumps on the road.


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## boyknacker (Apr 7, 2014)

When I got my GTR I thought the lowest part of the car was the sill to ground clearance. How wrong I was when I reversed down my 1 in 14 drive the first time. Guess what got caught, it was the 4 bolt flange at the back of the intermediate pipe on my 90MM Milltek.
When I changed to the 102mm SVM the problem went away.


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## Donga (Mar 3, 2013)

boyknacker said:


> When I got my GTR I thought the lowest part of the car was the sill to ground clearance. How wrong I was when I reversed down my 1 in 14 drive the first time. Guess what got caught, it was the 4 bolt flange at the back of the intermediate pipe on my 90MM Milltek.
> When I changed to the 102mm SVM the problem went away.


I think it depends more on what exhaust option you go for rather than the size.


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## DocT (Dec 17, 2014)

boyknacker said:


> When I got my GTR I thought the lowest part of the car was the sill to ground clearance. How wrong I was when I reversed down my 1 in 14 drive the first time. Guess what got caught, it was the 4 bolt flange at the back of the intermediate pipe on my 90MM Milltek.
> When I changed to the 102mm SVM the problem went away.


I've had my DBA GTR with 90mm Milltek for about 4 weeks now and it's pretty disconcerting how low the mid pipe is. It seems to scrape against the mildest of sleeping policemen. 

I though the 102mm would have worse clearance than the 90mm but apparently not?


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## Donga (Mar 3, 2013)

DocT said:


> I've had my DBA GTR with 90mm Milltek for about 4 weeks now and it's pretty disconcerting how low the mid pipe is. It seems to scrape against the mildest of sleeping policemen.
> 
> I though the 102mm would have worse clearance than the 90mm but apparently not?


As I said I think it depends on which exhaust (and Y-Pipe) you have as they all differ in shape and size (to a degree!)


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## borat52 (Jan 29, 2006)

ISR36 said:


> Hmm, I'm still in a predicament of what to do.
> 
> Logically, there must be an improvement of the 90/102mm over the 76mm, of increased flow etc.
> 
> I've spoken with Iain, who understandably rates his own 102mm over competitors, and having seen the quality of work at Litchfield, I'm not in any position to question him - howver, would anyone be able to advise how much difference there is between them? If you've been fortunate enough to have seen/tried both.


If you have bags of money, get a new 102mm and accept you've probably paid £2500 for at most 10bhp.

I bought my stainless exhaust for £300 and make 750bhp on a stage 4.5 car. Mine is a chinese copy of a GTC exhaust. The £2000 I saved on the exhaust paid for 1/3 of the cost of going from stage 4-4.5 which added 150bhp to the car. So £2000 got me 50bhp, whereas it would have maybe got me 10bhp if I went 102mm (and possibly zero).


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## Stealth69 (Jan 6, 2005)

If you are doing it for performance alone then you don't need to change anything passed the Y-Pipe, just down pipes and y-pipe! The standard centre and back box will flow 700+bhp easily


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## mindlessoath (Nov 30, 2007)

something I think has not been mentioned is that not all 4" are created equal. and what I mean by that is there are only a few that are true 4" all the way. some will reduce diameter near the end, sacrificing power. 

also here are some quotes from Felix at Kline...



> A very big size and difference in cross sections will primarily slow down exhaust gases. Depending on how much it affects the gas velocity it will produce turbulence and turbo lag. This translated in sound waves means the bass frequency will be accentuated therefore cabin resonance/ drone can occur in low revs.
> 
> What we always want to achieve is perfect gas velocity and keep it all the way out!





> When we designed our 3.5 inch system in Inconel we had in mind a setup and daily use similar to yours. The part is a bit overkill for a stock car. Also if installed with chatted downpipes it can cause some resonance due to low gas velocity after them.
> 
> I know it's hard to imagine a downsized system, but how crazy would it sound if I propose you this setup :
> 
> ...


via What's so great about my Amuse exhaust (or titanium exhausts)??? - R35 GT-R - Nissan GT-R Heritage


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## ISR36 (May 6, 2015)

Great responses - I think I'm just eager for the 102mm as it seems to be the new "in" thing.

If someone could confirm the quality of the SVM 102mm, and whether its rear tips are straight, or slightly angled like the Milltek is (or used to be), that'd be a decider too.

I do hear alot about how some aren't a true 102mm all the way through, is this the case for SVM or not?

Thanks,


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## Stealth69 (Jan 6, 2005)

Have a word with Andy at ACSpeedtech, as there are options available to you.....


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## Donga (Mar 3, 2013)

ISR36 said:


> Great responses - I think I'm just eager for the 102mm as it seems to be the new "in" thing.
> 
> If someone could confirm the quality of the SVM 102mm, and whether its rear tips are straight, or slightly angled like the Milltek is (or used to be), that'd be a decider too.
> 
> ...


Probably best to ring SVM and check on that, there is also the GTC 102mm (GTC is Ti, they dont do SS where as the other two are SS only I believe) and Litchfield 102mm, both being very well built.

If you want to go for 90mm. Go for Russ Fellows Exhaust :thumbsup:


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## paulmc (Oct 31, 2004)

Whifbitz do a 102mm, very good value


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## mindlessoath (Nov 30, 2007)

ISR36 said:


> Great responses - I think I'm just eager for the 102mm as it seems to be the new "in" thing.
> 
> If someone could confirm the quality of the SVM 102mm, and whether its rear tips are straight, or slightly angled like the Milltek is (or used to be), that'd be a decider too.
> 
> ...


the svm is not a true 102mm all the way. so your essentially paying a little more for basically a 3.5" with 4" piping. if you like the sound that's good.

I hear ets and boost logic have true 4"

4" Titanium Exhaust - Power and Drivetrain - Nissan GT-R Heritage


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