# Top mount twins - why?



## truupR (May 30, 2016)

Recently stumbled across a thread on here showing off pictures of top mounted twins .

Having recently upgraded my turbos to a pair of -5's, the power is sort of where I want it. I've got a slight overhead to push the boost up once the motor is built. But with a smidgeon over 500 at the wheels the car is in that sweet spot of being fast without being TOO much.

One thing that saddens me though, is every time I open the bonnet I can't even see those fresh turbos - which is what I absolutely love about RB's running top mount singles. It's such a focal point when you see the bonnet open with a huge top mounted turbo. After having a scoot through that top mount twin turbo bling thread it got me wondering as to why people opt for top mount twins over a top mount single? 

I know absolutely nothing about top mount twins so I'm hoping someone can enlighten me. I'm assuming you're able to fit much bigger turbos on a top mount, thus being able to run some serious power? Can you top mount any twin turbo setup? Even though my -5's are minuscule, it'd be cool to have the feature of being able to see them. I'd love to swap to a single setup some day but I'm not wanting that much more power from the car, so it seems like a bit of a waste spending a few grand to run the same power.

So my questions are, can any turbos be top mounted? whats the benefit? whats involved? Is it just a case of buying a top mount twin turbo manifold?

I'm taking a wild guess here and saying it'd probably cost more to top mount my existing setup than it would to just swap to a top mount single :chuckle:


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## 120506 (Jun 23, 2015)

I think twin top mounts are a bit......90s? 

Id gun for a small-ish single twin scroll top mounted....maybe one day.


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## lightspeed (Jul 11, 2002)

Its all about space. Low mounts put the weight down low. Where you want it for the twisties.

Top mount twins were popular back in the days when big singles were thin on the ground. Talking wangan, drag and bragging rights in nineties japan.

These days plenty of singles with high hp capacity so twin top mounts not so popular given the complexities of plumbing them.


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## truupR (May 30, 2016)

[redacted] said:


> I think twin top mounts are a bit......90s?
> 
> Id gun for a small-ish single twin scroll top mounted....maybe one day.


A single setup is sort of my 'end goal' with the car. Probably something small and responsive. Not after massive power, just something that's going to be snappy and not a total lag monster. Twin top-mount is something I've never really seen mentioned with singles being all the rage so I thought I'd get some info from the people that know.



lightspeed said:


> Its all about space. Low mounts put the weight down low. Where you want it for the twisties.
> 
> Top mount twins were popular back in the days when big singles were thin on the ground. Talking wangan, drag and bragging rights in nineties japan.
> 
> These days plenty of singles with high hp capacity so twin top mounts not so popular given the complexities of plumbing them.


The last bit is what I was curious about. If it's difficult to plumb in a top mount twin setup, that'd translate to a big cost - to which it'd make much more sense to go for a simpler single top mount. If it was a fairly straight forward state of affairs then I'd consider it. As you've both mentioned it's a very outdated setup and probably not worth the cost involved.


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## lightspeed (Jul 11, 2002)

But a pair of twin 3037s still looks the dogs.....


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## truupR (May 30, 2016)

lightspeed said:


> But a pair of twin 3037s still looks the dogs.....


EXACTLY! its like a top mount single.... but twice as good :chuckle:


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## CT17 (Mar 25, 2011)

I have a pair of top mount twins.
Yes I am very happy with the performance, it drives amazingly.
Went this route as wanted modern turbos like EFRs you can't fit down the side to replace my -5s, for some reason I wanted to stick with twins.

No I wouldn't do it again.

Compared to top mount single...
More expensive.
More complicated.
More weight.

Less lag?
Not convinced.
My big single (also RB28) is almost as good.


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## truupR (May 30, 2016)

CT17 said:


> I have a pair of top mount twins.
> Yes I am very happy with the performance, it drives amazingly.
> Went this route as wanted modern turbos like EFRs you can't fit down the side to replace my -5s, for some reason I wanted to stick with twins.
> 
> ...


Interesting that it costs so much. Any pics of the engine bay CT? bet it looks the business


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## CT17 (Mar 25, 2011)

truupR said:


> Interesting that it costs so much. Any pics of the engine bay CT? bet it looks the business


Well two decent sized turbos, all the pipework, messing around getting all to fit etc...

Not very bling as rest of engine was kept stock looking up to this point, despite making 680bhp.
I don't pull up at shows and open the bonnet.


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## paul450 (Jul 4, 2006)

top mount twins do look good,here is mine


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## Silverhks (Feb 15, 2017)

In my mind, the only reason to do to high mounted twins is if there isn't enough room down low. I know this is true for the EFRs because they are longer than the equivalent Garrett.
Full Race says that on big HP (1000+) build the twins are more responsive but I have yet to see much discussion of the 5-800 range. In fact the only person I've seen that talks about having driven both is CT17.


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## matty32 (Dec 18, 2005)

Old school i know but they always make me smile when lifting the bonnet


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## K66 SKY (Jan 25, 2005)

CT17 said:


> *
> Less lag?
> Not convinced.
> My big single (also RB28) is almost as good.*


When you say the big single set up is almost as good Richard, What or where do you find this set up to be lacking when compared to the twins?


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## goghat (May 13, 2007)

matty32 said:


> Old school i know but they always make me smile when lifting the bonnet


That looks superb


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## matty32 (Dec 18, 2005)

Thanks


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## CT17 (Mar 25, 2011)

K66 SKY said:


> When you say the big single set up is almost as good Richard, What or where do you find this set up to be lacking when compared to the twins?


My big single that makes 800bhp picks up and goes from 3,200rpm.
My twin top mount set up makes 680bhp but goes from 3,000rpm.

It's always going to be tricky to get direct comparisons, but there appears to be a slight difference in response.

My top mount twin turbo engine set up was not designed to cut corneres, it was all about minimal lag.
The big single was bought but again has a huge similar spec.
Both are RB28.

This is why I would not go top mount twins again.
I do not feel the extra cost, packaging issues and weight is worth it.
I would go big single. The pipe work is not too good on the twins.
It's too tightly packed and uses tight bends in the tubes. 

Just for info my tweaked -5 turbos before made similar power but were a bit more laggy and also more abrupt when power came in. Where the twin EFRs are smoother and more drivable.
The big single is equally smooth.


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## Lith (Oct 5, 2006)

CT17 said:


> My big single that makes 800bhp picks up and goes from 3,200rpm.
> My twin top mount set up makes 680bhp but goes from 3,000rpm.
> 
> It's always going to be tricky to get direct comparisons, but there appears to be a slight difference in response.
> ...


Very interesting input, thanks! 

It would be quite a bit more helpful with more info just to put things into perspective - what kind of differences in spec are there between the two setups? Like what cams/porting, are they both 2.8? And what is the single turbo, is it twin scroll? And what EFRs are they?

Sorry for all the questions, but right now it's really hard to tell how comparable the setups and how much to read into it - the twin EFRs are sold hard by Full-Race as being the "only way" but I've yet to see any evidence to suggest that it'd have any advantage over a well matched single for similar performance. The new Garrett G25 turbos could be very interesting as a high mount twins solution, however.


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## ShopGTR (Oct 4, 2007)

That's good info on your comparisons.

We did a Full Race twin EFR kit and must say that's a lot of stuff stuffed in there. The intake on the lower turbo is a tight squeeze on a 32 due to the power steering pump. 

Twins are great but it can be done for less money with the newer singles these days. 

That being said I still love my twins.


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## CT17 (Mar 25, 2011)

Lith said:


> Very interesting input, thanks!
> 
> It would be quite a bit more helpful with more info just to put things into perspective - what kind of differences in spec are there between the two setups? Like what cams/porting, are they both 2.8? And what is the single turbo, is it twin scroll? And what EFRs are they?
> 
> Sorry for all the questions, but right now it's really hard to tell how comparable the setups and how much to read into it - the twin EFRs are sold hard by Full-Race as being the "only way" but I've yet to see any evidence to suggest that it'd have any advantage over a well matched single for similar performance. The new Garrett G25 turbos could be very interesting as a high mount twins solution, however.


To be honest, that's not easy to list all kinds of stuff on both set ups or likely.
Both engine builds in my R32 (top mount twins) and R34 (Big single) are no expense spared £25k+ builds.
Both are RB28 (2.8) with porting etc... and both designed for minimal lag with good power and lots of low down torque and a wide power band.

They are not exactly identical but the single makes 100bhp more and spools 200rpm later. I can only have a feeling how they compare, and that is that at turbos designed to make the same power there would be little difference.
Only the single is easier, cheaper and lighter in use.
Which is why that would be my choice if doing this again.

Full Race are selling a twin top mount kit unique to them (AFAIK) so of course it's the best thing ever, it's their own product you can't buy anywhere else.
Bound to be the "only way" from their perspective.

I can't fault the kit, it is very good. But space is tight.
The lower turbo piping requires a different power steering pump and the top turbo piping requires a sharp 90 degree bend 2mm away from the NS strut top. As stated, it's noticeably smoother than my previous twin set up making the same power.


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## K66 SKY (Jan 25, 2005)

CT17 said:


> *I can't fault the kit, it is very good. But space is tight.
> The lower turbo piping requires a different power steering pump and the top turbo piping requires a sharp 90 degree bend 2mm away from the NS strut top. As stated, it's noticeably smoother than my previous twin set up making the same power.*


Sorry for all the questions Richard but you are the only one I know of with both. Out of curiosity, Would the R34 have had the same tight fitment issues with the twins set up?


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## CT17 (Mar 25, 2011)

K66 SKY said:


> Sorry for all the questions Richard but you are the only one I know of with both. Out of curiosity, Would the R34 have had the same tight fitment issues with the twins set up?


No problem.

There is more space under the bonnet with an R34.

You are still going to be fairly close to the turret top though, so you do have to use the tight 90 degree bend for the top turbo. As per the pic above.


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