Twin turbo or single

[f1racr]

Hi all,

Just wanted to run this past those racers out there. We're in the process of finally upgrading our powertrain and we're pretty set on going with twin's, but I've had a few people push me towards single...………

I'm assuming that a lot of twin turbo setups are used because they're probably easier to package and still keep everything as Honda intended (ie not cutting up trunk or rear firewall) but we don't have those restrictions, so interested in peoples thoughts to stick with twins even if we don't have to. Maybe it's a bit old school thinking, but I think they should be more responsive, especially down low which some people don't think is important, but I do, and also I just like the idea of having twins since it's a V config engine...……...also for noise reasons....

Just wondering what people out there are running and why. Also interested in overall power and when it starts to make good power (3000rpm starting to spool, 3500rpm really getting up to speed, 4000rpm pulling hard etc), I know some of you will want to be all secret squirrel, but any info you're willing to share will help

Also, I assume most are running liquid to air coolers ?

 

[Mac Attack]

It's not my dedicated racecar, but if it were, I would run a single just because of reliability, simplicity, and cost. Sure, twins may improve responsiveness, but is that really worth it when you'll spend most of the time above 4-5k RPM anyways?

If you're using a transverse J-series, I would imagine the layout by Operator and Autowave would adapt well (turbo above and to the rear of the transmission basically). Gravity drain would help keep it simple on the track.

My $0.02! I think [MENTION=4034]Coz[/MENTION] tracks a single turbo J-series and can probably offer more. I think LoveFab was building a twin turbo J-series but I don't remember the finished product being shown on Prime. I don't follow other social media so maybe someone else can help you there.

 

[mwagner10702]

Talk to SoS if you are considering a turbo setup. They have probably the best engineered twin turbo solution available.

 

[B-E-A-S-T]

Best Turbo Kit on the market for the NSX...prior forum posts have debated this, see link below...

http://as-motorsport.com/site/en/catalog-c-6/nsx-c-1/engine-c-18/asm-turbo-kit-p-497


Sent from my iPhone using Tapatalk

 

[f1racr]

Thanks for all the replies guys. We won't buy a kit, we're going to make our own, but just wondered what experiences people have. That ASM setup looks pretty sweet for a single. I've seen the [MENTION=4034]Coz[/MENTION] setup and have chatted with him on FB as well so that's under consideration.

Mac attack, the reason I think responsiveness is worth chasing is that when you're having to feather the throttle or having to come on and off boost it makes for a much more controlled car is the response is good. You'll hear the same thing all the time with other racing when they talk about driveability ……. I know the turbo setup isn't the be all and end all of drivability, but it does play a big factor so I prefer to have as much as I can get. I'm the same with brakes too...…… I struggle to drive a car fast when I don't have good brake feel. I'm not even sure if there really is any truth behind the twin vs single argument when it comes to response...…….might just be a big old wives tale from the old days when turbo tech wasn't as good, or it might be real and there is a benefit...…….. bloody cars...…..so complicated !

Again, thanks for the replies guys, all helpful for us to make what we think is the best call.

 

[sca037]

While I do enjoy the sudden whollup of a big single turbo spooling up on the street, I think the smoother (more linear) power curve of twins would be the better application for a track/race car.

And yes, a water intercooler is the preferred solution if you can make the packaging work.

 

[docjohn]

but as Mac stated if you are an advanced fast driver the motor will be above vtec for most of the session... every TA car I have seen is a single

 

[sca037]

but as Mac stated if you are an advanced fast driver the motor will be above vtec for most of the session... every TA car I have seen is a single

Fair point Doc, if you can stay within the 6-8K realm on track....that negates any need for the lower rpm torque a twin setup could provide.

 

[docjohn]

the sos twin setup is fantastic for the street.

 

[Mac Attack]

Well, either a single or twins will be a lot of fun.

I will say, however, that the SOS twin setup is far from being a superior F/I system. In order to package the turbines as close as possible to the exhaust valves (a good thing to do), they significantly increased the compressed volume piping going to the inlet (a bad thing). There's only so much space to work with, and you either gain on one side and lose in the other side.

Look at the overall layout and the sheer piping volume, bends, etc on just the induction side:

The problem I have with the SOS twin setup is the compromise they made on the front bank exhaust manifold to make this packaging work:

That has got to be the worst collector design I have ever seen, and I'm sure it is impeding adjacent cylinder exhaust evacuation. It would be interesting to data log the cylinder pressures and see the data.

Anyways, a proper collector for a twin turbo setup would be like Lovefab's J-series kit here:

Looks a lot better, doesn't it?

In my humble opinion, the one from Operator and sold by ASM is superior. This is the complete intake and exhaust system:

 

[Old Guy]

Interesting thoughts on the exhaust manifolds for turbo engines.

The turbine application engineers seem to be all about 'save the heat', don't sweat the flow. If you look at the Honda HPD's HR28TT and HR38TT twin turbo racing engines, they certainly didn't give any outward appearance of sweating the equal length runner thing. In fact the exhaust 'manifold' appears to be pretty much part of the cylinder head casting. I expect that the head castings has the ports for the outside cylinders angled in to the center; but, not by much. I expect that there still must be some pretty sharp angles in the exhaust paths for those outside clinders. I am also thinking the individual 'runners' on the HR series engine are pretty unequal. I grant that doing an integrated manifold design like that is not an option for an aftermarket vendor.

The HRxxTT turbo layout may have had been dictated by chassis packaging requirements limiting space for the exhaust system; however, if that was the case and they thought an exotic exhaust manifold was important, they could have relocated the turbos to make space for a more conventional manifold. I am thinking that in the case of the HRxxTT, exhaust system minimization with an objective to reducing heat loss was the overall objective. The designers appear to be of the opinion that there is more up side on improving the performance of the turbo than there is in improving the cylinder exhaust scavenging.

The AS exhaust manifolds always struck me as being sub optimally long; however, trying to jam a turbo into a package that was never designed to accommodate a turbo does present challenges.

 

[Mac Attack]

Interesting thoughts on the exhaust manifolds for turbo engines.

The turbine application engineers seem to be all about 'save the heat', don't sweat the flow. If you look at the Honda HPD's HR28TT and HR38TT twin turbo racing engines, they certainly didn't give any outward appearance of sweating the equal length runner thing. In fact the exhaust 'manifold' appears to be pretty much part of the cylinder head casting. I expect that the head castings has the ports for the outside cylinders angled in to the center; but, not by much. I expect that there still must be some pretty sharp angles in the exhaust paths for those outside clinders. I am also thinking the individual 'runners' on the HR series engine are pretty unequal. I grant that doing an integrated manifold design like that is not an option for an aftermarket vendor.

The HRxxTT turbo layout may have had been dictated by chassis packaging requirements limiting space for the exhaust system; however, if that was the case and they thought an exotic exhaust manifold was important, they could have relocated the turbos to make space for a more conventional manifold. I am thinking that in the case of the HRxxTT, exhaust system minimization with an objective to reducing heat loss was the overall objective. The designers appear to be of the opinion that there is more up side on improving the performance of the turbo than there is in improving the cylinder exhaust scavenging.

The AS exhaust manifolds always struck me as being sub optimally long; however, trying to jam a turbo into a package that was never designed to accommodate a turbo does present challenges.

The HRxxTT layout was the time of the J37 production engine IIRC (I'm not really a Honda fanboy and don't know all this stuff off the top of my head). The J37 head used that integrated exhaust manifold layout. Not knowing how it looks inside, and pretty confident that Honda knows what they're doing, I'd say that manifold design is pretty slick as far as balancing packaging, cost, flow, and scavenging. That is, even accounting for packaging and cost for a mass-production vehicle, it most definitely flows and scavenges much much better than the SOS manifold.

I don't have any data to substantiate the claims, so I can only go with how crappy the SOS manifold looks, and my suspicion that Honda knows how to make their engines volumetrically efficient.

Cast isn't a bad way to go, especially with turbo manifolds. They can be cast to flow well, take the thermal stresses, and be strong to support turbo weight. You see a lot of pictures on the internet that have new beautifully-welded turbo headers, but you don't see them later after they've been fixed from all the cracks. There are tremendous stresses placed on these things from heat, weight, and vibration.

Therefore, I have a suspicion that Honda's HRxxTT applications took the best balance of design and what they had available to them. The manifolds they used were strong and probably flowed very well. They even had production pieces they could modify. Here's a pic of a more recent HPD turbo engine with long tubular headers:

I think the trend inverting the intake and exhaust valves does result in power, driveability, and efficiency gains, but I haven't ever seen that quantified anywhere. Some of that is certainly about heat loss, but you also have to minimize heat loss because of thermal stress gradients, as well as not overheating nearby components. Based on that, you shouldn't necessarily conclude the trend today is about saving the heat and not sweating the flow. There are many variables to consider and balance.

That's why it's taken me many years to optimize my twin turbo setup. That's with degrees in thermo and heat transfer, compressible fluid flow, data analysis (inlet and exhaust tubing pressure transducers, local temps, and cylinder combustion pressures through my TFX engine analyzer), etc. Still working on it, but that's something I enjoy doing in my free time. I'm at the point where I'm happy overall, but now I have to keep an eye on engine bay temps as I button up the rear and focus on aero.

 

[Mac Attack]

Oh - I personally use a modified '97+ Honda exhaust manifold for my setup. It was cheap, strong, and has a nice heat shield. So, I compromised a little bit myself in the flow area, but I haven't seen any significant combustion pressure differences between cylinders.