Turbo selection for 2.1L roadrace engine - Honda-Tech - Honda Forum Discussion

Turbo selection for 2.1L roadrace engine

 
Old 02-23-2019, 08:11 AM
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Default Turbo selection for 2.1L roadrace engine

Iím looking for just a bit over 500 WHP max with the best response possible since itís for a roadrace application. Engine is an 88x88 long rod F20B running roughly 11:1 static CR with Sunoco or VP unleaded race gas only. Zero pump gas.

Right now Iím running a GTX2867R so the manifold is set up for the v-band Tial housing (.86 AR). Not sure changing manifolds is in the cards right now. So letís say I need to stick with this mani (or maybe mod the flange for a different turbo).

My origjnal thought was a Gen 2 GTX3071R, but Iím wondering if I can hit my power goal without pushing the turbo to its limits.

The way the race classes work is that itís based on average dyno WHP (measured within a certain powerband around peak WHP). WTQ is not taken into consideration, so the best kind of powerband would be one where you build torque as quickly as possible (to the max WHP limit) and let torque taper off as RPMs rise so that WHP stays flat.

I know this is possible with the smaller GTX2867R that Iím running now. What about the GTX3071R (.63 or .82 housing) or GTX3576R (.63 or .82 housing?). Iíve always thought the GTX35 series would be too laggy on a 2.1L, but Iíve read some pretty good stuff on the GTX3576R. Both of those would bolt up to my mani with some minor adjustments to the downpipe, intake, and hot side plumbing.

Now Iíd LOVE to try the G25-660, but not sure if we could easily mod the manifold to run the v-band flange for it. Downpipe and other plumbing would definitely have to change.

Would love to learn more, so Iíd really like to hear some recommendations and if you guys have great sources for data and info, please let me know!
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Old 02-23-2019, 10:44 AM
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Default Re: Turbo selection for 2.1L roadrace engine

Let's see the dyno graph of what you have now. Not one with just power / torque, but boost pressure rpm curve. Even if it is an excel spreadsheet with the data.

you're asking something pretty specific with 3 turbo families as possibilities (GTX35,GTX30,GTX28) all you've made this pretty vague and difficult.

i think you need to stay in the GT30 family, but stay on the smallest side. (You won't mac it a GTX3071 gen2 away 500 whp, I'll say that much)

You need to remember that turbos actually like boost pressure, so I'm sure your limits are going to be based upon your fuel's knock resistance threshold.

we'll need photos of the style exhaust manifold too.

you've got a lot of information to gather up before anyone can come closer to helping you out here. You've given a lot on your purpose, which is great, but unfortunately, we'll need more.

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Old 02-23-2019, 01:07 PM
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Default Re: Turbo selection for 2.1L roadrace engine

I was hoping youíd reply! Unfortunately, Iím going to make it more difficult as I donít have any dyno data with the engine that is going to be used, as it hasnít been installed yet. The current setup that was used for testing is a rebuilt H22A4 with stock internals. Testing was done using a 10 PSI spring on the WG (Tial MVS). It made 280 WHP on a Dynapack, but the turbo wasnít pushed hard, of course. Everything ran great.

Here are are a few pics of the manifold (the car has been built over the period of many many years!).



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Old 02-23-2019, 02:31 PM
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Default Re: Turbo selection for 2.1L roadrace engine

Originally Posted by 117 View Post
Iím looking for just a bit over 500 WHP max with the best response possible since itís for a roadrace application. Engine is an 88x88 long rod F20B running roughly 11:1 static CR with Sunoco or VP unleaded race gas only. Zero pump gas.

Right now Iím running a GTX2867R so the manifold is set up for the v-band Tial housing (.86 AR). Not sure changing manifolds is in the cards right now. So letís say I need to stick with this mani (or maybe mod the flange for a different turbo).

My origjnal thought was a Gen 2 GTX3071R, but Iím wondering if I can hit my power goal without pushing the turbo to its limits.

The way the race classes work is that itís based on average dyno WHP (measured within a certain powerband around peak WHP). WTQ is not taken into consideration, so the best kind of powerband would be one where you build torque as quickly as possible (to the max WHP limit) and let torque taper off as RPMs rise so that WHP stays flat.

I know this is possible with the smaller GTX2867R that Iím running now. What about the GTX3071R (.63 or .82 housing) or GTX3576R (.63 or .82 housing?). Iíve always thought the GTX35 series would be too laggy on a 2.1L, but Iíve read some pretty good stuff on the GTX3576R. Both of those would bolt up to my mani with some minor adjustments to the downpipe, intake, and hot side plumbing.

Now Iíd LOVE to try the G25-660, but not sure if we could easily mod the manifold to run the v-band flange for it. Downpipe and other plumbing would definitely have to change.

Would love to learn more, so Iíd really like to hear some recommendations and if you guys have great sources for data and info, please let me know!
Is that dump tube recirced right at the downpipe elbow?!
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Old 02-23-2019, 02:40 PM
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Default Re: Turbo selection for 2.1L roadrace engine

Originally Posted by Txdragon View Post
Is that dump tube recirced right at the downpipe elbow?!
Looks like it
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Old 02-23-2019, 03:31 PM
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Default Re: Turbo selection for 2.1L roadrace engine

Originally Posted by TheShodan View Post
FINALLY.. A real challenge
I love this feeling as well

Originally Posted by Txdragon View Post
Is that dump tube recirced right at the downpipe elbow?!
I'm glad you pointed this out. Billy (117), you'll want to install a bellow (aka flex joint) in the dump tube between the wg and downpipe. Otherwise you run a huge risk of things cracking/warping/leaking.

Also, I thought you said on facebook that you have a Gen2 2867 currently? The compressor housing in that pic is a first generation GTX2867r housing. The higher flow from the gen2 series is a combination of comp housing, comp wheel, and turbine wheel. Just a heads up for you.

Personally, I think you're best off with a gen2 GTX3071r. I think a gen2 GTX2867r will accomplish your goals wonderfully on paper, but it's going to be running on the hotter side to do so. And considering it's a road race car that will be on and off throttle very frequently and for long periods of time, heat is not your friend. Besides, the slightly slower spool time of the 3071 (compared to 2867) may help the throttle transitions, preventing the torque thump you get from smaller turbos that can cause some nasty traction problems coming out of corners. If you'd like me to expand on this concept, I can.
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Old 02-23-2019, 06:16 PM
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Default Re: Turbo selection for 2.1L roadrace engine

on second thought, another piece of info that could help the advice: What rpm are you planning to rev to? And what rpm range are you looking to have the best powerband?
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Old 02-23-2019, 06:47 PM
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Default Re: Turbo selection for 2.1L roadrace engine

Originally Posted by Txdragon View Post
Is that dump tube recirced right at the downpipe elbow?!
Originally Posted by Caoboy View Post
Looks like it
Yes, what's wrong with that?

Originally Posted by motoxxxman View Post
...you'll want to install a bellow (aka flex joint) in the dump tube between the wg and downpipe. Otherwise you run a huge risk of things cracking/warping/leaking.
It already has a flex point, you just didn't see it in the pic.


This guy has built many a professional race car setups, so he definitely knows what he's doing from a fabrication standpoint. I was really worried about boost creep, but he assured me that it wouldn't be an issue - and it wasn't with the 10 lb spring. Held just under 10 PSI of boost all the way to 8k RPMs.

Originally Posted by motoxxxman View Post
Also, I thought you said on facebook that you have a Gen2 2867 currently? The compressor housing in that pic is a first generation GTX2867r housing. The higher flow from the gen2 series is a combination of comp housing, comp wheel, and turbine wheel. Just a heads up for you.
Nope, never said that. It's a Gen1 GTX2867R with a 0.86 Tial housing. That why I'd love if a Gen2 GTX3071R would get me to where I want to be.

I'd love to have a dyno plot similar to this:


See how torque comes on early then tapers off. The power curve isn't as flat as I'd want, but it's pretty darn close. The power difference in classes is pretty wide. If I build to the lower class, I only need to make 380 WHP. If I build to the higher power class, I need 520.

Originally Posted by motoxxxman View Post
Personally, I think you're best off with a gen2 GTX3071r. I think a gen2 GTX2867r will accomplish your goals wonderfully on paper, but it's going to be running on the hotter side to do so. And considering it's a road race car that will be on and off throttle very frequently and for long periods of time, heat is not your friend. Besides, the slightly slower spool time of the 3071 (compared to 2867) may help the throttle transitions, preventing the torque thump you get from smaller turbos that can cause some nasty traction problems coming out of corners. If you'd like me to expand on this concept, I can.
GTX3071R is what I really hope will work, but I don't know if it'll hit the power goal I'm hoping for. Actually, I could run it lower, but if I want to move up a class, I'd need about 500 WHP, give or take.

Originally Posted by motoxxxman View Post
on second thought, another piece of info that could help the advice: What rpm are you planning to rev to? And what rpm range are you looking to have the best powerband?
Plan is to keep it at 8500 RPMs max. Powerband is as wide as I can make it. Because of the way the classing works out, it's best to build something that will build torque as quickly as possible up to the max WHP level, then let torque taper off as RPMs climb so that WHP stays flat. The only component in the power-to-weight ratio for classing is WHP. Torque is not part of the classificaiton, so if you can build torque quickly, and hit max WHP as soon as possible, and make power flat, you'll have a faster car than something that hits peak torque later and only hits peak WHP on a narrow band.

Another reason I want to keep the manifold is that I have a custom blanket already set up for it.

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Old 02-23-2019, 06:58 PM
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Default Re: Turbo selection for 2.1L roadrace engine

Originally Posted by 117 View Post
Yes, what's wrong with that?
Well, I'm no engineer but everything I know about recirc dump tubes says that too close to the turbo or a 90į angle, which we seem to be presented with both in your example; causes turbulence and therefore bad for flow.
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Old 02-23-2019, 07:12 PM
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Default Re: Turbo selection for 2.1L roadrace engine

Originally Posted by Txdragon View Post
Well, I'm no engineer but everything I know about recirc dump tubes says that too close to the turbo or a 90į angle, which we seem to be presented with both in your example; causes turbulence and therefore bad for flow.
Yes, it’s certainly not ideal, but it’s plumbed in closer to the bend rather than being perpendicular to a straight section of tubing. It’s a compromise to keep the packaging as compact as possible. Thought about adding some sort of transition there and on the elbow for the wastegate to smooth the flow a bit, but that will probably wait until we get all the other things sorted out. ��

Never heard that having the recirc too close to the turbo is bad. How do internal WG turbos get around that?
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Old 02-23-2019, 07:34 PM
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Default Re: Turbo selection for 2.1L roadrace engine

Originally Posted by 117 View Post

How do internal WG turbos get around that?
They dump from the turbo outlet, parallel to the flow of the turbo exhaust.

Somebody may offer a MUCH better explanation than I did here, but the idea is presented.
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Old 02-23-2019, 07:40 PM
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Default Re: Turbo selection for 2.1L roadrace engine

Totally get that part, and the flow from the wastegate is much better than what I have since it’s parallel to the exhaust flow. No argument there. Your post mentioned the recirc being too close to the turbo outlet. An internal WG is right there with the turbo outlet so I wasn’t sure what you meant with your comment.

I know the flow flow isn’t perfect on my setup, but it’s a compromise. Interested to hear other observations and learn new things!
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Old 02-23-2019, 07:42 PM
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Default Re: Turbo selection for 2.1L roadrace engine

My Samsung note paint skills are lacking but this is where you'll see the biggest problems. If this particular aspect were changed alone, you could see greater gain from the turbo you're already using, at a higher psi range. It seems as if you may be experiencing troubles with your exhaust causing some unwanted disturbance to your turbine.

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Old 02-23-2019, 07:54 PM
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Default Re: Turbo selection for 2.1L roadrace engine

I see no reason you can't hit close to 380 with this turbo.


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Old 02-23-2019, 07:55 PM
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Default Re: Turbo selection for 2.1L roadrace engine

Oh I donít think I was clear with my original post. We arenít having any issues that I know of with the GTX2867R. It runs just fine on the current engine, but since the current engine wonít handle us pushing the turbo to its limits, it hasnít been really tuned beyond using a 10 PSI WG spring. According to datalogs, it holds right at 10 PSI as planned.

I know the 2867R wonít make it to 500 WHP. The original goal was only for 325 WHP or so. To get to 500, I figured I would need to change turbos. Unfortunately, the new engine isnít in yet, so we donít have any baseline to work with, and there isnít enough time to get everything sorted with the 2867R before moving to a larger turbo.

The flow issue you pointed out may be an actual problem, but we havenít noticed yet. Maybe itíll become an issue when we push the turbo harder. If so, weíll have to deal with that as well.
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Old 02-23-2019, 08:01 PM
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Default Re: Turbo selection for 2.1L roadrace engine

Originally Posted by Txdragon View Post
I see no reason you can't hit close to 380 with this turbo.
Just for clarity, is that 380WHP or 380 at the crank?
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Old 02-23-2019, 08:27 PM
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Default Re: Turbo selection for 2.1L roadrace engine

Originally Posted by 117 View Post


Just for clarity, is that 380WHP or 380 at the crank?
if you hit near 320whp on that dyno sheet you posted earlier at only 10psi from this GTX2867R, she has more breath to give, brother. It's **my** belief that you're feeling left flat by inefficiency and if you can resolve your wastegate recirc issue, you'll see better turbo efficiency and benefit from what you're putting out now and even more so if you crank her up. I believe if you crank it up now, you may just be disappointed (providing nothing goes bang).
I'm truly not the expert, though these are my thoughts/suggestions.
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Old 02-23-2019, 08:33 PM
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Default Re: Turbo selection for 2.1L roadrace engine

Originally Posted by 117 View Post
Oh I donít think I was clear with my original post. We arenít having any issues that I know of with the GTX2867R. It runs just fine on the current engine, but since the current engine wonít handle us pushing the turbo to its limits, it hasnít been really tuned beyond using a 10 PSI WG spring. According to datalogs, it holds right at 10 PSI as planned.

I know the 2867R wonít make it to 500 WHP. The original goal was only for 325 WHP or so. To get to 500, I figured I would need to change turbos. Unfortunately, the new engine isnít in yet, so we donít have any baseline to work with, and there isnít enough time to get everything sorted with the 2867R before moving to a larger turbo.

The flow issue you pointed out may be an actual problem, but we havenít noticed yet. Maybe itíll become an issue when we push the turbo harder. If so, weíll have to deal with that as well.
Ooohhhh.. You're wanting a new engine with a new power goal? Well now I feel silly!! I do think you'll see improvement with the mentioned renovations on your current setup. As for a whole new set, I'm not the one with whom to converse about the best choice for your predicament. Lol!
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Old 02-23-2019, 08:58 PM
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Default Re: Turbo selection for 2.1L roadrace engine

After reading your additions to the info, here's my advice:
use the gen1 2867 for the 380hp class. It will make it with absolutely no problem at all.
use a gen2 3071 for the 520hp class.

definitely run a boost control solenoid wired into the ecu for ecu controlled boost. With that, you can shape your torque curve pretty much however you want. Based on your description, you basically will want the torque curve to be flat across the board right up to your exact hp goal, then taper boost/tq off to maintain flat hp up to rev limit rpm. Pretty easy to do actually with boost by rpm.
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Old 02-24-2019, 06:45 AM
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Default Re: Turbo selection for 2.1L roadrace engine

Originally Posted by Txdragon View Post
My Samsung note paint skills are lacking but this is where you'll see the biggest problems. If this particular aspect were changed alone, you could see greater gain from the turbo you're already using, at a higher psi range. It seems as if you may be experiencing troubles with your exhaust causing some unwanted disturbance to your turbine.
Very good, young padawan. Your skills in the Jedi arts are improving.

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Old 02-24-2019, 07:51 AM
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Default Re: Turbo selection for 2.1L roadrace engine

I didn't think the recirc would cause a serious issue with the turbo where it is. Would moving the WG to the right a bit and merging the recirc tubing to be tangential to the downpipe make a significant improvement (like the pic)? We've already moved the alternator to the right some to get more clearance.
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Old 02-24-2019, 08:21 AM
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Default Re: Turbo selection for 2.1L roadrace engine

Originally Posted by 117 View Post
I didn't think the recirc would cause a serious issue with the turbo where it is. Would moving the WG to the right a bit and merging the recirc tubing to be tangential to the downpipe make a significant improvement (like the pic)? We've already moved the alternator to the right some to get more clearance.
Although still not quite optimal placement, I believe that would still make a world of difference. It's far enough over that it's not right on top of the turbine and enough outside the bend transition to sorta give a parallel flow. Exhaust flows more like fluid dynamics, so think of water in a drain. Picture how this would flow compared to your current layout. It would flow smoother. Hopefully somebody could offer a better explanation, but I see it in my head as a good start on the right path.
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Old 02-24-2019, 08:44 AM
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Default Re: Turbo selection for 2.1L roadrace engine

Ultimately, optimal placement would be quite an extensive process for your setup. It'll need to be further down past the bend, more into the straightaway. Borrowed this example from Greg @ Go-Autoworks. Hopefully he won't mind. Lol!
This is a great example of recirc placement. Why not just vent it to atmosphere though? Is there any reason it HAS to be recirc? Legend has it that there is proof in the dyno that you get better results with open vs recirc although, that could just be due to poor placement. **shrug**


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Old 02-24-2019, 09:10 AM
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Default Re: Turbo selection for 2.1L roadrace engine

Doesn’t have to be recirc, but all exhaust has to exit behind the driver compartment. I can’t vent out the hood or anything like that.

Packaging constraints might make running the WG plumbing that far from the turbine housing difficult. The radiator is now slanted forward a good bit, which gives more room toward the upper core support, but it didn't gain much room down low where the downpipe is. I also have to retain the OEM subframes, so using something with additional clearance around the subframe area is a no-go.

Last edited by 117; 02-24-2019 at 09:33 AM.
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Old 02-24-2019, 09:33 AM
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Default Re: Turbo selection for 2.1L roadrace engine

Originally Posted by 117 View Post
Doesnít have to be recirc, but all exhaust has to exit behind the driver compartment. I canít vent out the hood or anything like that.
so not to the ground in the engine bay either?
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