Andy Hollis' One Lap Miata (K24 Honda power) - Page 21 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 12-07-2017, 11:09 AM   #401
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Originally Posted by emilio700 View Post
Engineers are wrong every day.
Truth.

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Every single tire manufacturer's website recommends rim widths too narrow for their tires optimal performance. Whether that's written by a lawyer or sanctioned by an engineer is irrelevant. It's wrong.
Bad example.

Those recommended widths have little to do with optimal performance, and everything to do with fitment and safety margins. They don't even come from the tiremaker. They are specified by the Tire and Rim Association, of which every tiremaker is a member. Lawyers have as much to do with those recs as do engineers, and they are same across all tire models/brands for any given marked size. Even when the actual size of the tire varies. This is especially bad when you have folks like Hoosier that make their tires over-wide versus typical, yet they still have to use the same rim recs per the marked size.
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Old 12-07-2017, 11:58 AM   #402
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Originally Posted by AndyHollis View Post
Bad example.

Those recommended widths have little to do with optimal performance, and everything to do with fitment and safety margins. They don't even come from the tiremaker. They are specified by the Tire and Rim Association, of which every tiremaker is a member. Lawyers have as much to do with those recs as do engineers, and they are same across all tire models/brands for any given marked size. Even when the actual size of the tire varies. This is especially bad when you have folks like Hoosier that make their tires over-wide versus typical, yet they still have to use the same rim recs per the marked size.
No, great example. The engineer at Hoosier told Emilio that, not the tire and rim Association. In the same vein, your friend at Borg told you the 7163 would fit based on the numbers without any real-world experience with that turbo, most likely. The phrase "fitment and safety" is pretty accurate to describe his recommendation, actually. The 7163 will be more efficient and safer, but the 6758 will work better in the real world. i see vendors and engineers alike consistently recommending "the larger turbo" when the best response and power band is always going to come from the smallest turbo that is able to make the peak horsepower goal. If you want to make 450 wheel horsepower with the best response and have the car spool the earliest and respond the best, that is the 6758. Period. If you want headroom to grow, then use the 7163, but you are absolutely giving up response and spool to do so.
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Old 12-07-2017, 12:51 PM   #403
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Here is some musings from someone that actually knows a crap ton about turbo k-series (Geoff @ FullRace) in regards to a 6758 on a K20.

"This (EFR 6758) is the turbo we spec as the high power R18 (crappy SOHC 1.8L from '06+ Civics) setups, it is the 2nd smallest turbo in the EFR family so a little small for most K20's but the spoolup and lowend torque will feel like a crazy supercharger!"


Add 400ccs and a little small changes to small.


I should say, I'm not arguing that a 6758 couldn't work well on andy's K24 but it will take a lot of work in the manifold and it will take a giant wastegate to prevent the turbo from choking the flow and causing a bunch of additional heat and back pressure.

In my experience, a 7163 would be a better fit for this application and will likely spool and behave like a 6258 on a Mazda BP engine.
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Old 12-07-2017, 01:17 PM   #404
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Hey guys, can we keep this civil? I'm all for education/discussion/disagreement/debate, but no need for "tone".

So I asked my guy (Matt) at BW for more specifics as to why he rec'd the 716 over the 6758. He said it was ok to post his reply here:
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They are right that a 6758 can make the same power as the current 7163 match (500 crank hp). It ends up right at the edge of the compressor map, down beneath any of the efficiency islands, so you are running 30F higher comp outlet temps at peak power. There are a couple reasons I am suggesting the 7163 for you over the 6758:
  • - Main use for the car is track driving on 200tw tires, so we are ramping the boost in over several thousand RPM to keep a linear powerband and a "big N/A" engine feel, so you don't need a smaller turbine. This strategy is based on what I have seen OEMs like BMW and Ferrari doing in the M3/4 and 488 (along with more engines yet to come).
  • - If your primary use was autocross on Hoosiers I would for sure recommend a 6758 since you want that hard hit right at corner exit and you can put the power down. That's what I recommended for JD (an autocrosser building a turbo-K20 BMW for Street Mod who we both know) a few days ago.
  • - No altitude margin on the 67mm compressor- it is right at the speed limit so your peak power drops with any altitude increase from sea level. The 7163 will be able to spin faster at altitude to keep the same power.
  • - Lower exhaust manifold pressure (7psi) and compressor outlet temperature (30F) at peak power on the 7163- both of those increase the chance of knock, so your engine will be happier running near peak power for long periods of time.
  • - Inertia penalty of the 63mm turbine is reduced due to the mixed flow wheel design- it is more like a 60mm radial wheel. So you aren't really gaining much response and you are losing a lot of flow. If you whack the throttle fully open at 1500-2000 RPM you will notice a slower response from the larger turbo, but as soon as you are above 2500 RPM there is plenty of exhaust energy to spool the turbo (the wastegate is opening up). We run time to torque comparisons all the time for OE customers and once you're above the wastegate point it takes a big inertia change to make a noticeable difference.
  • -Ability to make more power if needed- might help catch those 900hp GT-Rs

It seems like Andrew(?) from TSE is quite passionate about the 6758 being the correct choice. Always interesting to hear feedback from guys like him that work with the parts every day. I definitely agree that we can miss things and we tend to be conservative with the matches, but that is also based on experience matching thousands of different engines for OE customers. It would be interesting to hear if he tested a 7163 and 6758 back-to-back. The BP engine characteristics might make for a bigger difference between the two turbos than a K24 since there is less exhaust energy available. A 33% displacement increase does make a big difference in boost response, not even considering the better head flow from the K24. In the end it's your decision based on what your priorities are. I think my "tl;dr" is that the 6758 and 7163 are very close in terms of response, but the bigger turbo will make for a happier engine on the track. I'm fine if you post my reasoning in that thread. I think I might reach out to TSE as well just to learn more about his experience.Here's a matchbot sheet with a 6758 so you can see for yourself: BorgWarner MatchBot
The match link for the 7163 is here: BorgWarner MatchBot , if anybody wants to look at the #'s.

The altitude factor is one I had not previously considered...and we are headed to High Plains Raceway outside of Denver this year for One Lap.

Andrew, sounds like you may be getting a phone call.
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Old 12-07-2017, 01:34 PM   #405
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I don't disagree with anything he said there. On track, the 7163 will be happier, albeit less responsive. If you are going to ramp the boost in slowly, I would use a 7163 too. My personal mantra is to reduce response lag by using the smallest turbo that will do the job, in spite of the efficiency loss. You can cope with that in other ways (bigger IC, good cold-air intake). My experience with E85 and similar power levels on a much, much shittier engine (BP) indicates that detonation will be a complete non-issue on either turbo. I have not played with the mixed-flow turbine on the 7163, the inertia comment is interesting and very cool.

Matt emailed me, so I shared my results from Acamas, Soviet's 485whp uncorrected hero pull, fourwhls' restricted 400whp 6758 setup, and Emilio's hi-boost 6258.

Last edited by Savington; 12-07-2017 at 02:55 PM.
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Old 12-07-2017, 07:10 PM   #406
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I can confirm that the 7163 on a mazda designed 2.5 is totally fine for auto-x. Andy will be fine. Its better for auto-x than a 6758 on a 1.8 vvt.
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Old 12-09-2017, 08:16 AM   #407
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So...learn me some intercoolers...

I am loathe to add a ton of weight to the car, so I'd like to size this as close to optimal as possible. In/out are opposite of the BP motor, so piping will have to be fabbed. Car will also have a/c compressor in the way on the driver's side, along with a condensor to pass air over.

Also, there is a version of the EFR compressor housing that has a forward-facing outlet, so the over-the-top tube routing is a very real possibility. Example here: https://trackdogracing.com/intercoolerkits.aspx

Alternatively, I could do a more traditional "bottom" routing, with more bends, and the option of changing out the intake manifold for a downward facing center-feed.

Given the weight consideration, and the fact that I only care about what it does on the track for relatively short time trials...am I a fool for even considering tube and fin? I like the efficiency versus weight of the hybrid style that Griffin makes: RRE Intercoolers and Parts

What is working in the real world of 450hp track Miatas?
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Old 12-09-2017, 08:44 AM   #408
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If you're not afraid of a hole saw there is room behind the headlight and outside the frame rail to route the piping there. Leaves plenty of room for accessories and hood venting and keeps the bends to a minimum.

I'm not making anywhere near the HP you're looking to make so can't help ya on the intercooler selection.
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Old 12-09-2017, 09:12 AM   #409
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For your power goal I don't think you can go over the top. 2" ic piping pretty much tops out at 350hp on that motor. And bigger doesn't fit over the radiator.

If turbo k motors in civics are OK on the track with half width rads you could copy my garrett setup but it's borderline for 450hp for heat rejection, but being on track should help that.

Otherwise traditional through the holes behind the headlight is you best bet, and I think in your setup anything short of a garrett or bell core with custom end tanks will be a disappointment.
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Old 12-09-2017, 09:43 AM   #410
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TDR routing drops the radiator a bit by modifying the stock radiator mounts and also you trim the sheet metal in front about 1/2-3/4 inch. Then 2-1/2” easily clears the hood and radiator. Possibly a little bigger with more trimming.

It’s the same setup I ran on my 2000.

Can’t speak to the IC efficiency but the routing was straight forward with minimal bends.








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Old 12-09-2017, 07:23 PM   #411
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Quote:
Originally Posted by AndyHollis View Post
:
Those recommended widths have little to do with optimal performance, and everything to do with fitment and safety margins. They don't even come from the tiremaker. They are specified by the Tire and Rim Association, of which every tiremaker is a member. Lawyers have as much to do with those recs as do engineers, and they are same across all tire models/brands for any given marked size. Even when the actual size of the tire varies. This is especially bad when you have folks like Hoosier that make their tires over-wide versus typical, yet they still have to use the same rim recs per the marked size.
Pos-cat added for this, I've always wondered why the recommendations don't reflect real-world statistics.

In Australia, some tyre chainstores refuse to fit 205" tyres on 8" rims because they're not recommended by the manufacturer despite the user consensus that they work great on 8" rims.
It's easy enough to find someone who will fit them but I always found it odd that some performance tyres aren't recommended at their optimal width.
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