How do superchargers hold up to endurance racing? (1.6l Miata content)

In reply to Keith Tanner :

Was that comparison on a 1.6, 1.8, what boost, etc?

And what kind of drivability issues? Im now debating on the m45 jackson kit i picked up for my nb because of this thread.

Sorry, that's a 1.6. With the super, it was running the "big boost kit" sold by JR. On the turbo, it was whatever we could run and keep the injectors happy. Boost is not really an important number for the comparison and I don't really care what it was because both were limited in important ways, this is the best they could do with off-the-shelf parts.

https://www.flyinmiata.com/turbos/janel.php

Idle droop, tip-in problems, vibration, noise. This was my (at the time) girlfriend's car, so I'd already spent a lot of time sorting out the supercharger.

Jaynen said:

racerfink said:

Having driven a 1.8 N/A with a cam at the Watkins Glen Chump race two years ago, I can tell you that’s the way to go.  Just look at all the trouble GRM has with their turbo Miata.

How much does that bump a stock 99? I have a stock 99 now its more torque I miss than anything I think which is where a positive displacement SC could be fun

The car owner was running 25’s.  I got down to a 26.3 without touching any curbs.  The car had a concentric bolt loosen up on the left front on Saturday, so I tried staying off the curbs as much as possible on Sunday.

Do you know what cam was in it, Racerfink?

There are SEVERAL Ecotech miatas running Champcar reliably.

It is a fairly cheap and straight forward swap....

Hell, the guys that created the swap are running Champcar and had fast lap at WGI (like a 2:15 or something ridiculous like that).

In reply to WonkoTheSane :

I don’t, but I had run quite a bit of Spec Miata at that point, and it was noticeably stronger, without a lot of overlap sound/lope. 

Keith Tanner said:

My high power naturally aspirated Miata was pretty fun, and as fast as a turbo car on a kart track. Not as fast on a big track. Turbos can make more torque than supers, it's all about setup.

Here's a dyno chart. M45 supercharger vs GT2554 turbo. Same engine management (a Voodoo piggyback), same exhaust, everything. The chart is at altitude so the turbo is a little slow to spool, which increases the advantage the supercharger has at the low end. The turbo also does not have electronic boost control, that's straight off the wastegate.

https://www.flyinmiata.com/tech/dyno_runs/M45_vs_VoodooII_1.6.pdf

The turbo was intercooled, the super was not because it already had enough driveability problems.

GRM is having all that trouble with their turbo Miata because they're trying to have trouble. Seriously, if you saw the turbo they put in there, it was just waiting to explode. It looked like it had been fed ball bearings. Everything is being done to the absolute minimum because it's a perverse kind of fun. Don't take it as representative of what can be done if you really try.

But what if you don't really want to try you just want more power that survives the track as much as possible and for cheapish as well because we might as well complain that we want our cake and to eat it too

Keith Tanner said:

GRM is having all that trouble with their turbo Miata because they're trying to have trouble. Seriously, if you saw the turbo they put in there, it was just waiting to explode. It looked like it had been fed ball bearings. Everything is being done to the absolute minimum because it's a perverse kind of fun. Don't take it as representative of what can be done if you really try.

The only thing the 1.8 swap avoids is the perverse kind of fun.  But it does add the fun of being able to complete an endurance race.  Trade one fun for another.

In the long run, the 1.8 swap may be more costly, as you would be reliably using more and more tires as well as more and more fuel- since you would be finishing multiple endurance races....  

Let alone the constant entry fees that you could be spending money on.

Didn't the eyesore miata freebuild turbo 1.6 actually perform pretty well?  Seems like they had room to detune to keep heat down and increase reliability if needed

In reply to Keith Tanner :

Yah, and even when you can effectively get rid of the heat from supercharger intercooler, that's HP robbed directly from the crankshaft you are throwing away.

Turbochargers are mainly driven by heat energy retrieved from the exhaust, that would have been lost out the tailpipe anyway.

Sort of. Turbos add backpressure, which brings the detonation threshold down and you have to modify the timing accordingly. You can see the difference when tuning a supercharger versus a turbo. It has a lot to do with the turbo selection, but it's not a free lunch. They also tend to pump more heat into the engine coolant.

Still, there's a reason that every purpose-built race car on the planet runs turbochargers instead of superchargers with the exception of Top Fuel dragsters - and they're not allowed to.

Just to get slightly back on track, I have a thorough understanding of the difference between a super and turbo, there's no need to rehash that old argument.  And I do appreciate all of the other discussion.

The entire reason for the question is because of the cheapness and availability of the supers on Craigslist.

This wouldn't be a hacked together home brew kit, this would be a bolt in affair, possibly minus the aftercooler.  Between an already existing megasquirt sitting in the shelf, we're thinking this is a weekend project to get some more oomph.

I have a few friends that have used them successfully autocrossing and canyon carving for years, but none of them really go on track, hence the original question..

Make sure your IAT sensor can handle fairly high temps. We used to have trouble with the M45s pinning our Link IAT sensors. I don't know how hot the air gets, but over 100C.

If you're doing endurance racing with this, you obviously want to be conservative. Stick with the standard pulley to keep the boost and the heat down. Spend a lot of time tweaking and testing the idler/tensioner pulleys as they're a weak spot in that setup and a thrown belt makes for a very slow car. It won't give you huge power, but it will perk the car up.

Turbos run off a pressure differential (that is created by heat created by combustion that propels an air pump that pumps air that when faced with a restriction can create a pressure differential). If you remove the pressure difference between the inlet and outlet they won't spin. You can lose all kinds of heat before the turbo and it will still spin as long as there is a pressure differential, just less efficiently. They increase pumping losses on the exhaust stroke of the engine. They DO take power to run. They do not run off of 'waste heat', they just run less efficiently if you lose heat because your gas volume shrinks and your gas velocity goes down (and kinetic energy is exponential with speed something something) so your pressure differential across the same restriction (turbo) shrinks. GM has published charts saying that the WOT exhaust gases in a corvette lose 600f from manifold to tailpipe. And yet... it still does the boost thing even with a rear mounted turbo.

They also have a rotating assembly that weighs 1-2 lbs (guesstimating for a gt25 as mentioned) vs ~10 (guesstimating for an m45) that also has smaller diameters (moment of inertia something or other) and also has a comparatively TINY 'reaction' area that the boost you're creating is pushing back on. They take a lot less energy to make boost with, but it's not nothing and it's not free. 

I ran a Jackson M45 kit for my 1.6L for a season for HPDE/track days.  It made stupid heat- IAT’s were like 125*F over ambient at 6-7psi.  It also ate belts like that was it’s job.  No matter how I positioned or tensioned things, it would chew up belts at an astonishing rate.

This season I’m running an Ebay T3/T4 turbo with intercooler.  180HP at the wheels on a conservative tune, IAT’s no more than 20*F above ambient.   I’m an intermediate driver and I understand that the faster you go the more problems you’ll have, but so far I’ve had not a single issue.

Technically, a turbocharger IS a supercharger.  It's just driven by a turbine using exhaust energy as opposed to a belt or oil pressure turning some kind of compressor.

Just sayn.  

Wonko- it seems pretty clear that the #1 issue that people are noting is heat, especially over a long time.  Autocrossing and even most HPDE don't run a car anywhere near as long as you would in an endurance race.  So you really have to deal with that.  Either by using E85, a charge cooler, or both.

It will work, and will create boost, and sounds like will last.  But the side effects need to be dealt with, or it won't be all that effective over the long run.

alfadriver said:

Technically, a turbocharger IS a supercharger.

I remember reading through some old '60s era Hot Rod Magazines and they were even referred to as turbosuperchargers back then. Glad it's been shortened to just turbocharger, sounds a bit less silly.

Alfa - I agree with your assessment.

Keith & ShinnyGroove - Thanks guys, that's exactly the real world sort of data I was looking for!  I knew that IAT would be a problem, but it sounds like it's one that it can't be dealt with as "easily" as you can with a turbo.

IAT issues with a supercharger are definitely fixable.  It'll usually involve an air/water intercooler setup for the sake of making it fit.  Even some factory setups (such as the Eaton M112 on the 03/04 Cobras) squeezed in a heat exchanger under the blower.  

In reply to Vigo :

Sorry, but you are only partially correct.

The difference is a turbine designed to operate with a gas rather than with an incompressible liquid.

Were exhaust gases liquid, then energy recovery would be purely kinetic due to pressure differential and flow rate.

But they are hot gasses, and when hot gasses expand, they lose energy. That energy can be heat, or in a properly designed turbine, captured mechanical energy.

There is some kinetic energy captured from the gasflow, commonly called 'blowdown', but the majority is from the expansion of the hot gasses.

Were the turbine energy completely due to flow, the backpressure created at the piston crown would result in energy loss at least equal to that used to drive the turbine, basically the same situation as a crankshaft driven supercharger.

Doubters should consult any textbook covering thermodynamics and gas turbine design.

As efficiency become more important, designers are moving away from classical long separate branch exhausts (aka headers) that would maximize blowdown, to short direct exhausts merging within the head itself, to minimise exhaust gas heat losses before entering the turbine stage.

AFAIK, Honda began this trend a few years ago, and I see more and more new designs with this configuration.

It's clear that smaller motors employing GDI and turbocharging, along with the ECU controls required to make them run efficiently are the near future of the piston IC motor.

But long term I still believe that hybrid turbines driving alternator/battery drivelines will replace pistons. The turbines can be optimized to achieve peak efficiency at a fixed RPM, and operated only on demand as required to supply energy from whatever fuel is (or fuels are) used.

But they are hot gasses, and when hot gasses expand, they lose energy.

And if there were no pressure differential across the turbine, why would the gases expand at all?     

Talking about only one part of a pressure/temperature/density/volume scenario is always going to come up short, but..

I'm of the opinion that saying that turbos run off of heat does more harm than good because it leads to oversimplifications like the assumption that turbos run solely off of 'waste' heat energy and thus don't create any new (pumping) losses in the engine. 

But, there is no way to battle one oversimplification (turbos run off heat) with another (turbos run off a pressure differential) that can cover all the bases without turning into a dissertation. I just think the second oversimplification is less detrimental to  a layman's understanding than the first one is. I appreciate your post in spite of this opinion, because i know not many would agree with me and what you said is not wrong to my knowledge. It is a chicken and egg sort of question. 

But long term I still believe that hybrid turbines driving alternator/battery drivelines will replace pistons. The turbines can be optimized to achieve peak efficiency at a fixed RPM, and operated only on demand as required to supply energy from whatever fuel is (or fuels are) used.

My excitement for the advancement of powertrain technology is always stifled by the thought that only the robot chauffeur i just timeshared for 12 minutes will be able to drive it.  

In reply to Vigo

You made a flat statement, my post offered the rest of the story. Are both oversimplifications? Of course, as you say, a dissertation is not appropriate.

I think the folks here deserve better than a 'Layman's understanding', and are capable of handling the facts.

Less Filling! Tastes Great!

(Let's have a cold beer!)

I think the folks here deserve better than a 'Layman's understanding', and are capable of handling the facts.

I hope my use of the term wasn't taken as derogatory. I just think that someone who accepts the 'waste heat' theory at face value in the first place and looks no further is looking for an explanation that fits in one sentence, and that's where the difficulty in crafting the least-misleading oversimplification lies. Concision is more art than science in the case of my attempt, obviously.

Anyway, looking up 'blowdown' (a term i didn't know, so thank you) did lead me to an interesting fact, which is that if you use a turbine fully half of the size of your entire piston engine to simply add torque to the crankshaft (not compress the intake charge), you COULD create so little additional backpressure that the energy recouped by the turbine is a net benefit and thus it truly runs on 'waste heat energy' alone. Apparently this is called a turbo-compound engine, and while it may have no relevance to cars, at least i can now say that a turbine that adds power by capturing 'waste heat' actually existsed on planes for a short time until they realized that if your turbine is that big you might as well build a turbine engine and ditch the pistons. 

I'll try to summarize what I think I learned from Keith's excellent books, and my own experience with both:

Whether turbo or super, the main issue we're talking about is heat.  All other things equal, centrifugal compressors, like are usually found on turbos, usually make less heat than roots compressors, like are usually found on superchargers.

Intercoolers help with both, but they have a bigger job to do with a roots compressor.  In addition, since superchargers have the throttle before the compressor, adding an intercooler greatly increases the throttled volume and causes difficulties with idle, throttle response, etc.

In reply to ShinnyGroove :

The throttled volume issue is why a lot of roots blower setups use air/water intercoolers instead of air/air.  Much less volume added that way.