Supercharged but not intercooled ?

[chris7676]

There seem to be lots of MX5s that have been supercharged but don't have intercooler. Are they not suffering from heat related power issues enough to bother with cooloing? And how can a 0.5 bar generate realistically nearly 200hp as many do claim (that assuming base power of say 130 hp) ?

[MX-5 Lazza]

Mine runs around 9psi which I think is about 0.6 BAR and has been dyno'd at 242.9bhp

When comparing FI figures you need to compare oranges with oranges. With a turbo you get more power with more boost. With a supercharger, being a fixed-volume air-pump you get more power with more air-flow. What is seen as "boost" is just a measurement of restriction - If you can improve the air-flow through the head and out the exhaust you will get more power but the boost pressure will go down! If my car had a Mk1 1.8 head (which doesn't flow as well as the Mk2.5 1.8) but everything else stayed the same it would probably have less power and more psi.

Conversely, if I swapped my MP62 for an M45 and upped the pulley ratios to give the same "boost" pressure it wouldn't give the same power as I have now as the M45 doesn't flow as well as the MP62.

[RenesisEvo]

MX-5 Lazza said:

Mine runs around 9psi which I think is about 0.6 BAR

Would I be right in saying that the 0.6 bar boost is gauge pressure, i.e. in addition to atmospheric (and therefore actually 1.6 bar?)

[chris7676]

MX-5 Lazza said:

Mine runs around 9psi which I think is about 0.6 BAR and has been dyno'd at 242.9bhp

But yours is chargecooled? Which is lacking on most of them, hence my post.

[Night Runner]

RenesisEvo said:

MX-5 Lazza said:

Mine runs around 9psi which I think is about 0.6 BAR

Would I be right in saying that the 0.6 bar boost is gauge pressure, i.e. in addition to atmospheric (and therefore actually 1.6 bar?)

That confused me slightly - surely 0.6 bar is negative to atmospheric?

[MX-5 Lazza]

That's 0.6 bar boost i.e. 1.6 bar pressure

And yes, mine does have an intercooler (air/air - chargecooler usually refers to water/air). Personally I wouldn't want to go much over around 180bhp without some sort of protection i.e. intercooler and/or water injection regardless of Turbo/SC etc.

[Richyvrlimited]

chris7676 said:

There seem to be lots of MX5s that have been supercharged but don't have intercooler. Are they not suffering from heat related power issues enough to bother with cooloing? And how can a 0.5 bar generate realistically nearly 200hp as many do claim (that assuming base power of say 130 hp) ?

That'll likely be 200bhp flywheel power, and likely on a cold day. 0.5bar is 7psi, 200bhp peak is pretty realistic on a 5. Hell if you get a Rotrex supercharger kit you'll make more like 230bhp at that boost level - yes really. The Rotrex supercharger is an awesome piece of kit.

So yes you're right with no IC you suffer power loss due to elevated intake temps. However there's no free lunch, adding an IC setup to a supercharged 5 has it's downsides too.

Primarially you're massively lengthening the intake tract, this can lead to idling issues and really poor throttle response. You can alleviate this by running dual throttle, but this to is not a free lunch, you end up with a heavier pedal, and part throttle can be a lot noisier (supercharger whine).

I have up all these issues and converted my high boost high power IC'd setup into a low boost non intercooled 'coldside' setup. Final power is lower (much lower), but drivability is on another level, the car is more OEM than aftermarket.

[MX-5 Lazza]

It would be interesting if you tried my car. I have the dual throttles which I fitted to cure the idle droop. throttle response was never a problem, in fact I didn't notice any improvement in response with the dual throttles. I also get very little whine. Part throttle I hear no whine at all, the only time I hear anything (other than full throttle obviously) is when closing the throttle in which case there is sometimes a very minor little wheeze - certainly nothing you could call whine.
My throttle pedal also doesn't feel any heavier than stock. I guess it must be as I'm now pushing against 2 throttle springs but it's nothing noticeable.

I was going to mention all this on the thread where you said you were converting to a cold-side setup but didn't think that was the right time & place.

[Richyvrlimited]

MX-5 Lazza said:

It would be interesting if you tried my car. I have the dual throttles which I fitted to cure the idle droop. throttle response was never a problem, in fact I didn't notice any improvement in response with the dual throttles. I also get very little whine. Part throttle I hear no whine at all, the only time I hear anything (other than full throttle obviously) is when closing the throttle in which case there is sometimes a very minor little wheeze - certainly nothing you could call whine.
My throttle pedal also doesn't feel any heavier than stock. I guess it must be as I'm now pushing against 2 throttle springs but it's nothing noticeable.

I was going to mention all this on the thread where you said you were converting to a cold-side setup but didn't think that was the right time & place.

Should've done, I wouldn't be offended

Maybe I just didn't 'nail' the balancing, but I messed with it quite a lot and was never ever happy with it.

I have recently found out that my charger was leaking at the flange between the gearbox and the main casing, this could well have been causing the noise. ce-la vie!

I have driven other dual throttle setups and they were better than mine, I was still never 100% happy with it however.

I am pleased with my coldside setup, though I have to pull it apart again this weekend as I just can't get it to seal properly.

I missed the hotside power on track though If the car was a weekend toy I'd have never of changed it.

[MX-5 Lazza]

I didn't just because it was a thread about your cold-side fitting rather than a thread about hot-side problems.

I have driven a cold-side (M45 on a 1.8 Berkeley fitted & tuned by Phil) and I have to say it felt perfect. Not a great deal of power, I think it made around 160bhp tuned very conservatively, but it felt amazing to drive with instant throttle response (i.e. better than stock!) and incredibly smooth! If you could get an MP62 cold-side to feel like that but with around 200bhp that would be the perfect road based MX5

[Richyvrlimited]

MX-5 Lazza said:

I didn't just because it was a thread about your cold-side fitting rather than a thread about hot-side problems.

I have driven a cold-side (M45 on a 1.8 Berkeley fitted & tuned by Phil) and I have to say it felt perfect. Not a great deal of power, I think it made around 160bhp tuned very conservatively, but it felt amazing to drive with instant throttle response (i.e. better than stock!) and incredibly smooth! If you could get an MP62 cold-side to feel like that but with around 200bhp that would be the perfect road based MX5

My dads car is a 1.8 with M45 coldside fitted and tuned by Phil.

and yes that's the aim

[MX-5 Lazza]

What power are you aiming for? I guess an intercooler is out of the question (I'm sure I have seen a charge-cooler fitted sandwiched between the SC and intake manifold somewhere) so are you going for water injection?

[Richyvrlimited]

MX-5 Lazza said:

What power are you aiming for? I guess an intercooler is out of the question (I'm sure I have seen a charge-cooler fitted sandwiched between the SC and intake manifold somewhere) so are you going for water injection?

Probably on Big Gulp, that is a custom intake, or maybe BEGi's new offering which has an intergrated charge cooler.

There's zero chance of me getting a charge cooler inbetween the mani and the charger unfortunately. WI is the next job to sort.

Aim is indeed 200bhp ish. Probably won't get there but you never know.

[300bhp/ton]

chris7676 said:

There seem to be lots of MX5s that have been supercharged but don't have intercooler. Are they not suffering from heat related power issues enough to bother with cooloing? And how can a 0.5 bar generate realistically nearly 200hp as many do claim (that assuming base power of say 130 hp) ?

I can't answer directly, but hopefully give you some indication.

1. Dyno's/rolling roads measure torque slightly differently to a full SAE Net/DIN engine dyno. So the values, or horse poweres aren't always directly comparable.

2. No chassis dyno can truly tell you flywheel figures, they can only guess. And often massively get it wrong. So anyone quoting flywheel figures, take them with a pinch of salt as they could be 10-12% out (nearly always in the wrong direction ).

2a. Many dyno's use std figures and don't correct to industry standards for temp, humidity and altitude. This means they can be very misleading at times.

3. Boost is a measure of resistance not flow rate. So without knowing an exact setup it is impossible to judge power on just the amount of boost. ie running a tubular exhaust manifold or a different cam could affect boost pressure, but the blower would still be flowing the same cfm. Intercoolers, TB's, MAF's and even the superchargers in question can all vary boost pressure.

4. CR, as all of these are n/a engines to begin with, they run fairly high static CR's. This means lowish boost will see higher hp figures. The limit is you can only run so much boost with street fuels before pre-detonation becomes an issue. Hence why factory turbo/supercharged cars normally run much lower static CR's, but they then need more boost, say 14psi instead of 6-8psi.

[chris7676]

Interesting points. 300hp/ton - what is CR ?

[skinny]

compression ratio?

[snotrag]

300bhp/ton said:

4. CR, as all of these are n/a engines to begin with, they run fairly high static CR's.

Not strictly true I dont think?

While granted the compression ratio isn't as low as some factory Turbo cars, the MX5 engines use a noticeably lower (less than 10:1 in some variants as I recall) compression ratio than many other engines of its type. This is due to its heritage of coming from the Turbo'd 323GTX.

This is part of the reason why -

A - Turbocharging them is so easy
B - they are not very economical in relative terms
C - head skims and raising the CR shows noticeable power increase on NA engines



Its kind of a double edged sword really. As a comparision, the engine in my old GTi-6 was only 200cc bigger but so, so much more powerful and flexible in standard form. It ran a much higher Compression ratio (No VVT either, fixed cam timing still). But this also means that, the people who bolt Superchargers on then find them very quickly melting, with not a lot of boost, and have to uprate pistons and rods etc to suit.

Edited by snotrag on Tuesday 10th May 16:47

[Richyvrlimited]

snotrag said:

Not strictly true I dont think?

Edited by snotrag on Tuesday 10th May 16:47

Yeah the 5 engine doesn't by any stretch have a high static compression ratio. Honda's generally do, but the B6 & BP from Mazda definately don't.

That's partly why they take to FI so well.

[300bhp/ton]

What sort of static CR do they run?

Typically I'd say factory turbo motors would be 7.x:1, supercharged 8.x:1 and n/a 9.x:1 or 10.x:1. Although modern electronics and premium grade fuels do allow even higher static CR's.

[skinny]

think the 5 is around 9:1?