Do I install a Rev300 of buy an OEM SC - Page 2 - LotusTalk - The Lotus Cars Community
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post #21 of 39 (permalink) Old 08-07-2019, 08:27 PM
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OK, would you explain the thermodynamics a bit more completely than a single word? All I have so far is my own conjecture. Not inter-cooled, so at high ambient temperatures, the blower outlet temps are very high, the engine intake passages get hot which further heats the inlet flow so that velocities get very high and this increases pressure losses which in turn increase the back pressure on the blower resulting in less airflow? Am I getting close? If so, are there data? Does this happen at 59 F or only on hot days?
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post #22 of 39 (permalink) Old 08-07-2019, 09:59 PM
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OK, would you explain the thermodynamics a bit more completely than a single word? All I have so far is my own conjecture. Not inter-cooled, so at high ambient temperatures, the blower outlet temps are very high, the engine intake passages get hot which further heats the inlet flow so that velocities get very high and this increases pressure losses which in turn increase the back pressure on the blower resulting in less airflow? Am I getting close? If so, are there data? Does this happen at 59 F or only on hot days?
Since kfennell's response was "heat", I think it's safe to assume your post was addressed to him. He's offline, so perhaps you haven't seen my response, which explains "heat" and other factors a bit better (below).

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The factory supercharger (MP45) is very small, isn't intercooled and heat soaks quickly. The extra weight just adds insult to injury.
This is a very general explanation from a forced induction novice.

Whenever you compress gas (air/fuel) with a forced induction device (SC, turbo), heat is produced from the compression. An intercooler is to cool the compressed gas after the forced induction device (SC, turbo), before it enters the cyclinder. Cool, dense gas (air/fuel) makes more power and lessens the chance of pre-ignition/knock, and allows for more agressive timing.

The sizing of the forced induction device is important as it can be too big (lots of lag and a small rpm range of effectiveness), or too small (little lag but doesn't pull hard throughout the RPM range). The size also effects the efficiency. A small device out of its efficiency range and blowing hot air (more heat in the air than needs to be for a properly sized device) in a non-intercooled system can potentially be less powerful than without the SC/turbo, as the cool, dense air/fuel charge we seek isn't there.

Another scenario is that when the entire system (engine, forced induction device, intercooler (or not) etc.) is "cold", the SC/turbo adds power to the system as intended. Once warmed up, or when portions of the system are heat-soaked (easily done with a SC/turbo without an intercooler), cooling the systems (and more importantly the air/fuel charge) won't happen, or takes an extended period of time depending on the IATs etc.

The bottom line is most systems have adequately sized forced induction devices and properly sized intercoolers to add power and sufficiently cool the air/fuel before entering the cylinder, to consistenly produce a baseline of power. The MP45 is just too small to efficiently add power to the system without heat-soaking, and without an intercooler, the system pulls timing and thus reduces HP.

There's a reason there are no aftermarket tunes for the MP45. The system doesn't have any headroom to allow for more power. It's already heat-soaked under normal use.

Removing the MP45 and adding a proper SC and intercooler provides an opportunity for a healthy amount of power.

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post #23 of 39 (permalink) Old 08-08-2019, 07:56 AM
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I don’t track my car so the heat soak doesn’t matter to me. My car with the factory supercharger is way faster than the stock. I have done a couple of early morning back road quick races and I have beat them. It all depends what use you are going to give it.
Way faster than stock? The Elise SC "can" be faster than your standard NA Elise but it is only a couple 10th's. You have to be a damn good driver or abuse the drivetrain to get those times with high RPM dumps. In bench racing, we are talking 4.5-4.7 and in the quarter 13.2-13.4 depending on what mag you pull your stats from. Stock Elises have been tested to hit the same time as the SC version depending on variant. Lotus added the SC to get a better torque curve. So I think calling the Elise SC way faster is an overstatement.

Edit: That sounded kinda snarky, wasn't meant to be.

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post #24 of 39 (permalink) Old 08-08-2019, 05:05 PM
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I have driven both back to back and the SC feels like it pulls significantly more at every RPM. I'm not saying that's better than a bigger charger and intercooled. I'm just pointing out that I rather have a factory SC than a natural aspirated. Based on what the op wants to do with the car, he will be better buying an Elige with a factory SC than spending money and time to install an aftermarket SC and selling it within a couple of years. Most buyers rather buy a factory setup lotus SC than one that was aftermarket modified.

If you are planning on keeping it for a while and tracking it, then I would go with a NA Elige and add the Rev 300/400. I really enjoy my Lotus SC for the kind of use I give it. When I want to go faster I drive my Alfa 4C with stage 2 tune and intake.

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post #25 of 39 (permalink) Old 08-08-2019, 08:58 PM
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Originally Posted by kfennell View Post
The factory supercharger will be slower then NA on the track.
But not at the autocrosses.

On the the other hand, in Street Prepared, the Elise SC runs in the same class as the supercharged Exige. It is not the intercooler that makes the difference there, but the size of the supercharger.

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post #26 of 39 (permalink) Old 08-09-2019, 05:52 AM
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Thx. I am a gas turbine engineer, so I am fairly conversant with the thermodynamics of compression. This appears to me to be more of a matching problem at high temperatures than anything else. Bear in mind that when you cool the exit of the SC, you do reduce duct losses and valve port losses downstream of the SC. That allows more airflow (and fuel flow and thus increases temperature rise in the cylinder). So, yeah, cooling the SC outlet flow, despite the pressure losses inherent in cooling, gives much greater bhp and torque. But the performance crossover with NA still mystifies me unless we introduce the nasty unknown of the electronic control logic and all the various safeguard limits they presumably built into it.
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post #27 of 39 (permalink) Old 08-09-2019, 08:02 AM
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I have driven both back to back and the SC feels like it pulls significantly more at every RPM.
Yes, I agree with you there and why Lotus added the SC. Like I stated previously, it provides a better torque curve thru the RPM range and that's what you are feeling. It isn't much faster than the NA Elise by mag tested times 0-60 and 1/4 mile.

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post #28 of 39 (permalink) Old 08-09-2019, 10:38 AM
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What do we think real world 0-60 times actually are? The numbers commonly published are 4.9 sec and 4.4 sec. Do those sound right?
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post #29 of 39 (permalink) Old 08-09-2019, 11:05 AM
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Something I have not seen mentioned is elevation, though it doesn't seem that will factor in for the OP. I've ridden in NA, stock supercharged Elise, stock supercharged Exige, and a few different levels of BOE setups here in the Denver area. The stock supercharger in both cases is far better than NA at this elevation, heat soaked or not. The various stages of the BOE tune are just on another level. If resale is the goal though, go stock supercharger.
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post #30 of 39 (permalink) Old 08-09-2019, 01:31 PM
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Agree with above post
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post #31 of 39 (permalink) Old 08-11-2019, 07:49 AM
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Ive tracked my Rev300 Exige at least 3 times in the desert heat of SoCal and if I do get heat soak, its not enough that I can feel it or to coverup the fact that I'm still a novice as my laptimes have always gotten faster as the day progresses. I also will say that adding the SC took my car from letting everyone by on the straight to passing most now. My car went from a stock 180whp to just under 250whp and it transformed my car...

But back on topic, I think both SC (Kits) will hurt value. But thats why you keep the stock bits and put it back stock when it comes time to sell. Or better yet, try to sell it with the SC kit and if you don't get what you want sell the kit 2nd hand (you won't get much) and put it back stock and then sell.

I thought I saw some laptimes for the Exige and I've always wondered why the 240/260 doesn't put down better laptimes than what the standard 2007 version. Car and driver has the 240 slower than the 2007 Exige for lightning lap, too bad they didn't run the 2006 Exige... heat soak is an interesting topic.

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post #32 of 39 (permalink) Old 08-12-2019, 06:29 AM
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On a high 90s day with good drivers driving both cars with similar tires the Exige S lost 3 consecutive dragraces down the COTA back stretch against 2 different cars with 2 different drivers. This was a car with an upgraded intercooler, but importantly, the stock programming, which fully retards the timing at an impossible to avoid 160 degrees and starts at like 130?
Factory IAT/Timing retard with a stock calibration actually begins @86*F IAT, believe it or not, and increases to a max of 6 degrees @ 158* F IAT for engine protection. The factory had to deal with warranty considerations and the lack of control over the end-user's selection of proper fuel/octane..... their solution, aggressive timing retardation.
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post #33 of 39 (permalink) Old 08-12-2019, 08:17 AM
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I have tracked a REV300 Elise in South Florida and I have not noticed a substantial heat soak. However, if you use 98 octane gas versus 92/93 pump gas you do notice better performance. As mentioned in other posts if you want to maximize the value of your car keep it stock but the increase in torque changes the car.
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post #34 of 39 (permalink) Old 08-15-2019, 02:01 PM
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The factory supercharger will be slower then NA on the track, so theres that...
For real? Why is this?
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post #35 of 39 (permalink) Old 08-15-2019, 02:25 PM
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Two questions: Do you want to have lots of fun? Do you want to also get frustrated dealing with the manufacturer of your supercharger? If you said yes to both, absolutely go the BOE route. Further, if you want to maximize fun per dollar, just go for the Rev300. I went from the 300 to the 400 (along with some other upgrades) and the second increase in power isn't really worth the trouble.
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post #36 of 39 (permalink) Old 08-15-2019, 02:49 PM
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For real? Why is this?
timing is being pulled.

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post #37 of 39 (permalink) Old 08-15-2019, 03:13 PM
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I'm not going to persuade you one way or another. Everyone has their own reasons for increasing horse power.
No matter how good a car is...everything comes down to hp to weight ratio.
If you are happy with a 10:1 hp to weight ratio then you are good to go. In this case you seek more power.
If you want more power then you need to assess how much? I can tell you a M45 most likely is not going to meet your objective, why? because the increase in HP with the M45 will not be enough gain to satisfy your need for power. Those that have a M45 (I being one of them) and satisfied (I'm not one of them... well yes and no) then it meets one driving expectations. For me, when driving on the public roads, (not often I admit) the performance is very pleasurable. That changes when I'm on a road course because unless you are in a spec class, where you are competing with cars similar in hp to weight ratio, you will find yourself spending a lot of time glancing at your side mirrors to see who's behind you.
That's not fun for me as for many years (over 20) I have enjoyed a hp to weight ratio of <6:1 and that ratio still works today with all the new performance cars being tracked.

A noticeable difference at a minimum would be a Rev 300 and of course, Rev 400 if you track.
A M45 will leave you wanting more IMHO but like I said everybody has their reasons.

Just my .02
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post #38 of 39 (permalink) Old 08-15-2019, 06:59 PM Thread Starter
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Thanks for all the info. I think if I were planning to keep the car then I would go Rev300. If I plan to sell it and I want it to be legal in CA then the OEM makes the most sense.

But the OEM doesnt seem like itll give me enough change.

After all that though I think I might be on the fence for selling it and moving to an Evora S! The looks dont quite agree with me yet but its growing on me. I also need to drive one.
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post #39 of 39 (permalink) Old 08-15-2019, 08:27 PM
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Thanks for all the info. I think if I were planning to keep the car then I would go Rev300. If I plan to sell it and I want it to be legal in CA then the OEM makes the most sense.

But the OEM doesnt seem like itll give me enough change.

After all that though I think I might be on the fence for selling it and moving to an Evora S! The looks dont quite agree with me yet but its growing on me. I also need to drive one.
My car with Rev300 passed the notorious California emissions last year with zero effort on my part. I did nothing to it since my last track day other than washing it.. (it did have soot all over the back). But the guys at BOE know their stuff..

I love Lotus and my Exige but I have never been an Evora guy. I also thought the evora would grow on me, maybe it just needed a slight tweak but no.. The V6 Exige has grown on me tho. The new Vette is also growing on me, if I had an extra $60K, I might be putting down a deposit..

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