Who told you SRI doesn't work well at low RPM compared to stock? :pQuote:
Originally Posted by Omotesando
At low RPM, the flowrate of air is lower, so with the same cross sectional area, the velocity is lower. If you use a narrower pipe, then the velocity increases. That's why huge CAI piping has losses at low RPM.
The gruppem intake seems like a very interesting design. One of the main problems with the Euro is that the engine is very sensitive to heat. Since I installed the icebox I don't have this problem at all anymore. I'm pretty sure the CF shield works very well as a heat insulator, but since there must be some gaps between the heat shield and the car, do you notice the car bogging down slightly after a long drive? Any changes in the throttle response?Quote:
Originally Posted by Chris_F
I wish the Icebox did that for me - I want my Euro to drive all the time like it is a 4 degree Melbourne morning.Quote:
Originally Posted by sodaz
The difference in how the car revs compared to a 30 degree day is very noticeable. I have read some people say "all cars do this" - but the cars I have driven are only slightly different depending on air temp.
The length of CAI piping also has a big part to play.Quote:
Originally Posted by aaronng
But in terms of what OMO has said - I have read that some resistence in the intake design (eg the fins in the OEM box) help maximise low end torque but at the sacrifice of peak power. So a simple straight through SRI could quite possibly lose torque down low compared to the OEM box as it is a resistence free design.
Any engineers care to comment?
I have also read that lengthening the airflow's path actually increases torque - but I couldn't find much information on the net that actually justifies that.
Yeah, both length and diameter affects intake airflow characteristics.Quote:
Originally Posted by yfin
More length at low RPM means at the WOT, the air of low velocity in the tube has to travel through the piping to the throttle body first. As the existing air is sucked in, air from outside the filter is sucked in at a higher velocity. Hmm... how do I explain this.... It's like a train with many carriages. The link between each carriage has a little free play. When accelerating from a standstill or low speed, the engine pulls ahead, widening the gap to the 2nd carriage because of the "flexible" link and then pulling the remaining carriages behind it. Like an accordion effect. But when the train is at high speed, the links are rigid, because of the drag in the carriages behind. So if the engine then increases its speed sharply, all the carriages behind it also increase in speed accordingly and there is no accordion effect observed. I hope my explanation makes sense.
The stock airbox and comptech airbox provide a resevoir for an initial mass of air so that low RPM torque and response is maintained. An SRI is essentially the same length as the stock intake before the airbox. So response and low RPM torque is also maintained. BUT, in real world driving conditions, heated air from the engine bay reduces the density and thus negate most of the gains from the SRI. The CAI doesn't have as bad a heating problem, but the lack of an airbox and the long tubing means there is less response before sufficient intake air velocity is achieved.
With regards to lengthening the airflow's path, did you get that from the dual length intake runners? That's only for the intake manifold though. The effects of intake pulses is not as observable at the intake arm (too far and pulses are not as apparant). Lengthening the intake manifold path doesn't increase torque output. But rather each RPM range has an optimum intake length where the frequency of the intake air pulses match a particular RPM. A short intake is good for high frequency pulses (high RPM), while a long intake is good for lower frequency pulses (low RPM). Using the proper length means maximum potential torque can be realised from the engine in that RPM range.
I wish that was so Aaron. The Comptech Icebox definately loses some low RPM torque - I have done some back to back road testing with the stock lid on and off (both with resonator removed and the horn in place). It is not as much as a full CAI but the losses are there.Quote:
Originally Posted by aaronng
I think the design of the intake lid has a part to play as the Comptech lid is completely smooth.
It's odd though. Most owners at tsx.acurazine.com reported the same or more torque at lower RPM. But then again, it could be imaginary power from the mod (or any mod).Quote:
Originally Posted by yfin
Well, the air in the stock airbox would be more turbulent than in the Icebox. So it could be the additional turbulence causing better mixing and thus less of a local pressure drop at the intake arm opening in the case of the stock airbox. If there is a large enough pressure drop with the icebox, then it would be like the case of the CAI, which experiences quite a vacuum when at low RPM and thus a loss of low end power.
I've been testing low RPM response with the new intake, but because of the electronic throttle, I sometimes get a 0.5 second lag which is random (less likely to occur if I let the RPM be on the downward swing before I go WOT). I'll have to rely on a dyno instead anyway since my butt dyno is a moody bugger.
I agree - no one seems to notice but it is there if you do back to back lid tests. Take a look at the Comptech dyno. See the torque chart:Quote:
Originally Posted by aaronng
link
Between 1700rpm and 2000rpm there is a torque loss of about 2-3%. There is a loss of power as well in that range but so minute it could be a dyno run variance. So pretty much the only weakness in the Icebox is 1700-2000.
These are fairly low revs so you mostly notice the loss if, say, you are in a high gear such as 4th cruising along at a relatively low speed (can't remember the exact speed - maybe 40 or 50kph and then you give it WOT). But you really need to do back to back testing with the lid on and off to notice the difference.
I am quite excited about all the ECU options becoming available as the torque increases even at a low 1500-2000rpm look fantastic. More important to me than peak gains.
*blinks*
english plz, which is better hehe
Well I've driven for periods of more than 2 hours in the past, some city driving, some highway driving, then some more spirited driving through the mountain twisties, and out of interest when i stop i always feel the heat shield out of interest. And even after a couple of hours of this sort of driving it feels basically the same temperature as it was when i started the journey, if anything it's a few degree warmer, but it's really not that noticeable. And I've never noticed the car bog down after a long drive at all, maybe on an incredibly hot day, but even with the stock airbox that happens, like others have pointed out the euros are really sensitive to changes in temperature (for better or worse). Also about the gaps between the heat shield and the car... I should go out and take some macro shots... the heat shield is designed within milimetres of all the surrounding objects in the space it occupies. There are a couple of small gaps, but it's amazing how tight a fit it is, and with the foglight cover removed there would be more than enough cold air entering the chamber to keep air temps down. Also i think the advantage of having a shorter length intake tubing and the pod filter as close as possible to the throttle body (whilst maintaining the stock rubber intake tubing) is more of a benifit for high rpm power than having a filter on the end of a longer metal tubing. Yes INJEN and K&N designs have access to limitless cold air, but the metal piping of those intakes does heat up which must affect intake temperatures even slightly (nore more or less than the gaps in the gruppeM box) and the longer tubing as aaronng pointed out would also act as a further restriction. Suck some water through a really long straw, then suck some through a shorter one, youll feel the difference (its a similar affect as far as i know)Quote:
Originally Posted by sodaz
Cliffs: no noticeable drop in throttle response after hard driving for extended periods, gruppeM intake has very few gaps, CAI designs would be more restrictive due to the longer intake tubing, the metal material they use would possibly transfer heat (probably not much more or less than the gaps in the gruppeM box).
Don't want to make my above post any longer (people probably won't read it as it is lol).
But there's been some intresting discussion about intakes in this thread as there always seems to be when it comes to intake designs haha.
Personally i think aaronng's got the right idea by making a well shielded SRI - should get the best of both worlds.
And yfin, good point about the ecu!
With a well tuned and more aggressive fuel map (and 40+ degree cam duration), the gains to low rpm torque that the stock airbox lid provides may become obselete and more of a restriction than anything, especially with a lower vtec point.
Can't wait to see some euro's with the reflash or EFI euro1 ecu, and the gains they are able to achieve with different setups.
This is a very good discussion guys!
And thanks for the detailed analysis Chris. I'd love to see some macro shots of the gruppem. It's no doubt a very well designed product.
I think an ideal intake should have the following characteristics imo:
1. Good throttle response (low-mid RPMs) similar to stock box
2. Good access to cold air (no bogging down after engine bay heats up)
3. Good noise at WOT, but stock sounding when driving slow
4. Smoother acceleration throughout rev range
5. Noticable power gains