You really need to post up/link us to the other guy's mod list and/or dyno (log file)/tuner at this point.

It simply could be that the other guy's supporting mods aren't up to the task and the tuner had to pull timing/power to keep things happy. Keep in mind Harrop's flex fuel kit includes 1100idx's. Also, if the guy is on the stock clutch or stage 1 equivalent they would have to chop the gains to keep it from glazing.

Lastly there is a big difference in tuning. As Justin posted, variations can easily effect number. As can what the car is being tuned for. Tuning a car for max power for a few runs on a dyno is very different than tuning a car to run 30min track sessions back to back. A lot of tuning companies will also play it safer when they tune a larger volume of cars or if the user isn't very wrench handy. It's very common for a build to go wrong and the first bandwagon everyone hops on is it was a bad tune...

--

If you want to feel better here is a dyno pulled for the UK forums. Member MartinT and Mark's which were tuned by the UK's Abby Motorsports. And an unknown users car tuned in the US by TRL. They are all hitting just below the expectations posted above without e85, a smaller pulley OR larger injectors. 260WHP (300bhp/223.7kw.) This slots it right in between Harrop's advertised Stage 3 and 4 packages FWIW.



MODS:

Stock Engine
260whp
TD (Tuning Development) UEL catless header
TD 2.5" full exhaust with highflow secondary catalytic converter
HKS Intake Duct
Harrop Supercharger with a 95mm pulley.
98ron
Attachment 206476

251whp
Mark's Abbey Tuned 'ginger' 86.
Stock car, stock exhaust.
Harrop Supercharger with a 95mm pulley.
98ron
Attachment 206473


272whp
Car Tuned in January 2020 by The Racer's Line.
JDL 4-2-1 Headers
Harrop Supercharger with a 95mm pulley.
91octane
Attachment 206474

The only other thing I forgot to say that I wanted to say is a turbocharger is great, but the numbers can be misleading sometimes. In general, they have less parasitic losses, so they will make more torque for a given psi, but sometimes things are exaggerated. I am currently working on a K24 swapped car with a G25-660 clone turbo, so I am not hating on turbos when I say that the numbers can be exaggerated in a way that is just not possible for superchargers. I just want to point it out that someone should really compare the area under the curve and not just peak numbers.

For instance, a person may quote how their car made 300wtq at 10psi with their turbo, but when you look at the dyno this is only a partial truth. All they quoted was peak torque, but maybe the car is far from averaging even close to that number. Come to find out that the peak number was actually a boost spike to 12-13psi on the initial ramp up before a tight wastegate opened, so the peak wasn't even 10psi. Depending on the turbo size, the turbo may have a high boost threshold where there is not much happening down low, or it could have a smaller turbo, which limits the top end. In the example below, the boost spike versus the sustained torque/boost is a difference of maybe 25hp from 482 to 455ish, and the turbo is restrictive on the top end, so the horsepower really flatlines, as torque falls off. At 6k the engine is only making 350ish, which is quite a drop from 482. Go the track with such a car and shift at 5.5k+ and now the torque is 300-400ish the whole time, which is quite a drop from the peak of 482 someone might have boasted about.

I'm not saying someone can't have their cake and eat it too with a turbo, but it takes a properly sized turbo to equal or best the reliably and predictably, relatively-flat, torque curve and build in horsepower to redline as a supercharger. Newer turbos can spool fast and flow enough for bottom and top end torque. Turbo will ultimately be better, but I'm just trying to illustrate here that the quoted peak numbers sometimes don't tell the whole story for trying to make apples to apples comparisons. Check out the dyno graphs.

https://www.bimmerboost.com/images/i...11_53_22-1.jpg

Changing the subject slightly, and also showing how fickle superchargers can be...

I finally think I've (completely) nailed my belt issues with the 65mm pulley.
The slip and shredding is now a thing of the past (fingers firmly crossed).

The larger idler pulleys I squeezed in allowing a shorter belt than recommended, and also delivering an improved contact area over the 65mm made the biggest immediate difference.
A Grip-Tec 65mm pulley then helped with some of the (slight) continuing belt slip.

And the last piece of the jigsaw... finally fitted the supercharger focused Gates RPM belt yesterday (after having trouble sourcing the correct size for a number of months)

My gut feeling is the new belt has now removed any leftover (excessive) slippage.
They certainly appear to be a superior belt for this particular scenario.

Its been interesting to feel the power delivery changes after each step and subjectively the power increase (realising a more reliable "boost" pressure) feels like the difference between a cool night vs a hot day.

Happy days.

Which idler? -The one directly in front of the supercharger pulley? By upping the size were you able to get more of the belt's surface in contact with the 65mm pulley?



I always wondered if one could make a pseudo belt wrap kit for these cars or an AMG styled tensioner pulley lock/brace (to keep it from bouncing after belt installation.) To bad the front cover's bolt holes are super weak on the fa20.



Are you using an overrunning pulley for the alternator?

Did I miss something? I thought he just increased the size of the idler pulley, so the belt hugs the supercharger pulley more. Did he increase the crank pulley diameter?

When you go to smaller supercharger pulleys one potential issue with belt slippage is the load on the alternator. When you have you belt off spin the your alternator by hand and then quickly grab it so to stop it. You well feel a mass/force of the alternator when you do so. This is shock felt every time you quickly let off the pedal during load. What it does overtime is stretch your belt which can also cause slippage. Given he is going for a 100% no slip target, it may be worth looking into if he hasn't.



An over running pulley isn't related to the charging system overcharging --which I think you might be referring to given that you mentioned increasing the crank pulley's size.
It is a special pulley that has a 1 way clutch-like bearing inside of it so the alternator can keep spinning forward when the belt is abruptly slowed down.


I haven't heard much on this platform however, I've seen member using TVS blowers on other platforms (like Harrops Tacoma package) chasing this issue. Going for a 100 belt slip fix might include that. I don't have enough info on hand though.

This shows it.
https://www.youtube.com/watch?v=DJBMkfI9CYc

Yeah, I thought you meant over-spinning the alternator. I do know some people have been concerned about the alternator when increasing the rpms or crank size. In one case a guy raised the rpms and then did it again when he destroked the motor, and he had a supercharger with a larger crank and small pulley and was asking about the max rpms on the supercharger, but someone else chimed in about the alternator with all his mods. I think they said something like the alternator has to work at a wide range of rpms, but might have a spinning limit.

I didn't know if you got confused, but apparently I was just confused about what you are talking about, and I get point you are making now. This video was a better visualization of the effect. Seems like a no brainer, but I have to wonder why these things aren't standard unless the service interval is short or there is risk of damage or something. Is that the case?

https://www.youtube.com/watch?v=XYi_w3ieGUo

Yeah, I put two significantly larger idler pulleys in, and you see can the effect it has on the contact area... much better "wrap".
Although increasing the recommended belt size from 2440 to 2446, the belt is now much much tighter due to the enlarged idlers.

And talking about drag from the alternator, ever since fitting the smaller pulley and fitting 2 new high volume Spal fans wired direct to the battery, if the aircon was on and the fans (all) kicked in on idle the engine idle would drop and recover, albeit slightly (even with a reprogrammed motec working its wonders). So I put in a 2 second "delay on" in one of the fan relays, so very slightly staggering them, and the problem was solved. (amazing how much instant power drag those fans can cause)

I had a chat with the Harrop guys about the realities of %100 no slip, and they suggested its perhaps not an ideal scenario for most non track cars.
I got the impression that some (limited) slip can be/is desirable to mitigate some of the belt shock that can occur with with aircons and (like you suggested) modern high power/load alternators.
The RPM belts should also be more resistant to stretch.
If I was continuing to have issues, my next step was actually the alternator pulleys you mentioned, they are not too expensive, look look fairly easy to fit. (And since I staggered the two fans switching on, it seems to mitigate a little of the instant drag)

Very different topic, what has been your experience with that Fluidampr? Did you have it before the SC? I've debated getting one for my NA in anticipation for supercharging, but have since decided against it just due to the work required to put it on and it probably not having much of an impact on an NA motor. If you have before and after experience with it with the SC, I'd be interesting in hearing your thoughts.

It replaced a lightweight pulley, so it was a relatively recent fitment , a couple of months after the 65mm pulley and the built motor were finished. I had also fitted the much more solid engine mounts (the Cusco units) to control the extra engine twisting forces with the added torque (the exhaust system until then was a constant hassle juggling tight clearance issues).

The difference between the lightweight pulley and the Fluidampr was actually quite dramatic...but I think that might be as much about how inappropriate a lightweight pulley was on this set up!

So taking into account that I'm comparing it to something that I feel was not fit for (that) purpose, I still have positive feelings about it. The damper did seem to have an effect on lessening (some) of the added vibrations running through the new mounts.
It also felt like it smoothed out a little of the sharpness of the alternator and aircon loads as they kicked in or out.
The added rotational mass I feel is also a benefit with the smaller pulley, given the extra load, particularly at low revs... with slightly smoother idle, and perhaps a generally slightly smoother "feel" to the engine.

But I guess its a pretty subjective thing and its hard to quantify... but if I had to do it again, and spend the money, I believe I would.
Though I'm not sure there might be enough benefit/need with a fairly standard NA motor.

BTW. its very easy to fit, you just need a very long breaker bar to get the old one off... then a torque wrench for quite a low initial torque setting, then tighten the bolt for a further 90 degrees (ignoring the torque reading), and you're done. (a new bolt is probably a good idea too!)

Is it possible to bleed boost with these units? I watched a Harrop video and they mentioned the bypass valve could be used to bleed boost, but I haven't seen it anywhere else.

I'm looking to more or less flat tune 250whp with one of these.

I'm still unable to rectify the very rough idle..with multiple misfire..
Anyone want to take a look at the full log and maybe able to figure out what might be going wrong?
https://datazap.me/u/ojuniour/log-16...16-17-18-22-29

after the initial high idle start as the idle settles down 9after 15 to 20 secs or so).. that's when the misfires kicks in and really shakes the whole car..
It eventually smoothens out as the car warms up
Thanks.