zze86

anybody have good dynos of AP1 with stock vs a test pipe/HFC? Searching on the forum is exhausting, I get a lot of hits from Gernby's old posts which, while informative are based off his AP2, or have images that are down or for something completely different.

Looking for how the curve looks like and how it changes. Not too interested in the actual numbers.

TIA

Chibo

You want a tune that lowers VTEC to take advantage of the HFC. There are example dynos of this at Karcepts, Inc. - Karcepts S2000 e-Manage Ultimate Base Tune
You're not going to gain much back-to-back without tuning for it.

zze86

Thanks for the link. It's blocked from where I am at currently so will view it later on.

I understand a tune is required to get the most out of the HFC (or any mods for this car really) but I was most interested in looking at the torque dip at VTEC crossover and surrounding area. From reading Gernby's old posts and other old threads it seemed like the F22 seems to suffer a more dramatic dip than the F20. His conclusion was that the placement of the OEM cat really messed with the resonance tuning of the engine and his solution was to tune the exhaust resonance specifically around that area hence the URGE/Gernby exhaust. However, resonance tuning is pretty specific. You tune the resonance for a specific area in the curve for a specific engine. The F20 is not the F22 so I question whether Urge/Gernby exhaust is even compatible with the F20.

But I'm not really interested in the Urge/Gernby exhaust. In Gernby's testing, a TP and HFC created some rather large torque dips in his curves. Some that he just could not tune out with engine management. Which led him to the aforementioned resonance tuning. The same phenomenon can be seen on many other F22 examples.

From memory, the F20 VTEC crossover isn't as dramatic as compared to the F22 so I wonder if a test pipe/HFC causes as dramatic a torque dip on the F20 as seen on the F22. But then again, I'm old now so memory is not what it all used to be thus I was looking for dyno charts.

spaded.racer

You're over-thinking it. You will want it tuned(by a good tuner) to get it as smooth as possible.
This wasn't my final numbers but my tuned AP1, no dips... nice smooth power(PLM header->Berk HFC->Berk 3" single exhaust);

s2000Junky

The flow character around vtec transition/rpm is pretty identical between the f20/f22. The biggest difference between these engines is the ecu era they are accompanied with, which made leaner and leaner fuel changes as the years went on. Naturally, the early ap1's saw the most power gains with bolts ons, including TP/HFC before external tuning is employed. But regardless with the stock cat still in place all of these engines/years lose power if you try and lower vtec bellow 5300rpm due in large part to your fundamental question, so deleting the cat is an all around efficiency boost no matter what and is magnified x10 when you ask the engine to switch to secondary cam earlier then stock - typically 3500-3600rpm gains are realized). Your not going to get a dip in power switching over to a tp/hfc with no tuning unless your other bolts ons are already putting you on the verge of leaning out the factory tune to the point that you have surpassed lean best afr and now increase flow enough to starve engine for fuel. This potential would be most likely in 06+ DBW examples.

zze86

Thanks for the replies all. Good info about the factory getting leaned out over the years.

I will be installing a Megasquirt3 soon here and I am planning my mods for the next couple of years.

A complete plug and play ITB kit is already bought and waiting for baseline with the new ECU to be established.

A HFC seems like the next logical choice but I expect the VTEC engagement point will be lowered in the process of tuning and I recalled the issues with lowering the VTEC and a TP/HFC. As well, I seem to be especially sensitive to the harmonics/resonance (drone) at which the stock exhaust system is tuned. An off the shelf TP/HFC may exasperate it for me. Droning was an issue Gernby encountered as well and was trying to correct for also.

Thus, I was wanting to see if the F20 behaved in the same manner when adding just a TP/HFC. But I guess I should be looking for one with a lower VTEC engagement point as well.
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Digging up some dynos, if it suggests the same I may go a custom route.

flanders

You should really consider going for a test pipe if you are installing ITB's, on my car there was a huge difference between HFC and test pipe.
I only compared with virtual dyno but there was close to 20whp difference up top.

zze86

That is a big difference!

I am committed to a HFC though. Even if I take a hit on the HP front. Not to get too tree-huggery but even an aftermarket HFC removes a majority of the pollutants that a car spews out (when properly placed). This is one of my complaints with the Urge/Gernby solution. The cat is way too far back to be doing any good (chemically) except for perhaps being a large-particle trap. It may be that he placed it there for resonance (power) reasons so his priorities with that is a bit different from mine.

But, I think the solution to the power problem is rather easy. Just go bigger. The off-the-shelf HFCs available for the S are way undersized in my opinion, even for a stock motor. They are taking advantage of the higher flowing core which will produce better results than the OEM unit but they're still not ideal. They need to go bigger (radially) with a longer inlet diffuser and possibly a longer monolith as well. The pressure increases dramatically at the front face of the monolith structure. Since Pressure = F/A if you increase the area that force is applied across the pressure drops down accordingly. From fluid mechanics, lower pressure leads to higher velocity = higher flow. A long inlet diffuser should help to smooth the airflow (less turbulence along the walls) so that more of the cross-sectional area is actually reachable by the mass flow. The pressure differential across a longer core could also help excavate circumferential flow.

A paper with static CFD modeling that I found is attached if you're at all interested (Ibrahim, 2017). A second paper that is more robust but deals more with catalytic efficiency is also attached (Tsinoglou, 2004), but corroborates the pressure differential and higher velocities with the longer monolith (compare the two 750K graphs).

Of course, that's all theory and I haven't really dug into the harmonics/resonance thing yet either or actually tried measuring for space underneath the car so it may be that I end up with something similar to Gernby, lol. From his posts, it looks like he was testing with bolt-on, off-the-shelf parts and didn't go to a (much) larger TP/HFC. Ideally, I'd want a HFC near the stock location for quicker, higher catalytic efficiency that will eliminate (or reduce) drone without hurting performance too much.