|
Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain. |
|
Thread Tools | Search this Thread |
05-13-2020, 07:23 PM | #15 | |
The Dictater
Join Date: Apr 2017
Drives: '13 Red Scion FRS
Location: MD, USA
Posts: 9,432
Thanks: 26,115
Thanked 12,433 Times in 6,148 Posts
Mentioned: 85 Post(s)
Tagged: 0 Thread(s)
|
Quote:
Cams operate the valves that let air into and exhaust out of the cylinder. Cams operate in a cycle fixed to the rotation of the engine, turning 1/2 turn per engine rotation in a 4-stroke engine. The intake valves open on the intake stroke, the exhaust valves open on the exhaust stroke, with no valves open on compression and combustion strokes. NA gasoline engines are typically oxygen-limited, meaning the more air you can get in the cylinder, the more power you get. Lift is the amount of distance a given valve opens. More lift, more airflow, more power (or less power lost in the case of exhaust flow). The valves will only lift as much as the profile on their cam forces them to. Duration is the amount of time the valves are open. More time open means more total amount of air gets into or out of the cylinder at a given flow rate (determined by, among other factors, the lift). There are other considerations such as how 'sloped' the profile is because you can't go fully open to fully closed instantaneously. Greater slope means you need stronger valve springs, which in turn means you lose more energy to valve spring compression each engine cycle, so you have to balance that too. Now we bring in timing, which is the offset between top-dead-center of the engine and that of a given cam (every other rotation). AVCS makes timing almost infinitely adjustable, so we really don't need to worry about that in terms of hardware. Instead it is just tuning parameters. Based on the lack of cam products available, it looks like Subaru did a pretty good job with the cam optimization to begin with. There isn't much room to grow with lift because of physical can clearance (it's a boxer after all), and increasing duration would likely only help at higher RPMs, and would probably hurt at lower RPMs. Timing can be adjusted however you want with tuning. |
|
The Following User Says Thank You to Spuds For This Useful Post: | x808drifter (05-13-2020) |
05-14-2020, 12:42 AM | #16 |
Senior Member
Join Date: Mar 2014
Drives: '15 BRZ RA
Location: Greece
Posts: 3,787
Thanks: 2,416
Thanked 1,944 Times in 1,261 Posts
Mentioned: 29 Post(s)
Tagged: 0 Thread(s)
|
I was researching this topic for some time. Our cars don't have an external EGR system, but it looks that a similar functionality was implemented in the factory cams. Specifically, in the exhaust cam which retards the closing time of the valve. This was mentioned in an official engine paper (file attached). The Piper Stage 2.0 cams (272° 266°) are particularly good to eliminate this setting and enhance the scavenging effect. The HKS cams don't do anything to eliminate this setting. Does it really matter? Are there any considerable gains if the rev limit is not raised? No one really knows, because we don't have any dyno results.
. Last edited by nikitopo; 05-14-2020 at 02:33 AM. |
02-03-2022, 02:25 AM | #17 | |
Senior Member
Join Date: Jan 2017
Drives: brz 2017 hksv2
Location: italy
Posts: 2,196
Thanks: 500
Thanked 1,067 Times in 775 Posts
Mentioned: 65 Post(s)
Tagged: 0 Thread(s)
|
Quote:
EGR is not something implemented physically in the exhaust cam, it is achieved though VVT. The around +40 of retard in the exhaust cam combined with -10 of advance (so retard actually) in the intake cam that you can see in the avcs tables low rpm/low load is what gives an EGR effect You change cams and keep those Avcs tables, you still get and EGR effect, it's the combination of exh retard + int retard at low loads anyway |
|
The Following User Says Thank You to tomm.brz For This Useful Post: | NoHaveMSG (02-03-2022) |
|
|
Tags |
camshafts, engine, valve, valvetrain |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
HKS 2.1 stroker kit & camshafts | nikitopo | Engine, Exhaust, Transmission | 7 | 03-24-2020 06:51 AM |
Just ordered new Camshafts | Fonzi | Forced Induction | 21 | 02-11-2018 02:31 PM |
Piper Camshafts | brn12345 | Engine, Exhaust, Transmission | 120 | 10-02-2017 10:28 AM |
Camshafts and Boost! | Dream20b | Forced Induction | 23 | 01-16-2016 02:49 PM |
CAMSHAFTS! have they made any? | karma003 | Engine, Exhaust, Transmission | 21 | 11-04-2013 07:35 PM |