Sam's build thread

[sambb]

I do have nefmoto but have only used it to load a tune. Havent logged with it because to be honest it looked like Arabic to me - the naming of all the columns etc and I'd put it in the too hard basket. But I'll get into it cos I'll probably have a play with my K03s and some pre turbo water injection before I jump into K03 hybrid territory. I need left foot brake, maybe linear throttle (but not sure about that) and would love to try a 2 step so i'll need to reacquaint with nefmoto to do all that too I suppose. Yesterday I upped the boost to 1.4bar and the thing came alive so Its liking boost more than timing. I'll get back into finding the timing threshold at that level when it dries out and then i'll be good to go.
Cool re getting back on the track. Its raining up your way too yeah. enjoy!

[seangti]

Yeah we had a wet back end of last week. Forecast is dry this week. Hoping for a dry weekend.

I have left foot braking enabled on my car, though had the tuner do it so no idea how to go about it first hand. I do like it with the diff, good to trim the line a bit when you're a little too hot mid corner.

[Sydneykid]

I think its the intercooler causing pressure drop. To my mind if you have a K03s which is into overspeed territory very quickly it is saturated easily. I'm thinking that with a giant pressure dropping IC and a small trubo that if the turbo has to generate an extra 2psi to compensate for the IC pressure drop, it can only do this by spinning faster but if its already saturated then no more power can be made, just heat. I seriously think the seat sport IC is robbing me of power. Just my two cents but I think that a single pass IC with less pressure drop augmented with water spray or water injection is the way to go on small turbos. As it is I'm going to slowly accumulate parts for either a hybrid K03 or garret which might tale a while so I'll live with it and keep the big FMIC.

High school physics Sam, Boyle's Law, do you remember it?

Keeping in mind that it's not the volume of air but the weight of it that determines an engine’s power output. Using the more recent combinations (temperature added) to Boyle's law, and some rough maths. Assuming that the intake air temp after the small intercooler is, say, 50 degrees and the intake air temp after the large intercooler is 30 degrees. Noting that the temperature used in the formula is absolute, hence add 273.

(273+50)/(273+30) = 1.066 so 6.6% increase.
1 bar = 14.5 psi
14.5 psi + 6.6% = 15.5 psi
So roughly dropping the intake temp 20C will have the same affect as adding 1 psi of boost to the weight of the air into the engine.

Then add the effects of the cooler inlet air on lessening detonation, which means more ignition advance can be used and lower exhaust gas temperature, all of which help power production.

More convincing?

Sorry there's still a little bit more of the rules of thermodynamics left to consider (ooops, more high school physics), the volume of air (in a confined space) is reflected in the pressure, which in our case equals boost. The volume of air changes when it is heated (or cooled) and I don't have a chart handy with 20 to 40 degrees, but I do have one for 22 to 43 degrees. If, say, 2 m3 of air is heated from 22 degrees to 43 degrees, then the volume correction factor is 1.08 and the new volume can be calculated as (2 m3) x 1.08 = 2.16 m3.

Using our small intercooler versus large intercooler temperature difference of 20 degrees that's around 8% less air pressure for the same volume. Hence 14.5 psi (small intercooler) would be 13.3 psi (large intercooler) because the air temperature is lower.

Net result, roughly gaining effectively 1 psi of boost due to weight and loosing roughly 1 psi of boost due to volume.

Any measurable difference greater than say 1 psi between the inlet air pressure into the intercooler and the inlet air pressure out of the intercooler would reflect its internal restriction to airflow. I'd also measure the inlet air temp in and out to give an idea of the efficiency of the intercooler. A really good air to air intercooler is around 75% efficient ie; it will drop the inlet air temp 75& of the difference between the compressor output air temp and the ambient air temp.

Something like, say;
100 degrees out of the compressor
30 degrees ambient
75% efficiency
= 100 - 30 = 70 x 75% = 52.5 degrees temperature drop across the intercooler
100 - 52.5 = 47.5 degrees out of the intercooler.


Hope you had fun with physics today?
Cheers
Gary

[Sydneykid]

I have left foot braking enabled on my car.

As I am sure you know, left foot braking is a band aid, simply covering up what the real problem is. Something like it needs more negative camber and/or caster on the front and more toe out on the rear. Properly set up, varying degrees of throttle lift should give you more than enough weight transfer control to mitigate any mid corner understeer.

Cheers
Gary

[sambb]

So basically if I have to add 2 psi to compensate for the bigger IC's pressure drop I still have a net benefit in that temps are lower. The only thing though is the k03s is way out of its efficiency range at 1.4bar. To find that extra 2 psi means really over speeding it though which has its own downsides but the bearings in it are new so it should be right I suppose. That's partly why I want to do pre Comp water injection to try to shift the compressor map for a more efficient top end.
Re left foot brake I sometimes find it really hard to do throttle lifts without it really aggressively dropping its boost which upsets the car a bit. Maybe a stiffer divertet valve spring would make pressure dumps on slight lifts less abrupt... not sure.

[sambb]

Actually that may be something to do with a fly by wire throttle because sometimes a slight lift not even done abruptly will behave as though you've slammed the throttle plate shut. Could be the tunes operation of the throttle plate on decreasing loads not necessarily doing what your foot is doing??

[seangti]

Everything's a compromise, though I like this article on left foot braking - Left Foot Braking – Chris Harris | FluxAuto

[Sydneykid]

So basically if I have to add 2 psi to compensate for the bigger IC's pressure drop I still have a net benefit in that temps are lower. The only thing though is the k03s is way out of its efficiency range at 1.4bar. To find that extra 2 psi means really over speeding it though which has its own downsides but the bearings in it are new so it should be right I suppose. That's partly why I want to do pre Comp water injection to try to shift the compressor map for a more efficient top end.

The better intercooling should result in less boost being needed to make the same horsepower due to the increased "weight" of the air.
The better intercooling should result in less boost being seen at the engine due to the decreased "volume" of the air.
Net, horsepower wise, you should be better off.

As I am sure you are aware boost is simply a measure of resistance to airflow and its actually the airflow itself that makes the power, not boost. My philosophy is to make as much power as possible at the lowest boost possible ie; remove the restrictions. To me lower boost is a good thing, as I only care about the horsepower. As a result I don't ever tune via the boost gauge, it just leads you up the garden path.

I don't know whether or not the larger intercooler has more pressure drop, I'd be surprised if it did. But the only way to be sure is to measure it, measure the pressure before and after the intercooler. Maybe there is a leak in he system and that's why you are seeing less boost than with the smaller intercooler. Try spraying some soapy water over the pipework, joints and intercooler and see if there are any bubbles.

Water injection is useful, but I'd probably use a mix of methanol and water. The methanol lowers the inlet air temp and the water lowers the combustion temp. I don't use it in circuit racing as we would have to carry the extra weight of water to last the race length. Wheras with a hillclimb you'd only need a couple of litres or so.

Cheers
Gary

[Sydneykid]

Re left foot brake I sometimes find it really hard to do throttle lifts without it really aggressively dropping its boost which upsets the car a bit. Maybe a stiffer divertet valve spring would make pressure dumps on slight lifts less abrupt... not sure.

My view is if we consistently need left foot braking to generate sufficient weight transfer to mitigate the understeer, then the chassis set up requires too much weight transfer. My approach would be to change the set up such that it responds better to slight throttle changes.

I always find that it's tricky to set up the boost retention so that a small throttle lift doesn't dump too much boost to atmosphere. At the same time we also want to avoid reverse air flow, which firstly means locating the blow off valve as close to the throttle body as possible. Rule of thumb, I start of with a spring in the blow off valve that retains around half of the maximum boost. So if I'm running, say, 20 psi max boost then I want to retain around 10 psi in the inlet system. If the ECU allows I also dump a bit of extra fuel into the engine on slight throttle lifts and also retard the ignition ie; anti lag. It takes a bit of fine tuning on the track and can be hard on the turbo, especially one that is not designed for anti lag.

With the drive by wire throttle systems in the Audi and the Porsche it was possible to have linear response on increasing throttle whilst having non linear response on decreasing throttle. But again that requires a lot of on track tuning as it's not possible to duplicate on the dyno, well not without an F1 simulator budget anyway.


Cheers
Gary

[Sydneykid]

Everything's a compromise, though I like this article on left foot braking - Left Foot Braking – Chris Harris | FluxAuto

The trick is finding the least compromise

I have read that article or something similar before, the problem is is mixes the disciplines of circuit racing and rallying plus confuses trail braking to the apex with mid corner stabs on the brake pedal in an attempt to alleviate the understeer. Coming from karting, many of the drivers I work with trail brake on turn in, towards the apex, and then apply as much throttle as possible as early as possible for a faster exit. In a FWD car there is very little if any time spent transitioning from trail braking to acceleration, ie; there's not a lot of "mid corner". Plus any mid corner weight transfer off the front end is controlled by the rebound damper rates in the front, the rear swaybar and the bump damper rates in the rear.

The problem I have with the hand brake analogy is that we typically run around 95/15 front to rear brake bias in a FWD car, so there's not a lot of (ie; next to zero) effect on the rear wheels' slip angle from left foot braking. Similarly with the wheel spin, if it's spinning the inside wheel then fix the diff.

With the chassis set up properly we shouldn't need to mitigate understeer because there shouldn't be any.


Cheers
Gary