Bumpstick discussion thread
 

Starting in this thread, a discussion about camshafts has been started. I didn't want to thread hijack, so I started a new thread and linked it.

Tom was earlier inquiring about the EG33 camshafts for his turbo application. This thread is mostly for chatting about performance bumpsticks, and also their effect on forced induction (mainly turbocharging).

I came back for a quick visit to see if anyone aside from SVXtasy has boosted, and well, this is what I get. :D :p

http://www.subaru-svx.net/photos/fil...vian/29567.jpg

Above is an image of the stock camshaft configuration. I whipped it up real quick for the purposes of this thread... But in case you can't see it:

Intake: Opens 2* B-TDC, closes 54* A-BDC, centered @ 116* A-TDC, 236* duration.
Exhaust: Opens 55* B-BDC, closes 9* A-TDC, centered @ 67* A-BDC, 244* duration.

SVXride inquired about me having any camshaft experience with the EG33, and I can say yes and no. Before my X was in an accident, and thereby before I sold it, I very heavily researched changing the performance of the camshafts. I was in talks with Harvey here on SVXnet, Paeco Machining, and Chris over at EngineLogics (former F1 technician, I believe). I was a few weeks away from tearing down my valvetrain and sending the camshafts to Paeco, and then I decided to sell the car because of the accident. :mad:

Anyhow, back on topic... The general idea is that for boost applications, it is best to run a staggered lift/duration setup, skewed towards the exhaust side. Due to the turbo seeing more exhaust pressure for a slightly longer period of time, and the intake side of the engine seeing slightly higher intake pressures, the turbo can spool more quickly and reduce lag.

In terms of the stock setup, it is already setup fairly well for this. The only problem is that the cams are not very aggressive at all.

For an aggressive turbo application, personally I would suggest the following:
Intake: Opens 8* B-TDC, closes 60* A-BDC, centered @ 116* A-TDC, 248* duration.
Exhaust: Opens 62* B-BDC, closes 18* A-TDC, centered @ 68* A-BDC, 260* duration.

Giving the exhaust side more room to breathe, and for a longer period of time A-TDC, will substantially increase the efficiency of the turbo. The intake side is also given more breathability; however, it has kept the same center in order to allow a slight pressure increase on the intake side (decreasing the "workload" of the turbo).

According to Chris from EngineLogics, he has managed to give turbocharged engines HP gains ranging anywhere from 5% - 10%, simply by changing the cams to this config.

Of course you will lose the benefits of the IRIS system with this setup, as the overlap is too large for it to scavenge-collect pressure. However, with a turbo this system is hardly necessary anyway. The pressure buildup comes from the turbo! I hardly know the IRIS system as well as I know cams, but I suspect that removing the IRIS butterfly (or welding it into an open position) would be best with forced induction.

- Garrett

Now, for better performance on a naturally aspirated car, it would be wise to do the opposite.

Whether or not staggering the cams, skewed towards the intake side, gives better performance... Well, it varies car-by-car. Some cars do well, some would do better with an "even" config (same duration on both cams).

However, the SVX is much different (as always). :D

The IRIS system is very nice to have, and in my opinion should stick around. When I was going to have a new grind for my bumpsticks, I left the cam overlap at TDC stay stock. This would allow for the IRIS system to stay functional. Instead, I had planned on slightly increasing the overlap at BDC.

I had also planned on giving the intake cam 1.0mm more lift, increasing it to 8.0mm. The exhaust cam has 8.0mm stock, and I wanted to increase it to 8.6mm.

It may sound too good to be true, but up until a certain point, increasing the cam lift is very linear in terms of power gained. This is true for almost any production engine. Ferrari may be a different case. ;)

Changing the duration alters this effect, but if you keep it the same (or very close), most likely your percent gain in lift will be closely synonymous with your percent gain in power. 7.0mm --> 8.0mm = 14.3% increase. We all know that the SVX is almost always different from every car out there, so I was conservatively expecting a gain of only 10% maximum. I'm quite sad that I never got to see the day I made over 250hp in an N/A SVX.

However, I think my new 2JZ-GE engine will likely keep me pretty happy. Especially when I put some 264* cams on here. :D

[/dorkiness]

Garrett, I was wondering these couple of days about the thing you posted here, thank you, I guess this thread will be even more interesting than Tom's. can you ask about these config setups for the cams if they can really give good results without problems.... or messing the valves when using lower compression pistons? and what are the specs of these pistons? 8.5:1 ? 9:1?...

and for more info for some guys who are not mechanically experts in this field (like ME :mad: ) how these valves config can be achieved? modifing the cam heads? or stand alone management thing + cam heads mods?

im waiting in anticipation to an answer to silverspears question :D

Well, in regards to any problems, a moderately aggressive config (like the one I listed for the turbo application) should not have any downsides. Many many many 6 cylinder engines run longer durations, with an equal or higher compression ratio, and do not experience any issues. This includes valve/piston interference and idle quality.

For example, the 2JZ-GE has 10:1 compression, and can run a setup of 9.3mm lift and 264* duration without any interference or idle quality loss. Turning the engine into an interference setup only occurs once lift is in excess of 9.5mm, and idle quality starts to decrease when running 272* duration or more. :eek:

In regards to lower compression pistons, well, you'd likely be able to run more lift and duration... Unless for some strange reason you keep the stock valve clearance, but reduce stroke length to create a lower ratio - which would be dumb. I'm not saying that running more lift or duration would increase performance with a lower ratio, I'm merely saying that it is physically possible to make the config more aggressive.

I believe that the config I was going to attempt was as follows:
Intake: Opens 2* B-TDC, closes 58* A-BDC, centered @ 118* A-TDC, 240* duration; 8.0mm lift.
Exhaust: Opens 59* B-BDC, closes 9* A-TDC, centered @ 65* A-BDC, 248* duration; 8.6mm lift.

Before sending the camshafts to Paeco, my plan was to examine the head to be sure that there was proper clearance for the larger camshaft lobes. If it were possible, I had also planned on checking the springs to be sure that, given this increase in lift, they would not bind.

The general plan was to keep the overlap at TDC the same, thus, in theory, allowing the IRIS system to continue to work. The secondary theory was that with such a low increase in lift, the springs would not bind nor would the engine become interference... However, if the engine did, oh well. I do change my timing belt when I'm supposed to. :rolleyes:

Have I missed anything?

To cam or not?
 

The cam that you run in a motor depends on what the motor is powering. It is pointless to fit a cam that will increase the torque at 5000 rpm, if you have an auto that will spend most of its driving at 2000 to 3000 rpms. It really has to suit the overall gear ratio that the car has.

To obtain better filling at higher rpms, you have to use a cam with a longer duration, and the inlet lobe center will have to be retarded to move the torque peak, higher up the range. This will move the torque away from the low end rpms, to increase the top end. This type of output would not suit an auto, but would suit a 5/6 speed manual that can use the gears to keep the engine operating in the 3000 to 6000 rpm range, because it would be a 'dog' below 3000 rpms.

So the choice is;
If you are keeping the auto and the 3.5/3.7 final drive ratio, you need to keep the timing the way it is, and increase the torque by increasing the lift.
If you are keeping the auto but using a lower 4.1/4.4 final drive ratio, you could increase the lift and increase the duration, slightly.
If you are using a 5/6 speed manual, the low rpm torque is not important, as you can use the gears to stay in the higher rpms. This engine could use longer duration higher lift cams, with the lobe center retarded to move the torque peak further up the rpm range.

As for forced induction, I don't think anybody will be using enought boost to need the exhaust timing advanced or extended. But if this should be the case, advancing the exhaust lobe center will allow the cylinder to drop the higher pressure, before the up stroke.
Increasing the overlap, by holding the exhaust open so that the inlet flow will cool the exhaust valve, is used when the boost is high and held for an extended peroid. By the time you get to this stage, you would need sodium filled exhaust valves and a lot of other changes.

Harvey. ;)

great explanation, but you don't need a standalone anymore right? and why don't you do this setup you mentioned here?

Garrett,
thanks for starting this thread!! :D
Harvey,
thanks, as always, for contributing to it! :cool:

Let's see if I can summarize:

Slightly more lift on both the intake and exhaust is Good -- looks like 1mm should do the trick with only positive effects on hp/torque

Duration - don't touch the overlap, just increase the duration on both sticks by single digits

Sound right (yeah, I'm only looking at na engines)

-Bill

thanks for that mate! apreciated

if everybody agrees on that, now turboing the SVX became easy... I think, right? i expected this thread to become more and more active... what's the matter? too good to be true? :rolleyes:

You've just about got it.

However, you'll have to change the overlap on one/both ends of piston movement if you modify the duration at all.

I am just saying to leave alone the total overlap of 11* at piston TDC, and modify the total overlap at piston BDC. This is done by increasing the duration of the lobes, but modifying the center (also known as the peak lift).

If you compare the stock numbers to the aftermarket N/A numbers I was considering, you'll see that the 11* overlap at TDC is unchanged. However, the center has been moved slightly, therefore modifying the overlap at BDC. Doubly-so, the new center should also help increase performance.

Keeping the original overlap at TDC will be difficult to do once you get the new cams and install them...

My suggestion is to get some type of adjustable cam gears. Since the intake and exhaust cams are linked internally via helical gears, adjusting the intake cam will also adjust the exhaust cams evenly. Just be sure that you hook them together properly (which shouldn't be the hard part if you just put your thinking cap on).

BUT STAY AWAY FROM ALUMINUM HKS GEARS! The teeth eventually wear down, which allow play in the timing belt... Get gears with a steel outer ring or nickel plating.

Oh, and don't forget the new lift config. :D

Anyway, to get to the fun part: If the SVX truly is around 98% volumetric efficiency, this cam setup should yield numbers at least in the 250 - 260 crank horsepower and torque range.

I really was looking forward to having the first SVX with performance cams. :(

Oh, yeah... No problem man!

I think you should do this Bill...

I mean, at least 20 - 30 HP for only around $800 - $1000, and only the time required to remove the valve covers and bumpsticks?

DO IT. :D

Take it easy,
- G

G,
Count on it! ;) :cool:
-Bill