ECUtune Camshafts

[longassname]

There's already been some discussion of this project in other threads but it's time to make our own thread and consolidate the information on the camshafts I am developing.

I'm developing a matched set of camshafts, valve springs, and valves. I'll be posting information on the status of the project in this thread.

[longassname]

(copied and pasted from my post last week in another thread)

I've been busy with my transmission project as of late but I was able to get to taking the valve spring measurements today so that I can get the valves and cams ordered.

For the stock valves I got an installed height of 1.12 for the exhaust and 1.10 for the intake.

For the stock valve springs I got a seat pressure of 40lbs and an open pressure of 104lbs (compressed to .79).

We can reduce our base circle on our cams 2mm without cutting into the fiillets and that will give us the room we want to increase lift and duration. I'm going to get valves made 2mm longer than stock to match so I measured my seat pressure at 1.20" The combination of the stock outer springs with the new inner springs work perfectly. The seat pressure at 1.20" is 60lbs. Putting us in the 60-66 lbs range for both intake and exhaust--perfect.

The same combination compressed to 0.820" is 160 lbs. So that's our pressure at 9.4mm actual lift which is a little higher than what we'll see with 9.6mm on the lobe. Figure our intake open tensions will be a little on the shy side of 155 lbs and our exhaust open tensions a little over 155 lbs--perfect.

Coilbind height for this combination is .725" giving us .465 free travel subtract 60 thousands standard extra clearance that gives us .405 which equals 10.3mm safe lift (comfortably more than we'll be getting out of our cams).

[Budfreak]

subscribe

[mikecg]

You've got my attention. (Savings at $700 in climbing)

[Alcyone Lunacy]

Once you have them installed let us know how well this upgrade works; sounds great though! Put me down for some in the long run if they have no ill side effects.

Could some one explain in simpler terms how this benifits?

James

[longassname]

The measurements I posted thus far in this thread are really only for the benefit of those who already understand what they mean. They are important for the design of the components not to direct peformance improvements. Well....that's true with the exception of the valve springs. Subaru engineers pride themselves in maintining exceptionaly light spring tensions so the factory springs really aren't good for a performance set up. To get more horse power we do either or both of two things: 1) get more air into the engine per revolution 2) run higher rpms. Doing either of those things can quickly overwhelm the light valve spring tensions--particularly the seat tension. This is called valve float. It's also called a big loss of power. The supercharged cars are showing evidence of either inadequate exhaust cam duration to clear the cyllinder or valve float or both above 3500 rpms. As it turns out, having measured things up, supercharged or not the most sensible way to do the cams is to do the cams, valves, and valve springs together.

Originally Posted by Saxist

Could some one explain in simpler terms how this benifits?

James

[longassname]

When I post the final specs for lift and duration I will explain more but for now I will give you some general rules of thumb applied in camshaft design.

Increases in lift up to 30% of valve diameter typically improve low rpm performance.

Increases in duration typically improve high rpm performance.

Engineering constraints need to be tackled in order.
The first limitation is clearing the exhaust gasses
The next is filling the cyllinder with the intake charge

The main things that can be done to improve exhaust are opening the exhaust valve earlier and moving the lobe center closer to optimal

The main things that can be done to improve intake are increase duration and move the lobe center closer to optimal

[Trevor]

Originally Posted by longassname

The measurements I posted thus far in this thread are really only for the benefit of those who already understand what they mean. They are important for the design of the components not to direct peformance improvements. Well....that's true with the exception of the valve springs. Subaru engineers pride themselves in maintining exceptionaly light spring tensions so the factory springs really aren't good for a performance set up. To get more horse power we do either or both of two things: 1) get more air into the engine per revolution 2) run higher rpms. Doing either of those things can quickly overwhelm the light valve spring tensions--particularly the seat tension. This is called valve float. It's also called a big loss of power. The supercharged cars are showing evidence of either inadequate exhaust cam duration to clear the cyllinder or valve float or both above 3500 rpms. As it turns out, having measured things up, supercharged or not the most sensible way to do the cams is to do the cams, valves, and valve springs together.

There have been figures and figures posted, but I have seen nothing in respect of the average torque, shock torque or power, involved in driving the camshafts. Given the length and convoluted nature of the SVX cam belt, and the fact that each is driving valve gear for six cylinders and not four as is the nearest comparable, this aspect should be taken into account.

The increased lift and spring tensions being considered are a major factor involved in this issue. I would suspect there could be surprises in store. Was this a limiting factor in the minds of those who engineered the original?

[longassname]

Much higher spring tensions and lifts have been run on the eg33 before. The engine has just never been put back in an SVX.

Originally Posted by Trevor

There have been figures and figures posted, but I have seen nothing in respect of the average torque, shock torque or power, involved in driving the camshafts. Given the length and convoluted nature of the SVX cam belt, and the fact that each is driving valve gear for six cylinders and not four as is the nearest comparable, this aspect should be taken into account.

The increased lift and spring tensions being considered are a major factor involved in this issue. I would suspect there could be surprises in store. Was this a limiting factor in the minds of those who engineered the original?

[Ricochet]

Interesting. So these camshafts and springs will add minimal power on their own, but build a good foundation for boost?

[longassname]

There will be dyno plots posted of the cams on an NA motor. They should give a substantial power increase on their own and build a good foundation for boost.

Originally Posted by Ricochet

Interesting. So these camshafts and springs will add minimal power on their own, but build a good foundation for boost?

[curly2k3]

if i would've decided to keep and continue my build i would've been one of the first to buy a set, but i decided to start a new build. congrats on the progress you have made thus far, i cant wait to see some in a real use!

[longassname]

would the na guys who are going to run the cams like forged pistons with deeper valve reliefs to retain zero interfence in case the timing belt breaks? Figure I can get them made and resell them for about $950 a set complete with rings. They would be the same as the pistons for the supercharged cars except they would still have the domes and the valve reliefs would not be interconnected.

[longassname]

ok, guessing no interest in the na pistons. It turns out they are annoyingly expensive to get made anyway and I couldn't resell them for $950.