Cam Design Pros Weigh In

Ahhhhh....yes, new marks makes sense but maybe wait until test so you're sure?

 

Maybe paint this time and stamp it next?

 

The blower set looks great, very neat work.

What is vapor honing? Never heard that one before

 

Just wanted to follow along. Fascinating, wish i knew more.

 

I'm not going to profess to know more about cam timing than the people at Ferrari, but why is your exhaust valve not closing until 43 degrees after TDC? That seems really far into the power stroke to me. 75 degrees of overlap seems excessive also.

Where do you have base ignition or ignition at 3000 RPM as well as total advance?

Was this motor originally factory turbocharged, but now it's been converted to a mechanically driven supercharger?

I've been up all night working on the cam timing for my Toyota 4 cylinder and thought to re-read this thread. Just wondering where things stand with your cam timing stuff.

Ray

 

Here is a very good video which helps to rationalize what's taking place relative to your valves opening and closing, as well as how camshaft timing plays a role. This is my main go-to video when I am working with cam timing and trying to make sure I have the advance/retard setup correctly:



Ray

 

30 teeth on the 308 camshaft gears, so 360 / 30 = 12 degrees per tooth. Crankshaft to camshaft rotation ratio is 2:1, so 24 degrees of crankshaft rotation per tooth on the camshaft is what it should work out to there.

Ray

 

What about a set of adjustable camshaft sprockets for your 308?

Ray

 

Looks like a fun project. I'll check out post #22 later this evening.

Here's the fun I'm currently having over here w/ my little Toyota SOHC motor.

Ray

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Are you primarily concerned with lower RPM torque and drive-ability or higher RPM power? What RPM range do you typically drive it in? I mean, are we cruising around town all day at 3000 RPM's or revving it to 7500 RPM every chance you get and want it to pull to the moon?

How you drive and what type of motor you like will really dictate a lot of cam timing and selection.

Me personally, I much prefer motors which rev out very smoothly and pull clear to through into the upper redline and have the power band shifted up higher. I'm not really concerned with low RPM torque generally speaking. I'd rather have a 4-cylinder Japanese bike and spin the hell out of it than ride around on some Ducati torque monster, for example.

Where do you fall in the scheme of things with driving your 308?

Ray

 

Oh, I see. So you're a gambling man

Are you running stock pistons and stock compression ratio with your super charger there? Are there any allowances for retarding the timing during boost? I realize 6 PSI is fairly mild.

Are you running any sort of wide band O2 sensor off the exhaust system in order to monitor A/F ratios or anything along those lines?

Ray

 

Rolling cam timing doesn't really change things as much as many seem to believe. The lobes are what they are and as long as they are close to they belong they do what they do. Change the duration 20 degrees and its a different engine but the more duration you add the less sensitive it gets to a few degrees to timing. 5 or 10hp on top or down low is nothing to laugh at but not really noticeable on a 300hp engine.

 

Yeah, well again I'm no cam expert. However, in just looking over the diagram on page #22 there, I have to say it strikes me as a cam with a lot of duration on both the intake and exhaust that has to be dealt with here. Tightening up the overlap to 44 degrees seems a whole lot better for a boosted application.

If it were me, I might try delaying intake opening by another 8 degrees, so that it opens at 20 degrees instead of 28, although with that ungodly 260 duration, who knows how that might affect things when not under boost at lower RPM's.

For forced induction, I think lower duration lobes would probably work better. With only 6 PSI boost, it's probably not a major factor, however.

Again, still getting my feet wet with all this.

Ray

 

I've run JE pistons before.. they are good. Reading the plugs is always helpful. Having a wide band O2 sensor in the exhaust is super nice though, just saying

Ray

 

Cool project. Seeing Theiler's name in this pic made me comment. Theiler past like 30 years ago. I actually knew the man and spent a good bit of time with him. He was a very unique thinker that most in the business thought was nuts. I was an impressionable apprentice hobbyist at the time being a sponge for everything Ferrari. When I wasn't doing my day job I was either thinking about Ferraris, fixing Ferraris, or learning about Ferraris.

Theiler was a cross between top race team mechanic, DIY'er, and mad scientist. Things that I saw leave his shop were unique and worked! After they left his shop once in the hands of a new mechanic for whatever reason it was chaos because no one could figure out what Theiler had done except it was wrong by the textbook. Succeeding mechanics had all the quirks of working on a Ferrari with the puzzle that was Theiler's doing. The result often lead to Theiler's bad rep as a hack and "legend in his own mind." In medicine we call that "practicing outside the standard of care." Regardless of outcome positive or negative that never ends well.

That said there could be some genius in your motor if you can unlock Theiler's puzzle. Don't discount any crazy ideas. If it makes more power it is probably the way Theiler tuned it and intended. Sometimes he could be singularly focused not thinking about things like daily driveability because that's not what you came to Theiler for. So if you got bad MPG and poor vacuum but the motor runs like a cat on fire that might be exactly what it was made to do.

 

I tried to model this thing which the cams as 102-110. I picked a vortech V5-F blower, 1.5 belt ratio to hit the 6psi. I'm probably a little high on the baseline at 290 so 360 with the boost is probably also a little high but ballpark.

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Here is the prodata and if you look all the way to the right you'll see exhaust spoilage....that is the charge lost to the exhaust during overlap and its 0% except around 4500rpm which says the headers aren't working well there. It looks fine.

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Now looking at the original timing specs....this says it it makes more hp but the jagged lines down low say the simulator really doesn't quite know how to handle it and there is quite a bit more spoilage below 6k rpm. I'm certain its going to run much better now but surprised it may not make any more HP
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What software are you using for the modeling?

Ray

 

I have a copy of Dynomation6.
It seems pretty good but the further from normal something is the less I'd trust the software. Jagged lines mean its calculating a different answer on one side of the point vs the other and real systems rarely act like that so its possible but probably wrong. The $100k software the OEMs use would know what to do in most all simulations, but the $500 I can afford version is designed to help build performance engines and I'm sure has a lot of empirical corrections meaning its right because its looking at a database of real dyno info and an exhaust cam 25 degrees in the wrong spot is not going to be in the database, and that in turn causes the software to look at one example then another, and that is why there are jagged lines is my guess.

Long story short I trust it to look for optimal solutions but not so much for odd solutions.

Back to this build, here is HP and boost on the top graph, then intake and exhaust pressure in the lower at 4000 rpm. Notice that even with boost, during the overlap period (dotted line in the middle) the exhaust pressure is significantly higher than the intake pressure, which is why when you look at the prodata sheet you see charge loss it reversion (back flow out the intake) not charge loss to exhaust. Headers matter and produce very high pressure waves.

At about 5k rpm this starts to reverse as the headers begin to start savaging properly and you start to see charge loss to exhaust, but its only about a 1/2% so nothing that would concern me....my engine with no boost has nearly double the charge loss to exhaust as a comparison point. In general to make HP you need to limit the spoilage (exhaust left behind in the cylinder) and you do that by allowing a little charge loss out the exhaust, bad for pollution, good for HP
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