Carl Fausett

There is a particular class and division that we are aiming for and we need to be very careful to be judged into that group by the scrutineers. The class I am after is B/BGMS

That is "B" engine, (6.11 to 7.19 Liter ) Blown Gas Modified Sports cars. I have to run the gas they supply at the SCTA event, which will be 91-93 octane pump gas with no additives.

If I run any other gas, or provide my own gas, it bumps me to the "Fuel" catagory, BFMS (Blown Fuel Modified Sports) and I dont want to be there.

ptuomov

Well, those are very good power numbers for pump gas. I am starting to appreciate how difficult it is to get high hp/l numbers from pump gas with otherwise drivable motor.

You're at 731/6.5 = 112.5 hp/l, which is basically where I am now with 570/5.0 = 114 hp/l. Mine are from a dynojet and yours probably from a mustang so I'd guess the order would flip on the same dyno, but let's say they are approximately the same.

Getting the same hp/l from a 30% larger cylinder is not easy and your engine is also spending a lot of power to run the supercharger, while I am getting almost free boost from the turbos. It looks like the head, cam, and intake parts are doing a good job feeding the bigger engine, for what it's worth -- a noob observation.

With the valve float fixed, you'll leave my engine in the dust in hp/l, of course. The detonation constraint is relaxed at higher rpms.

Another thing that all these high-power engines are making very clear to everyone is that there isn't just one way to do things that is right. We've got strokers, big bore sleeves, stock long blocks, superchargers, turbos, itbs, etc. all being successful in making good power on a chassis dyno.

mark kibort

so, is there a possiblity that 15psi on the back face of the intake valve can push it open or hold it open, causing "float"? even if this was a possiblity, it doest jive with the fact that lots of these ricers are doing it with stock motors running a heck of a lot more boost. (i.e. 27psi on a 2.4 liter motor , making 440rwhp commonly)
if the valve spring broke, it could be just one of those things, or the spring design, with the dual spring, was or is flawed. I dont know, but wouldnt stock valve springs work, or just the aftermarket stuff from eibach work. ( I think my springs were eibach in the holbert car) scots were some purple looking things that were matched with the Devek B1 cams)

is that chassis the main pike peak car?

Carl Fausett

No, 15 psi on the back of the valve cannot push it open. But, to say that boost on the back of the valve would have no effect towards valve float is also in error. Its a contributor, but it is not the cause.

Yes, this is the Pikes Peak Hill Climb car, with aero modifications.

Carl Fausett

Absolutely.

I bristle when I encounter parisheners to the One Right Way church of science and engineering. There is often more than one right way but, rigid minds have difficulty contemplating that.

ptuomov

Isn't the pressure inside the cylinder also almost 15 psi higher at points when the valve float is likely? The only time when the intake valves are going to float is right after the max intake lobe lift (and possibly bouncing off the seat but that's another story.) The static pressure differential between the cylinder and the port near the intake lobe max lift is small and not influenced much by boost. Right?

So where is this boost-induced valve float coming from?

Maybe there's some additional kinetic pressure from the denser charge hitting the back of the valve, but so far nobody here has made that argument.

AO

Total bummer Carl. It seems like when you even say the word "Dyno" around 928's they fall apart. But as others have said, better here than there.

Best of luck next round.

smith 928

Boost should have not made the valve float . It might be defective valve spring , Seat, Harmonic balance.
Or a combo of things.

AO

And you know this through your turbo experience?

Carl Fausett

I never said our valve float was boost-induced. I continue to say that boost is a factor, not the cause.

In our case, the larger issues that we will concentrate on will be the beryllium-copper seats we used (they are soft and we used them to avoid valve bounce), the weight of the valve, the profile of the cam lobe at max lift, the spring harmonics, and other common factors.

I am reasonably sure the valve float was coming off the nose of the lobe, not bounce off the seat. I used the softest spring I could and still get the job done (too much spring is rough on a timing belt that is 6' long!) and its apparant that I went a tad too soft.

We refit, and try again. Its why they call it the "bleeding edge" of development.

Hardly a weekend goes by without some NASCAR team breaking a valve spring, having to drop in his spare motor, and start at the back of the pack. Not uncommon. I just dont have a spare motor waiting to drop in. :-)

ptuomov

In response to Smith 928: Andrew -- Do you think that boost makes valves float and if so, why?

I think that if there's an effect it is minimal, much, much smaller than the valve area times the boost pressure which is typically computed in internet writings.

ptuomov

Yes, you didn't. However, if one googles boost and valve float, one gets thousands of hits with nonsense logic of valve area times boost pressure.

I assume you're running your Webcam / 928MS R3 profiles. I also assume you're running your stainless valves and titanium retainers you're offering for sale. What spring specs are you running with those? Just curious.

Carl Fausett

Correct, correct, and correct. All performed very well (as did the aluminum torque tube).

I'm not going to say what the spring rate is on these springs just yet - I want to re-measure them after I pull them out.

smith 928

Ok what is the spring Rate on those springs?

smith 928

Ok sorry Carl my fault