Compression, dynamic/static, question...

[Slowhawk]

Originally Posted by dan0617

yes. Which is why static CR is almost meaningless although in the performance world it is discussed the most. Many people don't understand the definition or concept of dynamic so they talk static. SCR should be about the last thing you determine, it is the final mechanical adjustment to get the DCR where you need it for your selected boost, cam, ci, fuel octane, iat, etc, etc, etc.
,
That overlap helps pull the charge in at higher rpms on an NA motor. Too much overlap kills the cylinder pressure (and the part throttle drivability) at low rpm. On a boosted motor you want to control cylinder pressure some other way, because the blower is taking power and raising air temps to make boost and overlap is wasting it. So you then lower the IAT, up the octane, retard the timing, or lower the SCR to control the cylinder pressures and temps.

You pretty much nailed it.

[SSBUSDRVR]

assuming you've still got the 1:1 in the back, at 6000rpm, the blower would be up about 13,850. going down to a 3.0 will start making a 6-rib setup harder to keep from slipping. as for the IATs, i don't have much of a calculation or guess on that

Thanks for the reply. The EForce is a direct drive up front. There was a link somewhere for an 8 rib pulley system but can't seem to find it now. Have never experienced belt slip afaik with the 3.25 up until it grenaded.

[zebra]

that's right - no jackshaft on them. as for the pulley, just going from 3.25 to 3.0 gives you about 8-10% less contact area with the belt. just make sure your tensioner is tight & you get a shorter belt, and you shouldn't have a big issue. when i went from my 3.3 to 2.9, i got a bit of slip on top, but then i got a .75" shorter belt and that seemed to work fine.

[SSBUSDRVR]

Thanks.

[JANNETTYRACING]

Originally Posted by SSBUSDRVR

Thanks for the reply. The EForce is a direct drive up front. There was a link somewhere for an 8 rib pulley system but can't seem to find it now. Have never experienced belt slip afaik with the 3.25 up until it grenaded.

We offer 8 Rib drives for the Eforce.

Ted.

[ayousef]

Originally Posted by dan0617

yes. Which is why static CR is almost meaningless although in the performance world it is discussed the most. Many people don't understand the definition or concept of dynamic so they talk static. SCR should be about the last thing you determine, it is the final mechanical adjustment to get the DCR where you need it for your selected boost, cam, ci, fuel octane, iat, etc, etc, etc.
,
That overlap helps pull the charge in at higher rpms on an NA motor. Too much overlap kills the cylinder pressure (and the part throttle drivability) at low rpm. On a boosted motor you want to control cylinder pressure some other way, because the blower is taking power and raising air temps to make boost and overlap is wasting it. So you then lower the IAT, up the octane, retard the timing, or lower the SCR to control the cylinder pressures and temps.

incorrect, more overlap always makes more power (mid range to high rpm) assuming intake pressure is higher than exhaust pressure (which means you need a very good exhaust to reap the benefits), of course there is a limit to everything and usually drivability is what will restrict how much overlap you run in your cam. Blowers have no problem at all moving large quantities of air as long as they're not compressing the air, just like what happens when you are driving at high-rpm part throttle; freely moving air does not tax the blower and as a result does not increase IATs or parasitic drag, which is precisely why blowers have almost no parasitic drag at part throttle. A good argument would be that with FI you do not NEED to rely on overlap and as a result sacrifice drivability to make good power.

[SSBUSDRVR]

Thought running a lot of overlap in FI applications was very inefficient. It seems most blower Cams have small duration splits and increased LSAs Also as far as parasitic drag goes on these new blowers at low RPM,(some TVS based blowers anyway) is due to the fact of bypass valves installed.

We offer 8 Rib drives for the Eforce.

Thanks and bookmarked for future use.

[dan0617]

Originally Posted by ayousef

incorrect, more overlap always makes more power (mid range to high rpm) assuming intake pressure is higher than exhaust pressure (which means you need a very good exhaust to reap the benefits), of course there is a limit to everything and usually drivability is what will restrict how much overlap you run in your cam. Blowers have no problem at all moving large quantities of air as long as they're not compressing the air, just like what happens when you are driving at high-rpm part throttle; freely moving air does not tax the blower and as a result does not increase IATs or parasitic drag, which is precisely why blowers have almost no parasitic drag at part throttle. A good argument would be that with FI you do not NEED to rely on overlap and as a result sacrifice drivability to make good power.

very inefficient to put a large overlap cam on a blower setup. On an all out race car and a huge blower you might pick up some top end power with some added overlap. I'll give you that. But I stick by what I said. If you are using cam overlap to control cylinder pressure on a boosted engine you are not doing your build right. Pick the cam to go with your blower, converter, gears, intake, cubes, heads, etc. Set the SCR to control cylinder pressure and temps, along with octane and meth or race fuel.

[ayousef]

Originally Posted by SSBUSDRVR

Thought running a lot of overlap in FI applications was very inefficient. It seems most blower Cams have small duration splits and increased LSAs Also as far as parasitic drag goes on these new blowers at low RPM,(some TVS based blowers anyway) is due to the fact of bypass valves installed.
Thanks and bookmarked for future use.

All blowers have bypass valves, that's the only thing that stops the blower from forcing all that air into the motor at part throttle.

[ayousef]

Originally Posted by dan0617

very inefficient to put a large overlap cam on a blower setup. On an all out race car and a huge blower you might pick up some top end power with some added overlap. I'll give you that. But I stick by what I said. If you are using cam overlap to control cylinder pressure on a boosted engine you are not doing your build right. Pick the cam to go with your blower, converter, gears, intake, cubes, heads, etc. Set the SCR to control cylinder pressure and temps, along with octane and meth or race fuel.

You cant just do it like this, you cant spec a cam then decide what SCR you run because things such as maximum safe valve lift possible before the valve touches the piston will be determined by how much static compression ratio you have (due to having a dished or domed piston top). Its one of those things you have to choose simultaneously.

Turbo set-ups are where you need to watch the overlap and where measuring exhaust backpressure becomes valuable before you can truly determine the correct amount of valve overlap. Blowers and NA setups aren't too different, and can benefit from overlap. I remember from years back guys that picked up ridiculous amounts of HP by simply increasing overlap, im not stating any numbers because that will start a whole argument all by itself.

Also, overlap is not how you control cylinder pressure, infact any chance in cylinder pressure due to overlap will be a side-effect due to increases/decreases in volumentric efficiency throughout the RPM range, hence should be treated as such (a side effect). The only correct way of controlling cylinder pressure is static compression ratio, intake valve closing ABDC, boost and spark advance.

[old motorhead]

Comparing two cams with the same specs other than LSA will show the cam with the narrower LSA having MORE overlap and a HIGHER dynamic compression ratio vs the cam with the wider LSA.

[PQ]

Originally Posted by zebra

why don't you just Whipple Bonnie's car & call it a day?

Why don't I just pull it out and set in in my car and THEN do that.

Originally Posted by zebra

what i'm going for here is if 700+ to the ground is realistically possible... or is this going to top out in the mid-600s?

That's the aviator in you. lol

Originally Posted by SSBUSDRVR

So what does the EForce TVS spin at on 3.25 pulley? Is it really worth dropping down to 3.0 or 2.75 or will the IAT increases really defeat the purpose and or belt slip become an issue. Had none on the 3.25.(leaning now towards 9.5 compression 415-418) Old Cam had around 7 degrees of overlap.

That's the point where mine started slipping pretty badly. I bought Jannety's super-tentioner. Seemed to help just before my cam went shit on me.

Originally Posted by dan0617

yes. Which is why static CR is almost meaningless although in the performance world it is discussed the most. Many people don't understand the definition or concept of dynamic so they talk static. SCR should be about the last thing you determine, it is the final mechanical adjustment to get the DCR where you need it for your selected boost, cam, ci, fuel octane, iat, etc, etc, etc.
,
That overlap helps pull the charge in at higher rpms on an NA motor. Too much overlap kills the cylinder pressure (and the part throttle drivability) at low rpm. On a boosted motor you want to control cylinder pressure some other way, because the blower is taking power and raising air temps to make boost and overlap is wasting it. So you then lower the IAT, up the octane, retard the timing, or lower the SCR to control the cylinder pressures and temps.

Originally Posted by ayousef

incorrect, more overlap always makes more power (mid range to high rpm) assuming intake pressure is higher than exhaust pressure (which means you need a very good exhaust to reap the benefits), of course there is a limit to everything and usually drivability is what will restrict how much overlap you run in your cam. Blowers have no problem at all moving large quantities of air as long as they're not compressing the air, just like what happens when you are driving at high-rpm part throttle; freely moving air does not tax the blower and as a result does not increase IATs or parasitic drag, which is precisely why blowers have almost no parasitic drag at part throttle. A good argument would be that with FI you do not NEED to rely on overlap and as a result sacrifice drivability to make good power.

The coolest part of this thread is I now know what you guys are talking about. haha

Originally Posted by old motorhead

Comparing two cams with the same specs other than LSA will show the cam with the narrower LSA having MORE overlap and a HIGHER dynamic compression ratio vs the cam with the wider LSA.

More overlap = higher DCR?

I thought more overlap helped air escape before the valve closed?

[old motorhead]

More overlap = higher DCR?

I thought more overlap helped air escape before the valve closed?[/QUOTE]

You may be thinking a higher overlap would let the boost go straight through the motor and into the exhaust......the old high overlap cams "bleed" boost school of thought. That's kind of comical when you think about it. If the blower was blowing air (and fuel) straight through the motor, tuning a rig with very much overlap would be more than just a little difficult. When you narrow the LSA, overlap does go up, but the intake valve closes quicker as the piston is going up on the compression stroke. Thus creating a higher DCR. At least, that's my simplistic way of looking at it.

[PQ]

Originally Posted by old motorhead

You may be thinking a higher overlap would let the boost go straight through the motor and into the exhaust......the old high overlap cams "bleed" boost school of thought. That's kind of comical when you think about it. If the blower was blowing air (and fuel) straight through the motor, tuning a rig with very much overlap would be more than just a little difficult. When you narrow the LSA, overlap does go up, but the intake valve closes quicker as the piston is going up on the compression stroke. Thus creating a higher DCR. At least, that's my simplistic way of looking at it.

Ok. I forgot the lift vs duration part.