Cam for my 4.1 build

[87buickracer]

cams

I have a brand new 214/224 flat tappet cam with high rev lifters for sale and a good used comp cam 218 flat tappet with only 7k miles.my comp cam 218 flat tappet was awesome on the street.and smoked the tires on a roll on the street.I run a 3000 to 3500 stall converter.

pm me for price if interested.

 

[Shaun Tiede]

During early intake opening and WOT, mixture is scavenged during valve overlap. The more boost pressure, the more charge will blow through the intake and out through the exhaust.

Another thing to consider is a shorter but more intense opening exhaust lobe. This will help blow down the cylinder without the need to open the exhaust valve earlier. Because it is a faster ramp, it catches up to the earlier but slower opening ramp relatively early.Therefore, after BDC, it will act bigger, but smaller before BDC. That will also help keep some early torque because early exhaust openings can hurt torque.

Just watch what happens to idle vacuume and early low speed torque when you play with rocker ratio. More ratio on the intake has nearly no effect on vacuume and torque. It will give more upper end power with hardly any noticable loss in low speed power. However, more exhaust ratio does give more upper end power, but it is at the expense of early torque as well as idle vacuume. You'll see this example play out first hand in an N/A car that runs around an oval track.

Anytime you have a pressurized intake port, the more it will take advantage of overlap interms of flushing spent charge from the cylinder with fresh charge. In an N/A engine, you can get quite a bit more liberal with overlap in terms of using it to flush the cylinder of spent charge.

You also have to consider that you need heat to push the turbo.
Running a reverse pattern cam will do a better job of that.

Look at Blown Alky for a second. Alky burns slow and cold compared to Gasoline. You have 50lbs of boost in there. Nearing the end of the exhaust stroke, the exhaust valve is still open and the intake is starting to open. All of that boost pressure blasts charge right out the pipes. It knocks all of the BTU's out of the chamber. We have to keep leaning it out to get it to make any power because it is cold. It sounds rude, crude, and downright obnoxious, but the owner only thought it had power untill he tried a reverse pattern cam. Once he gets the fuel curve straightened out again, he'll admit he has considerably more power across the board.

Anytime I run a reverse pattern cam in that application in place of a single pattern cam, the engine pulls harder, pulls smoother, and is much easier to tune because it isn't so cold in the way of EGT's. It also has much better power in the early ranges of the power band.

You will most likely find power and drivability with an Unsymetrical lobe compared to a symetrical one. The shape of the lobe is very important, too.

Whenever you go to a reverse pattern cam with an effecient turbo, you will realize the gain. I've had many GN's running around with single pattern cams. Then the owner swaps the stock turbo with something better. Once he changes the cam to take advantage of the new turbo's effeciency, the car comes alive and is also more drivable.

Comparing cams at Duration @ .050 points is not going to tell you but about 20% of the information you need to know when picking cams. It is sort of like looking at 2 houses for sale, and forgetting to look at everything else but the kitchen. Few if any would buy a house only because of the kitchen. The same is true with cams. If you pay atention to the advertised, .050, and .200 numbers, then you have a much greater amount of information for comparrison sake.

You have to watch out for advertised numbers, too. Some cam companies will advertise a Hydraulic cam at a different point on the lobe than another cam company. If they both are the same at .050, but one is advertised at .006, and the other is advertised at .0045, you could be looking at 5-10 degrees difference in advertised duration without any more or less at .050. And you never knew it. A Hydraulic with an advertised duration figure published at .006 can be 5-10 degrees bigger in the engine than it is on paper without giving you anything bigger at .050 or anywhere else but at the seat. The more oil viscosity, the more those advertised numbers will blow up since the valve will open earlier than .006. Now if you understand what I just explained, you will see that one cam is lazier than the other. Not just bigger in advertised.

Understanding how and at what point the engine will see and interpret the cam means far more than what is in published print.
Much of that is nothing more than marketing and showing only what they want you to see but nothing else.

I hope I have not confused anyone even more.

 

[CTX-SLPR]

I've read what you said twice but I'm still convinced that you are talking about either an N/A or a crank driven supercharged application. I don't have any hard numbers but thermodynamically, for the turbo to be producing more pressure than than is in the exhauste it must be moving less air for the same or realistically lower amount of work since the energy that powers the turbo is in the volume, heat, and pressure of the exhauste gas moving across the turbine. With this kind of cork in the exhauste system I don't see a way you could have higher intake pressure than exhauste pressure so during overlap you'd self EGR till the exhauste closed and the cylinder was drawing down and there was no back pressure.
In the end, what you say is sound but I'm not sold that it works on exhaust driven supercharging quite like you are saying it does. Someone call up Kenny D and see what he says on this, I'm perfectly willing to be proven wrong.

 

[Shaun Tiede]

What I am saying is the charge moving into the cylinder from the intake port is blasted out the exhaust valve during valve overlap. This of course will happen on any engine N/A or otherwise. The boost pressure exacerbates this during overlap compared to when it happens on an N/A engine.

All I am telling you is when a really effecient turbo is matched to the engine, I have almost always seen much better results all the way around with a reverse pattern cam with a wide LSA.

If somebody wants to try one, then maybe I will consider sending one as long as I am confident I will get paid if they like it and I don't have to wait longer than 3 weeks. LOL!

 

[ijames]

Shaun, I don't doubt your experience but we are trying to understand your reasoning. On TR's, guys who have measured the pressure in the exhaust manifold pre-turbo with smaller turbos and boost in the 20's have seen exhaust manifold pressures of 35-40 psi, and one person reported exhaust pressure in the 30's with boost in the 20's even with an 88 mm turbo. Given that, the only way the cylinder pressure can be lower than the intake manifold pressure when the boost is up is if the momentum of the exhaust flow temporarily pulls a "vacuum" in the cylinder as the cylinder finishes emptying and the intake valve starts to close. By vacuum I mean that the pressure is lower in the cylinder than the average pressure in the exhaust manifold, not that the pressure is necessarily below atmospheric. Now I realize that that is basically the definition of "scavenging", but it is a little hard to accept that it can result in such a large pressure drop of over 10 psi.

By reverse pattern cam I want to be sure I understand - you mean that the exhaust lobe lift and/or duration is larger than the intake lobe, right? Have you looked at the Revolution X cams that Mike Licht at Full Throttle is selling? His most popular hydraulic roller I think is the 210/215 which agrees with your thinking size-wise, but I don't think the LSA is as large as you are recommending. Any thoughts on these?

 

[Shaun Tiede]

Yes, I understand how it is confusing looking back on how I have worded. So I digress. When I get more time, I will look at rewording it, etc. I can easily see where I've posed some twisted logic. No worries.

As for a reverse pattern cam, that means the exhaust cam is shorter than the intake.

 

[CTX-SLPR]

I've been thinking about this today between meetings and on my afternoon run. Here's why I think the reverse split pattern cam (more accurate discription) is preffered. I think the increased intake and small exhaust is so that you can have a longer intake filling time without increasing the overlap or LSA. This is just brain stuff, no testing or data backs it up but we all know that turbo cams minimize overlap and spreading the LSA just hampers the upper rpm filling. I think the overlap minimalization is due to the Self-EGR effect, not the fuel air getting blown out the intake valve, otherwise we'd be running pig rich all the time with all the unburnt fuel air mixture hitting it. Remember its unreacted and unless you are burning it in the pipes its still going to be oxygen rich when it this the sensor despite smelling like raw fuel coming out the tailpipe.

 

[Shaun Tiede]

The biggest reason I have used reverse pattern cams(for Turbo's) is to build heat to push/spool the turbo and therefore reduce lag. It also helps early torque which I should have better clarified.

I started doing a lot of cams in this fashion initially and long ago due to lots of people complaining about lag. Especially those who also drove them daily and in rush hour traffic.

As for pressure, when the intake valve begins to crack open, the exhaust has pretty well ended in that cylinder. Most of the combustion pressure in the cylinder is blown out during early exhaust opening long before BDC. Hence it is still during the latter stages of the power stroke.

Though this might be getting off the topic somewhat, it still is good to know: If I can compare two exhaust cams to each other by saying one might open 10 degrees eqarlier than the other, but if the other has a considerably faster ramp, then it will blow the cylinder down just as effectively if not more as it will catch the earlier opening lobe quickly. If I can delay the opening(which will help early torque and render more heat to spool the turbo), and still catch up to and pass a considerably earlier opening cam by the time the cycle is at BDC, then the valve is further off the seat after BDC which will effectively be a bigger cam after BDC. The same holds true for intake lobes.

If the lobe is shorter but quicker before TDC, the engine will see that the intake valve has a much bigger cam after TDC to fill the cylinder with. This is one key factor why a good solid lifter cam will whip the pants off a Hydraulic cam. It can have 15-25 degrees less seat or advertised duration than a hydraulic, and still catch it in lift by .050. It is also why comparing cams by duration at .050 leaves so much other information out of the picture.

Going back, I am sorry for the confusion as what I was saying regarding reverse pattern cams for turbos primarily helps with lag and early rpm performance prior to the turbo really waking up at WOT or not. I guess I should not write when I am dealing with 2 kids and feeding an infant. Too much ADHD going on. LOL!

 

[87GN_70GS]

The more effecient the turbo is, the less exhaust scavenge help from the cam the engine will need during valve overlap. You have to take valve overlap out because a really effecient turbo can seriously over scavenge the system during valve overlap from the high boost pressure in the intake port blowing a big charge right through the combustion chamber and out the exhaust.

Not quite sure what turbo engines you're familiar with but on ours, the exhaust manifold pressure is always higher than the intake manifold pressure. (Not convinced? Them instrument them). So the problem during overlap is reversion, with the exhaust charge going back into the intake, not over-scavenging.

 

[chasmat2316]

During early intake opening and WOT, mixture is scavenged during valve overlap. The more boost pressure, the more charge will blow through the intake and out through the exhaust.

Another thing to consider is a shorter but more intense opening exhaust lobe. This will help blow down the cylinder without the need to open the exhaust valve earlier. Because it is a faster ramp, it catches up to the earlier but slower opening ramp relatively early.Therefore, after BDC, it will act bigger, but smaller before BDC. That will also help keep some early torque because early exhaust openings can hurt torque.

Just watch what happens to idle vacuume and early low speed torque when you play with rocker ratio. More ratio on the intake has nearly no effect on vacuume and torque. It will give more upper end power with hardly any noticable loss in low speed power. However, more exhaust ratio does give more upper end power, but it is at the expense of early torque as well as idle vacuume. You'll see this example play out first hand in an N/A car that runs around an oval track.

Anytime you have a pressurized intake port, the more it will take advantage of overlap interms of flushing spent charge from the cylinder with fresh charge. In an N/A engine, you can get quite a bit more liberal with overlap in terms of using it to flush the cylinder of spent charge.

You also have to consider that you need heat to push the turbo.
Running a reverse pattern cam will do a better job of that.

Look at Blown Alky for a second. Alky burns slow and cold compared to Gasoline. You have 50lbs of boost in there. Nearing the end of the exhaust stroke, the exhaust valve is still open and the intake is starting to open. All of that boost pressure blasts charge right out the pipes. It knocks all of the BTU's out of the chamber. We have to keep leaning it out to get it to make any power because it is cold. It sounds rude, crude, and downright obnoxious, but the owner only thought it had power untill he tried a reverse pattern cam. Once he gets the fuel curve straightened out again, he'll admit he has considerably more power across the board.

Anytime I run a reverse pattern cam in that application in place of a single pattern cam, the engine pulls harder, pulls smoother, and is much easier to tune because it isn't so cold in the way of EGT's. It also has much better power in the early ranges of the power band.

You will most likely find power and drivability with an Unsymetrical lobe compared to a symetrical one. The shape of the lobe is very important, too.

Whenever you go to a reverse pattern cam with an effecient turbo, you will realize the gain. I've had many GN's running around with single pattern cams. Then the owner swaps the stock turbo with something better. Once he changes the cam to take advantage of the new turbo's effeciency, the car comes alive and is also more drivable.

Comparing cams at Duration @ .050 points is not going to tell you but about 20% of the information you need to know when picking cams. It is sort of like looking at 2 houses for sale, and forgetting to look at everything else but the kitchen. Few if any would buy a house only because of the kitchen. The same is true with cams. If you pay atention to the advertised, .050, and .200 numbers, then you have a much greater amount of information for comparrison sake.

You have to watch out for advertised numbers, too. Some cam companies will advertise a Hydraulic cam at a different point on the lobe than another cam company. If they both are the same at .050, but one is advertised at .006, and the other is advertised at .0045, you could be looking at 5-10 degrees difference in advertised duration without any more or less at .050. And you never knew it. A Hydraulic with an advertised duration figure published at .006 can be 5-10 degrees bigger in the engine than it is on paper without giving you anything bigger at .050 or anywhere else but at the seat. The more oil viscosity, the more those advertised numbers will blow up since the valve will open earlier than .006. Now if you understand what I just explained, you will see that one cam is lazier than the other. Not just bigger in advertised.

Understanding how and at what point the engine will see and interpret the cam means far more than what is in published print.
Much of that is nothing more than marketing and showing only what they want you to see but nothing else.

I hope I have not confused anyone even more.

So your saying a 218-224 @ 50. with a 115 lsa will make my 109 stroker with 9-1cr, ported GN1's & 70 bb qtrim a real pig

 

[Shaun Tiede]

I think it will be lazy under vacuume/before boost. I think it might also have more lag than you might be expecting. But hard to say since I don't know what you expect. It is hard to say what is or isn't lazy in regards to lag times since what is lazy to me might not be to another and vice versa, etc.

You have raised compression some. That will help offset. If you added stroke without adding connectiong rod length, that will help bottom end as well.(can also make it peakier and more octane sensitive potentially, but 2 new and additional topics there.)

Since the factory turbo that came on GN's was small relative to ones people upgrade to, they spool pretty quickly. It doesn't take much to get them going from my observation. They're more forgiving of the effect bigger than stock cams have on lag times.

Of course the bottom line is to try that cam if you already have it. You might like. It's not a big problem to solve if it does not suit your needs and wants.

To a person who tries a cam and likes it, I will ask them to think about how they can say the like it if they have never compared it to anything else in their engine accept a stock cam. I always ask compared to what. That is also another subject. LOL.