Cylinder pressure? Help.

[danmc77]

How do you calculate or determine cylider pressure when choosing a cam? I've been searching Hughes Engines site for a new cam, and they mention appropriate pressures for different cams.

 

[moper]

See the post on compression in this section...lol. Perfect timing...

 

[blue missile]

Dan,
good luck on trying to figure out DCRs using Hughes cams.I just went through this with Tim and there was no way they were going to either give the actual degree timing of the events or the advertised duration of their cams.They will only give out the .050" events which do you no good in figuring DCR. You need to know exactly when all the valves are closed.
I don't know what you are building but if you go to "wallace racing/engine calculators" you will find a huge amount of info and calculators.
I will be using Comp Cams Extreme Energy/High Lift cams which take advantage of the larger lifter diameter of the mopar lifters, for what that's worth.
Andrew

 

[danmc77]

Thanks for the info Andrew.

 

[fishy68]

I will be using Comp Cams Extreme Energy/High Lift cams which take advantage of the larger lifter diameter of the mopar lifters, for what that's worth.
Andrew

Actually Andrew for what it's worth even comp's extreme series dont' take full advantage of Mopars .904 lifter diameter. A cam can be ground much more aggressive than they are. They are decent cams and definetly more aggressive than the standard high energy or magnum series but still not even as aggressive as the ages old 284/484 purple cam.

 

[blue missile]

fishy68:
at your suggestion I went back and put the following cams through the Sim.
Mopar Purple: 280/280, 284/284, 290/290
Lunati: 276/284, 284/292

only the Lunati 284/292 had any improvment in the numbers by increasing HP<6000 and decreasing the Tq>6000. This by about 15Hp & 15FtLbs

I cannot tell you how many cams I have tried with this combo and I keep comming back to the XE285HL.
Thanks for the suggestion though
Andrew

 

[fishy68]

fishy68:
at your suggestion I went back and put the following cams through the Sim.
Mopar Purple: 280/280, 284/284, 290/290
Lunati: 276/284, 284/292

only the Lunati 284/292 had any improvment in the numbers by increasing HP<6000 and decreasing the Tq>6000. This by about 15Hp & 15FtLbs

I cannot tell you how many cams I have tried with this combo and I keep comming back to the XE285HL.
Thanks for the suggestion though
Andrew

Hey Andrew,

I dont' have the high lift series in my desktop dyno but I'm sure they are better than the standard xe series and quite possibley close to the same as a Lunati. Since I don't have them in the program I forget about them and didn't realize that's the series you were talking about. To compare them you can use the lobe intensity calculator in the cam portion of the program which will show which cam has the greatest intensity.

I have played with desktop dyno alot also with all the cams you mentioned except the xe285hl (didn't have the specs on it or I would've done it too) and noticed they are all pretty close. A 15 hp gain is a pretty large gain if your comparing cams of similiar size. But I have to ask about your statement that the Lunati showed a 15 hp gain at 6000 but also 15 ft.lb tq loss at 6000. How can it loose torque when the hp is greater? I don't remember the hp formula right off hand but I know hp is just a figure arrived using the torque and rpm and a given figure. If the tq was lower the hp would have to be lower wouldn't it? Did you possibly mean a tq loss down low and hp gain up high? Feel free to correct me if I'm wrong.

I'm sure you know Desktop Dyno is a very good guide but isn't all knowing. I first modeled my engine with the Comp XE274 and I had all the head flow numbers and exact compression ratio to put in it for correct readings. Put the car together with it and had problems with their junk lifters twice in 700 miles. Kept draing down terrible after sitting. Got tired of hearing clack, clack, clack for 2-3 minutes when the engine was cold so I modeled other cams and came up with the Lunati 60404 which is just slightly larger. Installed it and even though desktop dyno showed only a 11 hp increase and 10 ft. lb tq increase you'd sware it was closer to 30 ft. lbs and 30 hp it runs so much stronger. I haven't taken it to the track. Just used the G-tech. It dropped from 13.53 @ 105.6 to 13.01 @ 108.8. This was on street radials thus the reason for the slow times compared to the speed.

BTW if you have the specs for the 285hl handy and don't mind please pm them to me. I'd love to have them. Thanks, Tracy

 

[blue missile]

Tracy,
thanks for the reply. I have noticed that some people seem to think that a discussion of substitive information is called thread killing. Since I am new to all of this I don't understand that.

Your'e correct about the Hp & Tq numbers Rathar than using the words above and below I used the symbols < & > greater than, less than, a force of habit, my apologies.
As th Hp increases above the apex of the curve usually the Tq decreases before the apex. A normal trade off in design.

Here are the specs on the two cams:

XE285HL;part# 20-228-4, RPM range 2500-6500, valve timing .006, lobe center 110, intake centerline 106, adv duration 285/297, dur @.05=241/247, valve lift @1.5:1= .545"/.545", lift @ 1.6:1= .581"/.581" (what I'm using)
IVO=37, IVC=69, EVO=83, EVC=35

XE295HL; part#20-229-4, rpm range3000-6800, valve timing .006, lobe center 110, intake centerline 106, adv duration 295/307, duration @ .05 251/257, valve lift @ 1.5:1=.564"/.564", @ 1.6:1=.601"/.601", IVO=42, IVC=74, EVO=88, EVC=40

I will tell you, that so far only the most agressive roller cams can match the numbers for these two grinds. I do not want to go that route when flat tappets will produce these kinds of results.
I included the timing events so you can also look at the DCR and Cranking pressures created.
It was the DCR created by the 295 that has me selecting the 285. More in line with the design goals.

The only thing that really causes the numbers to go off the chart is the numbers for the new Brodex head for the SB LA motor.Thay went up into the mid 600s with no other changes.Right now they are simply not in the budget.

Hope this helps, let me know
Andrew

 

[moper]

Fishy, the old school 284 is not a fast rate cam by todays standards, just bigger duration at mid lifts than what was avaialabel in the early 70s.

I know you guys place a lot of faith in Desktop Dyno. I can tell you it is good at plotting trends, but not specific numbers. It is only a trend. The margin of error is more than the differences you are noting in the results. The reason it is like that is it averages a lot of things for the ease of the calcuations. The original version (which I played with a lot back in the mid 90s ) didnt have flow numbers, it had "stock, ported, and race ported" for heads...lol. I know it's gotten a lot better, but in terms of cam lobes, it is woefully lacking. That is why the roller profiles pull similar numbers, and even the hydraulic lifter calculations are iffy.

I do not want to be known as a thread killer, so if this was aimed at me, I apologize. It seemed to me there were two identical (or very close) threads posted simultaneously, and it's easier to stay focussed on one.

 

[danmc77]

As the OP, I'm enjoying the conversation. Don't worry about "thread-killing."

 

[blue missile]

Moper:
I do agree that D.Dyno is an aproximation of trends in component selection.
As for instance the cams selection gives you three choices, solid.hyd, roller.There is no way to address the agressive fast rate cams of today. so you select roller.Again only an aproximation.

The thread killer comment was aimed at myself. People have asked some questions and I have provided some at length answers, and the threads have died with no responses. Research is somthing I love and am very good at.However my practicle experience with some of these issues is non- existant.

Dan: did you ever check out the wallace engine calculators?
One of the things you wil need one way or the other are the valve timing events.

Andrew

 

[fishy68]

Tracy,
thanks for the reply. I have noticed that some people seem to think that a discussion of substitive information is called thread killing. Since I am new to all of this I don't understand that.

Your'e correct about the Hp & Tq numbers Rathar than using the words above and below I used the symbols < & > greater than, less than, a force of habit, my apologies.
As th Hp increases above the apex of the curve usually the Tq decreases before the apex. A normal trade off in design.

Here are the specs on the two cams:

XE285HL;part# 20-228-4, RPM range 2500-6500, valve timing .006, lobe center 110, intake centerline 106, adv duration 285/297, dur @.05=241/247, valve lift @1.5:1= .545"/.545", lift @ 1.6:1= .581"/.581" (what I'm using)
IVO=37, IVC=69, EVO=83, EVC=35

XE295HL; part#20-229-4, rpm range3000-6800, valve timing .006, lobe center 110, intake centerline 106, adv duration 295/307, duration @ .05 251/257, valve lift @ 1.5:1=.564"/.564", @ 1.6:1=.601"/.601", IVO=42, IVC=74, EVO=88, EVC=40

I will tell you, that so far only the most agressive roller cams can match the numbers for these two grinds. I do not want to go that route when flat tappets will produce these kinds of results.
I included the timing events so you can also look at the DCR and Cranking pressures created.
It was the DCR created by the 295 that has me selecting the 285. More in line with the design goals.

The only thing that really causes the numbers to go off the chart is the numbers for the new Brodex head for the SB LA motor.Thay went up into the mid 600s with no other changes.Right now they are simply not in the budget.

Hope this helps, let me know
Andrew

Thanks for the info Andrew.

Fishy, the old school 284 is not a fast rate cam by todays standards, just bigger duration at mid lifts than what was avaialabel in the early 70s.

Right. I didn't mean I thought it was a real fast rate cam. Just meant it does have a faster rate than the standard XE series by Comp cams. Sorry if it came out wrong.

I know you guys place a lot of faith in Desktop Dyno. I can tell you it is good at plotting trends, but not specific numbers. It is only a trend. The margin of error is more than the differences you are noting in the results. The reason it is like that is it averages a lot of things for the ease of the calcuations. The original version (which I played with a lot back in the mid 90s ) didnt have flow numbers, it had "stock, ported, and race ported" for heads...lol. I know it's gotten a lot better, but in terms of cam lobes, it is woefully lacking. That is why the roller profiles pull similar numbers, and even the hydraulic lifter calculations are iffy.

Gotcha. Have you used the newest version? Just wondering since I have the latest version and it supposedly has a much improved cam program. Or so they say. I never saw the original version so I don't know what it was like. I do know in the cam portion of the program it plots lift and duration throught the 360 degree cycle. Do you think it's still lacking due to rounding off?

I do not want to be known as a thread killer, so if this was aimed at me, I apologize. It seemed to me there were two identical (or very close) threads posted simultaneously, and it's easier to stay focussed on one.

Same here. Sorry to get off track of the original post.

 

[moper]

Blue - Don't be too worried if they die. It will come up again, and at this site especially, you can debate and disagree and it's all respectful. Well, maybe accept for one or two...lol. And they serve to differentiate between class and lack of...lol.

Fishy - What I meant was the MP cams, back in the 70s, had large durations which demanded faster rates of lift for thier time. They are not nearly as fast as the XE line lobes. But, rate of lift is important, but it's easy to make it a holy grail and create issues. (IE Hughe's mixed reputation a few years ago because they were so fast, everything that most engine builders and assemblers took for granted made the cams go flat. Not the cams' fault, but they pushed the limits to where it sorted out the men and the boys. Similar to some peoples' issues with Comp and the XEs. On the Desktop, the old one would take you lift and duration (total, not even @.050...lol) and factored in the average rate of lift (not manufacturer specific) as a straight line and figured it off that. Draw a straight line from the base line to the tip of a typical lobe. It isn't the same shape as a straight line. And even in types of hydraulic lobes, that shape varies. It makes a huge difference where that lift comes in in relation to crank/piston position in terms of cylinder filling and torque peak. It still averages. They are fun to play with. However I think trying to choose between relatively similar profiles in an engine will be an exercise in data entry, not really chrun out usefull info.

 

[fishy68]

Fishy - What I meant was the MP cams, back in the 70s, had large durations which demanded faster rates of lift for thier time. They are not nearly as fast as the XE line lobes. But, rate of lift is important, but it's easy to make it a holy grail and create issues. (IE Hughe's mixed reputation a few years ago because they were so fast, everything that most engine builders and assemblers took for granted made the cams go flat. Not the cams' fault, but they pushed the limits to where it sorted out the men and the boys. Similar to some peoples' issues with Comp and the XEs. On the Desktop, the old one would take you lift and duration (total, not even @.050...lol) and factored in the average rate of lift (not manufacturer specific) as a straight line and figured it off that. Draw a straight line from the base line to the tip of a typical lobe. It isn't the same shape as a straight line. And even in types of hydraulic lobes, that shape varies. It makes a huge difference where that lift comes in in relation to crank/piston position in terms of cylinder filling and torque peak. It still averages. They are fun to play with. However I think trying to choose between relatively similar profiles in an engine will be an exercise in data entry, not really chrun out usefull info.

Thanks for the clarification Moper.