squalor

iTrader: (3)

I read martin's sticky "Why LSA doesn't matter". he said he uses a valve event calculator to compute those valve events into intake duration, exhaust duration, intake center line and exhaust center line. Where can I get one of these calculators ?
In THIS thread I asked for a cam recommendation and PREDATOR-Z took the time to help me (thank you sir). He suggested a 224/230 XE-R 111+1 LSA Reading Martin's thread, I know this cam has 5* degrees of overlap. I ask for help to calculate the other way, to take these specs and get Valve Events.
I read the Reverse Torquer thread ... three times.
NightTrain66 said, "IVO- earlier you open the intake valve, the higher the lift point when the piston starts sucking on the port (good thing) but you have to watch the IVO/EVC and amount of overlap so you do not contaminate the mixture of next intake stroke.
IVC- earlier you close the intake valve, the more cylinder pressure (dynamic compression) you trap and the later you close the intake valve, the less cylinder pressure you trap but a later IVC also allows a few extre degrees for cylinder filling and can make a lil more top end power. The LONG runners on the LS1 are gonna have a stronger and longer pulse for better cylinder filling for a few degrees after the piston stops sucking on the port and my comment was that the people that use "DCR only" to determine IVC will be missing out on some power.
EVO- earlier you open the exhaust valve, the sooner you stop pushing on the piston (blow down). This can hurt TQ at low RPM, mid range and even top end. If using enough nitrous or have enough intake flow (sheet metal intake, etc), you can see some HP at high RPM by an earlier EVO. Most people lose alot of TQ with too early of an EVO.
EVC- the later you close the exhaust valve (tighter LSA, larger ex duration lobe), the higher lift the valve is at when the piston nears TDC so you can get more air out of the cylinder but you have to worry about where the air is going and make sure it is going out the exhaust instead of up the intake port (reversion) during overlap. The earlier you close the exhaust valve, the less reversion you have to contend with . Most LS1's will end up making more power by having a smaller exhaust lobe since you eliminate some of the problems with overlap by using an earlier EVC and not blowing down the cylinder by using a later EVO". I guess the exception to his last sentence is cars with poor exhaust systems, spray/F.I. or high RPM. Also, it seems a car with a exhaust system that scavenges well could have a higher DCR than calculated.
lil ss said, "My thinking is to get the .200 IVO point as early as I can, keeping the P/V clearence in check for all lifts. Get a semi early IVC point to keep DCR up. Since my set up favors the exhaust so heavily, keeping a later EVO point will allow me to keep TQ by not bleeding the combustion charge off as early. Have some decent overlap to get the intake charge moving. I feel I am set on the intake side of things with a XFI 236 106. This more or less mimics the TREX intake valve point but gains DCR by closing the intake earlier (44* ABDC @ .050 vs 50* ABDC @ .050). IVC 45* EVO 44* The EVO / EVC points are the ones I'm trying to decide on. I figure a XFI 230 lobe would be a good choice, but do I want it on a 106, 107, 108 is the question. I'm leaning towards the 108 to reduce some overlap in hopes I won't polute the intake charge as much with reversion. A 106 obviously would open the exhaust valve later maybe aiding TQ, but possibly at the expense of more reversion, potentially lowering performance with the polution". A 236/230 sounds too mean for me but early IVO/IVC makes sense for my cam only plans.
PREDATOR-Z said, "High midrange TRQ likes earlier EVO. Higher IVC, coupled with equidistant (IVO/EVC) or intake biased IVO/EVC from TDC will tell how far the power is carried". He was replying to PaintItBlack about how to keep a reverse split from falling after peak, iirc. His statement seem to contradict the others until I remembered there is no perfect cam, we compromise based on our needs. So with El Torro, he takes from the bottom to give to the top.
In the thread, "What LSA for 228r", HAZ-Matt said, "For the 110+0, the exhaust valve opens at 44* (0.050) BBDC compared to 48* for the 112+2. That means the 110+0 should make slightly more torque because of the slightly longer power stroke. The difference in the 8 degrees of overlap for the 110+0 versus the 4 degrees for the 112+2 means that the 110 will idle rougher, have a little less idle vacuum... the 110 should also carry power a little better past peak since it has a little more overlap and the overlap is centered right at TDC, whereas the the 112+2 is centered slightly before TDC". Is this what intake biased or exhaust biased means ? +2 advanced is exhaust biased, -1 intake biased.
WeathermanShawn said in the thread "Cam Thoery(not my sp)" Intake Valve Closing (IVC) is one of the most important valve events that determines your power band. Close it earlier, and the cylinder pressure (power) peaks earlier. Close it later..power band peaks later. Once the IVC begins to exceed 42-46 degrees you arguably begin to lose lower end torque and may not even gain further top-end power". Since 1500rpm manners is important to me, is this why PREDATOR-Z suggested a 224 ? What would I be giving up going to a El Torro if my exhaust has better scavenge ?
For a cam like El Torro 230/230
El Torro 230/230 .612XFI/.592XE-R 111+2 LSA/ 109 ICL 5>IVO 47>IVC 47>EVO 5>EVC 113>ECL 8* overlap
El Torro v2 230/230 .612XFI/.592XE-R 111-1 LSA/ 112 ICL 5>IVO 47>IVC 44>EVO 6>EVC 110>ECL 8* overlap
El Torro v2 has more PtV clearance. I guessed at the events for v2, did I get it right ? What would the DCR be with untouched 241s ? What would ..... I'm sorry this is so long but most of it is quotes from people smarter than me. I'll stop and listen now.

Darth_V8r

iTrader: (4)

I'll try to help, but honestly, it looks like my understanding is no better than yours. One thing I don't see addressed too much is intake runner length. You're pretty much stuck with 4800 rpm peak torque and 6300 rpm peak HP. you can influence it somewhat with valve events, but not by too much.

Your first cam (el torro 230/230) I get IVO=6, IVC=44, EVO=48, EVC=2, overlap=8 and DCR = 8.13

Your second cam (v2) I get IVO=3, IVC=47, EVO=45, EVC=5, overlap=8, DCR=7.93

When I hear "intake biased" I think it means that >50% of the overlap is on the intake stroke. I could easily be dead wrong, but that is how I interpret it.

If I put 224 in and keep all the other cam specs the same, I get DCR=8.34 on the first el torro cam and DCR=8.14 on the second el torro cam.

So, it looks like between the two el torro's, if your goal is low end torque, then the first cam is better due to higher DCR. In short, what you give up going to a 230 from a 224 is DCR.

There is an older thread caller "Torque coming out of my ears cam" that says the following:

So, this is telling me that if you are most concerned with 1500 rpm, you probably want to maximize DCR, even if it means lower duration. On that "torque" cam spec, there is only 6 degrees overlap

JakeFusion

iTrader: (7)

To maximize torque, several things need to happen:

IVC around 40-42 degrees, DCR of 8.7:1 or so, and pretty small CSA in the heads... think ~210cc ports that flow, like the AFR 210s, TFS 205s, TFS 215s, or AI 218cc ports. The more exhaust duration you throw at it, the more your RPMs will carry... but you end up with more overlap, so it becomes less streetable. The positive of overlap? Power.

So if you were to go with AI 218cc ported 241s using stock valves, you could run an XE-R (or EPS lobes would be my pick) 226/234 111+3 with 64cc chambers and .040" Cometics for 11:1 CR with 8.7:1 DCR. You'd have an IVC of 41 degrees and 8 degrees of total overlap. It would be a great street cam and work well with those AI ported heads.

squalor

iTrader: (3)

I really appreciate the replies, thanx.
Ported heads are not in my future, my wife-approval-factor is quite low right now.
I did get Event calculators, the Quick & Dirty calculator seems better than the Piano Prodigy one. Just wish I could find one like Martin's that lets you plug in events to give a grind spec.

So the cam Predator-Z recomended is 224/230 .581XE-R/.590 111+1 LSA/ 110 IVC , 2>IVO 42>IVC 47>EVO 3>EVC 112>ECL 5* overlap SCR 10.37 DCR 7.91 ? I don't know the chamber size of a stock 241.
The 42>IVC abdc starts making compression sooner. 47>EVO bbdc keeps cylinder pressure longer. This helps 1500rpm manners ? If I milled my 241s a bit I could run a later IVC and earlier EVO and keep the 1500rpm manners ?

I did get a set of headers better than what I thought I was getting. They are ceramic coated mild steel from Spoolin. 1 7/8" primary with 3" merge collector. My long primaries are 34" and my short primaries are 24" . Average of all #s is 28" plus port length. I've attached a pic of how I intend to do true duals. My muffler is a Dynomax Ultraflow 1721[http://www.dynomax.com/ultra-flotm-w...t-offset.html] instead of the bullets on Sabre002's car and my X-pipe will be closer to the collectors. I won't know how they pull with my LS6 cam, no overlap. I do think my LS6 intake and LS1 TB & MAF will be my limiting factor so that's why I'm looking at reverse-split. I hope overlap and less advance will help me carry RPM instead of exhaust duration.
Looking through Comp Cams catalog I see a spec called Tappet lift @ TDC , what does this mean ? Looking at different lobe shapes and ramp rates makes me wonder, is it the fast opening and closing from .006 to .050 that stresses springs or the rate from .050 to .200 that does the most damage ? Why is Comp concerned about slow close on the exhaust valve ?
How much lift can a stock 241 head use before diminishing returns ?

speedtigger

iTrader: (16)

Here is a tool that will tell you valve events from traditional duration and lobe centers:
http://www.wallaceracing.com/cam-deg-calc.php

Here is a calculator that goes the other way from valve events to duration and lobe centers:
http://www.wallaceracing.com/camcalc.php

CAMSTER

iTrader: (10)

Hey squalor you can do all the research and that's cool.

Here's what some of us prefer to do sense a cam change is lots of work and money and is so good to hit the mark on the first try, I can't help but to suggest the following;

There's a software design just to do this for you is hard to beat, even getting real close on your own still means you did not get as good as could be had.

You enter all your car info (is a lot) like intake runner cc, flow, compression, headers primary tube diameter, collector diameter, rpm shift points, red line intended, transmission type, gears, diff gear ratio. purpose, power expectation lots more, you get the picture.

You go to Camhelp@guerragroup.com and post a $25. payment using your pay-pal or cc their software will direct you to a long questionnaire take your time, Patrick G will call next day to ask any question he may still have, then will summit a proposal, will contain the grind detail specs, just so you know likely will seem lot smaller than you had in mind, my suggestion is just try it, my experience is it will do all you asked and more and yes with minimum size cam.

Is the best deal in high performance today.

Darth_V8r

iTrader: (4)

In the following, I'm assuming you are asking as much the why as the what, so I'm only responding to try to answer the why question more than make a good cam suggestion.

Your question on the 42-IVC and 47-EVO - answer is yes, but that 7.9 DCR will hold you back some.

Milling the head - yes, this can increase your DCR via brute force and allow for more intake duration, but I would still recommend the later EVO. Your headers will help reduce back pressure allowing you to run a later EVO and still get rid of the gases. Later EVO is good for torque.

How much lift? IMO, that is less important than time at or above 0.200" lift. Like Jake said, EPS lobes. Good duration and good total area, and relatively easy on the valve train. It's very deceptive, because 224-230 looks not much bigger than a stock cam, but the lobe designers have put so much more total area on the lobes that they make very good power. Don't get hung up on wanting duration for duration's sake. Get a cam designed for great power at 1500 rpm. If you want that cool-sounding cammed idle lope, it can be tuned in or out with a very wide variety of cams.

As to the what, take camster's advice and spend time on the phone with some pros and get a few recommendations. Take jake fusions advice to heart as well. I've read a lot of his posts, and he really seems to know his stuff

squalor

iTrader: (3)

Speedtigger, that second calculator is exactly what I was looking for

230/230 110+1 LSA would give 6>IVO 44>IVC 46>EVO 4>EVC 10* overlap
But a XE lobe would act differently than a XE-R or LSL.
Also what role does lift play in all this ? Lift = Torque More lift is better until I run out of intake and head flow right ? What lift is on the edge of sanity for a LS6 intake and 241 heads ?

Camster, that software assumes I know what I want. I thought I wanted a wife that looks like Mila Cunis. The wife I got is not that pretty but she sure can cook !
I'm just the kind of guy that wants to know the WHY of things. Also, if I'm going to mill, I need a cam to clay with to avoid fly cutting.

Darth_V8r

iTrader: (4)

Yes, the XER and LSL will give different behaviors. The 241 heads unless you port them reach diminishing returns around 0.500" lift. The EPS, XER, and LSL lobes might get you to 0.600" lift, and you think "no benefit". Not so fast - those lobes get you to 0.200" much faster and stay there mush longer, so you get alot more air in. 0.600" lift is probably getting close to the edge of sanity.

Duration, not lift, is what takes away PTV clearance. Your maximum lift occurs when the piston is WAY away from the top. Longer durations will cause problems. I don't honestly think 230 duration is going to be any issue.

Mila Kunis is Meg on Family guy. Just sayin...

squalor

iTrader: (3)

Here is a list I made with different Comp lobes and a few Bullet/Ultradyne asyemmetric lobes. The R1 numbers are ramp speed from 0.006 to 0.050 and the R2 numbers are from 0.050 to 0.200 , Lower number means faster ramp/ more lift.

Ultradyne Lobes
HR11 280 226 149 .600 R1=54 R2=77
HR14 284 230 152 .600 R1=54 R1=78
HR25 279 225 145 .585 R1=54 R2=80

LSL (LSR cams)
13096 275 225 149 .612 R1=50 R2=76
13017 277 227 151 .614 R1=50 R2=76
13097 279 229 152 .615 R1=50 R2=77
13018 281 231 154 .617 R1=50 R2=77
LXL
13158 278 226 147 .605 R1=52 R2=79
13159 282 230 151 .609 R1=52 R2=79
VVI
13184 274 226 149 .619 R1=48 R2=77
XE-R (base circle 1.440)
3722 273 224 146 .581 R1=49 R2=78
3723 275 226 147 .585 R1=49 R2=79
3724 277 228 149 .588 R1=49 R2=79
3725 279 230 151 .592 R1=49 R2=79
3726 281 232 153 .595 R1=49 R2=79
XFI
3015 274 224 149 .609 R1=50 R2=75
3009 276 226 150 .610 R1=50 R2=76
13080 278 228 152 .612 R1=50 R2=76
3016 280 230 154 .612 R1=50 R2=76
13081 282 232 156 .614 R1=50 R2=76
3035 276 224 147 .600 R1=52 R2=77
13137 278 226 148 .600 R1=52 R2=78
13138 280 228 151 .602 R1=52 R2=77
3036 282 230 152 .604 R1=52 R2=78
13139 284 232 154 .605 R1=52 R2=78
XTReme LS1 High Lift
3715 277 224 142 .568 R1=53 R2=82
3716 279 226 143 .570 R1=53 R2=83
3717 281 228 145 .571 R1=53 R2=83
3718 283 230 147 .573 R1=53 R2=83
Xtreme RPR (Xtreme opening with XE-R closing)
3673 277 225 144 .570 R1=52/49 R2=81/78
3674 279 227 145 .571 R1=52/49 R2=82/79
3675 281 229 147 .573 R1=52/49 R2=82/79
3676 283 231 149 .575 R1=52/49 R2=82/79
HUC
13045 286 231 149 .598 R1=55 R2=82

Darth_V8r

iTrader: (4)

OK, i'm going to focus on only the 149 @ 0.200" cams. Also, since there are no angles listed, we'll assume all of them are 110/110, and also every single one of them is way better than the stock cam. Also, I'm assuming we're talking intake lobes identical to exhaust lobes (except where listed), stock 241 heads, and a 0.041" head gasket:

Ultradyne DCR = 8.07, IVC=43, EVO=43, OL=6
LSL 13096 DCR = 8.24, IVC=42.5, EVO=42.5, OL=5
VVI 13184 DCR = 8.27, IVC=43, EVO=43, OL=6
XE-R 3724 DCR = 8.17, IVC=44, EVO=44, OL=8
XFI 3015 DCR = 8.27, IVC=42, EVO=42, OL=4
Xtreme RPR DCR = 7.96, IVC=46, EVO=46, OL=11
HUC 13045 DCR = 7.85, IVC=46, EVO=46, OL=11

GO back to JakeFusion's comments on how to generate torque:

IVC 40-42, DCR=8.7

Given the assumptions above, the best torquey cam on the list is the XFI 3015, because of the earliest intake close, latest exhaust close, and highest DCR on the list. It also has the lowest 0.050" duration at 224, compared to the others at 225-231. All have equal duration at 0.200" - 149 degrees, and in this excercise, all have the same LSA and centerlines.

Now, if you start adding the rest of the cam details and move events around, stuff changes, which is why I held that other stuff constant to highlight the lobe differences. DCR is calculated off the 0.006" IVC event. That is why the VVI shows higher DCR than the Ultradyne, even though they are both identical at 0.050" and 0.200" lift

Clear as mud?

speedtigger

iTrader: (16)

Pretty interesting discussion you have going here. I would like a share an opinion about the dynamic compression ratio thing. While I agree that DCR does give some insight in the relationship between compression and valve timing, I do not think it is a reliable indicator as to how much torque an engine will make or even how well an engine will perform.

The only thing that dynamic compression ratio predicts accurately consistently is cranking cylinder pressure. The reason I say this is because there is nothing in the DCR formula that takes into account engine RPM, flow and consequently volumetric efficiency. I offer to you that without taking those things into account, there simply is not enough information in that formula to predict torque or even detonation/pre-ignition.

DCR measurements and low speed performance often have a correlation and can parallel with engine performance simply because the formula is a mathematical representation between compression and valve timing which each have an effect on engines power production. But, since we are talking about a running engine where port size, length, charge velocity, overlap, cylinder contamination, etc. are all a part of the formula, DCR just can't accurately and reliably predict performance. There is not enough information in the formula.

The reason I think this is relevant is, if I understand your point correctly, you are postulating that a fast ramp cam with the same .200 duration will make more torque than a slow ramp cam. In my opinion, that will likely not prove true. I do think that the fast ramp cam might idle smoother, produce more idle vacuum and have better low speed street manners, but I personally don't think you will see any measurable power difference by having a faster ramp to .200". What happens after the cam reaches .200" certainly would have an effect if the lift and area under the curve is greater.

squalor

iTrader: (3)

I've been trading PMs with 99Bluz28 and he pointed out that the LXL lobe is LSL on the lift side, less total lift because it is XE on the close side, like the Ultradyne. This makes me think a grind with 0 advance, would actually come out 1 or more retarded, intake bias during overlap. Because it is fast open one could spec 45 or 46 EVO and end up the same as a XE at 47EVO.
DCR is Dynamic, compression raises with rpm and port size, length, charge velocity, overlap affect how much ? (NightTrain66)The LONG runners on the LS1 are gonna have a stronger and longer pulse for better cylinder filling for a few degrees after the piston stops sucking on the port. (Dart_V8r)IVO=3, IVC=47, EVO=45, EVC=5, overlap=8, DCR=7.93 on the Torro V2. With all that cylinder filling, would the DCR rise with RPM ? I wonder what RPM a merge collector starts working ? Probably well above 1500 RPM so if I wanted to run a El Torro I would have to cruise in 5th until I could pony up the bucks for a set of milled 243s, now I see why they're so popular.

I really appreciate the education you guys are giving me. I never considered compression as a part of cam selection.
Could I ask a few more questions ?
Looking through Comp Cams catalog I see a spec called Tappet lift @ TDC , what does this mean ?
Will Comp ask me what cam core I want my cam ground on ?
What did JakeFusion mean by, "pretty small CSA in the heads" ?
Is it the fast opening and closing from .006 to .050 that stresses springs or the rate from .050 to .200 that does the most damage ? Why does Comp recomend slow close on the exhaust valve ?

speedtigger

iTrader: (16)

LOBE..........Lobe #....ADV...050...intensity.....200...Intensity...L obe-lift..lift 106...lift 110...valve lift
Comp LSL...13018......281...231....50.............154.. ...77..........0.363.....0.081.....0.067....617
Comp LXL...13159......282...230....52.............151.. ...79..........0.358.....0.079.....0.065....609

I don't see any evidence in these numbers that the LXL lobe is an LSL on the opening side and an XE on the exhaust side. To me, it just looks like a softer lobe with less intensity both off of the seat and from .050 to .200. With that said, I am open to any data or credible sources to the contrary.

As for the lift at 106 degree and 110 degrees at TDC figures, those numbers are how much tappet lift the cams lobe has when installed on a 106 or 110 degree centerline respectively while the piston is at top dead center. This is given to allow users to determining their piston to valve clearance while the engine's piston is at top dead center.

Squalor, you are asking a lot a great questions. I don't know if everyone will be able to keep up with the rapid fire format though. LOL. Either way, I think you are going to have a lot of fun with this stuff. It is fascinating isn't it?

Darth_V8r

iTrader: (4)

Tigger, I think that DCR is actually one of the two main drivers for torque. In the end, it is all about cylinder pressures and air volume. If you close the intake valve earlier, you increase cylinder pressure. At the same time, if you open the exhaust valve later, you increase cylinder pressure. Pressure is simply force/area - ie pounds per square inch. Torque is simply force x radius. You could simplify the two equations to torque = pressure x area x radius. So, if you increase the cylinder pressure, you increase torque. DCR is a very good predictor of cylinder pressure. Increasing DCR increases cylinder pressure. Same on the later exhaust valve opening. Holds pressure in longer, which is good for torque.

Obviously, when you limit your valve events like this, you limit your overall duration unless you accept tremendous overlap.

So, why do you use later IVC and earlier EVO for top end power? Because when the engine is moving faster, there is less time to get air in and out, so you sacrifice your valve events to get more air in.

Now, to your point, all of the above is a somewhat static system. Because of the way air flows, increasing rpm has the effect of increasing DCR. So, a cam that develops less power at the low end can develop great power at the high end.

This gets back to Squalor's goal, which is power at 1500. You want the valve events that give you the best cylinder pressures at lower engine speeds to maximize your torque.

Darth_V8r

iTrader: (4)

Squalor, it looks like you're onto something. The long runners will develop a pressure wave and continue to feed air a little past the point the piston is still sucking in. Yes, this raises DCR with engine speed.

Can't answer as to the rpm when a merge collector kicks in, but the long tubes help prevent back pressure, which is good for exhaust scavenging. Even if the collector isn't at full efficiency, you can get away with a later EVO and still evacuate the chamber.

Can't answer as to why manufacturers make different recommendations. They all have their reasons and they're very difficult to weigh against each other.

Ported and milled 243 are always a good idea. Even if you don't do them right away, almost every aftermarket cam in the 224-230 range is going to run wwwaaaaayyyyyyy better than the stock cam for low end torque. This whole discussion is really about maximizing it

Sales@Tick

iTrader: (3)

Opening the exhaust valve later does not create more cylinder pressure. Cylinder pressure is created by cylinder filling and spark ignition of the air/fuel charge trapped in the cylinder, not when the exhaust valve opens.

Opening the exhaust valve later merely allows more time for the pressure created by cylinder filling to work on the piston. Just as opening it earlier allows the exhaust port more time to evacuate the cylinder.

DCR is not always going to show you how much torque an engine will make. It does not take into account that cylinder pressure is dynamic and not static. A DCR calculation is only good for cranking compression and low engine speeds as Tigger said. Since it does not take into account air mass rising and falling as RPM rises and falls, how can it accurately predict what the DCR will be at 5000rpm, or at 7000rpm? It cannot. Admittedly I used to use DCR as a way to build/cam an engine, but I do not look at it much anymore.

You may in fact think that closing the intake valve later will allow you to run more compression with less chance of spark knock. It may do this at low engine speeds when the piston is moving very slowly. This is because piston speed is slow enough that no real depression is created in the cylinder. Meaning not a lot of CFM demand from the piston I.E. the piston isn't pulling on the head enough to move enough air mass to fill the cylinder with enough air to create any pressure.

By grinding a cam with a later IVC you are directly increasing the amount of air mass the engine can ingest at higher RPM's. At higher RPM's by nature there is more piston speed which results in higher depressions in the cylinder and coincidentally more cylinder fill. As a by-product this means more cylinder pressure. So if you only go by a DCR calculator you very well may think you're decreasing cylinder pressure, but in reality you're actually increasing it at the very RPM's where spark knock is most likely to occur!

Not only that, but the earlier you close the intake valve the more of a pumping loss the engine incurs. The earlier the intake valve closes, the longer the piston is forced to pump against cylinder pressure. This slows the piston down and loses power due to a pumping loss. Of course everything is a trade off and in certain combinations it's necessary to close the valve earlier than it is later.

Everything is a trade off and there is no perfect cam for every combination. These types of threads popping up lately are a great way to discuss these things so that everyone can truly understand what goes into the physics behind a running engine.

Darth_V8r

iTrader: (4)

Hi, Martin,

FIrst off, thank you for chiming in. You said something I was trying to say way much better than I said it, and I thank you. The only thing I'll point to is back on post #1, where he said torque at 1500 rpm is most important to him, so I've mainly been focused on maximizing things at that engine speed.

I was honestly trying to say that the later exhaust opening HOLDS pressure longer, not increases it, helping torque. But I was also thinking that increasing DCR would by definition increase cylinder pressure upon ignition. I'm also thinking relative, not absolute. I'm not saying 8.73 DCR = 418.243 pounds of torque, but I tried to say in post #11 was that increasing DCR from 7.9 to 8.3 would have a corresponding increase in torque at low engine speeds. Sorry if that came out wrong.

Also was trying to find a way to say that when the engine rotates faster, you need the longer durations to get more air in and out at higher speeds. You said it better than I did. My gut tells me that the same events that maximize torque down low will become restrictive for airflow as the engine speeds up, requiring longer durations to compensate.

Post 1 is hard to follow, but buried in there is this:
So, I guess the crux of this whole discussion is not "what valve events make good torque down low or good power up high", but "Why do those valve events make either low end torque or high end power?"

Another question - what are you calling a depression? Like an actual imprint in the metal in the cylinder (you push your finger into playdough and create a depression) or like a stronger cylinder vaccuum (like a "tropical depression")? If I understand you right, as the engine rotates faster, the cylinder creates a stronger vacuum, which pulls air in faster than if it rotates more slowly, causing the increase in DCR at high rpm?

Sales@Tick

iTrader: (3)

CFM demand on the cylinder head during the induction stroke is driven by piston motion. The faster the piston speed, the more demand on the cylinder head. We refer to this in the engine building world as "Piston CFM Demand."

When piston speed increases(whether by stroke or by RPM) the depression created in the cylinder(vacuum) is increased.

Now, just because the piston CFM demand increases doesn't mean that the cylinder head, intake manifold, carb, TB, intake etc. can supply it. The piston always wins the CFM chase. Meaning the piston always demands more CFM than the cylinder head can supply at that current point in time. The induction system is always playing "catch up" if you will. Due to the distances between the piston and the parts of the induction system, these signals will be delayed accordingly.

To answer your question, "If I understand you right, as the engine rotates faster, the cylinder creates a stronger vacuum, which pulls air in faster than if it rotates more slowly, causing the increase in DCR at high rpm?"

It's not so much that the cylinder is creating a stronger vacuum, it's the piston motion that creates it. The higher the depression in the cylinder the more pull(vacuum) is placed on the cylinder head. If you have read my thread, "Why LSA doesn't matter," I show and explain some great examples of pressure diagrams showing exactly this, but in much greater detail. Those diagrams will show you at what piston positions that depression is highest, what it causes the pressure in the intake port to do, and how those signals get delayed and what causes that delay. All of it is driven by piston motion and the resulting pressures that motion creates.

The rise in cylinder pressure(note I didn't call it DCR) comes from the rise in cylinder filling(VE%). Anytime more air mass is entering the cylinder, the more cylinder pressure is created as a by product. Look at it this way; wherever VE is at its highest %(at or around peak torque RPM) that's where cylinder pressure will be highest. This is all driven off of piston motion and what the induction system is capable of supplying at a given RPM(piston speed).

Hope this helps.

squalor

iTrader: (3)

I'm not trying to "maximize" torque at 1500 rpm, I just want to cruise (no load) at 1500 rpm without bucking or surging, with enough vacuum to have brakes. My LS1 is in a '93 RX7, 2800 lbs. 900 RPM idle is a trade off I'm willing to make. Going from 26 mpg that I get now to 17 mpg is acceptable to me. I want generous Torque from 3K to 6 K and have the engine come into "tune" at 5500, half way between the LS6 intake torque peak of 4800 and HP peak of 6200.
But hey, this was not intended to be a "what cam" thread. When I read Martin's LSA sticky, that he thinks in terms of Valve Events and when PREDATOR-Z sez, "don't change my lobes, it messes up the V.E.s" I wanted to understand more. You guys opened my eyes on many levels. The role DCR plays in low speed drive-ability, the limitations of the LS6 intake and stock heads and now, the difference between DCR and cylinder pressure. I thank you all.
Please teach me something else ? IVO, EVC, overlap, Reversion and Contamination, exhaust scavenging. All these play a role in high RPM power vs low RPM drive-ability. For those of us who obey the speed limit 95% of the time (with M6 346ci cars) where can trade-offs be made and gas fumes avoided ?