Darth_V8r

iTrader: (4)

You can put a degree wheel on your cam sprocket and a dial indicator on your intake valve for the #1 piston. You can then use the peak lift, average of .050 or .200 lift to determine intake centerline. Then, you can use LSA to determine exhaust centerline

Martin Smallwood

iTrader: (2)

Just so anyone reading this thread knows, I am the author of this thread.

When I left Tick, they changed my old account that I used to use from "Martin@Tick", to "Matt@Tick" since Matt would be utilizing my old account after I left.

I spent a lot of time writing this thread and I was flattered when it was made a sticky.

I just wanted to ensure the credit was given to the original author.

Martin Smallwood

iTrader: (2)

That is true for a symmetrical lobe, but not an asymmetrical lobe.

An asymmetrical lobe will have peak lift occurring before the "mid-way" point of the lobe. The true center line is the "mid-way" point and not peak lift.

SoFla01SSLookinstok

Hey Martin,

Just want to say this is the most informative, beneficial, thread I've read. Being around cars for awhile, & knowing how things work, this was like the next level. I read it over & over.

I thought that was kind of weak, changing the name, as every post you made here, under that account, is changed.

Martin Smallwood

iTrader: (2)

Thanks SoFla01, that means a lot! I really wanted this thread to be as informative as possible and take things to a more advanced level while still allowing those who aren't quite as advanced in engine theory and physics to be able to understand.

It doesn't bother me that they changed the name of the old account. They did the same thing when I went to work for them and they changed it from "Chris@Tick" to "Martin@Tick".

It costs a lot to sponsor these forums and it wouldn't of made any sense for Tick to add another account just so my posts would stay under my name.

This thread though is my pride and joy so to speak, and I wanted to erase any doubt as to who the original author was.

panic

First, thanks for a very useful post.
However, with your kind permission?
Re: "If two camshafts no matter their duration or LSA both have the same amount of overlap and you put both cams in the exact same vehicle with everything else the same aside from the camshafts they will sound identical."

The cam with the earlier exhaust valve opening will be slightly louder (higher pressure release), especially with high static CR.
The cam with the earlier intake valve closing will be slightly louder (higher trapped compression).

Martin Smallwood

iTrader: (2)

There is very little cylinder pressure generated at idle so I doubt that an earlier ivc event would contribute to more lope at idle. Also remember that dynamic compression (ivc and SCR dependent) is just a dynamic way of expressing a static measurement. Your dynamic compression at idle versus your dynamic compression at peak torque will be two totally different figures.

I personally feel that DCR is only relevant for very low engine speeds such as idle and cruising.

I could possibly see an earlier evo event contributing to how loud the engine is at WOT, but again at idle there is such small amounts of cylinder pressure generated I again doubt that there would be little difference if any.

SoonerBrad88

iTrader: (15)

I'm sitting here thumbing through gen3 internals and see the author of this sticky as Matt@Tick and thought to myself who the heck is Matt!?
Thanks for creating this thread Martin, like the guy above I've read it time and time again and learned a TON from it. One of the best on the site IMO.

dr_whigham

iTrader: (49)

I need to see if we can get that changed. Kinda pisses me off it worked out like that.

Let me see what I can do, Martin

scotty2000ss

iTrader: (2)

I agree. Not only this thread but anything else Martin posted says "Matt" now. Complete BS in my book.

dr_whigham

iTrader: (49)

Nothing we can do guys... Many reasons. It would literally be impossible to change the name without affecting every post ever made in EITHER name.

Martin Smallwood

iTrader: (2)

Whigham is right, there isn't anything that can be done. Tick would have to spend more money and buy a brand new screen name for their account which would cost them more money out of their pocket just so my old screen name wouldn't be used. I can't expect them to do that and neither should the members on Tech.

When I first started to work there they switched the screen name over from "Chris@Tick" who worked there before me to "Martin@Tick". Chris didn't post much, but it's still the same scenario.

I do appreciate the support from old customers, current customers and members on this board about the entire situation with the screen names and who gets credit for who said what. Sometimes you just have to go with the flow and make lemonade when life hands you lemons.

tmiller97c5

Wow great info but my head hurts now

Darth_V8r

iTrader: (4)

Been a while on this bad boy thread, but a couple of questions that have been nagging at me since my most recent mods and also paying attention to other builds:

1. Is there a kind of "rule of thumb" IVC that dictates it's time to move to shorter intake runners? I've been thrilled with the cam you speced me, and I noticed my torque curve got smoother with shorter intake runners. However on LS7 stuff, it seems like shorter runners help raise the entire torque curve vs the more typical "sacrificing torque for HP"? Then I noticed the LS7 cam OE has a later IVC than lots of 5.7-6.2 aftermarket stuff?

2. When displacement increases, it seems like I'm observing power falls off faster on lots of builds. Particularly when stroke is increased more so than bore. Do you tend to delay IVC to counter this? Increase overlap? Both?

pantera_efi

iTrader: (1)

Hi Martin, I spent two hours reading this thread finding the time YOU have spent helping LS1Tech members.
GOOD WORK

My observation is about items not stated.
1. The L/D vs Lobe Lift of a 2" Intake Valve = .5" and a 1.6" Exhaust Valve = .4" stating the LOWER lobe requirement in "lift" for the Exhaust Valve NOT often observed, WHY ?
2. I spoke with Warren Brownfield at SEMA and asked him WHY when I increased valve acceleration I lost much Torque with the SAME Top RPM/HP.
He answered "GM PAID me a lot of money to explain this to them".
His answer was that port air speed is related to Valve Lift/RPM and it is VERY easy to open the Intake Valve too fast for a given RPM.
Do you have comment Martin ?
3. An engine REQUIRES an amount of Valve Overlap based on manifold performance both intake and exhaust with GREAT concern for RPM operating range.
I designed a camshaft for a LARGE LS-1 GEN IV 180/188 .550" lift on a 102 CL for operation at 1800 RPM.
The Torque was increased over the GM OEM camshaft, due you agree ?

MY POINT is that an engine requires an AMOUNT of Valve Overlap for good power at the specified RPM.

Thus LSA does not matter.

Lance

Martin Smallwood

iTrader: (2)

I nabbed this tidbit from one of my earlier posts in this thread.

"Where the intake valve closes is closely related to where HP and TQ will peak in relation to RPM. IVO also plays a role in this as well. You cannot make up for cylinder fill that wasn't achieved on the intake stroke on the compression stroke by closing the intake valve later. The IVO event is what gets things going on the intake stroke and gets momentum started in the intake tract. Of course where the exhaust valve closes and where overlap ends determines this as well. Resonance tuning at its finest indeed. That is another topic for another discussion though.

The intake tracts minimum cross sectional area, flange area, the intake tracts length(cylinder head and intake manifold), local velocities, low lift flow numbers, piston speed and compression to name a few will determine where the intake valve needs to close. These variables will also have a large affect in and of themselves aside from the IVC event as to where peak HP and TQ is made in the operating range. You cannot force an engine to peak at an RPM that the induction or exhaust system will not allow. I've seen cam grinders and enthusiasts try to add more and more duration in an attempt to gain a higher peak power RPM only to fail time and time again when the induction and/or exhaust system will not allow it. The cam merely accentuates the power curves where as the induction and exhaust system play a much larger role in setting the RPM where peak power occurs."

Note the text in bold. You cannot force an engine to peak at an RPM that the induction or exhaust system will not allow.

What you've noticed on the larger displacement engines where power is falling off earlier is due to the intake tracts length and cross sectional area, mainly the minimum cross sectional area and length. I can try to help bolster power after peak with a later IVC, earlier EVO and possibly more overlap, but I still cannot force the engine to do something that the induction system will not allow.

A given size engine will demand a given amount of airflow to generate a given VE. The larger the engine and the higher the VE wanted, the more airflow is required. The factory OEM manifolds, and OEM style manifolds cannot supply enough airflow to meet this demand, and mainly they cannot do it at the RPM needed for power to continue to climb or at least carry due to their length.

You can continue to increase the MCSA at the head all you want, but if the manifold is inadequate you will never see a gain in power output, and quite possibly could see a LOSS in power output. The OEM style intakes will only move so much air at a given RPM. Once you get rid of the manifold restriction it changes everything.

I have been doing a lot of testing lately involving the CID single plane intake that has opened my eyes to a whole new world and opportunity of added performance. This intake has anywhere from 4.0 in^2 at the plenum entry to 5.0 in^2 at the plenum entry and 5" long runners. This manifold is readily able to supply the airflow demanded by a large engine at high RPM, or a small engine that requires a high VE, and subsequently large amounts of airflow at higher RPM's to make the power required.

It's all about the amount of airflow that can be moved and WHERE in the RPM range that amount of airflow is moved and trapped in the cylinder.

There is no real rule of thumb IVC event that dictates needing a shorter runner, it has way more to do with airflow demand, and the RPM that the airflow is being demanded to create the VE necessary to make the power that is required of the engine.

Martin Smallwood

iTrader: (2)

Lance,

I don't think a lot of people know about or understand .25 L/D and that once you get past .25 L/D the valve is no longer the restriction. Past .25 L/D the MCSA (throat, pinch or both even...but hopefully it's the throat!) is now the restriction. Since the exhaust valve is much smaller the valve is no longer a restriction at a much lower lift than one would see on the intake side of things.

Then say we have a 116 ECL which is very common for EFI NA LS engines to be very close to this (114-118ECL) for a street engine. The exhaust valve with these common ECL's is at max lift 64 or so crank degrees ABDC. 50% or more of the exhaust gas in a well designed engine will be removed by BDC on the power stroke just from the massive pressure differential created by the high pressure spent gasses being evacuated from the cylinder when the exhaust valve initially opens. If more than 50% of the cylinder's contents are evacuated by BDC on the power stroke, then what good is adding a bunch more lift 64 crank degrees later going to accomplish for cylinder evacuation? You want the maximum amount of exhaust gas out of the cylinder by the time the exhaust stroke starts anyways so you don't have large pumping losses. Added lift and curtain area can help pumping losses on the exhaust stroke if needed or by altering the lobe profile to gain more area in that section of opening ramp, but if you're doing it the right way you're getting the majority out much sooner than ABDC on the exhaust stroke.

Air speed in the port is directly related to valve lift and RPM yes, very glad you brought this up. If you flow a certain amount of airflow through a given amount of area you create a given localized velocity. So since the induction system moves different amounts of airflow at different valve lifts, port velocity is going to change as lift increases or decreases. If the port flows more air at a given lift then it should also have higher port speed at that amount of lift.

As RPM increases the amount of depression in the cylinder increases. Since there is a greater pressure differential between port and cylinder due to higher depression in the cylinder, port flow will also increase with rpm until choke occurs. This is the same thing as flowing a cylinder head on a flow bench with say 28" of depression versus 40" of depression. The port will flow more air at 40" of depression than it will at 28". Consequently air speed will also be higher at higher RPM because of this increased depression until choke does or doesn't occur.

Running engines being raced down the street or track don't run at steady state with a steady depression and no pulsing like a flow bench does. They're constantly pulsing in the intake and exhaust ports with RPM rising and falling with each gear change. Every time RPM rises or falls the depression in the cylinder rises and falls. How well the head can recover when these pulses and changes in depression occur will determine how well the engine runs. Choke will also determine how well the engine runs as well. Drag engines need to be able to recover and accelerate through the gears several times during a run. Whereas a truck puller zings straight up to 9500+ RPM instantly, pulls down to 8800-9000 or so and sits there the entire pull. No need for acceleration there, just maximum flow and no choke at such a high RPM and depression. Drag engines need a very fine balance of both. Any type of racing where the engine experiences multiple gear changes or rising and falling in RPM will need similar flow characteristics as a drag engine and will need to recover and accelerate well.

As far as your engine with the 180/188 102LSA cam, I would need to know just how large it is, but I can say that an engine operating at such a low engine speed will need VERY little overlap, a VERY early IVC event and a VERY late EVO event. All of which you have provided with the camshaft profile you have chosen. Looks good to me and I can see why it gained power over the OEM camshaft at that RPM.

53te39

This is a really good read and what's even better is that the thread is still going. Thank you for expounding on this subject and sharing your knowledge.

G Atsma

^^^^^^Agreed!^^^^^^

Martin Smallwood

iTrader: (2)

Thanks guys. It took me a long time to put all of this together.