272/264 v 264/272
 

Hi crew,

it seems there are two schools of thought on the mixed cam combinations. (I guess I am largely referring to the HKS cams here) Some swear by the 272in264ex and others go for the 264in 272ex.

Wondering if anyone has done any back to back tasting of the two combinations or if anyone can shine some light on the thinking behind having the mixed cam combo and what it actually achieves. ie. What the actual effect of increasing durations of the intake v exhaust or visa versa is or what charateristic it may achieve. (Yes I have done heaps of searching and turned up very little)

Some food for thought is the diagram below which compares the EVO VIII MR and the EVO VIII cam timing but also give the duration and lift of the cams. The duration of the cams on both cars is the same with different timing used and more lift on the MR. Seems the intake has longer duration from the factory on both cars. Just found this type of diagram has helped get my head around cam timing. (Am still only scratching the surface :) )

Re the cam timing which is also an area I am interested in knowing more about, the intake opening on the MR has gone from 21 degrees to 17 degrees. I am assuming this is 4 degrees retarding of that cams timing?? This would add some weight to the testing of silver surpher where he has found about -4 on the intake is working well.

Just hoping to get a bit of a tech discussion going regarding cams selection and cam timing.

Thanks in advance for your feedback.

http://img.photobucket.com/albums/v9...p_image002.jpg

THis is new to me. I didn't realize the MR had different lift than the regular Evo8. Interesting...

Worth noting that the diagram is JDM and this may vary from USDM. Cant confirm exactly what your USDM VIII MR gets.

Here are the condensed differences:

Factory EVO
Advertised Duration - 260 deg Int / 256 deg Exh
Lift - 10.0mm Int / 9.5mm Exh
Lobe Centerlines - 109 deg Int /111 deg Exh
LSA - 110 deg

JDM EVO MR
Advertised Duration - 260 deg Int / 256 deg Exh
Lift - 10.0mm Int / 9.5mm Exh
Lobe Centerlines - 113 deg Int /112 deg Exh
LSA - 112.5 deg

Summary:

- We don't know the duration at 1mm lift, but there appears to be no difference in duration.

- The reported difference in lift works out to a tiny fraction of a mm, and is insignificant.

- The only real differences are the lobe centerlines and resulting LSA. To get the cam timing of the JDM MR, one would use a setting of -2/+1 for his factory cams. What this does is give a slight boost to high rpm power while at the same time sacrificing a slight bit of midrange torque and spool.

Great summary Ted. Cheers. :beer: Nice to be able to condense the tech down into something that is easier to digest.

I'm running 272in\264ex for more bottom end and quicker spool. My reference; How to hotrod small-block Chevys. This said 270 was a good street strip intake "stump-puller" cam.
Street cams have more intake duration than exhaust. (In our case, I figured less exhaust duration means a bit higher exhaust gas velocities. Quicker spool?? Never seen it mentioned before so form your own opinion.) The more radical the cams had more exhaust duration than intake. So, how much difference can you feel between 264\272, 272\272, 272\264? Probably not much if any. 280's though are a different animal. Big power, but not good for putting around in traffic.

Just my o2,

Ted B, your LSA explanation seems counter intuitive to me, could you please elaborate a little further? I would have thought that the tighter LSA on the factory setup would bleed have more valve overlap, causing slightly more chamber bleedoff at lower rpms (less midrange power) but allow for better breathing up top.

Whereas the JDM setup seems to trap more chamber pressure down low helping with spool, but giving up efficiency on the top end. I wouldn't expect these differences to be very significant on a stock cam grind either way. But that is how I always understood cam setups - please correct me if i'm wrong!

Evojon - please don't modify your evo according to how to hot-rod a small-block chevy! These two motors couldn't be less similar when it comes to cam designs! One is a large displacement 2V NA setup with a single in-block cam, the other is forced induction DOHC 4V design. A 270 cam on a small block is not even related to a 270 cam on an evo. And if you ran 10mm of lift on that chevy, i don't think it would even start up. From my understanding with turbo cam designs, LIFT is more important than duration. But, for better spoolup, a longer duration exhaust cam would be beneficial, to allow more of the gases to exhaust. Exit velocity is not affected by duration so much as it is by LIFT, so that isn't really an issue here.

I have the HKS 264i/272e Cams. They have allways made alot of power and torque for me. And the car drives nice around town with little or no jumping around at all.
Many here in town are surpriced at how well this Cam combination have done for me.

But, I think I am ready for the 280's now. If you have not gotten the Cams yet, go 280's.
They make more power for sure. And don't really idle too bad from what I have seen with all runing them. Also on the dynowed Evos here, the ones runing 280's, the graphs shows the spool about 300 rpms later. That is nothing.

But if you go with that high of a lift,Like the 280's,do you need upgraded valve springs?

Dude, 2v, 5v, blown, NA or turboed, does'nt matter that much, they are freakin high performance air pumps, same internal combustion 4 stroke. Compression ratios are different and tuning maybe different, but basically, it ain't that different.

Any more to add to this guys?? Keen to hear more on the theory behind the mixed cam sets and what each setup is liklely to offer.

Seems the bigger duration exhaust will improve breahting on this side and assist spool.

So bigger in the intake will allow you to get more air/fuel mix in for a bigger bang???

Wang, that's correct. A larger intake duration bias will typically help out top end breathing. And, obviously most importantly is that the combinations need to be matched appropriately for your goals.

Evojon - No offense, but for your own sake, please do a lot more research into this subject. Cam designs vary SIGNIFICANTLY from OHV and DOHC motors. The cam specs themselves can't even be compared due to the different valvtrain geometries. For example, a 224/224 (single) cam on an ls-1 is a good midrange cam. I don't think anyone would ever run a 224/224 setup on an evo, because the two cam specs represent completely different valve actuation in real life. Also a turbo cam usually has the exact opposite duration setup as an NA or supercharged cam.

Your statement is generally correct or less correct, but there is some variation depending where in the crankshaft rotation the overlap occurs. For example, tighten the LSA by advancing your intake cam 2 degrees and note the changes in spool characteristics and midrange torque. Re-correct the LSA (but on different lobe centerlines) by advancing the exhaust cam 2 degrees and one can see the initial difference wasn't due strictly to a change in the intake lobe centerline.

In the case of the US vs. JDM cam settings, the JDM settings delay the closing of the intake valve by 2 cam degrees, which results in a lobe centerline of 113 degrees. This helps high rpm power a bit. As far as the difference in LSA, one would think by conventional thought that the tighter LSA in the US spec car would make for better high rpm breathing, but there is more to the picture. For example, time and again a car with a setting of -4/-1 will make more peak power than a -3/-3 (at the expense of some spool time), despite the tighter LSA in the latter setting.

I don't have any tangable data to provide, but I went from 264/272 to 280/272, and noticed a big increase on the top end. It pulls much harder up top. The idle is somewhat to be desired, as it sounds like half of a mustang under the hood. I have had some issues with the 'hunting for afrs' as the case with most untuned 280 cars. My .02 is just to go straight 272, or 280. You can always make up the difference in the tuning.

Ted,

I am just trying to get my head around your statements below as I am relatively new to the study of cam timing and very keen to understand it. Be clear that my querying is not doubting your statements but seeking to understand... :)

NOTE: My comparison or theorising below is based on the diagram I posted in my first post. I notice you compare US v JDM cam timing in your statement below so I am not sure if this is the same as what is in my diagram. If not, this may be the reason why my theorising doesn't match yours.

You mention that in the chart comparing the two EVO VIII cam types the intake valve is delayed in closing by 2 degrees. On the std evo VIII it closes at 59 degrees and in the MR it closes at 63 degrees. I would have thought this would have been a 4 degree difference and would be regarded as retard, as in its opening 4 degrees later (from 21 degrees on the std VIII to 17 degrees on the MR) and closing 4 degrees later. So in effect would be represented by a -4 adjustment on the intake cam wheel. (It seems both have a 260 deg duration on the intake and the change is timing.) The exhaust cam timing and duration seems unchanged. So just to focus on cam timing, if we make the assumption that the cam profiles/duration are identical (just for this comparison) to achieve the settings of the MR cams with the std VIII cams you would need a -4in 0ex cam gear setting, correct??

Also on the centre line, I am not sure exactly how this is calculated, but I am guessing it is a representation in degrees of where the centre of the cam is. Using the MR intake cam, if its total duration is 260 degrees, then I am assuming the centre is 130 degrees after it opens. Given it opens 17 degrees (I am assuming BTDC) then its centreline would be 113 degrees ATDC as you mention. Am I on the right track??

And just my general theories I am getting together in my head to help me make my own decisions on cam timing, advancing the cam timing makes the event of the inlet valve opeining happen sooner and allow the intake charge to get into the combustion chamber sooner with the risk of the exhaust valve still being open and losing some of the charge straight out. Retarding makes the event happen later and possibly offers less time for the charge to get in but less chance of it getting lost out the exhaust port. On the exhaust side, advancing the exhaust allows the exhaust port to open sooner to get the exhaust gases out at the risk of opening too soon and robbing the power stroke, where retarding it will open the valve later and may cause pumping losses on the exhaust stroke by preventing the easy evacuation of exhaust gases... Am I remotely on the right track???

Some other theories...

advancing the exhaust cam will get it open earlier and get more gas out and improve turbo spool.

advancing the intake will get more charge in and improve top end

Happy to have any feedback on any of the above as I am just trying to flesh out some cam timing principles so when I am making changes I am clear on what I am trying to achieve by doing it and can compare my theories to the actual outcomes. I am sure I am over simplifying it, but just trying to grasp basics at this stage and work my way up.

Thanks in advance for all your feedback.

Be careful:

The cams turn at half the crankshaft speed, so an adjustment of one cam degree = two crankshaft degrees. The valve events, lobe centerlines, and LSA are all reported in crankshaft degrees, but the cam wheels are indexed in cam degrees. Therefore, to retard the valve events by 4 degrees, one needs to use a setting of "-2" on the cam wheel. You need to be mindful of this, or you will find yourself very confused.



Correct.


Just keep in mind that the single most important event is the point where the intake valve closes, which means the overall position (particularly lobe centerline) of the intake cam can be viewed as the centerpiece of the configuration. Once that is set, one can trim the position of the exhaust cam to set the LSA wherever desired. This is a very basic strategy, but it is a starting point.



Somewhat, but advancing it too far will begin venting combustion gases before their work is done.


Advancing the intake takes better advantage of the low speed sucking/pushing effect of the pistons, but can compromise efficiency on the top end, where the inertia effect is the driving force for air movement.


Once one gets a solid mental picture of the cams in motion with respect to the crankshaft, he can predict the general characteristics of any given cam set just from effective lift/duration and lobe centerlines, without the need for a calculator, charts, etc.

Thanks Ted. This is what I am working towards. Just want to have an understanding of what the changes I am making I are doing rather than blindly following the pack.

How bout another question.... :D

I am installing a set of 272in and 264ex cams. I am trying to make a comparison to these and the stock cams and theorise on the cam timing. Do you know if the information on the centreline of the HKS cams is out there???

Would be interested in how the timing of there opening and closing compares to stock at a 0/0 setting and then compare how the well known cam timing changes out there move these events as compared to stock.

I am always a believer that the companies who build these motors do there R and D and have them setup in certain ways for good reason. Possible sometimes it is a compromised one setting to suit most applications, but at least it is a good starting point. Be nice to see how the aftermarket stuff comapares to stock.


ps. Oh and thanks for pointing out the difference between cam degrees and crank degrees. I am starting to get the picture now... :)

You can find a good list of most available EVO cams and the specs thereof by going to the last post in this thread:

https://www.evolutionm.net/forums/sh...ad.php?t=86242

Thanks Ted. Had been following that thread but had missed your latest update with the centrelines etc added. Thanks again.

Ted,

just been doing some sketches to try to get my head around the opening and closing events of my intended cam install. (Note this is the HKS 272in 264ex)

Going by the numbers you have provided I have calculated the following. On the 272 the intake would open at 26 deg BTDC and close at 66deg ABDC. The exhaust valve driven by the 264 cam, the exhaust would open at 62deg BBDC and close at 22deg ATDC. Am I on the money here??

Just keen to know if I am gaining any understanding and manipulating the numbers correctly.

Thanks again for all your feedback.

Have been doing some more thinking and sketches. Basically trying to get my head around the cam timing changes now. Please advise if you thing the following theorising is on track... :)

-2in +1 ex. Change is to open intake 24BTDC as opposed to 26BTDC and close 68ABDC as opposed to 66ABDC. Centre of this cam now at 112deg. Exhaust goes from open at 62BBDC to 63BBDC and closes at 21ATDC instead of 22ATDC. Centre of cam now at 111 deg. New LSA of setup is 111.5 deg. Sound right??

Compared to the -4in -1ex where the centre of the intake is now 114deg and the centre of the ex is 109 but the LSA remains at 111.5.

Any comments on the effect of these two settings?? Same LSA but different event timing of the opening and closing of valves.

Sorry if I am being painful, but really keen to get my head round this.

Post #21 is correct.

Post #22 is correct so long as you realize that your referrals to "-2in +1ex" and "-4in -1ex" are crank degrees. When those terms are typically used, they usually refer to cam gear settings, which are always expressed in cam degrees.

Thanks again Ted.

Thanks for pointing out the cam degress v crank degrees isssue again. Seems I didn't quite have it. So if I was talking about using these settings at the cams, (eg -2/+1) the the effect at the crank is 2:1. eg. A 2 degree retard at the cam will give 4 degrees at the crank on the inlet and a +1 degree at the cam will give 2 at the crank.

Thanks again for all your help. Slowly getting there.

Would have taken this to PM but am hoping this discussion may also benefit others.

Just for my information. I'm not quite up on the advance / retard terminology.

The word "Advance" means adjusting the cam gears such that the valve will "Open sooner" than it normally would?

The word "Retard" means adjusting the cam gears such that the valve will "Open later" than it normally would?

Thanks,

~j.

I am sure Ted will confirm this, but yes you are spot on. Advancing makes the opening and closing events happen sooner, retarding delays the event.

i'm a little confused... don't people generally retard the exhaust and advance the intake?

so is this a way of saying that a tight lsa produces power but a retarded light lsa might produce more (with some losses in the spool etc)? (at least for this example) because i want to know if i'm thinking along the same track.

Correct. Remember that the only measurement expressed in cam degees are the actual cam gear settings. Everything else is expressed in crankshaft degrees.

A tight LSA (104-108 deg) tends to create a shorter, peakier power curve. Race engines that focus power into shorter, narrower powerbands typically use a tighter LSA.

Wide LSAs (110-116 deg) are best suited to street engines that require good idle vacuum and broad rpm power. A wide LSA tends to result in a broader, smoother curve.

A tighter LSA can create reversion problems if the exhaust backpressure is too high. Because of this, a turbo with an undersized hotside will be a limitation with a tight LSA. For example, the tight LSA (106 deg) in my setup that worked so well with a TME appears to have exacerbated a serious backpressure issue with the 20G9-6, which resulted in a substantial loss of midrange torque despite no change in boost pressure.

This is very basic, because just about every important design characteristic of an engine affects the behavior of any given LSA. Here's a decent article that I found with a quick search that gives a little more info:

http://www.hotrod.com/techarticles/18218/index.html

Great article Ted. Will take a few reads of that one before that all sinks in.... :)

Thanks Ted. That article you dug up is very useful reading. I'll bookmark it for my future reference.

I just wonder if there are differences/exceptions for NA and FI setups.

There are considerations that vary between NA and turbo setups, especially where overlap and the potential for reversion are concerned.

Hoping for some elaboration. :)

Hi Ted B,

I'd really appreciate your contribution on overlap in turbo engines...

speaking of valve opening at TDC, not of LC angles, and independently from cams duration ( btw i'm referring to 264 cams ), how many millimeters or inches do you look for ?

Thank you.

Dont forced induction engines usually beifit from more exhaust than intake duration and lift? it does not have to suck air, its being crammed in, so more exhaust would help turbo spool and even out Idle on a super caharger..No? On my blown 355 small block I have 1.6 ratio rocker on intake and 1.7 on exhaust to even out the cam profile a bit.

mayabe I'm wrong :crap:

I am not quite sure of what you're asking, but valve lift for both the intake and exhaust sides will be low at TDC just after the exhaust stroke, simply because TDC lies right in the center of the overlap period - when the exhaust valve is closing and the intake is just starting to open.

On overlap . . .

With an NA engine, any residual exhaust backpressure in excess of 1-2 psi creates a pumping loss that reduces power. With a turbo engine, exhaust backpressure tends to be much greater. When the ratio of backpressure:intake pressure is enough to force exhaust gas back into the cylinder during overlap, increasing the boost pressure further isn't going to do any good. A primary cause of excessive backpressure in a turbo engine is a turbo that has a compressor:turbine efficiency ratio that is mismatched for the application.

For example, in his A/B testing of 20G9-6 vs. 20G9-5 turbos, D. Buschur and Robert of F.P. measured exhaust backpressure to compare the P.R. (pressure ratio) of the two turbos, which is the ratio of exhaust pressure to intake pressure. The results were as follows:

20G9-5 - 28 psi intake, 32 psi exhaust 420whp - 475 ft/lbs

20G9-6 - 28 psi intake, 48 psi exhaust 385whp - 397 ft/lbs

If these results are correct, it shows that the 20G9-5 has much better PR, and is better balanced where compressor:turbine efficiency is concerned. This being the case, a cam setup with large overlap (like mine) is not going to work well with the 20G9-6, because as the power levels rise, the high pressure exhaust gas will try to push itself back into the cylinder and compromise VE.


A PR of 2:1 is typical for a street setup where quick spool is preferred over peak hp numbers. A smaller hotside or larger compressor with no change in hotside will drive the PR upward.

Race engines and high rpm, high hp applications want to see a PR as close to 1:1 as possible. They achieve this with larger exhaust systems and hotsides that compromise spool, but allow large volumes of air flow at high rpm and boost pressures.

Obviously, a large overlap cam set works better with a setup that has a PR of closer to 1:1 than 2:1.


Don't think of the intake charge as being crammed in by the turbo, because that's not really what's happening. The air is still being sucked in, but the air charge has greater density. The exhaust gas also has greater density (a potentially offsetting factor), so keep that in mind.

Typically, the exhaust cam can apply a bit more lift and duration without advsersely affecting low speed performance. However, depending on the intake/exhaust flow characteristics, it may not be doing anything productive.

Hi Ted,

exactly what I meant, and thank you for your contribution !


Now I have, at TDC, 0.016" exhaust valve opened ( LC 115 ) and 0.07" intake valve opened ( LC 113 ):
I'd like to know your experiences/numbers on that.


Let me explain my scenario...

- GT3071 .63 - ext wg - 2.5" turbine exducer bore
- comp T04S ported shroud ( for surging problems I had @ 3500 rpms and 29 psi max boost )
- DP begins with a 2.5" 90 deg curve and then it becomes 3"
- 3" full exh system

- in track use I'm getting high EGTs, 1700F at the 3rd cyl exh valves, but I suspect that at high rpm/full boost I'm getting higher values where the 4 runners get into 1 just before the turbine flange

- black patina in intake plenum, I'm quite sure is reversion at high rpm/full boost caused by the small ar turbine

1. Reduce boost ?
I mean to have a 29 psi peak boost and then reduce it with an overboost option to a value that will give me lower EGT ?
I'd like to avoid this option...

2. Turn to a bigger ar turbine ?
I'd like to avoid cause I'd like not to loose some low to mid power and spool up characteristics

3. Find out a better cam timing ?
This is the option I'd like to develop, if possible, and if could take me to some results...




I even suppose that with -5 setup you're getting lower EGTs....

Would be very interesting to look at the power curves of those 2 options and see where they have peak torque/peak power/spool up...



I think this is the point to analyze...

Thank you !

Which cams are you using, and how do you have them timed?


These three things appear to be significant. What mods have you made? What method of tuning are you using? What do your fuel and timing curves look like?

Sorry...
I'm using Jun 264/264. I timed them with the LC method.
Factory spec was 110i 115e, I retarded the intake to 113i to decrease what I think is reversion..


Full forged internals, FMIC, 2.5" fmic pipes, 4-1 tubular manifold, 850 FIC, Walbro 255 hp.
It was tuned by Motec engineer, on street and then on rr:
I don't know how the fuel/timing curves look like, I know only it's 10.5 afr at WOT.

Could it be interesting that I have a very flat curve ? 425 4whp at 6000 and 410 4whp at 7000 ?

Thank you.

Ted was wondering if you had any details on how exactly buschur measured the exhaust back pressure, since the turbo/manifold are fully divided. does he have 1 pressure sensor per bank, or 1 pressure sensor hooking together the two banks?

So your cam gears are set at -1.5/0, yes?

That shouldn't contribute to the high EGTs, but it may contribute to the surging issues. With a 3071, 29 psi of boost at 3500rpm is more air than the engine can accept, which has the compressed air trying to force its way back through the intake. A diffferent cam setting may alleviate this somewhat, but I suspect there is another aggravating factor. The fact that you're getting 29psi out of a 3071 at only 3500rpm makes me wonder . . .

You quoted 425whp at 6000rpm. I assume this is with race fuel and recorded on a Dynojet?


Two things that contribute to high EGTs are an overly rich AFR and lazy ignition timing. Both cause fuel to be burned in the exhaust, and shorten turbo life.

As far as the black residue in the intake plenum, I suspect that is the result of oil vapor in the PCV system. Do you have a catch can in your PCV system?

I don't know specifically where he tapped it, but the divide shouldn't make much of a difference because the backpressure should be equalized everywhere between the exhaust ports and turbine housing.

exactly...


Probably, but I wonder if anyone else have the exhaust valve 0.016" opened at TDC !
Retarding a bit the exhaust cam could lower the EGTs a bit, but the reversion could increase...




You're talking about retarding the intake cam.. correct ? For example 115i ?
BTW now I ported the comp cover and I have no more the surging issue...



That wondered me and other people on the dynojet !
And it was with pump gas !

Maybe it's due for the "strange" GT3071 I have ?
T04S .70 comp cover and T31 .63 turbine ?
Probably I get less surging with its own comp cover, the T04E .50...



This is not possible... I threw PCV system to atmo when car was brand new
;)


Thank you Ted.

No, I am talking about advancing the intake cam to 110 deg and tightening the LSA to 110 deg to make the engine more mechanically efficient at lower rpm.


No, you do not have a strange 3071. Your 3071 is normal.

You are running 29 psi on pump fuel, and this is what I suspected. This does not appear to be normal, and is almost certainly the cause of your problem.

I don't have any first-hand experience with a 3071 on an EVO, but 29psi is too much boost on pump fuel. In order to run this much boost without getting detonation, the ignition timing has to be retarded quite a bit. If the ignition timing is retarded far enough, the air/fuel charge is still burning when the exhaust valve opens. This creates high EGTs. Also, the mixture is burning inside the turbine housing, which is causing the turbo to spool quicker, and this is the cause of the surging issues. The high heat is not good for the turbo, and you aren't making any more power than you would with less boost and a more realistic ignition curve.

Also, your AFR is a very, very rich 10.5:1. This is only going to make things worse, because you're going to have unburned fuel igniting as soon as it contacts free oxygen in the exhaust system.

What I would do is bring the boost down to ~23-24psi, bring the AFR to ~11.2-11.5:1, and retune the ignition curve. You should make the same power, but you won't have the surging issues and your turbo will last longer.

Ah ok... so run 110/110...



Ok... very clear...





Thank you very much ! :thumbup:



PS: I even have many other ideas in mind...
make and hand made divided exh manifold, and buy the new .78 divided exhaust turbine for the GT3071...
less backpressure than .63 and better spoolup...
But this is another story....

{thumbup}

Hi Ted...

if you're still following this thread...

I'd like to have your personal opinion/advice on that...

It seems TO ME that THE ISSUE ( if I considered all the things correctly ) is too high EGT...

then I THINK I have to decrease intake temps to let me have slower combustion = more advanced ignition map AND to let me have a leaner AFR without det.

IS there anithing else I could think about ?

Decrease backpressure ( for example going from .63 to .82 turbine ) could help me ?

Going from 264 to 272 intake cam could help me ?

Please, your ideas no this...

Thank you.

As far as I can see, the only thing that is really going to help you is to reduce the boost to a level that is more appropriate for pump fuel, retune the AFR, and retune the ignition curve to something more reasonable.

Ok.

Thank you again !

I thought this should be noted. I read through this thread looking at 272/264 cam info. Ran into this. Figured I would clear up the fact that the cam is not really all that small. The duration is shown @ .050 for the LS1 cam. The cams being discussed for the Evo's ex. 264,272,280. These are advertised duration.