Wangracing

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.

Erik@MIL.SPEC

iTrader: (94)

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

Wangracing

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

Ted B

iTrader: (6)

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.

Wangracing

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

evojon

iTrader: (28)

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,

Trojan man

iTrader: (10)

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.

04AWDTURBOEVO

iTrader: (26)

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.

ace_2822

iTrader: (27)

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

evojon

iTrader: (28)

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.

Wangracing

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???

Trojan man

iTrader: (10)

****, 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.

Ted B

iTrader: (6)

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.

sgplancer

iTrader: (25)

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.

Wangracing

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.