How Much Of A Difference Higher Lift Makes ? + Camshaft Duration

[cobrAA]

I will be emailing kelford later today, thanks for the info.

And sorry I pissed off lithium that much... Lots of info, thanks guys! Bottom line is we can't really compare any camshaft from different brand because they are all measured differently.

[XKLABA]

I will be emailing kelford later today, thanks for the info.

And sorry I pissed off lithium that much... Lots of info, thanks guys! Bottom line is we can't really compare any camshaft from different brand because they are all measured differently.

Well no, they are all measured the same, you just have to know how to read the cam card

Cams aren't really that hard and people way over think them, IMO you choose a cam to suit the application/intended use of the engine

You also can not choose a cam for turbo because it worked in a NA, they are two different animals and need to be designed and built that way, simple explanation is NA needs air velocity turbos need air volume, that is the simplest explanation and as much as I can go a lot deeper in to this this thread is about cams, not head design intake designs exhaust design etc etc

[djr81]

They quote 50 thou and 1mm. They are different values. They know what they are doing

Yes you are right. I was looking at the valve lift curve which has them marked as the same thing. But the tables to the left show them separately. For these cams there are 4 degrees difference between the durations at 1mm and at 50 thou.

26_a_in_260_915_ex_252_915_32_33_e.pdf

26_b_260_915_32_33_e.pdf

RB26DETT_256-925_3233_e.pdf

[bigmikespec]

You also can not choose a cam for turbo because it worked in a NA, they are two different animals and need to be designed and built that way, simple explanation is NA needs air velocity turbos need air volume, that is the simplest explanation and as much as I can go a lot deeper in to this this thread is about cams, not head design intake designs exhaust design etc etc

If you have a 1:1 ratio of exhaust manifold back pressure to boost pressure (or better) choosing an NA cam is a good place to start!

[GTSBoy]

If you have a 1:1 ratio of exhaust manifold back pressure to boost pressure (or better) choosing an NA cam is a good place to start!

True.....but when you say NA cam what you really mean is standard, OEM spec NA cam. Not a hot NA cam.

[bigmikespec]

True.....but when you say NA cam what you really mean is standard, OEM spec NA cam. Not a hot NA cam.

I mean a hot NA cam... big duration and lift.

[GTSBoy]

I'm not sure I follow you. In order to minimise reversion of hot exhaust gas into the cylinder you want to keep total duration under control and you certainly want to minimise overlap - compared to what you would do for an NA engine. Are you sure you don't mean the exact opposite of what you said?

[Ben C34]

Cam talk rules. Can go on forever and get nowhere fast.

The one difference with double overhead cams is that overlap can be adjusted. So perhaps an aggressive na cam can be dialled back in to something more sensible with the turbo.

[XKLABA]

Cams are, more than most things, an exercise in matching lift/duration to all the other stuff you have going on (rev range, turbo, CR, etc etc etc). A 272 may be an absolute weapon on an RB30/26 but hopeless on a 26. I don't know I haven't tried one. My limited experience was to go from Poncam B's to a 256/252 combination on a 26. Car made less power on an extra pound boost but was quicker. The biggest difference was in the low to mid range. So based on that extrapolating to 272 I cant reconcile it with what I had.

Longer duration move your torque up the rpm range, which is more power. Careful cam selection can get you a wider torque curve which is what everyone is chasing.

The caveat was just to remind people that duration is measured at a small amount of lift. How much lift affects how much duration. Something to be mind full of so everything is apples and apples.

Ultimately if shorter duration made more horsepower you would keep stock cams.

What was the lift and love centres on the 256/252 cams, also did you check cam/bucket clearnces

on mine both sets of cams where setup on the dyno to give best response and most linear power graph as possible, not just dropped in and that'll do

If the stock cams had more lift I would have found a set to replace the Poncams, I may have found a lobe which [email protected], if this can be scaled down to a 32mm base and fitted to an RB stick it will be

[Piggaz]

Wasn't it a 248 at 10.56?

[XKLABA]

Nah that one was [email protected], and still a possibility

[Piggaz]

http://www.jimwolftechnology.com/wolfpdf/CAM_SPEC_CARD_VQ35_INCL_REVUP.pdf

[XKLABA]

Shit, your right, [email protected]

So now what was the 252s

Edit, found em, [email protected]

I gotta stop doing 12 hour days

[bigmikespec]

I'm not sure I follow you. In order to minimise reversion of hot exhaust gas into the cylinder you want to keep total duration under control and you certainly want to minimise overlap - compared to what you would do for an NA engine. Are you sure you don't mean the exact opposite of what you said?

I am very sure, PM me if you like.

When boost pressure is higher than exhaust manifold back pressure (very few other than flat out race engines get this right) then you want overlap.

[GTSBoy]

I am very sure, PM me if you like.

When boost pressure is higher than exhaust manifold back pressure (very few other than flat out race engines get this right) then you want overlap.

Ahhh, but now I see what you mean by "or better". You mean less ex manifold pressure than boost pressure. You see, seeing as that is relevant to approximately zero percent of us, I assumed you mean the other way around.

Continue on as you were!

[XKLABA]

So you have a result of a race engine which has less exhaust manifold pressure the boost pressure cause that is something I would like to see proof of, ie a data log

Higher duration cams on any turbo application is not the best way of building them unless you want it to rev it to the moon which defeats the purpose of turbo charging

Duration is the working range of your engine, different turbos can blur this and unfortunately good is the enemy of better

this is a theory I have had since I first started building turbos engines back in the 90s and was proven to me when we turbo charged a mates 20v R1 and I have the reason why but I'm gonna let you try and figure it out for your selves

[bigmikespec]

So you have a result of a race engine which has less exhaust manifold pressure the boost pressure cause that is something I would like to see proof of, ie a data log

When I get to it I will measure it not to prove it to anyone but having higher boost than manifold pressure is what I want to achieve and I won't know without measuring.

[zebra]

overlap will depend on your static comp ratio.

no point in having huge overlap unless you have 11:1 comp or something crazy.

its all about matching everything to where you want the power to be made.

either way

lots of lift is good on these motors

btw lots is a relative term.

unless someone with more money than I can develop an aftermarket head for rbs with raised ports larger cam journals that are raised and bigger diameter lifters.

so we can see what .600+ thou lift does

[XKLABA]

I've pesonnaly never seen it happen and can't imagine it's possible and I have been involved in a few turbo charged race car builds, the only way to lower manifold pressure is bigger exhaust housing and bigger turbine wheel, both of which induce lag, the turbine would need to be bigger then the comp wheel for starters

Then add to that you want to use high duration cams, I hope your happy to rev this thing past 10k chase my guess is your going to have to

The only reaso you use high duration cams is if you want to increase your high range

[cobrAA]

I've pesonnaly never seen it happen and can't imagine it's possible and I have been involved in a few turbo charged race car builds, the only way to lower manifold pressure is bigger exhaust housing and bigger turbine wheel, both of which induce lag, the turbine would need to be bigger then the comp wheel for starters

Then add to that you want to use high duration cams, I hope your happy to rev this thing past 10k chase my guess is your going to have to

The only reaso you use high duration cams is if you want to increase your high range

What can be considered as high duration ? Is it dependant on the engine make or theres some sort of concensus ?

You went with TYPE-R, if you could, wouldn't you have prefered if it came with a higher lift ? like 10.25 ?