296 cam - too much for the street?

[Gareth]

Hello,

 

I am building a hot street N42 L28 for my 240Z, and I need to choose a right cam for it. I am considering a 296 duration / 8,4 lift grind. Would this be too much for a semi street/track car? The Z is generally prepared for track action (10 point rollcage, stiff suspension and so on, I'm ordering Arizona Z Car brake kit in a few days), so it should easily handle the extra power. The basic specs of the engine are:

 

- N42/N42 L28

- modified head

- new springs, valves, guides, seats, seals, lashes, HG etc.

- forged pistons (10,5-11:1 compression)

- stock rods and crank, strenghened bolts and bearings

- lightweight flywheel, performance clutch, Quaife LSD

- triple Solex 40mm carbs on a Kameari manifold

- 6-1 headers, 2,5" exhaust

 

If not the 296, what would you recommend?

 

Thanks in advance.

 

Tony

[JMortensen]

Based on just the numbers given that cam should be a good aggressive street cam.

[olie05]

I have a 272/282 split cam with .480" lift (12.192mm) and I want to go bigger.

 

This is on a street driven 280z with n42 head and flat top pistons.

[TravRMK]

I would tend to think that those 40mm carbs would be a bit on the small side for that cam.

[Collectindust240Z]

My cam is a .300/295 from Delta. I'm also running 40mm Dellortos with 36mm venturis on a shaved p90 and flat top f54 block. Sounds nice and nasty, good throttle response, not at all unstreetable. Idles at 900rpm. I agree with Jon. He talked me into the bigger cam, I'm glad he did.http://s130.photobucket.com/albums/p259/subewrc/Z%20stuff/?action=view&current=Zpics047.flv

[thehelix112]

The advertised duration of a camshaft indicates ABSOLUTE FRIGGING NOTHING about its profile. One could grind a 300 adv. deg duration cam that wouldn't flow enough to idle, and one could grind a 300 adv. deg duration cam that wouldn't work without the pneumatic valve springs and would come on at 7000.

 

Get more specs and get back to us.

 

If you have adv duration, and 0.05 duration then you're one step closer to having some idea what the profile is like.

 

Dave

[Gareth]

Thanks for the replies guys. The detailed cam specs are:

 

Duration - 296 deg.

Lift - 8,4mm

Lobe separation angle - 106 deg.

VC (what does this stand for?) - 31 (?)

 

This is the most I could find. Is there anything else that I should know?

 

As for the carbs, even if the Solexes will be too small for that cam, I am going to experiment with motorcycle carbs of different sizes. I already have two sets of three single choke Mikuni carbs, taken off a 900cc Triumph bike. I have access to different motorcycle parts, so it shouldn't be a problem to get a sufficient fuel system for my L28.

[janaka]

I'm running a Schneider cam- .460 valve lift, 270 intake duration, 280 exhaust duration. ported head and flat top pistons dual SU's.

IMO its a nice cam but if I was to have built the motor (came in the car) I would have went bigger. Its got a nice idle (not super lopey though) and gets me 10L/100km on the highway at 75-80mph so I can't complain that way

[thehelix112]

Are you sure the lift is 8.4mm? Thats really really really small. I'm not the most knowledgeable person, but that sounds smaller than stock to me.

 

The relatively low lobe separation angle would indicate that it has quite a bit of valve overlap, which doesn't make sense unless you are running a pretty aggressive cam profile. But I would recommend ringing the manufacturer and asking for more details. Preferably the profile equation.

 

Dave

[JMortensen]

Are you sure the lift is 8.4mm? Thats really really really small. I'm not the most knowledgeable person, but that sounds smaller than stock to me.

 

The relatively low lobe separation angle would indicate that it has quite a bit of valve overlap, which doesn't make sense unless you are running a pretty aggressive cam profile. But I would recommend ringing the manufacturer and asking for more details. Preferably the profile equation.

 

Dave

8.4mm on the cam x 1.5 rocker ratio = .496" lift or 12.6mm for you...

[thehelix112]

Ahhh.. thanks.

 

Dave

[Tony D]

0,496? Or 0,514"?

(8.4mm/24.5= 0,3428571)*1.5=0,5142857"

 

Metrically, you got it right, though...(8,4*1.5=12.6mm at the valve), which is over 1/2 and inch, not less than half...

 

But agreed, given this 8,4mm cam lift probably means the duration is probably lift to lift. You need to find out duration at 1mm lift (at the valve) for somewhat od a normal comparison of our ,050" duration ratings here in the US of A.

[thehelix112]

I disagree Tony. I'd check your calculator's accuracy. By making the number smaller to start with (8.4/25.4) you are limited by its floating point accuracy.

 

12.6 is less than 12.7 which is half of 25.4, and = 0.496"

 

Dave

[Zmanco]

I think Tony D. is a little dyslexic today. It's 25.4 mm/inch, not 24.5.

[Tony D]

It's not 24.5? I thought it was 24.5? Now I got to go look again.

 

let's see.... 1mm = .040" right?

 

I'll be damned, it's 25.4.... now someplace else somebody reamed me for using 25.4.... CRAP! O.K. it's 25.4. I should use online converters, and not my memory.

 

Or we all should convert to the METRIC SYSTEM because english measurements SUCK! I guess if JPL can miss Mars, I can miscalculate a Cam Lift...

 

It's not rocket...er...yeh!

[olie05]

It's not 24.5? I thought it was 24.5? Now I got to go look again.

 

let's see.... 1mm = .040" right?

 

I'll be damned, it's 25.4.... now someplace else somebody reamed me for using 25.4.... CRAP! O.K. it's 25.4. I should use online converters, and not my memory.

 

Or we all should convert to the METRIC SYSTEM because english measurements SUCK! I guess if JPL can miss Mars, I can miscalculate a Cam Lift...

 

It's not rocket...er...yeh!

 

uhhh.. aren't you a field engineer!!!!????

 

I guess you guys use the 'merican system in the field anyway.

[Tony D]

uhhh.. aren't you a field engineer!!!!????

 

I guess you guys use the 'merican system in the field anyway.

 

Actually, I use the metric system. The English system is fraught with B.S. pitfalls like this. I can't remember the last time I used a fractional tape measure...

 

Matter of fact, when I do manual alignments on machine drivetrains, I use my METRIC Dial Indicators, METRIC Tape Measure, and METRIC everything else. When I'm done, even though I can still measure a misalignment, when the customer checks my work for acceptance, they can't measure ANY misalignment unless they use very 'high precision' dial indicators that measure to 0.00001".

 

English measurement are simply too imprecise for my work. It was fine 20 years ago, but today everything in my industry is metric for the most part (internally in the machine)---when you start dealing with forces and pressures, it's just too easy to do that.

 

The exception: Gauge Pressure. PSI is a better more precise gauge for the layman. Unless you get KpA, MpA etc.... Bar is simply not a good gauge unless you have digital instrumentation and several placeholders.

[JMortensen]

Matter of fact, when I do manual alignments on machine drivetrains, I use my METRIC Dial Indicators, METRIC Tape Measure, and METRIC everything else. When I'm done, even though I can still measure a misalignment, when the customer checks my work for acceptance, they can't measure ANY misalignment unless they use very 'high precision' dial indicators that measure to 0.00001".

 

English measurement are simply too imprecise for my work. It was fine 20 years ago, but today everything in my industry is metric for the most part (internally in the machine)---when you start dealing with forces and pressures, it's just too easy to do that.

I am not understanding the significance of this statement. I mean really, if you're using the metric system (which I believe to be superior), does a difference of 1mm not equate to .040"? So if you're accurate within .00001, does that not relate directly to the metric system as well, where you would be accurate within .000254mm?

 

The reason the metric system is better is because it's a plain old 10 base system, not a 12 base system with 64th based fractions. It's much easier to say 20.5 mm and understand what that means than it is to say 25/64ths. You have to do some math to figure out the decimal equivalent of 25/64ths. The MEASURING is not more accurate. The description of the distance measured is just simpler.

[WEBEZEEed]

Someone tell me what on earth has .00001 tolerance? that's one one hundred thousandth of an inch.Can that kind of tolerance be consistently duplicated? (maybe the Hubble mirror?)

[Tony D]

We all digress from the initial question at hand.

0.0001 (one tenthousandth) was what was supposed to have been posted. But nevertheless, the equipment to measure the Metric Equivalent of that hundred-thousandth is easier to read and morereadily available than stuff that will read the English Equivalent.

 

The significance of the statement was that buy foolishly trying to convert his METRIC specification cam into English Measurement the error was induced. As you can see, my conversion of the METRIC specification was correct. The 0.040" approximation was correct, but I didn't convert from metric to English using that 0.040" number, rather the 25.4 (or 24.5 in my case) standard conversion.

 

And I will disagree on Measuring in Metric not to be more accurate. I can use run of the mill dime store Harbor Freight indicators with METRIC graduations, and do an alignment on a geartrain that will STILL show misalignment when using the Metric Scale, but when the customer uses standard ENGLISH Dial Indicators, they don't even MOVE unless you use a last-word type of indicator (much higher in cost than HF Tooling I can tell you that!) It's a root of SPC that you must improve your measuring tools to improve your production process. The ability to read precise tolerances more accurately and quickly with tooling made for run-of-the-mill METRIC measurements will be FAR more precise than equivalent ENGLISH graduated measuring instruments.

 

Case in point: Your standard cheap ENGLISH Micrometer will read to 0.001", and may have a .0005 marking scale somewhere...how accurate who knows, but it's there. Really it's accurate to 0.001"+/-0.0005"

 

Standard cheap METRIC micrometer will read to what? 0.01mm? Accurately (not eyeballing or guessing). What is that, 0.0004" accuracy out of the box with a scale (as mentioned) base-10 for another decimal place? Add another zero in front of that for an 'eyeball equivalent' for measurement. It's an order of magnitude more accurate than the similar English Graduated Instrument.

 

I can remember when I had to do instruction in the field and our shaft displacements were set to 0.02mm. Try to find ANYBODY in the Millwright Field that has a last word they carry with them regularly---people could not BELIEVE that we were requiring measurment to 0.0008" (Eight-Tenthousandths of an inch) shaft displacement before installing our pinion gears. Most guys were 'just a hair below a thou'. Yeah, that's precision measurement for ya!

 

And as for what has a tolerance of 0.00001", check out the specifications for the mechanical seal assembly on a variable displacement hydrostatic pump. Their surface flatness is measured in helium light bands... a bit tighter than 0.00001"! It's all what you are used to...there is a reason Germans have Hydraulic Technique to the point they do: they have been dealing with a totally different measuring system that is far more precise and who's daily tolerances are less than what is normally even measured in an English System. What scares me the most is most of Eastern Europe can precision machine stuff because they are all set up with this kind of measuring system and tolerance requirements. We simply add more decimal places to keep up. Shouldn't we simply go that way as well, and get used to a more fine system of measurement? The more numbers you have, the greater chance for error. .5mm is less of a hassle than .020" (or .02" if you will...)

 

But again, we digress from the original topic too far, methinks!