LS2 stroker cam selection

[frijolee]

I think you should cam it for huge torque in the 3500 rpm range - peak at 5500 - and be all done my 6k. People get too aggressive with overlap and kill low end power, but don't have the rest of the system tuned to utilize the high rpm potential of the cam which leads to peaky and lackluster results.

That sounds reasonable to me.

Would be interesting to know how big the intake runners are. You really don't want a hogged out intake runner. People spec'ing your cam will want to know also.

Is this in fact as simple as "make damn sure the valve is close and fill the port with water" and an indicated syringe?

Regarding the headers - maybe think about stepping down in primary size since you can't get full length? Big and short is tuned for the wrong area of the torque curve. Maybe also consider designing a Tri-y for more clearance and low rpm tuning ability?

Length is what kills me.  I basically need the collector to be right under the firewall as I need to be into the 3" tube for the boat side run.  My collectors are already bought and intended for 1 7/8" primaries in a 4:1 merge.  I could easily do a 1 3/4" to 1 7/8" stepped header though.  This is the exhaust run I'm planning except with the high portion to the front and an additional ~90 turn to mostly horizontal to aim back at the firewall.

What are the vehicle specs going to be like for weight and gearing? How do you want the thing to drive?

Weight:  Was hoping for 4500 lbs.  Could easily end up over 5000.  Not quite sure.

TH400 gearing, not sure if they have variations, if they do I'm not sure what I have.  I do have a 4 speed atlas transfer case that'll do a double low range and go 11:1 on crawl.   

How I want it to drive is pretty subjective.  Anything more specific you're looking for here?  Mostly I want to be able to stand on it from a slow speed roll and get to full bogie torque without much lugging of the engine.  That's the most fun on fire roads and sand. Seems like I'd be playing with torque converter to align to power curve.  On the trail in rough stuff and rocks I'm rarely full throttle (I'm more of a crawler than a bouncer since I don't want to roll it).

Thanks for all the help!

[frijolee]

In my continue​d looking some torque focused cam are using durations only slightly larger than stock.  Case in point:

http://www.tickperformance.com/tick-performance-towmax-stage-1-camshaft-for-4-8l-5-3l-ls2-lq4-lq9-engines/

The stage 2 version is damn close to the mild cam we've been talking about.

http://www.tickperformance.com/tick-performance-towmax-stage-2-camshaft-for-4-8l-5-3l-ls2-lq4-lq9-engines/

[MPbdy]

Questions:

-Is it appropriate to be thinking about cam's primarily in terms of the 4 valve events?  It seems like if I have that I can pretty much back into durations, LSA, centerlines etc.  Lift and ramp rates I'd be leaving to the manufacturer.

This is the best way to be doing things.  Generally you would place the IVC first and then look at EVO.  That will more or less define the cam for you.  Different people have different opinions on which events are most important.  It is hard to argue against IVC being the most important - but you will always find someone haha.

-In the past I started by shooting for a specific amount of valve overlap and timing the EVC vs. IVO.   I agree with your statement about the earlier the exhaust value opens the more low end torque I give up.   That makes sense.  What about the other end?  IE how long I leave it open makes a huge difference on overalap.  For a torquey motor what does valve overlap give up?  Since I likely can't fit "proper" long tubes it seems like overlap doesn't matter as much.

It is good to know how much overlap makes sense for your combination for tuning/rowdiness reasons.  I like to think of it as a limited resource and you need to find the optimal use for it splitting importance between LSA and duration.  Overlap generally is going to cause misfires and combustion chamber dilution at lower rpms, and a period of increased VE when the engine "comes into tune" when the exhaust really starts scavenging on the intake.  You do not need long tubes for scavenging to occur.  Long tube exhaust pulse tuning will however allow you to increase the VE of the engine by creating a larger than atmospheric pressure differential between the combustion chamber and the intake port because of a partial vacuum in the exhaust primary.  Without exhaust scavenging you will not be able to start filling the chamber until the piston starts going down the cylinder.  With scavenging during overlap the intake charge is flowing into the cylinder while the piston is still going upward on the exhaust stroke.

At slower engine (piston) speeds you have more time for air to flow into the cylinder which means less duration is required for optimal efficiency.  Overlap can still be a good thing for performance, but you don't want tons of duration to go along with it.  It is possible to both overscavenge and lose intake charge out the exhaust - as well as to have reversion of exhaust gas into the intake tract and pollute the incoming air/fuel mixture with non-combustable gas.

As an aside - people cite 0 and negative overlap at .050" as if there is no actual overlap happening.  There is still going to be overlap at lower lifts than .050" and while flow is not immense, there is still overlap.

-Can you help me understand the sign convention on your Cam Motion charts?  Using the mild cam as an example...  I'm used to thinking in terms of BTDC and ATDC, but some of the numbers throw me.  For instake, if the Intake open at 0 and has a 218 duration I'd expect the close to occur at either 218 or -142 relative to the crankshaft.  By your mild cam shows 38, which is 180 degrees off from what I think it would be.  Either some references must are relative to TDC and some to BDC, or else I'm thinking in terms of crank degrees of rotation and the cam specs are all relative to the cam only. 

Intake - Opens BTDC (- if after) Closes ABDC.  Exhaust closes ATDC (- if BTDC) opens BBDC. Comp is showing valve events at advertised duration which is why they are so different.

-However, it this was a question of degrees relative to cam rotation, why are the lobe centerlines only 8 degrees apart?  I assume this is related to sign convention above but the numbers make them look that way.  By definition the intake centerline (intake valve fully open) has to happen on the downstroke sometime ATDC.  Similarly the exhaust centerline must be BTDC with piston on the upstroke. 

Cam duration and center lines are relative to crank rotation which turns twice as fast as the cam.  Lobe separation angle is in degrees of camshaft rotation - so it is a physical measurement of

-Remind me: does the 4 degrees advance drive the split in centerlines?  IE I know +4 ground in advance will shift whole cam so looking at the mild cam, this this what drives the different in intake and exhaust centerlines?  (IE 117 = 113+4 vs. 109 =113-4).  I'm confusing myself quickly.

Advance does not alter lobe separation.  Lobe separation angle is expressed in camshaft degrees.  ICL is in degrees ATDC.  ECL is in degrees BTDC.  Generally ECL is not taken into much consideration for tuning purposes.  Peak piston speed in a 4" stroke engine is at 78* ATDC.  You want your cylinder head flow and valve lift to match up well in this area.  This is why mid lift flow is so important because that is your point of max depression.

[MPbdy]

I like the idea of the step header.  We want good velocity to keep efficiency up at low rpm.

A 4" stroke is going to increase piston speed at a given RPM which will make the cylinder head "feel" like it is supply an engine turning higher RPM.  A larger engine also has greater airflow demands at a given rpm as it should be burning more air and fuel.

Compared to a 5.7 or 6.0 cam you could add 4-5 degrees of duration to each the intake and the exhaust and expect the cam to behave similarly as far as idle quality, tuning, and torque peak.

I actually really like the "mild" cam.  I've been pondering this on a 2 hour 45 minute long drive I just took in bumper to bumper LA traffic in my rx7 with no AC.  My ears have stopped ringing at least

Mild in quotes because it'd be an absolute monster in the low end. 

I'd say find someone to make you a bomb 10" 2400 stall converter that multiplies good torque and hold on.

I really REALLY like the B&M nitrous holeshot converters.  We have beat one to utter piss cutting 1.40 and under 60 ft times in our wagon for hundreds of passes with years of use before that.  Granted that is a 5000+ stall, but the 2400 stall should work perfect.  It's a 10.5" metric design that they classify as 10".  They multiply good torque but still lock up pretty good for decent efficiency.  There may be better options out there, but I'd do some reading and see what you think.  You need something tight enough that you can crawl with and not have to floor it to get it to move up a hill.

http://www.bmracing.com/products/20412-torque-converter-holeshot-2400-for-gm-th400-th425-th375-th350-and-375b/

Oh yeah - Put a roots blower on it please.  Your short 1 7/8 headers and 10:1 compression would be perfect for that

[MPbdy]

PS - that header design looks badass

The truck intake will pick up a good bit of power over the LS3 if you can fit it because of the bigger plenum - I think I have a brand new one on the shelf if you're interested.  Came off our L92 crate.

Lastly, overcamming this thing would be the absolute worst move you could ever make.  Total fun killer.  You won't get a dyno queen out of this exercise, but it'll be an absolute blast.

[frijolee]

Ok, I think I have it.  LSA is in cam notation, all others relative to crank.

Each version of intake vs. exhaust is relative to it's normal travel.  As such intake valve open and close events occur with measurement relative to TDC on open on BDC on close.   Exhaust is the opposite since it "starts" at BDC and "ends" relative to TDC. 

Positive and negative are relative to normal positions with positive been the usual and negative being opposite.  IE positive IVC is after bottom dead center since that's the normal closing position (the air's velocity keep a bit extra moving into the chamber even thought the piston is technically already on the way back up. Similarly IVO typically starts before TDC since it takes a moment for the air to "react". 

Man it's been too long since I last spec'ed one of these.  It's sure a hell of a lot easier when each number has a legend like Comp does it.  Is it fair to assume when they're using advertized/actual durations that the lobes would be symmetric?  IE since there's 50 degree difference on those cams between advertised and 0.050 numbers I'd just be adjusting be 25 degrees on each number to get events at 0.050 lift...

I think your suggestions are very very close to my intent.  You can't make much of a dyno queen putting power through 10.5" diffs and 41 tires anyways.    Thanks for the offer but I'm fine with the LS3 intake.

[MPbdy]

Duration at .050" numbers were made to compare cams from different manufacturers.  Advertised values are very difficult to measure in practice and cam manufacturers choose to fudge their advertised numbers often.  Comp uses .006" others use .004 or .005" which makes them impossible to compare.

Asymmetrical lobes are commonplace as well and plebes like us won't be given that much info haha.  Acceleration rates, jerk, and lobe profiles are really what is required to make the super fine cam selections.

Do you still have the AFR heads you mentioned in your build thread?  What are they?

[frijolee]

Makes sense.

Now I need to find what's available on the market in the kind of range we're talking about.

Heads were AFR 205s.  Already sold them.  The deal I got on the stroker made upgrading the 98 not make much sense. 

[MPbdy]

Comp will grind you anything you want.

[frijolee]

Hey Daniel (@MPbdy),

Finally ready to pull the trigger on this.  Torque converter I have at the moment has a hand written C9 HD on it.  From what I can tell the C9's were a stock GM converter for the TH350 and TH400.  Stall is likely stock and numbers trend around 1800 or so but with some variations.  It's close enough that I'm tempted to try to run it. 

Flipping back through our notes.  I'm still liking the small cam.  Not entirely sure I'm perfectly clear on why the big exhaust duration works, but I'll likely go with your recommendation there.

I also did the intake/exhaust port volume test.  Isopropyl Alcohol was a good call vs. water.  Tested three ports for intake and three for exhaust.  Average worked out to 222 g intake and 75.3 g exhaust.  I found a spec for density of Isopropyl as 786 kg/m^3.  That means 0.786 g/cc but mine is a 91% solution. so I divide by .91 for a density of 0.8637 g/cc as tested.  Assuming my math works out, that suggests I have an intake port volume of 257 cc and exhaust port volume of 87 cc.

Pushrods are 7.400" for both intake and exhaust.  Not sure on valve sizes so assuming stock in absence of further info.

Apparently you really do want me to do a supercharger.  The splits on the cam motion blower cams were making me laugh.
http://www.cammotion.com/camshafts/supercharged-ls-camshafts/cs-216-232-ls-supercharger-camshaft-216-232-115-6-for-centrifugal/

Any other thoughts on manufacturers and/or how to spec this?

[MPbdy]

For crawling I think converter selection is going to be pretty critical.  I suppose you don't need a ton of torque multiplication since you have many ranges and tons of mechanical advantage.  1800 stall speed will be plenty to get the engine into a usable powerband with a smaller cam.  I don't know if a higher stall converter like 2500-2800 with a lot of torque multiplication would be detrimental for crawling, but would make a huge difference in acceleration. 

Trying out the stock converter you have should be just fine.  I'd consult with converter shops who specialize in offroad/crawling builds if you ever decide to get something else.  The converter is one of the most critical components in making a package come together.  Sort of like...the camshaft of the transmission if that makes sense.

Regarding intake runner volume - I see that 91% isopropyl IS .786 g/cc which gives basically a 280cc intake runner which makes sense.  Stock intake runner volume is 260cc for an LS3/L92 head.  280cc is pretty damn big which is a criticism of ported LS3 heads.  Since they start at 260cc already the only place to go is from big to huge.  Won't really hurt anything, but with a small cam and LS3 intake you won't really be utilizing the large port.  The good thing here is that you have a stroker crank which does put more demand on the heads and the bigger runners will help support that. 

https://www.noco.com/documents/ISOPROPYL%20ALCOHOL%2091.pdf

Blower cams have large splits because they have a denser intake charge - you cram way more air in through in a shorter duration.  The exhaust needs to be open both early enough and long enough to evacuate everything without stalling out at higher RPM.  Because the air is being forced in you don't need to rely on overlap to make power compared to an NA engine which needs the engine to scavenge through the exhaust.  That points to the other defining characteristic of a blower cam which is a wide lobe separation angle.  This both keeps overlap at a minimum and opens the exhaust valve sooner to help evacuate the cylinder.

LS3 heads are pretty out of balance when looking at the intake/exhaust flow ratio.  Because of the big intake valve and large port a ton of air can come in.  You crutch the weaker-by-relation exhaust by keeping it open longer.

Factory LS cams all have anywhere from 6 to 20 degrees of split between the intake and exhaust lobe, so 10 degrees is not out of the question.

[frijolee]

Another data point.  I pulled the trigger to have cam motion do an analysis for me...  They came in damn close to what we've been talking.

Duration at .050": 218/226.
114 Lobe Center Angle with a 11 Intake Center line.
Lift with 1.7 Rocker Arm Ratio: .595"/.587".
This should work well in this combination to make good torque and plenty of vacuum for the brakes.
Not too big for the 1800 convertor, but likely to "push" on the convertor in the low range transfer case.

I think there's a typo in intake CL but I'm verifying

[MPbdy]

I like it.

They're very likely talking about a 110 ICL - but good to verify with them.

It will have a very mild lope to barely detectable depending on idle rpm.  Will be easy to tune and drive like stock more or less.  Glad they didn't recommend something like Comp did the first time...

[frijolee]

Just to close the loop for anyone looking in the future...  I did pull the trigger on the cam motion recommend.

Questions I'd sent in:

Thanks for the speedy reply.  This is very much in the range of cams I was considering so that's some great validation.  A few questions follow.  First, can you please give me a double check on the intake CL?  Was that supposed to be 11x? 

I'm looking at valve events since that's always the easiest way for me to think about the changes.  If I have it right this would be

Ivo BTDC: -2
Ivc ABDC: 40
Evo BBDC: 50
Evc ATDC:  -4

For events at 0.050, is that correct?

What the process for placing a custom cam order and what's the current lead time?

When do you recommend the higher end cam materials?

If you have the time, I'm attaching a pic of the cam specs I was considering...  I am going to take whatever your final recommendation is but some descriptive comparison between what you recommended and the other would be very helpful/educational for a curious customer if you're willing.

Last one: Does your recommendation allow 7.400 pushrods?  I can verify actuals if needed.

Alternate cam for consideration the 218/228 that Daniel and I had been circling the drain on...

Their response:

That was 110 intake center line with 114 lobe separation.
The is not much difference between the specs we provided compared to what you provided. Our spec had three less degrees of over lap which should yield a smoother idle and stronger idle vacuum signal which should make it a little more responsive in the operation of slightly on and slightly off throttle usage, but is so close as to maybe negligible.

It takes about 3-4 days right now to make this. You can order by calling with payment and shipping info.

The base 5150 material we use is well suited for most grinds we make, including this grind. The 8620 is mainly suggested for higher lifts and duration, or in solid lifter applications, or in blown, turbo, or heavy nitrous applications.

Push rod length in non-adjustable valve train engines are always best verified at engine assembly time. So many factors can change in a build that affect this. As far as the cam goes base circle size is reduced when lift is added because the lobe cannot be made taller and still go through the cam bearing into the block. Other factors affecting this are head gasket thickness, cylinder head and block machining, head gasket thickness, push rod seat height in the lifter variation between brands and even part numbers of same brands, and valve stem height in the cylinder head.

All pretty reasonable stuff so I pulled the trigger.  I'm optimistic on my pushrods working out since lift is quite similar vs the cam I'm replacing.

Last neat detail.  When I called in to place the order they transferred me to the see gent (Bob Cook) who made the recommendation and who'd been answering my questions, to actually place the order.  Not sure if he's the owner or a tech savvy sales guy but the continuity was kinda nice.

$399 for the cam plus shipping (same as this default cams), the $30 I paid for the recommendation, went towards the cam price.  Great service all in all from Cam Motion.