How strokers affect how a cam "acts"

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Lustle said:
What I would do, is figure out your cam THEN figure out your static compression ratio. Yes you can build your cam to your current compression ratio but it's going to probably end up being smaller than you want in order to keep up the DCR. You want DCR at 8:1 to 8.5:1. Use: Wallace Racing: Dynamic Compression Ratio Calculator to figure out your DCR.

For example. Say you want to run the XE268R. At your elevation (Spokane - 1800 feet). Calculator says:
10:1 static compression = Your dynamic compression ratio is 7.95:1. Your dynamic cranking pressure is 158.58 PSI.
10.7:1 static compression = Your dynamic compression ratio is 8.52:1. Your dynamic cranking pressure is 173.47 PSI.

So you would want to be somewhere between 10:1 and 10.7:1 static compression for that cam. Quench of course plays significantly into this. Ideal quench is .035 - .040. Better quench = more DCR because you have less chance of detonation. CC your heads. And depending if your pistons are flat deck or out of the hole, you need to adjusted your head gasket based on that.

In the end your static compression ratio depends on your cam. Get your cam figure out, then build your compression ratio.
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my heads are open chamber x heads
 
5000 pounds, 4.10s and 32s
This thing needs to get moving before it makes power. This is not gonna be a race truck.Those 32s are gonna drag his 4.10s down to be on par with 3.07s and 24s. The 2400TC is gonna drag the engine down to well below the torque peak. The tranny is no help with just 2.45 low gear.The truck weighs more than 40% more than most of our As and the engine is just 13% bigger than most of our 360s.
Guessing, a torque peak around 3900/4200, this is around 37 to 40 mph. This engine needs all the help it can get,just to get the Roadspeed up to where the power starts.
You can move the torque peak around some with cam selection, LSA and installed centerline, but with the typical street cams we are used to, the variation is only in the range of about 600 to 800 rpm. So if you put a teensy weensey cam in there, the torque peak might come down to 3200, but of course the engine would run out of steam really really early. If you put a bigger cam in there to torque-peak at say 4500, the power peak might come in as late as 6000, but trying to get moving with the gear handicap, will be miserable , no matter how high you pump up the compression and still burn pump-gas.
IMO,
that's IMO,
the gearage and stall is the first thing that needs addressing. Then build the engine to work with the new torque multipliers
 
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the gearing and stall is something that is already done. this is a budget build. I have the block machined already and forged h beam rods for this engine as well. the only parts i have to buy are the pistons, cam only and crank. i have all the valvetrain parts already. One thing to also keep in mind is in a truck the converter stall being too high will make off road use terrible and overheat the trans
 
In that case your engine will need the smaller cam, and adjust the Dcr to play nice with it, and let the cubic inches get you rolling.That will make the best of it.
 
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What you are doing is handicapping the lack of gear by using a cam you think will help low speed.

I can tell you that you'd be better off saving your money, getting better gearing and THEN calling a custom cam grinder and working with them to get the correct cam for your application. From the sound of things, I doubt your correct cam is laying on the shelf.


Too many guys strangle the engine by not using enough gear. You have a 32 inch tall tire. And a 3.9x gear. That's like having a 3.08 gear with a 26 inch tall tire. Or close to it, I don't feel like doing the exact math, but maybe AJ will come along and actually do the math for you. I just don't feel like doing it right now.


As I have said countless times in the last 4 decades, and especially in cases like this, you need to focus on gearing and a cam that does NOT come off the shelf. Every vehicle is the sum of th compromises we have to make. The better you limit and control your compromises, the better the end product.


I have posted many times several custom cam grinders. I no longer even deal with cam companies who have cams on the shelf. It's not worth the argument.
 
It's a Ram Charger, not a race car.
Double duty & master of none of it.
 
rumblefish360 said:
It's a Ram Charger, not a race car.
Double duty & master of none of it.
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Right, I got it. But everyone wants performance with out the commensurate parts. Don't matter what the chassis is. There is an expected level of performance. You have to get there somehow.
 
I think for this combo, a really good case could be made for a roller cam, or a solid FT.
But it would only ease the pain of the lack of gearage/TC.
I also think a much better case could be made for a BB;a 451 perhaps?
2400 is a pretty short stall, and the 3.075 equivalent gear has a white-knuckled death-grip on slowperformance.
Look, your current set-up will cruise at, if you dare or care,at 65=about 2800.You could at least bump up your TC to that. It ain't much but every little bit helps.
And 4.88s will get you an equivalent to 3.66s with 24s. The cruise rpm might jump the same 19%,percent to 3333 rpm@65 . Again not much improvement on paper, but a world of a difference to the engine.
You can think of that 19% gearing change as almost the same as a 19% improvement in cubic inches. That would appear to make your engine grow to 495 cubes.
That is to say, if you lined up two identical trucks like yours; your 416 with the 4.88s and 2400TC, and the other with 495 cubes the 4.10s and also a 2400, well, which one would you rather have?
This is over simplified cuz there are way too many variables, to make this a direct comparison, but IMO it is a reasonable analogy.
Oh and one other thing.With a 6000 rpm shift, the 4.10s will get you about 54 mph, while the 4.88s will get you 45.That is 16.6% sooner. The upshot of that is that 4.88s will put down a much higher average power from zero,up to that 45 mph, than the 4.10 will put down on the same run. Which one do you think will be faster ?
I'm not trying to be a dick; I just want you to be aware of the difficulty you are up against.As are others here.

I suppose you could lower your performance expectations a bit, and make a really fine cruiser out of it. I can totally see that. With a cam that makes tons of torque at 2400, that beast could be made to blast off the line. But it will all be over pretty soon, and time to shift. This can still be made into a big-fun streeter, and who knows.......... :) maybe, more smiles per the miles.
 
AJ/FormS said:
I think for this combo, a really good case could be made for a roller cam, or a solid FT.
But it would only ease the pain of the lack of gearage/TC.
I also think a much better case could be made for a BB;a 451 perhaps?
2400 is a pretty short stall, and the 3.075 equivalent gear has a white-knuckled death-grip on slowperformance.
Look, your current set-up will cruise at, if you dare or care,at 65=about 2800.You could at least bump up your TC to that. It ain't much but every little bit helps.
And 4.88s will get you an equivalent to 3.66s with 24s. The cruise rpm might jump the same 19%,percent to 3333 rpm@65 . Again not much improvement on paper, but a world of a difference to the engine.
You can think of that 19% gearing change as almost the same as a 19% improvement in cubic inches. That would appear to make your engine grow to 495 cubes.
That is to say, if you lined up two identical trucks like yours; your 416 with the 4.88s and 2400TC, and the other with 495 cubes the 4.10s and also a 2400, well, which one would you rather have?
This is over simplified cuz there are way too many variables, to make this a direct comparison, but IMO it is a reasonable analogy.
Oh and one other thing.With a 6000 rpm shift, the 4.10s will get you about 54 mph, while the 4.88s will get you 45.That is 16.6% sooner. The upshot of that is that 4.88s will put down a much higher average power from zero,up to that 45 mph, than the 4.10 will put down on the same run. Which one do you think will be faster ?
I'm not trying to be a dick; I just want you to be aware of the difficulty you are up against.As are others here.

I suppose you could lower your performance expectations a bit, and make a really fine cruiser out of it. I can totally see that. With a cam that makes tons of torque at 2400, that beast could be made to blast off the line. But it will all be over pretty soon, and time to shift. This can still be made into a big-fun streeter, and who knows.......... :) maybe, more smiles per the miles.
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Exactly. The OP is wanting to move a big load and do it some what efficiently and he has a relatively short stroke, relatively small bore (compared to say a 400 Chrysler) and not a lot of gear. To me, trying to finesse a cam to get it to move is the hard way to do it. If you are going to do it the hard way, you are better off to stop looking at online catalogs and off the shelf cams and ha someone grind you up a custom cam.


Thanks for doing the math AJ. I just didn't feel like doing it all. But math is math and math don't lie.
 
to recap;the OP says
340 to 416 stroker
heavily ported x heads
performer rpm airgap
650 proform mech secondary
2400 stall converter
4.10s
32s
i'm going to be running 9-1 compression. this will be for hot street use and alot of high rpm use as well.
Don't really care about the negatives of a mech secondary on a truck or running a solid roller in one either i just would like to know if i'm going to kill myself off the line with the larger cam or if hughes is right and that cam would work well for what i intend on doing. I normally wouldn't run a solid roller in a 4x4 but i have the block and heads with brand new lifters,pushrods and valve springs that would work perfect for either cam. which makes this a super cheap route and more power plus i don't mind adjusting valves
--727,5000(pounds) roughly,no idea on torque output
--the heads are x heads that have been heavily ported off an 11 second 340 with a .655 solid roller cam that would make power to about 6700. i'm putting w2 heads on so that's why i'm using these heads. I basically came up with this build because i have a 340 block that is already machined and ready for assembly have roller lifters, springs and heads, forged h beam rods that are the correct length. so all i truly need is a crank pistons and cam to complete the assembly.
--So say my build was 416 stroker with a forged crank 72 cc ported x heads that will take 6700 rpm with a huge solid roller so airflow is not a big issue for my powerband. the comp XR268R camshaft with 268/274 230/236 .552/.564 lift with harlands 1.5 ratio. want to run the 4032 forged icon pistons to have a tighter piston to wall clearance, performer rpm airgap intake and 750 proform carb. What should i put my compression ratio at then? where i am at the temperature varies from 0-100 winter to summer. I intend to run it on 91 octane pump gas.
--the gearing and stall is something that is already done. this is a budget build. I have the block machined already and forged h beam rods for this engine as well. the only parts i have to buy are the pistons, cam only and crank. i have all the valvetrain parts already. One thing to also keep in mind is in a truck the converter stall being too high will make off road use terrible and overheat the trans
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There is no way i'm gonna be pulling 54 mph out of a 4.10 gear with 32s. this truck has 3.21s in it currently and that's what it runs. I'm going with 4.10s cause that is what the axles i have for it are geared at and i don't have money to play with it
 
I'm gonna venture into very uncomfortable territory for me, and throw something at you.Others can chime in and shred me, but here goes.
I imagine you will be running headers
I imagine you don't care much about gas mileage
I see those heads working really great at mid to high rpm,and I see them working with the headers and wanting lots of overlap.
I see your combo making good torque with about a 60 degree ICA.
I see your chosen cam, the XR268R has specs that math out to just 52 degrees overlap. That means in conjunction with the other specs, that this cam is gonna power peak pretty early.I seem to remember YR mentioning 5200, and that sounds about right. Now the heads and 1.5 arms are overkill for this powerpeak. The 110 cam will not carry the power much further than about 6000rpm, so again you are kindof putting a lot of stress on the valve train, for no good reason.1.5 arms would be plenty.
The fact that this is a rollercam also comes into play.The fast ramps are helping to keep the Dcr up. Perhaps more than necessary.
So to my way of thinking this cam could be made to work, but I think a bigger one with more overlap and same or slightly later ICA, that pulls to a higher rpm would take better advantage of your heads, and would work better.
But I get a little lost with roller cams.The advertised duration, and the lash spec always mess me up, cuz they are not rated the same as flat-tappets. To that end, I'm with YR, and whoever else mightof said it; make the call/go custom-cam. Then finalize the Scr to work with the custom cam.
You have too many very nice parts to squander a wrong cam and Scr on.IMO, there it is again, IMO you need a custom cam with a fast-rate, like the rollers,a lift to work the heads with your chosen atms, plenty of overlap for a top end rush and just the right ICA to maximize low rpm torque, within what the cam-grinder can do. I think Custom is the best solution, and the only one that stands a chance of marrying your parts.. May the Force be with you.


20-743-9 - Xtreme Energy™ Mechanical Roller Camshafts
 
I'm confused to what the problem is.
Your engine not gonna spin anywhere near 6700. With your combo that cam states it works with 9:1 and all the rest. It not a very big cam when I was gonna with my 273 (I want 400 plus hp) that's the cam I based my engine around it gave the best powerband from low to high on my dyno program for the 273 but my plan was to use that as a bases for a custom cam though.

When they say a cam acts 2 sizes smaller is the recommended powerband of the cam.
That ones 2000-6000 is based on 360 size with 416 is probably more like 1200-5200 so if you want the 2000-6000 powerband which it don't seem that you want that then yes move up 10 or so degrees and yes you'll need more CR too.

It also matters on your head flow and if they made peak power to 6700 with 340 then with the 416 probably do it a 1000 rpm less.
So 5700, you could go up one cam step (5degrees) which would be about 1600-5600
Powerband. Depends what matters most off the line or using up every last rpm the heads can support.

P.S. There's a difference between pulling to 6700 and peaking there my cousin stock car pulls to 7000 grand but there's no way he's even peaking over 6000.
 
elitesrock2 said:
There is no way i'm gonna be pulling 54 mph out of a 4.10 gear with 32s. this truck has 3.21s in it currently and that's what it runs. I'm going with 4.10s cause that is what the axles i have for it are geared at and i don't have money to play with it
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I have no idea what this means.

Here is the math
(54mph x 1056 x 4.10rear gear x 2.45tranny low)/32 tire x Pi (3.1416) = 5698
add 4 or 5% for slip and you get 5926 to 5980rpm

If you find a cam to pull to and actually rev your 416 to 7000;
then first pull out the 5% and recalculate. eg 7000 less 5% =6650,and
(6650 x 32Pi)/1056 xR1R2 =63 mph
This is the math.

If you leave the 3.21s in it, you are dreaming.Slap yourself hard.
 
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It's a really smart question, but as usual, the argument is stupid.

This is really simple, so let me make it simple, instead of some wannabe rocket scientists trying to make themselves sound smart.

A larger Cubic inch engine does not eat duration. It eats camshafts.

As engines gain cubic inches, they require more air and fuel. That requires not only hanging the valve open more, but longer as well. It's really not difficult to understand. A 273 engine will have way less of a camshaft requirement than a 440. Likewise, to make the best power, the 440 will want a lot more camshaft than the 273.

It never ceases to amaze me on here how a handful of people try to lose everyone in a bunch of wantin to be smart sounding BULLSHIT, which always makes the thread even more convoluted that it ever was.
 
RustyRatRod said:
It's a really smart question, but as usual, the argument is stupid.

This is really simple, so let me make it simple, instead of some wannabe rocket scientists trying to make themselves sound smart.

A larger Cubic inch engine does not eat duration. It eats camshafts.

As engines gain cubic inches, they require more air and fuel. That requires not only hanging the valve open more, but longer as well. It's really not difficult to understand. A 273 engine will have way less of a camshaft requirement than a 440. Likewise, to make the best power, the 440 will want a lot more camshaft than the 273.

It never ceases to amaze me on here how a handful of people try to lose everyone in a bunch of wantin to be smart sounding BULLSHIT, which always makes the thread even more convoluted that it ever was.
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Thats not necessarily true. Look at cams for 340/360 vs 440 since most cam companies run the exact same grind for both. If what you said was 100% true the recommendation would be totally different for same level of performance (powerband). But they dont it the exact same cam recommendation for both. But if what you said was true a 440 would need 15- 20 degrees more duration.

Since most decent street cams for a 360 are between 265 to 285 a 440 would be 280 - 305 which we know is isn't true that basically means it's impossible to over cam a 440. Plus there's quite a few on here running 270-280 plus cams in there 273 and they all seem happy with them.
 
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It is 100% true in the way that I meant it.
 
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