How strokers affect how a cam "acts"

[elitesrock2]

Reading on hughes engines i noticed they recommend when going to a stroker to look 2 cam sizes higher than normal to get the same results. I'm not looking at a hughes cam at the moment but am considering going to a comp solid roller. heres what i got now
340 to 416 stroker
heavily ported x heads
performer rpm airgap
650 proform mech secondary
2400 stall converter
4.10s
32s
this is not for an a body this is actually for a ramcharger 4x4 but i have all the valvetrain components aside from the actual camshaft so i'm going with the roller.
what i'm currently looking at is the xr268R which is 268/274 230/236 at .050 .552/.564 lift
operating range of 2000-6000 rpm. asks for a 2500 stall. now by hughes logic that would act 2 sizes smaller.
so would it be beneficial to run the XR274R which is 274/280 236/242 at .050 .564/.570 lift
operating range of 2200-6300 rpm calls for a 2800 stall.
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

 

[AJ/FormS]

9.0 is the right compression ratio for the 268.

What transmission?
What kindof torque do you think that engine will make at TC stall?
And how heavy will the truck typically be, with you in it?

 

[elitesrock2]

9.0 is the right compression ratio for the 268.

What transmission?
What kindof torque do you think that engine will make at TC stall?
And how heavy will the truck be?

727
5000 roughly
no idea on torque output

 

[elitesrock2]

trans has full manual valve body,bolt in sprag, hurst quarter stick

 

[AJ/FormS]

If you are looking for off-the-line snap;
I think you are gonna want a bit more gear and/or a bit more stall. And here's why; From personal experience with cars, I have found that to be really snappy off the line,the engine needs to be loaded with less than 1.4 pounds per ftlb of torque at the ground.
How did I get to that? Well, check out this hot 360 dyno graph;
http://www.hughesengines.com/Upload/TechArticles/land_dyno.jpg
This engine will take off very well in a 3650pound car with about 8.7/1 starter gear and 27 inch tires, and a 2800TC. So looking at the graph and extrapolating the torque curve down to 2800, I get about 340 ftlbs there. Ok, now multiply that by the reduction ratios in the tranny and rear, and I get 340 x 2.45 x 3.55=2957.. Now correct that for the 27s {12/(1/2x27)}and I get ; .889x2957=2628 to the ground. Finally 3650/2628=1.39 and this is pounds of vehicle per ftlb output, at the crank. This makes a very snappy take off.
I did the math for a sluggish combo, namely a teener with a 2.45x 2.73 gear and 24 inch tires,and 3350pounds and it comes to about 1.8 pounds per ftlb.
Your combo,guessing at 340ftlbs@2400, with 2.45x4.10s and corrected for 32s would math out to 1.95 pounds per ftlb.( I guessed at the engine output). So your combo might be a little slower than sluggish(1.8);if I guessed right at the 340@2400. Remember this is the start-up gear only.But this start up gear will take the truck to about 55mph at the top of first gear.
To get up to teener status (1.8) would require 5000/1.8=2778 output, and that maths to 369 crank ftlbs.I think a bit of TC will get you there.
To be really snappy,your combo will want; (5000/1.4=),3571ftlbs to the ground, just to equal that above 360, in its 3650 chassis. So with 32s and 4.10s, and a 2.45low, your engine will need to put out 474 ftlbs at your chosen stall of 2400. I don't think that is doable with either cam.So I'm thinking you need more gear,AND more TC.
This is all just math.
If you put 4.88s in it, the requirement would come down to 398 ftlbs, and I think that is doable, with just a bit more TC.

Again this is all just math and guess work on my part,and I'm only trying to be helpful.If you can find a dyno graph for an engine like your proposed one, you can do your own math.
Here is a formula I just worked out;
crank torque required= chassis weight/Q-factor x (1/ R1R2x cF)
Where;Q-factor is how snappy you want it be;1.4very to 1.8not-so-much, R1R2 are the torque multipliers, and cF is the tire correction of (12/.5x the tire diameter in inches). Your correction is 12/.5x32=.75... Your torque multipliers are 2.45 x 4.10=10.045. Your weight is 5000.Your Q-factor is between 1.4 and 1.8
So here's an example;crank torque=5000/1.6 x [1/(2.45x4.1x.75)]= 415
So then just look on the graph, find 415 ftlbs, and read the rpm. That is the stall you will need; in this example.
Like I said, just trying to be helpful.

 

[oldkimmer]

I say stay with the smaller cam as ur gonna need decent low end for drivability. Kim

 

[Lustle]

Ahhh the old "cubes eat duration" myth. They don't really. A lot of the engine builders/testers on here will tell you that. Read this:

I totally agree. When I started this thread it was because I kept reading that LSA doesn't effect idle quality when I KNOW it does. LSA has a larger effect on idle quality than duration does. I also wanted to dispell the notion that cubes "eat" duration--totally false as well. When I decide on cam timing events I take into consideration so many aspects of the build from the hard parts to the totally subjective aspects it would take a long time to put pen to paper. I do have a bit of a "system" but its more based on experience and it wouldn't translate to paper well at all. J.Rob

RAMM is a respected engine builder who does great work. As he mentions, cubes don't "eat" duration. So the idea of going two steps up just because you add 76 cubes? I wouldn't.

When picking a cam. Look at it for everything it does. Pick it based on valve events, duration, lift, type, LSA, etc. The bigger the duration/intake valve events, the higher static compression you need to get proper DCR. The tighter the LSA the narrower the powerband/more torquey it is. The higher the lift the more you have to worry about piston/valve clearence. Make sure the cam matches the heads. Why put in a cam that lifts to say .600 when your heads give up flow at .450? Etc etc. Then pick it based on what you want it to do. This is going in a big heavy ramcharger, with 4x4, for I assume offroading? Even if you aren't offroading. You're moving a vehicle that weights what, 5000lbs? That takes torque. Adding stroke will help add a ton of torque. But keeping the cam smaller will help as well. It's great to say "Oh I got a 500 horse stroker" but if it doesn't make torque till 3000 rpm, what good does that do you? It'll still be a dog off the line. I see you mention high rpm street use, but doing what?

Also 9:1 compression isn't nearly enough for either cam you mention. Here's DCR:
XE268R - Your dynamic compression ratio is 7.14:1. Your dynamic cranking pressure is 137.78 PSI.
XE274R - Your dynamic compression ratio is 6.98:1. Your dynamic cranking pressure is 133.72 PSI.

On good 91 pump gas you can "theoretically" run up to 8.5:1 DCR on iron heads. You want hot street use? Get that DCR up to 8:1 or better.

And as a good "rule of thumb", whenever you're looking at cams. Whatever one you like best. Pick one size down from it. People ALWAYS overestimate what cam they want. A slightly too small cam is always a lot more fun than a slightly too big cam.

 

[RustyRatRod]

Cubes don't "eat" duration, but stroke does have an effect..

 

[elitesrock2]

Ahhh the old "cubes eat duration" myth. They don't really. A lot of the engine builders/testers on here will tell you that. Read this:


RAMM is a respected engine builder who does great work. As he mentions, cubes don't "eat" duration. So the idea of going two steps up just because you add 76 cubes? I wouldn't.

When picking a cam. Look at it for everything it does. Pick it based on valve events, duration, lift, type, LSA, etc. The bigger the duration/intake valve events, the higher static compression you need to get proper DCR. The tighter the LSA the narrower the powerband/more torquey it is. The higher the lift the more you have to worry about piston/valve clearence. Make sure the cam matches the heads. Why put in a cam that lifts to say .600 when your heads give up flow at .450? Etc etc. Then pick it based on what you want it to do. This is going in a big heavy ramcharger, with 4x4, for I assume offroading? Even if you aren't offroading. You're moving a vehicle that weights what, 5000lbs? That takes torque. Adding stroke will help add a ton of torque. But keeping the cam smaller will help as well. It's great to say "Oh I got a 500 horse stroker" but if it doesn't make torque till 3000 rpm, what good does that do you? It'll still be a dog off the line. I see you mention high rpm street use, but doing what?

Also 9:1 compression isn't nearly enough for either cam you mention. Here's DCR:
XE268R - Your dynamic compression ratio is 7.14:1. Your dynamic cranking pressure is 137.78 PSI.
XE274R - Your dynamic compression ratio is 6.98:1. Your dynamic cranking pressure is 133.72 PSI.

On good 91 pump gas you can "theoretically" run up to 8.5:1 DCR on iron heads. You want hot street use? Get that DCR up to 8:1 or better.

And as a good "rule of thumb", whenever you're looking at cams. Whatever one you like best. Pick one size down from it. People ALWAYS overestimate what cam they want. A slightly too small cam is always a lot more fun than a slightly too big cam.

the 268r is actually the smallest solid roller they have. and what i will end up running.

 

[RAMM]

Cubes don't "eat" duration, but stroke does have an effect..

Thankyou Lustle and RRR. The only effect you need to be concerned with is your high rpm comment. What is high rpm in this case? Your 416 will peak at 5300-5500 rpm or possibly sooner if the heads are not executed well. A bigger cam will not extend this . No way no how. Make the most of your power curve . J.Rob

 

[rumblefish360]

Ahhh the old "cubes eat duration" myth. They don't really. A lot of the engine builders/testers on here will tell you that.

He has a 340 to 416 stroker.
A slight bore increase with a lot of extra stroke.

Cubes don't "eat" duration, but stroke does have an effect..

How do you say it?

Paaaa-Zack-ly!!!!

E-rock2, considering the intended application of the engine, the idea of the given advice on this thread is IMO sound advice and it will make the ride mist enjoyable. When Hughes recommended the cam to gonup 2 sizes, it was with reguard to street strip/bracket cars. IMO. While it would apply to all engines, I think it was more intended for what I was saying.

Unless you have a "Hot Rod truck", I wouldn't go 2 sizes up. 1 at best and most. A half step up would be what I would do at most myself.

Considering your moving a lot of weight, you might want to be careful of any cam larger in duration.

I myself see that XR268R as the largest cam (duration @ .050 wise) as large as I would go.

(I also think you may want to reconsider carb size.
Is this a "Hot rod truck?
Perhaps I have what your thinking in my head wrong.)

 

[elitesrock2]

Engines Strokers increase the displacement of an engine which in turn makes the cam act smaller. Generally if you pick a cam 2 sizes larger than the characterisitcs you are looking for, it wil be a good choice. If you are confused...please call us.
This is a quote from hughes camshaft recommendation.
now the high rpm comment is because it will be used in the mud as well as "street" racing more so on the open roads around here. For some reason in my area it is commonplace to race trucks more than cars. and most the trucks out here are roller cam 383 strokers from the 67-72 area.

 

[elitesrock2]

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.

 

[elitesrock2]

And I have basically decided on the 268 cam. but i'm still curious on the myth of dispacement eating duration

 

[RAMM]

And I have basically decided on the 268 cam. but i'm still curious on the myth of dispacement eating duration

What are you curious about? J.Rob

 

[Lustle]

Engines Strokers increase the displacement of an engine which in turn makes the cam act smaller. Generally if you pick a cam 2 sizes larger than the characterisitcs you are looking for, it wil be a good choice. If you are confused...please call us.
This is a quote from hughes camshaft recommendation.
now the high rpm comment is because it will be used in the mud as well as "street" racing more so on the open roads around here. For some reason in my area it is commonplace to race trucks more than cars. and most the trucks out here are roller cam 383 strokers from the 67-72 area.

Well with mud and street use. I would think the smaller would be better. It's a lot of truck to get moving. And you're going to need torque for that.

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.

If I was you. I would phone some custom cam grinders (racer brown, bullet, etc) and see what they tell you. A phone call is free. And a custom ground cam, built exactly for your setup doesn't cost anymore than an off the shelf. In fact I believe jim over at racer brown is cheaper than the comp options. I could be wrong on that.

But when you call. Have EVERY spec ready. You better know how many farts you drilled into the seat cause they might wanna know that. Take a look at this to get an idea: Page Title

If you talk to those guys. They will really help you build a custom cam that will make the most out of your setup. And help you figure out how to get the most out of what you got. Honestly a 416, with heavy ported x heads, 10:1 compression, the right solid roller cam, proper exhaust and a good ignition/intake setup (dump the 650, get at least a 750 double pumper doesn't matter what brand), should make an easy 550/550 horse/torque. It will be a lot of fun no matter what it's in.

 

[elitesrock2]

Well with mud and street use. I would think the smaller would be better. It's a lot of truck to get moving. And you're going to need torque for that.



If I was you. I would phone some custom cam grinders (racer brown, bullet, etc) and see what they tell you. A phone call is free. And a custom ground cam, built exactly for your setup doesn't cost anymore than an off the shelf. In fact I believe jim over at racer brown is cheaper than the comp options. I could be wrong on that.

But when you call. Have EVERY spec ready. You better know how many farts you drilled into the seat cause they might wanna know that. Take a look at this to get an idea: Page Title

If you talk to those guys. They will really help you build a custom cam that will make the most out of your setup. And help you figure out how to get the most out of what you got. Honestly a 416, with heavy ported x heads, 10:1 compression, the right solid roller cam, proper exhaust and a good ignition/intake setup (dump the 650, get at least a 750 double pumper doesn't matter what brand), should make an easy 550/550 horse/torque. It will be a lot of fun no matter what it's in.

Now what compression should i be looking at then? I've always been told 9.4-1 with good quench is the magic number for pump gas. I know theres different types of compression such as dynamic and static

 

[273]

I'm still trying to figure it out myself.

They way I see it.
It not exactly stroke that matters but cid to airflow. Take 273 vs 340 both have the same proportional head flow to cubic inch. So at the same rpm it should take similar amount of degrees (cam) to fill the cylinders. So same cam should act similar in both engines.

Now let's bore and stroke the 273 to 340 size but keep 273 top end. Now the engine is way under headed for the size. So now you need more cam degrees to try to fill the cylinders at same rpm (or cam will act smaller). That's why bigger cubic inch with the same top end moves the powerband down but will have similar hp.

So when you stroke an engine we use similar top ends. 750 air gap with port or unported eddy heads. And move from 340/360 to 416/408 you need more cam to try to fill the cylinders or more head flow but our choices are limited there.

 

[AJ/FormS]

Here's a quick study;4 different strokers,all same 4.04bore,same 87cc total chamber volume, all same 6.123rod,all same 60* ICA

Stroke...Swept......Scr.......Dcr....psi
3.31......695.31.....9.00....7.81@155
3.58......752.03.....9.64....7.95@159
3.79......796.15....10.15....8.41@171
4.00......840.26....10.66....8.85@182

As you can see, the Scr/Dcr/pressure is climbing through the roof. To take advantage of the trend, a bigger cam with a later ICA, will "eat up" the Dcr, so you can actually drive the thing.

I think the phrase "strokers eat up duration" or however it is said is simply a restating of what is going on here. Its actually the inverse. De-stroking eats duration, cuz the cam's ICA has to be continually decreased to keep the pressure up. Decreasing the ICA usually means less intake open duration. Or at least moving the installed centerline, or changing the LSA.
Just a thought.
Edit,swepts added

 

[273]

Here's a quick study;4 different strokers,all same 4.04bore,same 87cc total chamber volume, all same 6.123rod,all same 60* ICA

3.31stroke, Scr is 9.00,Dcr is 7.81@155psi
3.58 stroke,Scr is 9.64,Dcr is 7.95@159psi
3.79 stroke,Scr is10.15,Dcr is 8.41@171psi
4.00 stroke,Scr is10.66,Dcr is 8.85@182psi

As you can see, the Scr/Dcr/pressure is climbing through the roof. To take advantage of the trend, a bigger cam with a later ICA, will "eat up" the Dcr, so you can actually drive the thing.

I think the phrase "strokers eat up duration" or however it is said is simply a restating of what is going on here. Its actually the inverse. De-stroking eats duration, cuz the cam's ICA has to be continually decreased to keep the pressure up. Decreasing the ICA usually means less intake open duration. Or at least moving the installed centerline, or changing the LSA.
Just a thought.

I don't understand why started with different Scr. If you where to build each engine to a certain level (cam) each engine would have similar CR example 10:1 or 10.5:1.

 

[elitesrock2]

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.

 

[AJ/FormS]

I don't understand why started with different Scr. If you where to build each engine to a certain level (cam) each engine would have similar CR example 10:1 or 10.5:1.

The Scr changes cuz I kept it simple, using the same 87cc total chamber size for each. But with each increase in stroke the swept volume increases.
The swept volume for these strokes are;695.3,752.03,796.15, and 840.26cc
I used the 87cc as a baseline, cuz it is easy to achieve, and it was what it mathed out to on the smallest stroke, nothing magical about the number.
I'll edit the swepts in.

 

[273]

The Scr changes cuz I kept it simple, using the same 87cc total chamber size for each. But with each increase in stroke the swept volume increases.
The swept volume for these strokes are;695.3,752.03,796.15, and 840.26cc
I used the 87cc as a baseline, cuz it is easy to achieve, and it was what it mathed out to on the smallest stroke, nothing magical about the number.
I'll edit the swepts in.

I understand how you got the different CR for each but don't see how it answered the original question. I could see maybe if each example had the same Scr. No matter what stroke if you where to build an large cam with aluminum heads your probably gonna run 10.5:1 and even if the chambers are the same the more stroke the bigger the dish on the pistons you'd run.

So wouldn't you use the same CR and find the effect (or trend) of the different strokes on the Dcr with same overlap ??

I feel it's got to do with cid and head flow more than anything else. Example lot of street strip engines are gonna use a 285 ish cam no matter the displacement or stroke.
Cause there more likely balanced in the head flow to cid ratio.

Also I've seen you touch on this before that 360 is slightly better to build than 318/340
Is cause just say a (I use @ 0.50" duration) 220 cam is a good streetable cam in a 318 and a 225 for 340 and 230 for 360 and probably 240 for 408 for example . Yes it depends on you definition of streetable.
It would seem cid is a cam eater but in these engines more than likely be running similar cylinders heads (cfm) the bigger engines will need more cam help to compensate. I think if you ran the same head flow to cid ratio for each engine then the cam needs would be more similar for that powerband.

 

[Lustle]

Now what compression should i be looking at then? I've always been told 9.4-1 with good quench is the magic number for pump gas. I know theres different types of compression such as dynamic and static

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.

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.

 

[moper]

What will you be using this truck for? Most don't match "hot street use" and "a lot of high rpm use" in the same paragraph as 4x4 Ramcharger.