Comp cams xe268h for 318

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For the Wallace tool, you want to use the intake closing angle (ICA) based on advertised duration. Use that number 'as is' for most hydraulics.
 
nm9stheham said:
For the Wallace tool, you want to use the intake closing angle (ICA) based on advertised duration. Use that number 'as is' for most hydraulics.
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That sounds more like it. My advertised dynamic was 8.19/1 and my @.050 was 9.08 with a 9.68 static ratio. I didn't think it could be that close.
 
toolmanmike said:
That sounds more like it. My advertised dynamic was 8.19/1 and my @.050 was 9.08 with a 9.68 static ratio. I didn't think it could be that close.
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Your instincts were right. Looks like advertised would need to be something like 225* for that close LOL
 
The spread is typically close to 2 points
You have to be really careful tho when inputting cams from different manufacturers, as NONE of the advertised duration start on the base circle. Some are at .008, some at .006, some at .004...... and there can be a lotta degrees between the highest and the lowest.
I believe Hughes are at .008, and Comps at .006
Hughes cams are an enigma. They had a 270/276/110 that I bought/installed in 2000. At that time they advertised that their cams made more power than anybody else's. I bought it. The thing is this cam is advertised at .008 tappet lift, and everybody else sells 268s at .006 lift. So how big advertised is the Hughes really, at .006? IDK I never measured it, but after studying WyrmRiders comments, Ima thinking it was an easy 5 or 6 degrees bigger, so say it was 276/282/110...... and so, of course it makes more power than a 268/276/110 .... cuz it's actually a full size bigger.
Or is it?
this Hughes cam came with an .050 spec of 223/230/110, and a
Comp 268/276/110 specs at; 224/230/110.... so what's up?
Well the lift on the Comp is .477/.480, to the Hughes at .504/.515 Gosh that's nice.
So is Hughes wrong? Probably not, I know that HE2430 was a sweetheart of a cam with 1.6 arms on it.
Alls I'm saying is be careful what you input; garbage in is garbage out.
I have played with that first edition DD program for many many exciting hours.
 
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nm9stheham said:
For the Wallace tool, you want to use the intake closing angle (ICA) based on advertised duration. Use that number 'as is' for most hydraulics.
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Another stupid question where do you get the ica ? I dont see it the cam specs?
 
dartfreak75 said:
Another stupid question where do you get the ica ? I don't see it the cam specs?
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Good question. That is the problem with the Wallace tool and stymies many folks, I suspect.
  • Cam card IF it gives you open and close angles for advertised durations (rather than .050" duration). But you don't get the cam card 'til you buy the cam so that is no good.
  • Might be on the manufactuer's cam website
  • You can hand compute it (hard for many people to figure out)
  • Or.....use the tool I laid out for you. It computes the ICA for you with 4 inputs of any cam data (well, except for Hughes).
Is you computer a Microsoft operating system?
 
You want the Formula?

You know I got formulas..... right

Can I get a yes, yes?

OkOk you twisted my arm here it comes

It's coming out of my head so hang tuff, the wheel are turning.
Ok, all you need is the adv intake duration, and the ICL(installed centerline).
>>Take the intake duration and divide it by two, then subtract the specified ICL . Take the result of that and add it to 360*. Now subtract the intake duration from that, to get the compression degrees. then take those compression degrees from 180* and out pops the ICA, I need an aspirin.
Now lets convert that to math....... maybe two aspirins; here it comes;
180less(Intake duration/2 less ICL)+360 -Intake Duration = Ica.
Example1; a 276 cam, in at 106
180 less{(276/2) less106)+360-276}=Ica of 64*. Hey it works!! And another;
Example2; a 292 cam, in at 104
180 less {(292/2) less104)+360-292}=Ica of 70* Badaboom that one too!
Lessee what else can I give away? anybody need a green couch?
 
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AJ/FormS said:
You want the Formula?

You know I got formulas..... right

Can I get a yes, yes?

OkOk you twisted my arm here it comes

It's coming out of my head so hang tuff, the wheel are turning.

Ok
take the intake duration and divide it by two, then subtract the specified ICL (installed CenterLine.) Take the result of that and add it to 360*. Now subtract the intake duration from that, to get the compression degrees. then take those compression degrees from 180* and out pops the ICA, I need an aspirin.
Now lets convert that to math....... maybe two aspirins; here it comes;
180less(Intake duration/2 less ICL)+360 -Intake Duration = Ica.
Example1
180 less{(276/2) less106)+360-276}=Ica of 64*. Hey it works!! And another;
180 less {(292/2) less104)+360-292}=Ica of 70* Badaboom that one too!
Lessee what else can I give away? anybody need a green couch?
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Haha thanks that is helpful much appreciated!
 
Ok some good news the summit cam sold on Ebay last night so now I have no choice but to get another cam lol.
Done some number crunching and some research came up with this I found the cam cards for the two cams I'm considering and punched them in the Wallace calculator. I put the abdc numbers in texts for the corresponding cam. Here is my question what is an acceptable dcr? I used 8.6 scr that may not be exact but close enough for now. Thanks for you guys help thus far.

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Woo-hoo on the cam selling! OK on no computer.

You are using the right ICA number there, so that is good. Some perspective info on DCR:
  • Stock earlier LA318's DCR is usually in the high 6's to 7. Ditto for a stock LA360. It got up into the mid 7-ish range when the Magnum's came out. (These number are for sea level.)
  • So if you hit 7 or better for DCR, you are getting better than a stock LA318. OP, your prior cam was heading for the low-mid-6's. (Put in an ICA of 67.)
  • The higher you go, the better the low RPM torque, throttle response at low RPM, etc.
  • When you approach 8, then you start getting close to where an iron headed engine will detonate on pump premium. So that is an upper limit, but you won't get there unless your static CR is in the mid-upper 9's or higher.
So you can see that either of these cams exceed a stock LA318 by a bit. 'A bit' ?!?! LOL... Before you say 'why bother'... remember, this is just for evaluating low-mid RPM torque; the added lift and duration is what will make the mid-high RPM torque and HP much better than stock.

If you want more low RPM uumph, then put in 9 for Static CR and see the DCR number push up towards the mid 7's; that would be for the thinnest head gaskets and milling of your 302 heads down to 60 cc's or less.

Now that you have this tool working, you can also see the effects of changing cam timing. To see the effect of a 4 degree advance in cam timing, subtract the 4 from the ICA you put into the calculator. Example: For the 262, the ICA goes from 57 to 53 with a 4 degree cam advance. This explains/models the old advice to advance the cam for better low RPM torque.

In general, DCR is a tool to let you:
  • See how a combination will do for low to mid RPM torque. It does not model all aspects of low RPM operation (like reversion, and cylinder clearing effects related to SCR), but helps in narrowing down your cam for certain applications.
  • See how close you are getting to detonation tendencies around the peak torque RPM
  • A .1 change is not a big deal for most situations, and, getting beyond that level of accuracy is not realistic anyway. (So I don't get hung up on DCR at that level.)
  • However, a half a point difference WILL show up with significant changes in low RPM torque and driveability (throttle response). And even a .2-.25 point change will be felt the first time you press down the throttle.
  • Going low-mid 6's tells you the engine will be doggy at low RPM's.
  • It is a numerical way to try to be objective in cam and compression selection and has been used since the 60's for hot-rodders. You don't have to blindly follow someone else's formulas or build, or to build and experiment.
  • It was/is tough, and beyond the abilities of most hot-rodders, to do by hand. The online tools make it easy to compute and evaluate for anyone interested.
  • The value to the engine builder may vary with the application. IMHO, it's highly valuable for applications needing a wide torque band (daily driving, cruising, road race, rally).
 
Man thank you so much the pieces of the puzzle are really starting to come together. Things are starting to make so much more sense now. One thing i really want to have is that snappy throttle response I hate that bogged down rev. Like setting at idle in park/neutral and you hit the gas and you get that quick waaaaapa. That is what I'm looking for not that you hold it to the floor and it takes 5 secs to hit 3 grand roooooo grrrrrrrr..... lol I always thought that had to do with lift and how much fuel was getting poured into the heads no idea about dcr and all the other stuff that affects performance. The more I learn the more I want to know. Haha one quick question please. I know I'm not in risk or anything but if I were to build another engine say 10:1 scr and get in or about that 8dcr how do avoid detonation? Is is simply a change in fuel? Or can you do something to the combo timing jetting advance retard etc?
 
dartfreak75 said:
I know I'm not in risk or anything but if I were to build another engine say 10:1 scr and get in or about that 8dcr how do avoid detonation? Is is simply a change in fuel? Or can you do something to the combo timing jetting advance retard etc?
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Most all of the things you mention will effect how close you come to detonation:
  • Octane
  • Ignition timing
  • Cam timing (raises or lowers DCR)
  • Cam duration (to change DCR)
  • Fuel/air ratio
Other things:
  • Combustion chamber shape - closed and smaller is better due to a faster burn... slow/long burn rates raise the probability of detonation
  • Head material - AL raises detonation resistance by running cooler on the inside surfaces
  • Setting up the piston and head and head gasket relationship to achieve a small quench gap
  • Ignition system - high spark energy makes the burn process start faster and a faster burn helps (like in a smaller combustion chamber)
  • Certainly few more that I can't think of right now LOL but these seem to be the most important for most uses
 
dartfreak75 said:
One thing i really want to have is that snappy throttle response I hate that bogged down rev. Like setting at idle in park/neutral and you hit the gas and you get that quick waaaaapa. That is what I'm looking for not that you hold it to the floor and it takes 5 secs to hit 3 grand roooooo grrrrrrrr..... lol
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That's why some of us have kept poking at ya LOL. For a driver car, the throttle response makes it a loooot better. You potentially end up with a bit less peak HP but you more than make up for it with throttle response and an overall wider usable RPM range. Push up the SCR and then you can put in that bigger cam, get the higher HP peak (as long as the heads will flow), but the DCR stays up and you don't give up the low RPM torque.

dartfreak75 said:
The more I learn the more I want to know.
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Kinda like drugs... not that I know firsthand, thank goodness LOL
 
nm9stheham said:
That's why some of us have kept poking at ya LOL. For a driver car, the throttle response makes it a loooot better. You potentially end up with a bit less peak HP but you more than make up for it with throttle response and an overall wider usable RPM range. Push up the SCR and then you can put in that bigger cam, get the higher HP peak (as long as the heads will flow), but the DCR stays up and you don't give up the low RPM torque.

Kinda like drugs... not that I know firsthand, thank goodness LOL
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Thanks man yes it is.I wouldn't know either. It has been years since I have been in the car building game (other than working on my every day drivers) I thought I knew quite a bit now I'm realizing I didnt know crap lol
 
AJ/FormS said:
Bore, stroke, rod length,Scr, Ica, and elevation
then go here,
Wallace Racing: Dynamic Compression Ratio Calculator
and pay close attention to the V/P, which you can read about that here
V/P Index Calculation

to get a picture of where you are starting from , plug 7.8 in for Scr and 50* for the Ica,These are the specs for a stocker with a 240/248/112 cam, in at 110....
plus the basics; 3.91x3.315, 6.123rods, and your local elevation; 300ft IIRC. I get 132psi@109VP, and you already know what that feels like.
I took the liberty to max out your compression for this cam, with a bore job and hi-compression pistons and retarded the FACTORY cam to a Ica of 53* so you can rev it a bit. This is about the max you could run on pumpgas. I get
Scr of 9.25 @161psi @132VP @7.97Dcr.
This would make a real stump puller, with fabulous first gear performance. and tons of grunt in second at say 30 to 45 mph just where you need it.
With 2.76s and the 2800TC, you won't get any better, to somewhere between 45 and 50 mph.
As a comparison this 132VP is more VP than a factory 340(128)calculates to , more than a factory 360(121)calculates to,and even a 440Magnum calculates to just (136) with the 4bbl cam.
And we haven't even talked about the fuel mileage improvement,or what the 4bbl and headers are gonna do for you. These V/P numbers are most valuable to know, from a factory stall to in the range of 3000 to 3500, after that the combo better be making power elsewhere cuz the VP advantage has diminished to nothing. That factory 240 cam is done pulling around 4500rpm. That doesn't mean you have to shift it there, in fact with the standard TF ratios, the 1-2 split is 59.2%, so for low-ET this combo might need to be revved yet higher, perhaps 5000 or a bit more.

And for anyone reading this that has a manual trans, you know how much time you spend from 1600 or so to 2800 or so. For you guys VP is really really important. If your combo is doggy in there, I know you ain't happy. And nothing sounds worse than a Mopar impersonating an old Mustang, having to slip the clutch out so it don't stall, and then rev it to near 4000 to find some torque in second; Man, I would be so embarrassed . With VP like this, and typical street gears,and street flywheel,you can just dump it and go. I'm not kidding. As a comparison my 367 calculates to 156VP and spins 295s/325s to waaaaay past the speed limit. I have to lift at 65,lol. Actually I have to cuz that is 6900 with my gearing,lol. Oh! we're not talking about high rpm in this chat,sorry,lol.
Ok so with my 10.97 starter gear, it really is a blip the throttle and slip it out, without any gas pedal, deal. It was pretty similar with a 9.44 starter gear. But with 3.23x2.66 it needed a bit of gas-pedal, and/or easy on the clutch pedal. This is where big VP pays off;throttle response and low-rpm driveability and the ease of initiating tirespin without racegears. 156 is a lotta,lotta VP. 132, as you can see, is quite a bit.
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156 VP is a snappy engine.

I have VP 152 in my duster with a 340.
And a VP of 155 in my old 360 truck de-tuned down from 212 in my old truck with a camshaft and head-gasket change.

Both vehicles built with the intended use.

The old truck is a complete torque monster spins the tires on the on-ramps on the interstate in 3rd gear, not just a chirp, fish tailing, its a 4x4 with a 4 speed, stock tires.
My wife says I ruined it for a winter vehicle, too much power.
 
first of all dartfreak get away from comp for any hyd shorter than HE275 there are much better choices
I would not use the comp XE268 I do not like to give up area under the curve
however comp does show the .006 timing on their individual cam webpages- however sometimes they show the .050 and call it .006
always check 180 + Intake open + intake close should add up to the intake .006 duration if it adds up to the .050 duration - well what's not to like or WTF
other vendors with .006 specs should give the same intake close at the same duration and lca or you can calculate from there
low compression LA motor I'd try and keep the intake closed to earlier than 56 @.006 problem with the XE256 is lack of lift/ area
(compare with a OHCam motor where they can get good lift with short duration- size of the lifter makes a big difference)
understand what nm is trying to say
AJ the Hughes/ Engle were .008 most likely .006 now
 
sireland67 said:
156 VP is a snappy engine.

I have VP 152 in my duster with a 340.
And a VP of 155 in my old 360 truck de-tuned down from 212 in my old truck with a camshaft and head-gasket change.

Both vehicles built with the intended use.

The old truck is a complete torque monster spins the tires on the on-ramps on the interstate in 3rd gear, not just a chirp, fish tailing, its a 4x4 with a 4 speed, stock tires.
My wife says I ruined it for a winter vehicle, too much power.
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Good numerical perspective on low RPM torque.... but you can be sure it GOES anytime you push on the tall pedal on the right, no hesitation. With a manual trans, start out in 2nd. Ford C4 and C6 trans had the feature that you could start in 2nd gear too; can you do this with a Torqueflite? (I just never paid attention...)
 
Excellent info guys
BTW TF has no second gear start without a manual VB
Back to second on the OD 518 42- rh etc is munged due to a VB design that is not fixable (prove me wrong)
you can't get back to second at higher speeds moving the shift lever just gets you out of OD
and if you have "back to low" do not try it at high speed- it does work
 
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