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Help with Cam selection (again) |
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jpnjim 
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Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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 Topic: Help with Cam selection (again)Posted: Oct/13/2018 at 6:55am |
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heres an intense 224 degree .552 lobe compared to a less intense (but not mild) 231 degree .512 lobe: lobe name .006" .020" .050" .200" 1.6:1 lift HM2243450A 271 248 224 144 .5520 1hf231320 285 258 231 143 .5120 The first cam would be considered at the mild end of things with 224 net duration, but its open past .200" for 144 cam degrees of rotation, longer than the 143 degrees that the much bigger 231 cam is open. That tells you that the 224 cam is going to breath a lot better than a typical 224. Now look at the .006" numbers, the intense 224 has just 271 degrees advertised duration, that tells you it's opening quickly, closing quickly and getting its work done fast without a lot of gross duration ^that can be good for cylinder pressure (all things being equal, lobe seperation and cam advance plays a big part in this too). The more serious (but less intense) 231 cam has 285 degrees advertised/gross duration, so it would have much more overlap with it's other lobe (all things being equal), most likely lower DCR (not because of the overlap, and again, all things being equal), and it would be easier on valve components compared to the intense 224. If you didn't have all the other numbers, you could look at the 224 degree .552 lift and guess that it would be more intense than a 231 .512 lift cam. If you found a 231 degree .480 lift cam (at the same 1.6 ratio) it would be a good guess that the smaller lift cam was even less intense. Last thing, lifter size can allow for greater intensity, AMC's and Chryslers have the widest lifters of all regular production V8's, many cams were originally designed for narrow Chevy lifters, and it shows in their mild intensity and lower lifts (Small Block Chevy's use 1.5:1 rockers so that makes their valve lift lower too) Edited by jpnjim - Oct/13/2018 at 7:00am |
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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jpnjim
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Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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Posted: Oct/13/2018 at 6:27am |
Your welcome, I like to try to wrap my head around the numbers sometimes, so these threads can get pretty interesting I'll give you my understanding, right or wrong here it is..... Cams are tough to figure because different manufacturers can use different points in the cam to advertise their duration at, I'm just going to type about Hydaulic Cams here because Solid Cams add even more issues to the numbers to confuse things (me!) even more. There are crazy aggressive 300 degree duration cams and very mild 300 degree duration cams, the STOCK 401 cam is very mild, but has an advertised duration of 296 intake/304 exhaust! (The stock 304/360 cam is 264/264 duration, 401 stock lift is .4576, 304/360 lift is .4256). So you can look at the advertised duration and lift and take a good guess at the cams intensity. Then you read their descriptions, which are all over the place too. Some advertise their cams in the range they best work, others list the entire range that the engine would work. So the same came could be listed as working from 2800-5500 by one company, and 2200-6000 by the other cams advertising department. Then they started using net duration. That's the .050" duration in the lists I copied earlier. .050" duration is great because its a standard point that all the manufacturers seem to be using (hydro cams), and comparing one .050" number to another .050" number is apples to apples, for the most part. If you want to figure intensity you look at the advertised duration (usually .006", but not always). A big .050" duration with a not big .006" number = a fast acting/intense cam. The .200" number would most likely back this up. How long the cam stays open past .200" says a lot about the cam's profile, the bigger the .200" number is compared to the .050" number, the more intense the cam will be. So you can have a lazy 225 degree (at .050") cam that acts like its smaller than its middle of the road numbers wpuld suggest, or you can have a pretty intense 225 degree (at .050") cam that is much faster acting ^the fast acting cam might have the same .200" duration as a slower acting 230 degree, or bigger cam so the intense cam could move almost as much, or maybe even more air during its shorter event timing. Lift tells you a lot too, but if you have the .006", .050" and .200" numbers you can start to compare them all to each other and see how it all fits togther. ^this seems to work for me, but I'm the guy who will keep reading the same thing 20 times over until I think I understand it or my brain starts to hurt. Lobe seperation is the next big thing to consider but I'll leave that for next time.  |
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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AMXrated
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Joined: Jul/26/2015 Location: Indiana Status: Offline Points: 290 |
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Posted: Oct/13/2018 at 12:50am |
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Also, noticed Crower had this cam on clearance on their website.
Too small for my application, but it's a good deal for $98. https://www.crower.com/clearance/amc-290-401-power-compu-pro-hydraulic-camshaft.html |
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You can have my Hurst shifter when you pry it from my cold dead hand.
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AMXrated
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Joined: Jul/26/2015 Location: Indiana Status: Offline Points: 290 |
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Posted: Oct/13/2018 at 12:02am |
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@jpnjim: Thanks for the thoughts/analysis. I am absolutely blown away at how much you guys know about this stuff. The last time I worried about cam specs, we called them 3/4 Racing cams...probably dating myself.
I've heard really good things about Howard's, but never got a reply from the guy after I asked him to reconsider his spec's targeting a 1600-5500 RPM range. I even sent him a follow-up email this morning. |
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You can have my Hurst shifter when you pry it from my cold dead hand.
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jpnjim
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Posted: Oct/12/2018 at 7:42pm |
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I copied your original two recommendations:
The biggest problem is the 10.26:1 CR 360 would make me want a bigger cam to get the DCR down, and 2.23 first gear T-10 with just a 3.54 rear would want me to get a smaller cam to help me pull the gear. My T-10 Javelin with a 360 had 3.91 gears and it was a chore coming out of the hole sometimes. I like the 112-114 lobe center to close the intake valve a little later, and lower the DCR without going crazy on duration. Howards cams are high quality, they make customs fast (mine took around a week) and the price is very good. Their
"Aggressive Flat Tappet Hydraulic" line of lobes are a pretty good
compromise of intensity without the higher lifts you'd end up with the
same durations in a .904 lobe. File Name @0.006" @0.020" @.050" @.200" 1.6000 lift 3HF223323 270 247 223 137 .5173 3HF225327 272 249 225 139 .5227 3HF227330 274 251 227 141 .5280 3HF229333 276 253 229 143 .5333 3HF231333 278 255 231 145 .5333 The 904 lobes have a higher intensity & a bit more lift File Name @0.006" @0.020" @.050" @.200" 1.6000 lift HM2243450A 271 248 224 144 .5520 HM2263500A 273 250 226 147 .5600 HM2283525A 275 252 228 148 .5640 HM2303541A 277 254 230 150 .5666 I bet if you went with something like the 3HF229333 276 253 229 143 .5333 on a 114 you'd be at a healthy
compromise between what the 10.26:1 compression ratio wants to run on
pump gas and what the (tallish) 7.89 first gear wants to pull a bubble
fender Javelin in first gear. If you want to drop the DNC a little, then maybe go a little bigger, or pick something from the "Standard Ramp Hydraulics" that have greater .006" duration, without bumping up the .050" duration too much: File Name @0.006" @0.020" @.050" @.200" 1.6000 lift 1hf225310 279 252 225 137 .4960 1hf225327 279 252 225 138 .5227 1hf225330 279 252 225 138 .5280 1hf227313 281 254 227 139 .5013 1hf227320 281 254 227 140 .5120 1hf227327 281 254 227 140 .5227 1hf231300 285 258 231 139 .4800 1hf231313 285 258 231 142 .5013 1hf231320 285 258 231 143 .5120 ^these
would potentially bleed off some more cylinder pressure for the same
.050" duration (since the gross, or .006" duration is higher), but they also give up duration at .200". The second lobe from the top is the intake lobe Howards chose for you, this is the exhaust: File Name @0.006" @0.020" @.050" @.200" 1.6000 lift 1hf235325 289 262 235 147 .5200 I'm not a cam designer, so I don't really have a recommendation just putting some thoughts down  Edit, it also makes some sense why Howards recommended the relatively mild 1hf225327 intake lobe, and the fairly aggressive 1hf235325 exhaust on a 112, trying to find a good balance between DNC and low end torque.
 Edited by jpnjim - Oct/12/2018 at 7:54pm |
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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jpnjim
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Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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Posted: Oct/12/2018 at 6:46pm |
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Cam designers like to run a few more degrees of exhaust duration to help make up for a restrictive exhaust system. A lot of the time they'll choose an exhaust lobe with less intensity so it can have that extra duration, while still having about the same lift as the intake. In that case, the intake, or the exhaust lobe may have slightly more lift than the other, just the luck of the draw of using existing lobes. I'd say only the Bullet designers would know if they're actively trying to maximize intake vs exhaust lift, or if the extra intake lift is just the by-product of the more intense intake cams they are using. |
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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AMXrated
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Joined: Jul/26/2015 Location: Indiana Status: Offline Points: 290 |
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Posted: Oct/12/2018 at 6:08pm |
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I've noticed that in many cam designs the gross lift is either the same for Intake/Exhaust or the Intake is slightly higher than the Exhaust.
But in a few designs (like the custom spec'd by Bullet), the Intake is higher than the Exhaust lift. What is the effect of that? Also, I have read that AMC engines like for the Exhaust lift to be slightly higher than the Intake--is this true or just another one of those "you shouldn't believe everything you read on the internet" things? Thanks.
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You can have my Hurst shifter when you pry it from my cold dead hand.
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Greyhounds_AMX
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Posted: Oct/12/2018 at 2:49pm |
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That's one of the things my spreadsheet is trying to illustrate via the graph on the right side. It a plot of the flow that heads will pass at the lift of the selected cam as is goes thru the travel.
The curve is then integrated to get the total area under the curve, and thats the "Intake Area" and "Exhaust Area" listed in the table. The difference in area under the curve of the two selected cams is shown on the graph. Edited by Greyhounds_AMX - Oct/12/2018 at 2:59pm |
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1968 AMX 390 w/T5
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Ken_Parkman
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Posted: Oct/12/2018 at 1:16pm |
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More lift is almost always better as long as you do not exceed durability limits. More lift is still better even if the flow separates and falls off at high lift - a typical problem with too large a valve for a given port configuration and usually happens above .25 l/d. the point is peak lift is only for an instant, but with higher lift you get more overall flow area under the curve. And flow separation characteristics on a flow bench may not be the same thing in a running engine when the delta P is much greater.
Also I don't worry a lot with lifter diameter for street type applications. Yes a .904 lifter is better, but I had a conversation with a lobe designer one time and he told me there is not much in it on less than all out circumstances. to make a difference the contact patch has to move far enough from the centerline to be close to the edge. Much more of a concern on the race technology. Edited by Ken_Parkman - Oct/12/2018 at 1:20pm |
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AMXrated
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Joined: Jul/26/2015 Location: Indiana Status: Offline Points: 290 |
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Posted: Oct/12/2018 at 12:44pm |
Thanks RD--That is an interesting read. If I'm reading the data right on the stock unported heads, flows don't stop after .450, but they do start to decrease at an increasing rate after that point and the gains get incrementally smaller. And, you're probably right on the cam selection--no one's going to be able to tell me what I need since everyone's set-up and preferences are different. Going to have to just make a decision and go for it. If I had to make the call right now, think I'd go with the bigger Crower. Should have the pistons in tonight (unless the wife wants to go out to dinner...). Hopefully can do a clearance check tomorrow, although it looks like the Wiseco's have pretty healthy reliefs on them so I doubt it will be a problem.
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AMXrated wrote: