cr vs. cam.

[Krep]

I have been getting mixed info. on the required cr. for the 509 cam. Some say over 10 to 1 is need but then I hear that it will work fine at about 9 to 1. I have a 400 auto with a 3000 stall and 3.91 gears. the car is a 73 runer. Does anyone have any advice on what I should be looking for. Also the block is already together so any changes can be to the top.

[DartGT66]

I don't know if there is somekind of limit where it starts to work, but I think that achieving certain cranking pressures is a good hint. I'm not really in to this subject, but I think you should be at the 150 psi level with the cam you use and pump gas. Like I said before, I have used this cam in a low CR engine, about 8.7:1, and didn't work. It wind higher, but lost low end, the previous 280 cam providede the same ET's in that low CR engine. Instead of the CR, the engine was 'ready' for the bigger cam, so I draw the conclusion that the CR was the reason why it didn't respond to the cam.

[ChristianCuda]

Krep

As far as CR goes with the 509 I would suggest that you have an actual 9:1 and not just 9:1 pistons which may give 8:1 and have the heads ported otherwise the cam will not work at all. Using the Mopar Porting Templates will help tremendously. Also make sure you either have double springs or atleast the P3690933 sigle w/ dampner valve springs. If you dont have either of these the cam wont do you any good.

Christian
68 cuda 383

[bbaspense]

In my smog 400 I run a Comp cams 484/292 cam with a 3000 converter and 3.91 gear in a 3700 lb Aspen and make gobs of power. I run stock pistons with ported 452 heads and stock intake. I run 13.30's all day. I'd run the 509 in a second with the low cr. I think it would work.

Jason
indychamp@hotmail.com
Jason's Aspen/Volare Club http://www.geocities.com/indychamp

[cdignition]

the MP .509 cam requires over 200 psi cylinder pressure to work properly...otherwise bottom end suffers horribly, signal to carb is weak and causes crappy idle....you can run it lower, but it just dont like it.

[Runner1971]

man 200 psi seems high to me for a street motor.

[1965 Viper]

200 psi cranking pressure..THATS ALOT..I dont think thats requirred at all...of course if you have that..Then Obviously its gonna make the Cam really "wilder". Ive seen 8:5to1 with a 509 440 in a 2700lb duster run 11.40s all day long...Thats 2700lbs tho..Im gonna say this...with that 73 runner, do yourself a favor and have a true 9:2 to1 compression. Thats all I really have to say at this time.

[bubby440]

my 440 with the 509 had 150 lbs of cranking pressure. ran fine at lower rpm and would light MT L60-15 S/S at will.

[Warren J]

When you call cam mfg they will recommend cams based on comp ratio, cranking preassure, car weight, rear end ratio and torque convertor. Actually they will tell you that this cam will work best with this much stall and this much gear. If you look at the specs on the 509 cam it will work best with more cr and a stall convertor and a deeper gear. That doesn't mean you can't use it with a differen't combination. You can run almost any cam you want, but you would match a cam to your combination to get the most from what the cam was designed for. If a cam was designed for power between 3500-7500 you probably would not pick it for your combination, would you? Most people over cam their cars, but they still work, just not as designed.

------------------

[SubLime440]

Remember...Everything is relative to where you live... Cylinder Pressure is relative to the atmospheric pressure of where you live...
Since I live in Denver CO....I'm at 5900 ft above sea level...
Example...at sea level my gauge reading would read 178 psi, while in Denver my gauge reading is 148 psi...see panic's web site, it is an excellent resource...http://victorylibrary.com/mopar/cam-tech-c.htm

Just an FYI

[rumblefish360]

They work as a team. When one isn't up to snuff, the combo falls short. Thats why the recomendations are given in such away.
Larger cams need more compresion to work well in the street. Even more so at the track for best performance.
This cam will work @ a true 9.0-1 compresion.

[rumblefish360]

They work as a team. When one isn't up to snuff, the combo falls short. Thats why the recomendations are given in such away.
Larger cams need more compresion to work well in the street. Even more so at the track for best performance.
This cam will work @ a true 9.0-1 compresion.

[Street-N-Strip]

Originally posted by Krep:
I have been getting mixed info. on the required cr. for the 509 cam. Some say over 10 to 1 is need but then I hear that it will work fine at about 9 to 1. I have a 400 auto with a 3000 stall and 3.91 gears. the car is a 73 runer. Does anyone have any advice on what I should be looking for. Also the block is already together so any changes can be to the top.

My $.02: you don't have enough compression, gear or converter for the MP .509" cam in a 400. If you've got an honest 9:1, stick w/ a smaller cam to keep from killing your torque. Stick w/ something having advertised duration in the 275-285 range.

I don't know why people keep shoving the .509" in low-compression engines and thinking they're doing well going low 13s. I went that fast w/ the dinky MP 272/.455" in a 3800# car using 3.55s, a stock 2200-stall converter and a basically stock '70 440 engine. Also, same car went mid-to-high 12s just by adding some mildly ported '452' heads and 1.6 rocker arms using that cam.

[451Mopar]

As everyone mentioned, the compression ratio and cam timming should be considered together to get the most power for a given fuel octane rating. If the compression ratio is too high the engine will ping on pump gas, and if the compression ratio is too low, the lower RPM torque suffers along with lower engine vacuum and efficency.

Everyone I know of that has good luck running the cam with fairly low compression is running a high stall torque converter and usually 3.91:1 or more gear, so the lack of low end torque really is being masked by the chassis setup.

The street cars I know of (only two) that run really good with this cam, and a fairly tight converter and 3.23:1 gears are both running compression ratios in the 10.5:1 or higher range. These also run really good at the track too

Here is what I look for in choosing cams:
Duration: The duration determines the basic RPM range of the engine.

Lobe seperation angle / overlap: This will vary more by application, and helps to fine tune the engines torque curve. Generally higher LSA (less overlap) is used with milider cams, the combination gives good low speed torque and vacuum and extends the rpm range of smaler duration cams, but they usually give up some peak power for a wider torque curve. Lower LSA(more overlap) produces more lowspeed reversion so idle and vacuum suffer, but when combined with headers, the higher overlap allows the exhaust to scavenge at mid to higher rpms which produces more power, but usually in a narrower RPM range.

Valve lift: as much as the head will flow, but with consideration for cam lobe and valve spring life. Example, a stock small block head flow stalls out around 0.500" lift, there is not much to be gained (on a street car) by using a 0.550" or bigger cam, they will just wear out the valve springs faster.

Here is a little comparison equation I use to help compare cam/compression, I call it Dynamic Compression or the re-calculated compression ratio from the point the valve closes (but ignores slight variations due to connecting rod length.)

DYNMIC COMPRESSION:
% OF STATIC = 0.5+0.5*COS[I.CLOSE IN RADS]
DEGREES IN RADS = I.CLOSE*[PI/180]
D.COMPRESSION = STATIC COMPRESSION* % OF STATIC

I.Close is the intake valve closing point after botton dead center.

To find the intake valve closing point:
I. CLOSE = [INTAKE DURATION /2]+LOBE CENTER-180-Degrees ADVANCE

When I use this formula, I try to use duration rated at 0.006" (Advertised duration for most cams, not the 0.050" duration.)

If you take and plug in the numbers for almost any stock chrysler engine made durring the mid 60 to early 70's you will find most of the engines had very close to 7:1 "dynamic" compression.

With a 292 duration cam with 108 LSA installed at 108, to get right at about 7:1 takes almost 11:1 static compression ratio.
If your worried about gas quality and drop the compression ratio to 10.5:1, you get 6.7:1 "dynamic" compression.

I know this is not the best "scientific" formula, but it does make for an easy way to compare different cam/compression combinations and thier effect on (running) compression ratio.

[toolman]

One motor compared to another is like comparing apples to oranges so you are going to have to weigh alot of possibilities and then mabe take all the answers and average them out or take a wild guess. I'm not sure I even understand what I just said! Anyway, your motor should run with the 509 but I think that you would be happier with something smaller, once you try the 509 out. There is almost no bottom end, so to stay up with normal street traffic, you will have to give it more gas. I have to, and with my exhaust system, it sounds like I am racing someone even though we are going a normal speed. I think it would be more impressive if you could give it hardly any gas and your car pulls out ahead of the rest. I have a low compression 383 with the 509 and 3500 stall converter in my 69 Coronet. It seems very fast, but I feel that a smaller duration cam would be better. It sounds awesome when idling(the 509), but the other problems that come with that cam make it a poor choice for a short stroke street motor. I had a heluva time figuring out my carb and timing!

[This message has been edited by toolman (edited January 26, 2001).]

[72Bird]

I have to disagree with some of the things said early on in this post. I ran the 509 in a 440 with 8.9 comp, 452's that were ported but with stock valves, 3500 stall, 3850 Lb B-body ran 12.40's at 109. My buddy has a 292,501 Comp(almost the same, not enough difference to matter) in a 80,000 mile 440 that has probably 250 passes on it. Compression is about 8.7, Torker intake,452's that have stock valves and no port work except valves have been deshrouded, The motor turns 12.20'in a 3600 lb. b-body with 3500 stall and 3.23's. We have never had any problem with that low of compression. So these cams will work fine with stock heads and lower compression. They idle fine, had to barely crack secondary's on mine to get idle, but no problem after that.

[cdignition]

Just remember that i was talking about cylinder pressure, not static compression ratio. Two diffrent things totally...Just imagine how much better both of those cars would go with the right gear and cylinder PSI matched to that cam.

[This message has been edited by cdignition (edited January 26, 2001).]

[Dart]

CD - 200 psi? A little high I think.

[72Bird]

The cylinder pressure on my motor was 150-155, I dont know what the pressure was on my buddys car, probably around the same

[djswwg]

In my 440 the cranking compression is 180# with the 509 cam. It has TRW (now federal-mogul) so-called "11.5:1" compression forged pistons. Big dome!The car weighs 3880 with me in it. Lifts the wheels every run and cuts 1.65 60 foot times. My brother had the 509 cam in his "10.65:1" 340. Much harder to make idle and lazy off the line up to 2700 or so rpm. Put in the 284/480 cam and solved ALL those problems. BTW both cars use 3500 stall. So here's what this all means. The smaller the cubic inch the less radical cam you can use. For example, if you built a 383, 400, and a 440 all identical, the 440 will idle better and be more torky at lower rpm than the other two. The 383 of course would have the lumpier idle and be lazier off the line. The more overlap the cam has the more compression you need. If in doubt, always go with a cam one step smaller than the one you really hope is the one for your engine. (same goes for carbs, but that's another story) In the end, you'll be happier, especially with a street car. AS a footnote, has anyone used Mopars biggest hydraulic cam, the 320, in a 440? I'd like to try it in my car without any other changes, (except the matching springs of course), but again, I don't want to be guilty of over-camming. Any input is most appreciated. Thanks in advance, djs

[451Mopar]

There was an article I read a few years back that broke down cam sizes into each valve open/close event. The article claimed that the two most important valve timming events are the intake valve closing point, and the exhaust valve opening point.
The idea was that an early closing intake will build more cranking compression, but a later closing intake valve allows more air to be "rammed" into the cylinder ar higher RPMs due to the airs inertia.
On the exhaust side, an early opening exhaust valve allows the cylinder pressure to "blow-down" before the piston reaches BDC so it does not take as much effort to pump the exhaust out, but if the exhaust valve opens too early (for the application) you loose some of the pressure that is pushing the piston down.

The intake opening point and exhaust closing point make up the cams overlap. The intake needs to start opening a bit early so the valve is off the seat when the piston starts down on it's intake stroke, at the same time the exhaust valve is closing. Durring this time a good exhaust system can scavenge the exhaust and help pull the intake charge into the chamber, but this usually happens to higher rpms. At low rpms, a cam with alot of overlap will have reversion in the intake resulting in a rough idle.

So it is possable to have a small duration cam with alot of overlap if the lobe seperation is very tight, or a large duration cam with a wide LSA to reduce overlap, but the installed position of the cam will shift all the opening and closing points, so it intresting to look at the individual opening/closing points of the cam and not just the general size (duration) or overlap.

[PRO]

Most people dont know what their true compression is,it requires ccing the heads,calculating the head gasket and valve relief volume and checking the cylinder fill volume at .500,now who has done that?I have,my 360 is an actual 10.52:1 motor,I have a 509mp cam in it,(180 cranking comp)I have run the 509 for years in various 440 and 383s varying in comp from 8.5 to 9.8,MP reccomends 10;1 or higher based on 243* of duration @ .050,now Ive run it on less,much less and it worked well especially with a 4 spd and 3.91 gear,an auto with 9;1 or less w/o a big stall(2500 or more) and it was TOO BIG,now having experienced with 10.5 comp I see why they reccomend it with 10:1 or more,its a TORQUE monster!!!my 360 runs like a little big block,but most guys with a serious motor(good heads and comp) wont even consider the MP cam,there are much better choices these days but Im completely satisfied with it,360,.020 over,hypereutectic pistons,10.5,Edelbrock alum heads,509 cam,tunnelram,1.75 headers,4 spd,3" exh,3.23 posi,3200 lbs w/driver,91 octane,street tires and exh went 12.28 and gets 18 mpg @ 75 mph so I cant complain I do wish it revved a little higher,it redline at 6000 but its installed 2*advanced,it turns on at 2200 ,if I were you Id go the 484.284 mp or somewhere thereabouts.......PRO...

[rumblefish360]

I agree with pro even tho I said the cam would work @ a lower compresion ratio. This can be a powerful cam when comboed right.
When he use's the race gas, I bet its even better.
I also agree with the 284 .484 choice. It will make more torque than the .509 and work better on a lower compresion eng.

[cdignition]

Any cam will run in almost any motor...if theres just enough squeeze, it will work...maybe not right but the thing will run.

[72Bird]

In my 440:


Deck clearance was .030, gasket thickness was .015 or whatever steel shims are, 98 cc chamber heads for a compression of 8.9, actually 8.7-8.8 This motor pulled like hell from 2500-6000. Wouldnt pull over 6000 at all. Would have been a 11 second motor in 3850 lb car, if I would have messed with it a little more.

[Sport]

Bird Is that 98cc chamber correct, thats the biggest I have heared of ,what head casting was that head.Sport

[Sport]

Krep the 509 cam is pretty big, for a 400 street car.I have run that cam with a cyl. psi of 150,I wouldnt recommend useing that cam with any less reguardless of c/r.With 200 cyl.psi that cam would be torguey as heck. But you would not be able to use pump gas.Popular engine builders claim that the 440 will start to have detonation with pump gas at about 160 to 177psi.cyl.pressure depending on who you talk to and what your advance curve is with steel heads.Any cam will work better with more cyl.psi.But if you are limited to to pump gas you are limited to a arbitrary max cyl.psi.Sport

[72Bird]

Sport

They are 452 castings. Everybody asks what castings when I tell cc. The chambers have been polised and deshrouded. I am going to have them re-cc'd before I use them again, all of the chambers were marked 96-98.

Bird