Cam too big?

[pparaska]

Just got off the phone with Comp Cams tech line. I had chosen the XS268S-10 230°/236°@0.050" .488"/.501" lift 110° lobe sep cam. It' an Extreme Energy solid flat tappet lifter cam. I didn't tell the Comp Cams tech that I was looking at that grind though.

 

I described my car (engine specs: 327 cu.in., compression 9.7:1, Holley Contender high rise dual plane, 750 vac sec.) 5spd, 3.7:1 gears, 26" tire, 2700 lbs. and street performance use. The guy came back and suggested the Xtreme solid flat tappet cam ONE SIZE LARGER:

XS274S-10 236°/240°@0.050" .501"/.510" lift

 

I was shocked, thinking that I'd hit the largest suggest cam for my use and the larger one would be too much for the street. I asked if it would it be o.k. around town or too peaky, and he thought it would be fine. He said it'd probably have a useable power band from 2200-6200. Pretty much what I'm looking for. And it ought to work well at 70 mph in 5th gear in my car (2270rpm with a 3.70:1 r&p, 0.68:1 overdrive ratio, and a 26" tall tire (255/45-17) ).

 

What do you guys think? I'm looking for a visceral feel to the car, a nice lope in other words, and don't want to give up ALL the low end, but Desktop dyno shows my current cam (a 224@0.050" solid lifter Magnum grind) having near 400 lbft at 2500 rpm. So if I give up a bit of that, I think it will still be a strong performer around town, plus give me some more top end and the low end lope that I want just for effect.

 

Feedback appreciated!

 

[ July 25, 2001: Message edited by: pparaska ]

[Guest firebern]

Pete,

 

The new paint is awesome, the car looks great. I am eager to see the final result.

 

The roll bar is very nice too,

is it custom made?

 

Great job!

Fire.

[pparaska]

Fire, as awesome as that paint looks in pics, it's not up to the standards of the painter and he's redoing it free. Thanks, I love it to, from 10 feet . The color absolutely glows now after the wetsanding and compounding - it really brightened up after that.

 

The roll bar was the S&W kit, modded. The hoop had a section taken out of the middle and rewelded with an internal pipe in it. That was done to get it to fit between the wheelwells.

[DavyZ]

Pete, from all my research, I would err on the side of conservative. I think the cam you picked out (first one listed) would be fine, although a nice lumpy one ! The cam the guy suggested seems a bit too much for the street (more like a strip cam) IMO. You are already pushing it IMO with as big as a cam you picked out, but I believe the streetability will be pretty nasty. I'm very surprised he picked out one even bigger. A lot of guys make the mistake of over-camming their engines--"if a little is good, more must be better," as you well know. Hmmm. I'd ponder this a bit more before going with the "suggested" grind. Call them another time and speak with someone else--bet me they give you a different opinion!

 

I remember calling about my own mild performance cam--they suggested a grind lower, but I was near the bottom of the cams anyway! Shoot, there was nowhere to go but one conservative grind up for me!

 

Davy

 

[ July 25, 2001: Message edited by: DavyZ ]

[Guest Anonymous]

I also think your first selection might be a bit more streetable. The 110 lobe separation will help to give it a bit more torque down low while keeping the drive-in idle sound. The next one up might be pushing things IMHO. Most of the rag's I've read say try to keep it around 225 @ .050 duration or there abouts. The Z being lighter and with your gearing can probably go a bit more than that. I know the gearhead mentality in us all is to go up another size on cams, but I know from our previous communications that you, like myself, like some torque down low. Cam grinders/manufacturers idea of 'streetable' and mine are quite a bit different. My Brother's FE 390 that he put the full Edelbrock RPM package on was rediculous and not streetable in my opinion. We finally changed the cam out to a Crower of less grind and its great now. Before it had little vacuum to speak of, overheated alot and was dead until 2500 rpm's, after we put in the Crower it had better torque and can smoke them for as long as you like. Just my .02 but bigger ain't always better...

 

Good luck with it,

 

Lone

[pparaska]

I am still on the fence, but I will call back and hopefully get someone else.

 

Remember that you need to subtract 6 to 8 degrees from the 0.050" duration numbers of a solid lifter cam to make it comparable to hyd. lifter cam.

 

1) The comp cam guy even noted that the solid lifter cam will give more torque down low than a hyd, so it will help.

 

2) The other thing to remember is that the Extreme cams have a typically higher 0.050" duration to say a Magnum grinds, due to the accelerated ramps.

 

These two reasons are why I think this cam may actually be more streetable than you might think. Much of the "225@0.050" rule of thumb is based on typical slower ramp profiles with hydr. lifters.

 

Another thing to note is that the recommended rpm range for the hydraulic version (XE274H) of this cam in the Comp Cams catalog http://www.compcams.com/catalog/056_057.html is 1800-6000. Those ranges are usually for a 350 engine, so the 327 range would be several hundred rpm higher.

 

I'm slowly becoming convinced this XS274S cam may not be too unstreetable after all. The Extreme grinds have better low rpm torque than a typical grind (of the same 0.050" duration), from everything I've read and heard about them.

[blueovalz]

Pete, I don't know that this will be a big help or not, but thought I would share this with you. The cam I currently run in my car is an original Ford LeMans Cam. It has 252 degrees at .050, which sounds like a lot, but this cam was designed in the '60s for road racing applications, thus it has a very broad torque curve. I have swap it with 7 different cams from various manufacturers and I have always gone back to this cam (it's got to be over 35 years old now) because of the range of torque. The others were just too peaky. Before you make a decision, see if you can find out what the specs were on some of Chevy's old road racing engines (like they 302 they used in Trans Am racing) or some of the old competition Vette stuff before dated before that.

[z ya]

Pete, Keep the 274! My cam is a solid with

292 duration and 480 lift.Its 230* at .050.

Yes it as a very rowdy idle but it is totally

streetable. With the stick shift an 3.7 gears

you will have more than enough to boil the

tires! This 274 will help extend your rpm band were the 327 loves to be!

[Guest dankinzle]

I agree with zya I have a 288 solid roller with .567 lift and it shakes at idle but it's not bad at all. I get like 14" or so of vacuum at a idle of about 1600 (i have an autotrans too).

[Kevin Shasteen]

Pete,

 

I know you cant compare Apples to Oranges; but, bare w/me for a moment while I compare Apples to Oranges-then I'll give you my stance on your Camshaft dilemma.

 

When I rebuilt my Olds 350 I didnt want a "Barely Streetable" engine but I did want a nice peppy car. I had a chance to go w/a cam (Hydraulic) w/about the same spec's you're wanting. I went w/the smaller one; the "Lift" is similar to your 268 cam but the duration was slightly smaller. My LDA was 112. I really, really, really enjoy the fact that my engine is streetable & has the performance sound I was looking for. Just FWI.

 

My Olds idles at 750 easily; has a decent idle/just a hint of "Obvious Performance"; the dual exhuast helps. Granted the Chevy Cyl.Heads should breathe better than an Olds head. My cyl.heads were ported & blueprinted w/the intake. Really runs nice.

 

Now...back to the Ranch & your current two cams. Using the Crank Slider Mechanism Graph (you pointed me in the right direction a few months ago) & using David Vizard &Dema Elgin of Elgin Cam's process of choosing cams & comp.ratio's...this is what I've come up w/on your engine.

 

You say you have 9.7:1; I'm assuming you've confirmed this & are not guessing-so that is the figure we'll use.

 

For starters; your 268 cam's Valve Events are as follows: .488/.501 Lift & 110 LDA

 

IVO = 28* BTDC

IVC = 60* ABDC

EVO = 33* BBDC

EVC = 61* ABDC

 

The 274 cam's Valve Events are as follows: .501/.510 Lift & 110 LDA

 

IVO = 31* BTDC

IVC = 63* ABDC

EVO = 35* BBDC

EVC = 63* ATDC

 

The valve events themselves are not that different as you can see; its the Lift that I'm wondering about.

 

Going w/the Slider Crank Engine Map Graph: this would tell us where the piston is located in the cylinder when the IV closes (IVC) on each cam. First we'll take the 268 Cam's IVC of 60* ABDC & then we'll look at the 274 Cam's IVC of 63* ABDC & apply it to the Crank Slider Map Graph.

 

My print out of your 327 SBC indicates that .804% Cyl.Volume remains at 60* ABDC for the 268 Cam while .784% Cyl.Volume remains at 63* ABDC for the 274 Cam.

 

According to the process we proceed as follows:

 

327 / 8 = 40.875 x 16.387 = 669.82 cc's per cylinder displacment

 

268 Cam again, (using .804% Cyl.Vol):

 

669.82cc x .804 = 538.53% Cyl.Vol Remaining after the IVC.

 

538.53/7.5 (7.5 is the Pump Gas Constant) = 71.80cc's which represents your "Final" Combustion Chamber required for the 268 cam. Its comp.ratio is determined as follows:

 

669.82cc + 71.80cc/71.80cc = 10.32:1 CR

 

Now lets take the 274 Cam (.748% Cyl.Vol @ IVC)

 

669.82cc x .748% = 525.13% Cyl.Vil Remaining after the IVC.

 

525.13 / 7.5 (7.5 Pump Gas Constant) = 70.01cc is the "Final" Combustion Chamber cc's Required to run w/the 274 Cam. Its comp.ratio is determined as follows:

 

669.82 cc + 70.01cc/70.01cc = 10.57:1 CR.

 

Now you can see, according to Vizard/Elgin's process your cam choices are slighty large for your 9.7:1 engine: you probably could get by but your cyl's would be loosing too much cyl.pressure prior to the IV closing.

 

Your current engine 9.7:1 CR requires a cam that w/an IVC of around 50* ABDC: I dont even think Comp.Cams sells a Solid Cam that closes the IV any sooner than 60* ABDC. Even if they did it would hinder the entire reason for choosing a Solid Cam...so the 60* or the 63* ABDC IVC should be okay; its the Lift & Duration I'm concerned with for a street engine that you probably wont be thrashing to terribly often...go w/the 268!

 

I personally think you can get by w/the cam's you are looking at-but if Vizard/Elgins process for picking cams/comp.ratio is accurate...then those cams are pushing the "Too Big" arena for a street engine.

 

If in the future you wish to up the comp.ratio then you can go w/a larger cam. That 268 will be plenty for the lighter Z which will be ran on the street....hey, why not pick up some Alluminum Cyl.Heads w/smaller Combustion Chambers...what's another $1000?

 

I love this Crank Slider Engine Map Graph thing...it is so cool.

 

Hope this helped shed some light on the subject: good luck Pete on your cam choice.

 

Kevin,

(Yea,Still an Inliner)

 

[ July 25, 2001: Message edited by: Kevin Shasteen ]

[pparaska]

Kevin, thanks for running those numbers.

 

But I thought the pump gas constant was 8.5, not 7.5? That's what my spreadsheet and notes from before say.

 

Anyway, using this method, even if I went to the smallest cam (12-674-4 or XS256S-10):

Valve Timing At 0.015

Open Close

Intake 22 54

Exhaust 65 17

These Specs Are For The Cam Installed At 106 Intake CL

Intake Exhaust

Duration At 0.05 218 224

Lobe Lift 0.31 0.318

Lobe Separation 110

 

(from their web site)

 

my motor still would need a compression ratio of 9.9:1 to work out with this method of cam selection. That's an incredibly mild cam.

 

I don't know how much I trust that cam selection method now. Ain't no way I'm putting a 218/224 @ 0.050" cam in my motor. I've got a 224/224 solid Magnum cam in there now and it's mild.

 

Terry, the old road race grinds were pretty radical on valve springs. I've had the old 327/350 cam - man that thing was dead until about 3000 rpm in my 327 10:1 motor I had years ago. But it ran like stink up top! Even pulled on a bud's GT500 Shelby from a 15mph roll until about 90 mph. Surprised the heck out of both of us (I had this motor in a 70.5 Camaro with a stock converter TH400 and 3.08 gears - bad combo.) All I read about cams these days says that the old grinds had too much high acclereation to get decent duration, causing lots of valvetrain problems. Maybe Ford just had it right on your cam and no one else at GM could figure this out. Duntov was pretty sharp though!

[Kevin Shasteen]

Its 8.5-1 = 7.5 for Pump Gas & 9-1 = 8 for Race Gas. It just depends on what you like. Somehow I get the feeling you really like the "Rumpity Rump" Cammy sound of an engine! Then go w/the larger cam.

 

Remember what Lingenfelter said in his book. When you come across two cam's of equal or almost equal lift; go w/the cam that has a larger lift & smaller ramp. To determine the ramp's agressiveness: just subtract the Duration @ .050" spec from the Advertised Duration spec.

 

Happy Rumpity Rump hunting to ya (I have a gut feeling that your going w/the larger cam).

 

Kevin,

(Yea,Still an Inliner)

 

[ July 26, 2001: Message edited by: Kevin Shasteen ]

[pparaska]

Right. I was looking at the factor only, not the factor-1. The spreadsheet was using 8.5-1 for me and I got the same numbers you did for the compressions.

 

I don't understand why this method says a 9.7:1 (it really is that - I measured it) 327 only needs a cam of less than 218@0.050 cam. That would be a stump puller. Come to think of it I had an RV cam in 327 that was just like that. Ran out of steam at 5000 rpm - no thanks. but it had incredible throttle response and low end for such a small motor.

 

[ July 25, 2001: Message edited by: pparaska ]

 

[ July 25, 2001: Message edited by: pparaska ]

[Kevin Shasteen]

Pete,

 

That's why I like this method; I'm conviced & whe hear it all the time, that most engine builders over carb & over cam their engines.

 

Definately something that makes you "Stop & go Hmmm(?)."

 

About the "Runnine out of Steam" thing; wouldnt that have more to do w/the Cyl.Head's Intake Port Entry & not the camshaft. If you went w/a Cyl.Head that has a larger Intake Port Entry Area (Sq.In's) the Peak Power would climb higher than that of an engine w/Cyl.Heads whose Intake Port Entry was smaller. Remember, the cyl.head ariflow goes supersonic when airflow reaches 57% of 1200 fps when combined w/the heat the engine produces.

 

You definately need a cyl.head that can breathe at those speeds-but the single most restrictive restrictiion is the Cyl.Head's Intake Port Entry X-sectional Area....atleast that is what Vizard would have us believe.

 

Early rise tomorrow (I mean this morning); I'm tired-going to bed. Good Night all.

 

I'm sure Pete will be counting Solid Cams tonight in his sleep & not Sheep!

 

Kevin,

(Yea,Still an Inliner)

 

[ July 26, 2001: Message edited by: Kevin Shasteen ]

[Mike C]

Hi Pete, considering the weight of a Z car, I think I would go with the larger cam to more closely approximate the power band of the L6. Especially since the smaller one is so close in size to the cam you have already. What type cylinder heads do you have? That would be my number one concern over changing cams. Airflow+power as I'm sure you know.It's interesting to hear ya'lls take on older cams. In my experience they have very slow ramp profiles and low lift numbers relative to new cams since they had to contend with much more poor spring material 40 years ago as well as cam/lifter manufacturing. Aftermarket cam manufacturers measure advertised duration at different lift points, and GM at .001. Comp measures their hydraulics at .006 lift and Crane theirs at .005. This means a given comp is actually a bigger cam than the same number in a Crane grind so watch out for any formulas that involve advertised duration. (The crane 266 compares to the Comp 260) Usually, mechanical cams are measured at a different lift point for advertised durations so that you can compare apples and oranges at .050 which basically lets you maximize the area under the curve when comparing to grinds. I have a comp 280sr (mechanical street roller 236/236@.050 and .550 lift) in my '69 Camaro. Power band is 2000-6500. This car has a 355 with 9.8 flat tops, ported 492 castings, 1 3/4" Heddmans, Victor Jr., Barry Grant stage III 750 (1040cfm didn't gain any speed or mph over the 700dp, boy it sure idled well and starts easy though) 4.10 gears and a super T-10 (2.62 first)let the 3500# car/driver combo run 12.70's at 110mph with a 2.0 short time on McCreary DOT tires. Makes more torque than you could ever use on the street as traction is the number one priority with the car. Let the clutch out at 1800 and it bogs slightly. Let it out at 2200 and it spins the tires halfway through second gear, let it out at 2000 and it hunkers down and goes. I used to have a 9.8 331 in the car with a Crane 284, 228@.050 .480 lift, and it pulled 6800 rpm in first with 4.56 and a TH350 with a stock set of 1.94 heads so your setup I would think would pull better than 7k which should make for a giddy driving experinces!

[pparaska]

Mike, I agree on the weight and gearing (3.70s, Tremec ratios, 26 inch tire) helping things and that the 268 Extreme solid being so close to the 270 Magnum solid. The latter is really mild - very sligth lope at 800 rpm. I think the 274 Extreme solid (flat) tappet cam will be perfect, even though some of the general and new rules of thumb shown above point to it being "too big" for my motor/car.

 

I did run all three cams mentioned above through Desktop Dyno on my motor. The difference between the XS268S-10 Extreme solid flat and the CS270S-10 Magnum solid flat I have now in the engine was very minor. Just a tad more high rpm torque and power(above 5500) - maybe 10 ft-lbs.

 

The XS274S-10 Extreme flat on the other hand gave up about 10 ft lbs at 2000 rpm but hit about the same torque peak (3500-4000 I believe), but the top end increased hp by like 30 hp. The hp peak moved up about 4-500 hp. It had a slightly (< 5 ft lb) lower torque peak, but the torque band was flatter and longer and therefore higher in the 5000+ range. I think this cam would be ideal for my uses.

 

I realize that computers can't match real life, but this is exactly the kind of thing simulations like Desktop dyno are good for - comparing combinations against each other. I really doubt the 400 ft lb peak that it shows for the 270 Magnum solid cam I have - I bet it'll be lower.

 

My heads are 461 double hump castings, with 2.02/1.60s. Only thing done to them was they were port matched to the intake gasket. With the bigger cam, I think I'll need to upgrade the springs, as the ones on there (Lunatis, close to the spring that Comp recommends for the smaller 268 and 270 cam) don't have the pressure at .500" lift that Comp recommends for the larger 274 Extreme Solid flat cam. I may just wait and drive the cam I have if it checks out o.k. (I expect it will).

 

I agree that the heads are more of a limiting factor now than the cam to making mid to high rpm torque and power. That upgrade will have to wait until the next salary plus-up and pending wifely approval . It'll be a while on that last one .

 

Cheers,

[Mike C]

I feel your pain! There is probably 50hp or so in your heads with the cam you have. More with the bigger stick. Clean up the bowls, unshroud the chamber if not factory 2.02 heads and work the exhaust ports as much as possible. Multiangle valve job and a back cut or 2 on the valve. Screw in studs are highly recommended if not there already. The book "How to build and Modify small block chevy cylinder heads", I think by Vizard, is a great place to start. He shows some modded 186's that flow 260+ cfm at .500 lift. You may start thinking about a VIctor Jr. intake as well which almost equals the 300-36 at lower speeds but significantly out performs it above 6000 rpm.

[pparaska]

I'm thinking of selling the 461s and just starting with a lighter (AL) better port and chamber design. AFR, Brodix, not sure which. Supposedly, a set of good 461s are sought after by the gold-chain to-the-numbers Vette guys. Hoping to cash in on that and get some lighter, new technology.

 

The 461 heads do have a 3 angle job, but just stock valves. 7/16" screw in studs and guide plates, Pro Magnum roller rockers (1.55:1).

 

Oh yeah, I bought Mike Kelly's used Victor Jr. - it's sitting in the garage. I plan on doing a side by side comparison with a G-tech or Home-dyno to see the differences between the 30-336 (that's the one I have - you're right) and the Vic Jr.

 

Do you have experience back-to-back with the 30-336 Holley dual plane and the Vic JR.?

[Mike C]

The 355 in my camaro was in a '78 Z/28 with a Comp 292 magnum hydraulic cam and a '69 Z/28 intake (almost identical to 300-36), 4.10 and a T-10. It ran 13.7's at about a C-note. Car was lightened so probably about same weight as my car. I changed to the street roller and Victor Jr. and ran 12.7's@110 I figure the cam was most of that, but I have had no low speed carburetion troubles with the single plane, and it will spin the tires at will on the street. Car Craft or somebody did a test recently on the single plane Victor Jr. vs. dual plane high rise and said maybe a 10 ft lb drop below 3000 but a 30 lb/ft 30 hp gain on the top if memory serves. Have you looked at the older 282s Comp mechanical cam? It looks like a nice grind that would be easier on cam and lifters as well as springs. I knda' like the single pattern grinds with a free flowing exhaust. Small blocks suffer intake woes but exhaust is pretty good for most part. Is the cam you are looking at one of the new tight lash mechanicals? Are you familiar with them and how quiet they are? I'm planning on a new motor for the Camaro with the cam I have and the 355 will get a hydraulic roller and find a new home between the rails of my '64 'vette, the mechanical roller is just to loud for what I hope to be a regular driver. I just need to win the lotto still!

[pparaska]

quote:

---

Originally posted by Mike C:

...Have you looked at the older 282s Comp mechanical cam? It looks like a nice grind that would be easier on cam and lifters as well as springs.

---

 

Dang, you're right. I'd looked at that before but now I see that it does need less spring. Probably not a ton of difference between the XS274S-10 and the CS282S-10 that you mentioned. It's 236/236@0.050" and .495/.495 lift (1.5:1 rockers). That would be just a lifter and cam purchase and change - a bit cheaper to do ($185 at Summit, for example).

 

quote:

---

Originally posted by Mike C:

I knda' like the single pattern grinds with a free flowing exhaust. Small blocks suffer intake woes but exhaust is pretty good for most part.

---

 

Good point. My exhaust is pretty free flowing. (My web page has the details.)

 

 

quote:

---

Originally posted by Mike C:

Is the cam you are looking at one of the new tight lash mechanicals? Are you familiar with them and how quiet they are?

---

 

Looks like it is - the Magnum series all use .022/.022 lash, and the Extreme use .015/.015 lash. No idea one noise. I personally like the noise and the lope. Guess I'm showing my age .

 

I'd love to see all you cars some time. Like most gear heads my age, the C2 vette and 69 Z/28 are favorites of mine . Is the vette a Bloomington Gold type numbers matching car, or the way I like it - a driver?

 

Oh yeah, a timing chain question: The Morse type chain is loose (1/2" total slop) after the run in. May some of that is due to main bearing wear, but doubtful it's much. I'm looking at the cloyes hex-adjust piece. $95 ain't cheap, but it'll probably last. Any ideas or opinions appreciated. I want it to last without stretching!