StrayDog

1300/5600 street driving range , 9.5 comp ratio , 308 rear gears, XE 262 looks just right.........have to limit lift due to block being milled, & larger valves 2.19 " intake & 1.72 roller rockes..Tourque is the goal ,thinking XE 262 or Crane power max 272 .....................anywon running either cam ??? :confused:


[Modified by StrayDog, 11:14 AM 5/30/2002]

SWCDuke

Why not just run the OEM L-36 cam? It's spot on for the rev range you want.

Duke

StrayDog

SWCDUKE.......THE L36 cam was designed in 1966, OR 1965 very old technowledgy... 214 intake...218 ex,461/480 lift , for a 10.25 comp ratio., computers now design cams ..the XE262 specs are 218 Intake 224 ex 504/510 lift , my 427 has Endlebrock alm heads with large swirl polished valves 2.19'' intake & 1.88" exhaust, that flow better than the stock heads.....35/50 or more hp & lots more tourque , just via a cam change........my engine , L36 CAM, revs strong to a 5600 redline & im looking for 6000 rpm........ just want to go with a cam that will work with my 9.5 comp ratio & the heafds noted above.......want more omfhhhhhhh :crazy:


[Modified by StrayDog, 7:05 PM 5/30/2002]


[Modified by StrayDog, 7:05 PM 5/30/2002]


[Modified by StrayDog, 7:07 PM 5/30/2002]

StrayDog

where are the hot rodders ????? anyone out there ?????? :eek: :crazy: HELP

396 RAT

where are the hot rodders ?????????

Were still in the stone age, running solids...... :lol:

Kid_Again

...good point, why are you sticking with the hydraulic cam?....go for a slightly milder grind and solids will give you the horsepower...though i would think you may want to consider how you want the torque curve to look

SWCDuke

You've just been sucked in by all the marketing hype. Cams are ground by the same machines today as back in the sixties. "Computer" designed is just marketing hype, and the aftermarket has less resources for cam design and development than GM did 35 years ago. (Think of the number of people and time invested by GM to design a dozen or so cams over ten years.)

I have not researched big blocks, but I have yet to find an aftermarket small block cam that makes as much power with equal bottom end torque as the '70 LT-1 cam. GM did their homework back then, and my computer simulations bear them out, but they did it the hard way - intuition from experience, the Optron, and a lot of dyno work. You get the picture when you take a lift-crank angle diagram and realize that the LT-1 lobes and lobe phasing look like no others you have ever seen.

Back in '69 one of my fellow ME grad students at the U. of Wisconsin had a '67 L-68 with a CR 4-speed and a 3.70 axle. (The standard L-71 drivetrain was a CR with a 3.55.) To this day it is one of the strongest accelerating cars I ever drove or rode in. The Z06 I had from the GM press fleet last year reminded me of it. The only car I ever drove that was DEFINITIELY quicker than Jim's '67 was a GT-40.

The L-68 is basically the same engine as the L-36 - same short block, cam, and heads. It just had the three carbs, and I think the extra ten rated horsepower was mostly in the eyes of the marketing guys. That engine had so much off idle torque, it would light the tires at 1500 in second gear. Of course, the redline bias-plys were junk, but that thing had awesome low end torque and would still pull strongly to about 5800.

Newer isn't always better, but GM doesn't spend their advertising budget trying to sell 35 year old parts, From my analyses and experience, it's tough to do better than the vintage GM parts, and computers don't design cams. They just do the arithmetic faster than a calculator or pencil and paper. It still takes a good engineer with a thorough understanding of high speed valve train dynamics and the airflow characteristics of the specific engine to design a good cam.

Another gem of wisdom I have learned is that as you improve airflow (heads, manifolding) you don't need as big a cam. Improving airflow with the same cam will increase top end power and the useable rev range with little or no effect on the bottom end. That's the key to having the broadest torque bandwidth. Big cams are just a (poor) bandaid for lousy heads and manifolds.

You can increase top end power and useable revs over your current setup, but you'll likely lose some bottom end in the deal, and you may not be satisfied with the outcome. Looking at the specs you quoted, both cams look pretty close, but the XE probably has more acceleration, so it achieves more lift and has more area under the lift-crank angle curve.

When you get down to cams that are this close in spec, your best bet is to invest the fifty to a hundred bucks for a PC engine simulation program. It's a lot easier to change cams on the computer than on the car. These programs give fairly accurate absolute results, and you can take the difference to the bank. The combination that makes the best torque curve on the computer will be the one that makes the best torque curve in the car if you model everything correctly.

Duke

P.S. The epilog on Jim's car: He finished up his grad work and while driving to his next duty station (He was active duty Air Force) the engine developed a serious problem and stranded him. He was down for a week while a new short block was installed under the five year 50K warranty. A hundred miles down the road the new short block seized up. The main bearings were too tight. I lost track of Jim in the mid-seventies, but I recall that he had sold the car by then. I sometimes wonder if it's still out there. It was a Maroon coupe, and I recall it had a black interior with A/C. There probably weren't too many with its particular option combination.



[Modified by SWCDuke, 9:09 PM 5/30/2002]

tapio

Nice post, Duke. However, I am anxious to see how the XE262 is performing in my rebuilt 327. I will share my experiences soon, when the engine will finally be reinstalled in the car.

Tapio


[Modified by tapio, 9:04 AM 5/31/2002]

Kid_Again

...ah, the relentless pursuit of data...seems to end threads in a satisfying manner........... :cheers:

...for clarity, and duke carefully characterized his position, it is now a matter of public record that the strongest puller he ever rode in was a 3x2...yup, that's a data point as far as i'm concerned....so, please trash your demons and double pumpers and do as i do - oval port tripower :eek:

achapman

Duke,

Great post, as usual very enlightning and indepth. If you would be so kind as to recommend some of the computer software that you have worked with, and please add your pros and cons.

Tks - :cheers:

TheOman

StrayDog

I have an XE268 in a small block and I am very pleased with it. As I recall the Comp numbering system, as the numbers went up the grinds got more aggressive. I am assuming that the XE262 for the BBC is equiv to the XE262 for the SBC but honestly I never checked the BBC specs or even the numbering for BBC cams from Comp.

I know the comparison is rather thin but here goes. Usually folks say that a bigger engine can be more tolerant of a bigger cam than a similar config small block. With the XE268 I am a-l-m-o-s-t temped to wish I went up another step. You have the displacement and I would consider at least an XE268 or equivalent BBC grind from Comp.

FWIW I have about 9.75 compression, Edelbrock heads and a stock Chevy L-79 intake. Also I have a 750 Vac secondary carb and MSD distrib and 6 Al Box.

StrayDog

THE OMAN.what rear gears & tranny..............my 66 big/block pulls hard to 5600 rpm , best et 13.7 @ 102 mph, not bad for 3,08 gears ....my driving range is 1300 / 5600 rpm, looking for cam, compatible with 9.5 comp ratio & 308 rear gears, also would like to go to 6000 at the drags...that would allow me to cross 1/4 mile in 3rd, also considering crane 272 , based upon their recient adds cstating 15 hp & more tourque in compariso to xe 262


[Modified by StrayDog, 11:57 AM 5/31/2002]

ghostrider20

What is wrong with the solid cam?
On the Desktop Dyno comparative hydraulics produce 10-20 less horse.

Duke advice with the desktop dyno is worth the money. I am planning a 283 for another formum member and it has been invaluable.

Mark

TheOman

I have a Richmond 5 Speed with the 3:27 low gear and 3:36 gears in the back. If I had a 3:08 rear or the Richmond 3:00 first I would like the car a little more but it really is OK as is. I run 2:15 70 -15 tires. Don't do any drag racing anymore. Busted tooooo many parts when I was a kid so I don't know how fast the car is is isn't.

I should have added the car lugs along in 5th (1 to 1 remember on the 5 speed) very nicely at engine speeds below 2000. I really am surprised at that but them is the facts. Oh yeah it is a 350 Cube engine not a 327. I suppose some of the low end smoothness is due to the MSD. I have seen definite imporovement in low end drivability via the MSD on my LS-6 car and although I never had the 350 cube combo running with anything but the MSD I just surmise that the MSD helps the SB just like it helped the BB.

SWCDuke

[QUOTE

...for clarity, and duke carefully characterized his position, it is now a matter of public record that the strongest puller he ever rode in was a 3x2...yup, that's a data point as far as i'm concerned....so, please trash your demons and double pumpers and do as i do - oval port tripower :eek: [/QUOTE]

Yeah, but remember I did say that I think the extra ten horsepower was in the marketing guys' imagination. I do have to say that the 3x2 had absolutely fantastic throttle response. Trips gets knocked a lot, but if the vacuum operated contol linkage is setup right, the response is superb. I recall in Corvette News that the 3x2 system was described as "very fuel injection like" in terms of throttle response.

The L-68 made more torque/power below about 3500 than the L-71, so the initial acceleration surge from low revs with the short gears was truly awesome.

Duke

SWCDuke

The two programs I use are DeskTop Dyno 2000 and Engine Analyser. They cost about 50 and 100 bucks respectively. DD2000 is easier to use for the novice, but EA has more flexible input that probably allows more accurate modeling of specific engine configurations.

Both show about the same top end power, but EA typically shows less peak and low end torque. With both programs, cam modeling is critical, and it's tough to model some factory cams because their timing data doesn't jibe with what the programs need for input. I modeled the factory mechanical lifter small block cams by taking lift-crank angle diagrams, so I could get the actual "seat to seat" timing numbers at .006" valve lift including the actual rocker geometry. Also, the 30-30 and LT-1 cams have asymmetrical lobes. The programs assume a symmetrical lobe. Most aftermarket cams have symmetrical lobes, and their "advertised duration" is at .006" valve lift at the specified rocker ratio. Real duration is a bit less because rocker ratios are typically lower. I wish the programs would allow the user to type in the lift-crank angle numbers as this would yield more accurate results.

The real value of these programs is not to predict peak power, but to COMPARE one configuration to another. Users should focus on the torque bandwidth, and shoot for at least 80 percent peak torque at 2000 revs for a good street high performance engine. I don't concern myself with top end power, but concentrate on the torque bandwidth, and I will glady sacrifice a few horsepower at the top end for an equal torque gain at 2000.

A well configured smallblock can make one HP per CID at the top end and still make the 80 percent torque bogey at 2000. With some head work the factory SHP engines are very strong by my criteria except for those equipped with the 30-30 cam. It's a real torque killer. The LT-1 or L-79 cams are the way to go.

Duke

achapman

Duke,

Thanks for the input on the software programs.... will check them out... :)

StrayDog

SWCDUKE..........Could you please :blueangel: , use your program & compare the following cams , on a 433 big block, 9.5 compression,stock chevy corvette ex manifolds, no headers & factory 2 1/2" side exhaust ,Endlebrock performer alum heads , 780 holley, alum high rise,1.72 roller rockers, MSD, distributer Ignition system ,,,,12 deg initial 36 deg total @ 2800 rpm,,,,,#1,Comp cam XE 262 , 218/224 dur @ .050,,,,504/510 Lift, 110 Deg sep, ,,,#2 Comp cam 268 high energy 218/218, deg,,,.485 /.485 lift , 110 deg sep & #3 Crane power max H-272.. 216/228 Dur ...454/.480 lift...112 deg sep...my driving range is 1300/5600 rpm , 4 speed wide ratio 308 rear gears , want fat tourque curve...THANKS...THE dog :) :seeya :flag

SWCDuke

Ever hear the story about the man and the fish: If you give a man a fish he eats for a day. If you teach a man to fish, he eats for a lifetime!

I have to place some limits on doing homework for others. Buy one of the PC engine simulation programs and run cams until you find the one that gives you the torque curve you want. Suggest DD2000 for starters. The fifty bucks will pay for itself by allowing you to select the right cam if you're realistic about your requirements, and you'll gain a lot of insight into how engines respond to changes in valve timing and other parameters.

Duke

Kid_Again

...straydog......give the software a try, it is very easy to use, and as was noted, the power in the software is the ability to run comparisons...it also allows you to model changes in stepwise fashion and it will draw a 3D map of the results...very :cool: ....you will need a PII processor if you do that kind of stuff or pack a lunch because it will take all day.......

...the first time i used this software, i loaded in on my laptop for a trip to europe...farted with that thing for the entire trip, no sleep and crashed at my first meeting :lol: