smthnpls

I'm in the process of building a new motor for my 79. I'm putting flattop pistons 30 over. using stock 1.94/1.50 heads with z28 springs. I'm considering the Comp cams 268H. I'm going to keep the orig gears in the rear and may put in a 2000rpm stall converter. I still want a driver, not lose my vacuum, but love the lope sound of a mean cam. I also want the best response off the line to blow away these pesky 5.0 Mustangs. Any ideas? :chevy :cool:

ORVette

which rear gears?

The_Dude

I have a 268H. It's a little soft on the bottom, but not bad. I'm sure it helps that I have a manual trans, but I also have 3.08 gears. Vacuum isn't a problem at all and the lope sounds great. :cool:

Troy, did you get that big block yet? :cheers:


[Modified by The_Dude, 11:02 AM 9/19/2002]

gkull

I'm going through the same thing!:)
http://forums.corvetteforum.com/zerothread?id=391101

I ran a bunch of simulations with the XE262 &268 &274 But I still like the results of other Crane cams that I had in my vette in the past. They are the Powermax 272 and 278 with 1.6 roller tip rockers

Jvette73

I wiped a lobe on my XE268 and downsized to the XE262. I like the 262 better. Better off the line and smoother idle for the daily driver. With the 268 it was uncomfortable idling in gear with the auto tranny. I would have to push it into neutral till the light changed. The 262 is much more comfortable idleing in gear. Even with 2004r/3.90 it was difficult to spin a little tire with the 268. The 262 will spin the wheels a little if you want it to. Thats my expierence with the two anyhow. The 262 still has a noticable idle and sounds plenty mean thru the 2 chamber flowmasters when on it.

redwingvette

Call crane and ask. I would be curious to here what there "experts" would say (386) 258-6174
Information that is needed to make the right chioce is:
Tire size
Rear gear ratio
Type Transmission (if auto-What Torque converter)

Without that information it is hard to say what cam to use.

Ryan77

I run the 268XE from Comp Cams, but if you want a little more off-idle power, go with the 262.


[Modified by Ryan77, 6:29 PM 9/19/2002]

smthnpls

well..it seems like the 268 might be over camming (is that a word?). I do want the quicker response off of the line, so it sounds like the 262 maybe what I'm after. Thanks for the experts phone #..I think I'll call them to see what they think.. :cool:

Vetterodder

Your original post refered to the 268H, which is a different (and milder) cam than the XE268H, and I suspect that the two are being confused. The 268H is 218º/218º @ .050", 268º total, .454" lift. The XE268H is 224º/230º, 268º/230º total, .477"/.480" lift. The 268H falls in between the XE256 and the XE262. While any of those cams will work with your stock converter, all of them (especially the bigger ones) would work even better with more stall than stock.

rpounds

You said you are using stock heads. Would that be the 882 castings with 76cc chambers? Those heads do not flow well at all. I doubt that you will be able to take full advantage of a cam like the 268H. The 262 is a better fit, especially with your differential ratio. Also, check out the Summit 1101 or 1102. If you have access, run them all on Desktop Dyno. You might be surprised.

If you don't have access to DD, post some of your vital statistics and I will run the numbers for you.

Ron

Justin79-L-82

I have the XE262 with stock l-82 heads but i had some head work done to them. And they are 2.02/1.60 so they are a little bigger. I'm really happy with the my cam


[Modified by Justin79-L-82, 2:23 AM 9/20/2002]

smthnpls

yes..it was being confused.. I was refering to the high energy 268H, not the extreme energy cam. I think I'll be putting in a 2000rpm stall converter..how will that run? The heads are 71-72 with a cast #3973487X which is supposed to be a 75cc chamber. I was told that these older heads were better to use. :crazy:

Jvette73

if you really like off line launch I would recomend a 2500stall vert. It would work good with any of the cams mentioned. Its definatly needed with the XE268, even though the manufacturer says the 268 is ok for stock vert. :bs

1LE

I ran the 270 H comp cam in my 350 with a B&M Holeshot 2000 converter. Stock heads with 1.94 valves, and headers. Up top I had a Holly double pumper carb. Don't forget a tranny cooler. It should be used when ever you go to a higher stall converter

gkull

quote: I run the 268XE from Comp Cams, but if you want a little more off-idle power, go with the 262.

After running all kinds of simulations. I went back and reread some articles about dynamic compression ratios. Which is easily measured by cranking pressure. They state that 185 cranking psi is about the tops for 91 octane pump gas.

One of the tested motors with an XE268 had only 140 or so cranking psi. Not any get up and go off the bottom and poor 1/4 mile times even though it had a long list of hot parts and headers. The problem was it was a low compression motor to start with. It was something like 9.4

So to keep cranking pressures up in a less than 10:1 motor you need cams with very little over lap. 112 - 114 lobe centers. This would be like the crane 272. If you have over 10:1 or even 10.7:1 something like the XE268, Summit K1105 or crane 278 would be the best choices.

Comp cams is out there to make money and people like the sound of a car with a lumpy cam. Well lumpy cams just don't always run that great in the real world. So my new 355 ci is going to have 10.5 or so compression and a Summit k1105 with edelbrock E-tech 200cc & 64 cc chambers. Weiand Stealth intake 650 speed demon carb with vacuum secondaries 1 5/8th headman headers. It's going in a 78 with 3.36 gears and an shift kitted TH350 TCI 2000 stall with TCI flex plate

redwingvette

I am getting ready to put Edelbrock Performer RPM heads on which will put me a little above 10:1 comp. Crane's "expert" suggested I change my cam to their H-272. It has alittle more lift then the cam I am using now (454/480 vs 440/454). The one I have is suppose to be better for low end torque.

GTR1999

Interesting, I'm building a 9:1 350 w/ WPTorquer 67cc heads, performer,Q-Jet. Comp cams told me to go with the 268XE cam not the 262xe or 270H. I called twice and spoke to 2 different guys and they said the same thing. I called Crane and they said to use the 272 energy cam over the Powermax 272? So now you have me second guessing the part selection? I'm running a M-20 with 373's so maybe that's the difference?
gary

Jvette73

gtr1999, with 9to1 I would definatly go with the 262. im using flatop stock pistins with 64cc heads milled 12 thousandths. i figure that puts me to 10.5 to 1. I ran the 268 and it worked good but was a slight lug on the very bottom end. The 268 didnt really come in till about 3000rpm. When I switched to the 262 it was much more even throughout the band. im runnin 3.90 with 2004r that has a 2.74 1st. So my starting ratio is even lower than yours. And still the 268 would not break the tire. 235/60-15 The 262 will break the tire slightly now. The 268 did have slightly better power above 5000rpm.

Ryan77

gkull--- I know what mean about no off idle power with the 268XE and low compression, but my motor will be running 10:1 compression when I stroke it to a 383 with Trick Flow 64cc heads. Hopefully it will be better then or I'll go down to something like the 262. What do you think?

gkull

Ryan77 - when you go to 383 your talking about a whole new world of power. I was worried about over caming. but i wanted performance. so i went a custom grind solid roller 240/248 @.050 .635/644 and it runs great. I have 13-14 inches of vac @900 rpm idle and originally had my rev limeter set at 7500 rpm.

with my 4.11 rearend and 3500 stall I can smoke my 315/35/17 tires for most of a 1/8th mile drag strip.

In my 79 L-82 I first put in a Crane 272 power max with about 10.7 C/R and it had ping problems with my fully ported 186 casting iron heads and 1.6 roller tips. So i up the cam to Crane power max 278 and it got rid of the need for octane boosters at sea level. Then i went to big heads with 2.055/1.6 and it really ran well. That is untill it popped. So i used my Dart iron eagle 230 cc on a solid roller motor 355ci.

At some point they become unsteetable.