What factors should one include when choosing a cam if you have an overdrive trans? I'm curious to know if one should keep duration(.050 or adv.?) under a certain guideline so that the engine does not bog down in overdrive or run terribly inefficently.

Right now I have a 355 with Home-Ported World S/R Heads(1.94/1.5 valves), Roller Rockers, 650 DP, MSD Street Dist. with Vacuum advance, Dart Sportsman Dual Plane Intake, 9.0 Compression, and currently a 203/212@.050 cam. This is all backed up by a Tremec TKO 5-speed and 3.42 gears. This all puts me in around 1,900rpms when I am on the highway.

I want to upgrade the cam to something bigger for the dragstrip but I don't want the low-end to go completly away from me and have terrible car on the highway. What duration #s should I not go above when choosing a cam? I want something that is both gonna make my car powerful and fairly fuel efficent. I have been looking at the Comp. xs268(230/236@.050 with .488/.501 Lift) would that be too much?(Remmember it is a solid so it will act 6-8 degrees smaller then a hydraulic) Any help or comments would be appreciated. What are you guys with overdrives running for cams?

PS- I plugged the cam I have now into dyno2000 and compared it to the xs268 with a half point upping of the compression(to 9.5) which I can do with a gasket change and the results show that there is almost no low-end difference @2000rpms to the much smaller hydraulic...this doesn't seem right? Do solids give that much more torque down low?

I used an xe268 on mine (the hydraulic) on my 350+.060 with 3.36 gears and a lockup 2004r. I never had any problems in OD. Plus, your combo looks like it has more torque than my old one (which is now in engine heaven). I wouldn't worry about it. graemlins/beers.gif

My neighbor runs an Erson 990AH cam {268/268@.050} in his chevy II and the rear end has 4.30 {i think thats the ratio for a ford 9"} gears and a richmond 6 speed and it runs fine on the highway, granted he's geared deaper but i think youde be fine.

May not be of any help, but I run a 427, UD solid 288/296 F10 (@.050 255/263) in my 70 and find that if I am in OD lockup around 2000 it will buck and complain under light throttle. I run 2500 at 70 or so in OD and run just fine. Around town I leave it out of OD until 55 or so.

I have a 355 spec'd out almost the same as yours in a 56 chevy w/ a comp 270Magnum cam and it works fine w/ a 700R4 200 stall converter and 3.55 rear end gears. 60 mph is 1900 RPM in OD. It took a little work with the advance curve but now that its dialed in it will pull from 14-1500 rpm in OD w/ the lockup on. I usually turn the lockup off at that rpm, but sometime forget and it handles it ok. Since you're looking at a solid, look at a Crower 00320 grind. Its got 230/236 @ .050" on a 112 lobe separation which should help the bottom end a little. If I had it to do over again, that is what I would run in my 355.

My unprofessional, but educated guess is that you'll be OK at the 230/236 @.050" level. It would help a bit if you could have it done on a 112 LSA, and most assuredly phase the cam in slightly advanced.

Also bear in mind, that you can loosen up the lash a bit for daily driving, and then cinch it down 2-3 thou for the strip. A degree of tunability hyd's don't have.

Its close. The comparos here with bigger cams and 4.30s are pretty meaningless to you. My 439 with 243/251 on a 110 would not enjoy 1900 rpms. 2300 is more like it for a smooth engine. But to compare it to a 355 is difficult for me.

If friedguy had no issues with the hyd 268, you should be fine.

Wonder how much more $$ it is for Comp to do one on a 112 LSa for you. That'd be some added insurance.

Imho, pick the cam to suit your cruise rpm in OD IF THAT'S WHAT YOU WANT b/c otherwise your motor will be still "on the cam" down low, (as I say it), b/c a bigger cam will be out of the OD cruise range at a lower rpm and will buck under load chugging around town..

Outta OD, it will be fine though so which do you want???

pdq67

Thanks for all the help guys.

Fried_Guy and Wheels68- What kind of highway mpg are you guys getting with your combos?

I really don't know... I never checked.

And I couldn't tell you now either... put it this way... 8.0 DCR and a .065" quench is a bad idea graemlins/clonk.gif

Originally posted by Fried_Guy:
I really don't know... I never checked.

And I couldn't tell you now either... put it this way... 8.0 DCR and a .065" quench is a bad idea graemlins/clonk.gif hows 7.9-8.0 DCR with .70-.80 quench sound?!....still running strong...even ran it on 87 before and it did pretty good.

I get 16-18mpg on the highway with my combination depending on how fast I go and the type of road. Drove it to Oregon last year and averaged 16mpg but that was doing 80mph (2500 rpm) on I-5 through CA and 65-70 in the hills of Oregon. Combo is a 355 9.2:1 compression, pocket ported s/r torquers;.043" quench; Comp 270M cam; Q-jet carb w/ 700R4, 2200 stall, 3.55 gears and 27.1 in tall tire. This is in a 56 Chevy which has the aerodynamics of a brick. My DCR is pretty low at 7.4 but it runs good on 87 octane in the 100 deg summer heat here. I built it as a driver and didn't want to pay for premium. Regardless of the low DCR it seems to run OK. Right now it runs 14.4 in the 1/4 with an open rear axle and 2.3-2.5 sec 60 ft. Hopefully, a posi and some decent tires in the near future will help improve the time. You will probably do better with an 8.0 DCR and premium gas but you need to get your quench height down from .70 -.80 to run that DCR.

Originally posted by Wheels68:
You will probably do better with an 8.0 DCR and premium gas but you need to get your quench height down from .70 -.80 to run that DCR. I didn't know but thats what I had been running for the past 5 years and 20K miles! I bought this car when I was 16, long before I knew anything about DCR and the motor was already in it from previous owner(he had shop put it together). I ran the numbers for the 2 valve relief pistons(had reciepts), when I had heads off I used a cheap mans cc kit, and also checked deck height(damn thing was .030-.036)...ran all the numbers and I am running 9.0 Compression with a 246/262(might be 268) Pure Energy Comp cam. Don't ask me how it is not pinging but there is absolutely no sign what so ever of detonation, and like I said I have ran it on 87 before when I was young and stupid and didn't know better!

When I put the new cam in I'm gonna use a steel shim gasket to give me .045-.050 quench and about 9.5 CR. As mine runs now with the wimpy near stock cam it has a best of 14.3@96.5mph w/ 2.1 60ft and gets 18mpg highway with a double pumper and no vacuum advance.....my car pretty much breaks all the rules apparently!