The Stovebolt Site Forums The Shop Area Engine Shop Lets talk cams!

Truck has been parked for the season but i want to get a head start for next season. Im interested in changing out the stock cam in my 235 that only has 1200 miles on it. Currently the pull is nice from the 1500ish to 2000 ish rpm area but drops off after that like crazy. I have searched this site and other and have found lots of great info however i cant get consistent nor detailed info about the rpm ranges affected by different cams.

I was thinking about going with what Patric calls a 3/4 mild 254 cam. After talking to him the suggested going with the 3/4 264 cam that is more aggressive. Both of these cams already are more aggressive than the stock 261 cam that people use. My truck is for street use and currently has dual intake, headers, HEI and a 3 speed and overall is geared short. Compression is holding nice at an average of 143psi per cylinder. I will change the rear end ratio next spring to help it out and then possibly install a t-5 trans later.

Can anyone comment or provide more detail on the affected rpm ranges for the different cams? I dont care one bit about sound or having it idle a bit rough as long as its still drivable in the city. Patric never had any real number answers but swears i should go with the 3/4 264 one as it would pull hard thru the entire rpm range. Can anyone back that up?

I have no cam spec's, but I can tell you that if you do anything which adds to higher RPM power, will take away from lower RPMs.
235's are not really high RPM engines. I would save your money for that T5 conversion.

If you are set on putting in a different cam put the 261 cam in. That is the cam that the Corvette motors used with the tri-power and split exhaust. And as Dave mentions, but your money towards the T-5 and embrace the grunt of the 235.

I have no experience with either cam you mention, but I'm going to assume the "254" and "264" are advertised duration. Another specification or two I'd be interested in seeing are total valve lift, and something called "lobe centerline". Duration, lift, and centerline are all important to know when figuring where a cam starts producing usable power and how much low-end performance has to be sacrificed to get a gain at the top end. "There's no free lunch" is a phrase that definitely applies here. To take advantage of a higher lift and longer duration cam, compression must be increased, carburetion gets bigger, valves and ports must be enlarged, exhaust restriction needs to be reduced, and all of it has to work together. Once all that is done, low end performance will be much less than what a stock engine has. You will give away low speed torque to gain horsepower at high RPM.

Pay your money and take your choice, but in my opinion, the 254 cam would be as far as I'd go for a street-driven engine, considering the other specifications you've noted.
Jerry

Stock 261/Corvette cam: I = 244, E = 244, lift .414
Patrick's "3/4 mild": I = 245, E = 256, lift .425
Patrick's "3/4": I = 252, E = 264, lift .436
Patrick's "3/4 rumpy": I = 277, E = 270, lift .436

Go with the 245/256 cam unless you're willing to make some major modifications to ports and mill the head or something else to raise the compression. I think you've already got more carburetion and exhaust than you'll ever need. BTW, that's probably why you've got the flat spot in the first place.
Jerry

Lincoln, do you think it is not Scavaging the exhaust like it should due to too large of diameter?

He insisted on over-carbureting the engine. Nothing short of putting one carb back on it is going to help much, but modifying the engine to come close to having a use for the carbs might help a little. I've seen this scenario play out many times since a friend back in high school in the early 1960's put 3 Stromberg 97's on a bone-stock 216 in a 51 Chevy sedan. The results are always the same.

Let me retract the idea of installing a T5 transmission for this thread and conversation. Yes it will be a great install allowing me to better stay within a tighter rpm range between shifts but due to the simplicity and cost of just tossing in a new rear end ratio that will better my top speed to a point and still make it user friendly in first gear.

Not saying im trying to get the torque curve lower than what it has now but something that will possibly open up my torque curve. With the possible new ratio in the rear end I would still like to try and retain the low end for first gear starts.

A buddy I met from this site this summer has a nice 235 done up with if i recall correctly a 261 cam installed. I already sent him emails asking questions but im still trying to gather other opinions from people. His truck did nothing but pull. Granted first took a bit of slipping to get going by the feel of it but all of first it pulled hard, all of second pulled hard and all of third it pulled. It never actually felt like it flattened at all.

He never had a rpm gauge installed so i did not know exactly where it sat for a rpm range during the drive but after he provided me his ratios and tire sizes i can see how the engine swings at road speeds with gearing calculators thus helping me out.

I should post up my gearing charts and basic speeds reached around where I live to better show you guys where I might want to improve my curve. 90% of my driving is a mix between 30mph to 50mph. At this moment highway seeds are not too much of a concern, thats when i will look into a t5 for the od.

I have a Howards M4F cam that I got from Patricks 12 yrs. ago. It's in a 261 60 over engine. It pulls good in all gears. Don't know how that cam compares to what Patrick is selling now, but ask Him, I'm sure he will give you an answer.

I have a Howards M4F cam that I got from Patricks 12 yrs. ago. It's in a 261 60 over engine. It pulls good in all gears. Don't know how that cam compares to what Patrick is selling now, but ask Him, I'm sure he will give you an answer.

I'm building a 235 to power my weekend warrior and I decided on the 3/4 264 cam.
I'm hoping I'll know by spring how it works out.

Dave

Did you flip a coin to make that decision or was it based on particular information? Im trying to find more detailed info but always come up with the same responses in posts "i got cam xxx and I like it" or "i would go with cam xxx if i were to get one"

But why? lol

Choosing a camshaft should be a simple process, but people insist on making it difficult. Decide what RPM range you want the engine to have its best performance, and choose a cam, carburetion, exhaust, and gear ratio to make the engine do its best there.

Low-RPM torque- - - -short duration, high lift, with moderate sized valves and ports and a relatively small-diameter exhaust system. calibrate the distributor to get its centrifugal timing advance in a slow, steady curve that maxes out about 2200-2500 RPM.

Medium-range horsepower increase with a slight loss of low end torque- - - - -Increase valve and port size slightly, open up the exhaust a little, and choose a cam somewhere in the 250-265 degree duration range. DO NOT OVERDO IT ON CARBURETION! You'll lose midrange torque in huge quantities!

High RPM horsepower- - - -Increase compression as much as possible to offset the compression loss caused by a long-duration camshaft. Cam duration needs to be in the 270-290 degree range, depending on combustion chamber design and volumetric efficiency. Big valves and open ports would help, but their effect is wasted on a stovebolt engine. Stovebolt engine head design sucks like a Hoover upright, so a radical cam is a total waste of effort. Domed pistons and/or radical head milling helps compression pressure, but not breathing. Multiple carburetors and big exhaust pipes are also only moderately effective due to the lousy breathing capabilities of the head design. Low end torque goes away almost completely due to reversion of exhaust gas into the intake at low RPM. At this point you've got an engine that only does one thing- - - -make pretty good horsepower at full throttle- - -high RPM. It has no use whatsoever on a street-driven vehicle.

The more radical a cam grind gets, the less suitable the engine is for street operation. There's no free lunch.
Jerry

You think it would be simple. I am worried about getting something too aggressive and loosing my bottom end. With all the stop and go and slow driving i do i want to keep it low buy try to gain a bit if possible. I was set on the stock 261 cam at first but then thought that possibly having some of the other mods done it would better be suited for the mild grind.

Aren't you planning to go with two carbs? Anything else you do won't make much difference- - - -the midrange performance is gone already.
Jerry

Already have the dual carbs on it. So essentially I'm now just wasting money trying to do anything I take it.

It will still look cool.:)

It depends on the dual carbs, and maybe the exhaust system?

If you can alter the rate of opening of the secondary barrels to kick in with the last few degrees of throttle shaft movement, and then more or less dump wide open for increased acceleration when you really need full throttle, the advantages Carb King mentions about having better fuel distribution from the duals will come into play. You would need to make some pretty radical changes in the geometry of the secondary throttle linkage to accomplish that. The flat spot/bogging down problem you're experiencing is a classic example of too much too soon where throttle opening is concerned. A more radical cam will only make that problem more obvious unless you're geared so low the engine is screaming all the time.
Jerry

What size exhaust are you running wolf?

Fenton headers with 2.25" pipes with delta 50's.

Ouch! Those pipes could ventilate a medium-sized Kentucky coal mine! 1 3/4" pipes would be a much better choice to keep the velocity up coming from the manifolds to help scavenge the cylinders. Your intake and exhaust system is designed for a much bigger, freer-breathing engine than the stovebolt can ever be. Try connecting a couple of 1/2" chains capable of pulling 20 tons with a short length of 2-ton capacity 1/4" chain, and you'll have approximately the same situation.
Jerry

so other than the poor selection of carbs the exhaust is really hurting me. Its no big deal as making a new set from 1.75" will be easy. I can just drop it and build it next to the other set.

This situation is not too uncommon, especially when the idea that "bigger is better" takes over. Engine performance has to be looked at from a whole system concept, from air cleaner to tailpipe, and all the components need to work together. The whole idea is to keep everything flowing along smoothly without any "slow down" areas or choke points. One sneaky little trick to improve the breathing a little bit on a stovebolt cylinder head is to install 1.6" exhaust valves which happen to be readily available as hotrod parts for small block V8's, and use 1.94" intakes that were used on early Powerglide-equipped 235's. Pocket porting the area right under the valves will help with gas flow a little, but the basic design of the head gets you to a point of diminishing return for a lot of expensive work pretty quickly. Even with bigger valves and some pretty trick porting, the head design is still the choke point that just can't be effectively eliminated. Matching the carb(s) and exhaust to the flow capability of the head will result in a smoother-running overall engine with fewer RPM points where the performance drops off due to mismatches. It's a learning curve that some folks just have to experience for themselves instead of listening to some of us who discovered all these things 50 years ago.

Along the same line of reasoning, every new generation also thinks they invented sex, drugs, and rock and roll!
Jerry

Seems like these motors are doomed due to head design no matter what cam ya choose. 7:1 compression is achievable after a bowl of chili. Maybe with the dual carbs you get a better a/f ratio to more cylinders. darn wikipedia, depressing..

The guys with the 270 GMC's on the 1/4 mile dirt tracks used to give the flathead Ford V8's a run for their money back in the early 1950's when I started watching the family-owned 34 Ford 3 window coupe run around in circles. The Chevy engine cars didn't stand a chance. Dad ran a bored and stroked "239" flathead V8 at almost 300 cubic inches, with 11.25:1 compression and an alcohol/Hydrogen Peroxide fuel mix that would eat the bottom out of the float bowl if the carb was not run dry between races. The favorite saying back then was "Build 'em little, wind 'em tight, and get the chemicals just right!" BTW- - - -that engine outran a bunch of competitors running multiple carbs with ONE big Zenith 2-barrel!
Jerry

What about Lsa on the cam? Would that improve the sequence at all Lincoln? Limited revs and all, what are the specs of Patrics 3/4?

I've always been told performance is in the combination of the parts not a particular part. I chose a cam based on gearing, tire diameter and what rpm I spend a majority of my time at. I also run an auto trans so that was a factor.

Moving the lobe centers closer together might help build a little more torque- - - -I've done that on a few round trackers on a "short" 1/4 mile (measured around the fence, not the infield) to get a better holeshot off the turns. Advancing the cam a few degrees also builds low end torque and drops a few HP on the top end. For all practical purposes, the engines most of us are building for daily drivers or weekend cruisers are going to have maybe 125 HP or so, and the RPM is going to top out somewhere in the 3K range. The horsepower addicts are going to stuff a 500 cubic inch big block in there some way, and between the two of us, we can pass everything on the road. You pass all the cars, and I'll pass all the gas stations!
LOL!
Jerry

I've read that going too big on the rocker ratio causes valve overlap, loss of performance. 1.6 seems to be the magic number. I've seen radical gains in valve lash settings. I've also lost 1000rpm by running too small of air filter. I know i have a h.o. Motor but the principals still apply. Wolf I assume you have the factory 3:55 rearend and you said 3 speed earlier. What size tire are you running?

Thanks for all the input guys. A quick overview of my current setup. Just rebuilt 1955 235ci bored over .040, 848 head, dual Edelbrock water heated intake, dual weber/carter 32 carbs with auto choke, Hei distributor, Fenton headers, 2.25" separate exhaust runs each with Flowmaster Delta 50's, 3 speed trans (not stock), 2001 s-10 4x4 rear with 3.73 ratio, tires with overall diameter of 25". Truck pulls nice when in the 1500-2200ish area. was hoping that i can possibly get a cam to possibly compliment the few things i added like the headers, intake and carbs.

After sorting out my carb issues a while back i think it goes quite well now but i cant stop at that lol. Posted a video of it going from 0-70 a while back and i think its not half bad BUT I WANT BETTER! Granted i never drive it full out like that but still it is fun to blast it like that.

She gets off the line quite nice now but Im in third in no time. As mentioned above a few posts back i want to just slip in a new rear ratio prob around 3.23 or 3.08 and that should make my life easier. I don't mind a bit of slipping to get it going.

oh and the exhaust is connected with a cross pipe or "H" pipe about 5 feet away from the headers.

Taller tires would be the cheapest route

What 3 speed do yo have? I have a 66 Saginaw 3 speed in my 50. Nice synchronized transmission. I have a 3.08 12 bolt rear end. I can go 70+ MPH all day long, but it is a real dog in first gear under a load on an incline. Clutch really slips. I am going to switch to a T-5 and a 3.73 rear end. I can then pull stumps and drive 70 MPH (not at the same time of course). I also like the idea of extra gears to keep the engine within its optimal power band more often.
Carl

I too like the T5. No need to slip the clutch. I'm shifting to 2nd almost immediately. Putt in 3rd around town. That reminds me, I have to get the Saginaw 4 speed and 3 speed overdrive in the Sell forum. I thought I might go back to one of them but I know I won't.

Dennis

Im all over the t5 but looking at a faster, cheaper fix for now a $180 rear kit is looking good. The t5 would have a cost along with having the drive shaft cut and rebalanced, possible adapter plate if i choose not to hack and slash the shaft, the time to do all the work. I rather not do the work from below but wait till im ready to do some work that warrants the cab to come off so i can work from above.

I rather not do larger tires as they are all new as it is and i dont care for the larger in the rear look. Have them all the same so i can rotate without issues. A new set of 4 would cost way over $180 anyways.

lol funny I have the same 3 speed trans you have.

I'd do a little more leg work. If your going to do the ring and pinion swap your going to have more invested than just the cost of a ring and pinion. Your going to need a pinion seal, crush sleeve, pinion nut, probably some shims, gasket and gear lube. Not saying your right or wrong but look at the whole picture and then do some more homework about a T-5 swap. Sometimes the difference in cost is less than you think at first. A little more planning and research goes farther than digging in fast....

Got a T5 to install and just thinking about what exact rear ratio to get. Still in serious thought about this cam thing. Was talking to Delta cams directly today and they said hands down to go with the 264 cam with all the current engine additions I have installed.

Delta said they have the following.

254 grind = smooth idle with good low to mid torque
264 grind = slight rumpy idle with good low to mid torque
E2 278 grind = racing setups or vintage drag only
The bulldog = 254 grind on the intake side with a 264 grind best suited for carb applications that use one (1) progressive 2 barrel on the stock intake. same cam tom L sells as they make it for him.

Picked up the phone right after and called Patrick he also said hands down the 264 grind is the way to go if i can tolerate a slight rump in the idle.

With the T5 you can keep the 3.73 gear. There's lots of gear/tire/mph/rpm calcs out there. Maybe a 3.42 rear. Just my opinion. As for the cam, I'm staying out of this one.

keeping the 3.73 ratio i have and the t5 ratios i have I'm still short with my smaller size tires.

oh come on.....chip in with the goodies you have to say about cams. I am all ears!!!!! chicken................?