Inliners International Forums General Discussion Engines cammin up

so I got this cam grinder who says he can regrind my cam to whatever I pretty much want for my 261, so question being what is stock duration, and lift/ centerline lobe seperation? The next being is that I want a good performance cam like a clifford 264, or patricks rumpy cam, f-298? or langdons bulldog specs? does anyone know what the specs on what these cams are, so that I can tell the grinder what I need, or can any of you tell me what kind of specs I could use, so that i can get some good grunt out of this thing? I would preferably like a good choppy type of idle but would like to cruise in od at 2000-ish comfortably, its in a 56 chevy truck half ton, will have a new and rebuilt later style 12 bolt chevy with 3.40 gears, headders and a couple of webers, and maybe a little minimal porting and polishing, but nothing too crazy on the head, and should be bored .060 or .080, totaling 269-271 cubic inches, any help guys????

Well, since nobody else has answered this, I guess I'll throw my two cents' worth in. For a street cam that you probably aren't going to race with a whole lot, aim for something around 260 degrees advertised duration, not much (if any) over .500" lift, and 110 degrees lobe separation. That should give you good low and midrange grunt, and a slight lope to the idle. The more duration the cam has, the rougher the idle, and the higher in the rpm band the max horsepower comes in at. Check Comp Cams catalog. They have several cams and kits for the later Chevy engines, but the specs should give you an idea what to have your cam grinder duplicate.

good good, glad to get a hit finally, the grinder is waitjing on me, yeah that is about what I figured except for the lift part, I was figuring about .450 or .410-ish, I know that the 250 and 292 type like the higher lift cam like .510 and all but I dont think that would work with the 261 too well, and if I go with like .450-.470-ish do I have to worry about intake valve to piston clearence? I guess this means that for the most part that I should deck the head and block just enough to clean it up ehh, being that I'll be looking at 9:1 or 9.5:1 anyway, this should be good for a street motor, good preasure without higher fuel rating needed right? so would a 264 advertised duration be pretty good, I know that clifford sells that one and its pretty popular for the hydraulic, but mine is mechanical, should I go to like 268? Does anyone know if its true that higehr lift and shorter duration lends itself more to torque or not? is this a myth? so I just take the lift that i want at the valve and devide it by 1.5 to get the right cam lift right? so .450 would be like .300 at the cam right? do I need to know what lift at .050 or is that something he should know based on overall lift and duration? Is hydraulic better for torque/HP, and if so, what is required to convert to hydraulic?

When ever you go from a stock cam to a aftermarket cam( meaning lifts) and you have a flat top piston Is it always Safe to check the valve to piston clearances. I don't know much at all about you motor, If they came with dished pistons or flat tops.So when
ever you deck the block Or mill the head it is always to play things safe Especaily when it comes to a flat top Or Domed piston.
Just my 2cents.

Hi again. The lift and duration theory is definitely NOT a myth. As a very rough rule of thumb, with pretty much any cam, lift gives your torque and duration gives you horsepower. A while back, I ran a Sig Erson RV cam in a 194. The can specs were 256 degrees advertised duration and .487" lift, and with headres and a 2-barrel carb, it put out LOTS of torque for a motor that size. I don't think Erson offers that cam now, but the Comp Cams 260H is pretty similar, and I think your 264 would work fine. The only difference between solid and hydraulic lifters (aside from the mechanical construction) is that you don't need to do valve adjustments on a hydraulic lifter once it's been set, but you DO need to adjust solids periodically. What determines torque and horsepower is the cam lift and duration. It has nothing to do with the type of valve lifter used. If you have 1.5 ratio rockers, those figures would be correct, but I don't know what the rocker ratio on a 261 is, but what you're mainly concerned with is total lift at the valve, and the valve/piston clearance. Your cam grinder should either know or be able to find out what the duration at .050" is. As Larry said, it's always a good idea (although somewhat time consuming) to check the valve to piston clearance with any new cam you put in a motor. You can do this by putting a 1/4" layer of modeling clay on the piston top, installing and torquing the head, then rotate the engine by hand one full revolution so that both intake and exhaust valves open and close, then pull the head and measure the impression in the clay on the piston top. And you could run either a 264 or 268 degree cam; the 268 will still give you good street performance, but will have a bit more lope to the idle than the 264, and the power band will start a bit higher in the rpm range than the 264, but will give you a few more horses at the top end. Everything in tuning an engine is a compromise; when you gain some here, you lose some there. As the engineers put it, "There's no free lunch". So basically you try to make your best guess as to what will produce what you want the engine to do and take a shot at setting it up with components to achieve that. So far it sounds to me like you're on the right track. Good luck with the project. Oh, yeah one last thing, a compression ratio of 9.1 to 9.5 should work fine, just remember to have your machinist install hardened valve seats for unleaded gas and you should be fine to run pump gas.

just food for thought, based on my 3.40 rears and the old school muncie OD tranny that I have in my 56 chevy short bed truck, what do you guys think the motor would like more for cruising in OD at 70mph at about 2150-ish, a hydraulic 264 or a mechanical 268 cam more? so I can just swap out the lifters and call it good and this will make it hydraulic? no mods to the cam are necessary at all? is it also true that hydraulics are better for low end torque while still retaining good top end power, while mechanicals do better up top but trade off down low by not being as good off idle as hydraulics? I am not trying to be redundant but I just want to get everything perfect, and lobe seperation, is it best to have as little as possible like 102 degrees-110?

If you need power mostly under 3000rpm you can leave the cam stock or maybe go to a 254 grind, at the most.
The stock 261 solid lifter grind gives peak hp at 3300 rpm!
Pretty good for an engine with only 4 main bearings...

You can call Delta Cams in Tacoma.
They have various grind patterns for the 235/261 and can give you expert advice, which grind works best for you and why.
Delta makes the popular 'bulldog' grind with an asymmetrical 254/264 in/ex duration, offered by a few vendors.
254 at the intake gives good idle and 264 at the exhaust extends the hp peak beyond 3500rpm.
A good cam for racing while still giving good idle, but not so ideal for mostly street/freeway use below 3000rpm.

Hydraulics have a tendency to float at higher rpm, but should be fine under 3500rpm.
Solid lifters can be tweaked for power at higher rpm.

Because of the .060 overbore on my 261 I went with Delta's solid lifter grind of 254 in/ex with .433 lift and about 110 lobe sep.
I have a 3.55 rear with original 3 speed and typically drive around 65mph at 2800 rpm on the freeways.
This cam has still plenty power left for passing and climbing up mountains without losing power.
Also a great cam for hauling - Delta calls it the RV grind.


Read the famous McGurk article I posted on your previous thread.
It lists various cam specs used for the tests and the graphs show clearly the effect they have on the power band of the 261.

good good this is kinda where I was wanting to head, I am just trying to figure on the whole because I am going to have to sacrifice here and there, pull and push for what i need. for the most part I am just trying to figure if a 264 or 268 cam is not going to able to cruise in OD for long periods to sacramento or napa, or san francisco, and not have the cam loping while cruising at like 2100-2200RPM in overdrive, but would still like to to have a good powerband to a max of 4500RPM(although I seriously doubt that I will be there often, other than at the cool april drags or something) but can pull up to speed easily and still be ok and not have vacume/loping trouble at 2100-2200RPM while freeway flying, but still have a kinda mildly lopey/choppy idle, maybe I want too much?

oh I did look at at the dyno figures and they were very helpfull, yeah I dont know I am just pulling my hair out on this one, but the data looks great, because in straight gear 3rd I would have very good power in the 3000-3500 rpm range with that data, and OK Power at cruise? but ya know what would be cool, is if there was a graph that showed the torque ratings at the various RPM's or maybe one of them does and I didnt realize it, I will look again, thanks so much for your help up to this point, I thinking I want like .470 lift for great torque, is this too greedy?

dbane261,

Is this what was mentioned? 261 Torque vs RPM Plot The May 1955 HRM article had a table of both torque and HP for the nine dyno tests. I like the 18 and 82 cams. One can always covert from HP to torque with the equation HP = Torque * RPM/5250 or Torque = HP *5250/RPM, with torque in units of ft-lbf. I like to look at the torque vs. RPM curves to get a good feel for how different mods affect the engine's performance.

I have a McGurk cam spec sheet with some of his other cams, and also a Racer Brown cam card that a friend says is a good street cam. Would anyone be intersted in seeing these?I have also heard from others that Delta Cams is a good source for 235s, etc.. I admire your desire to dig into this subject.

Good luck!

awesome job sir, looks like if I build it the way that I am hoping for then I should be a able to get great torque for cruising at 2100-2200 RPM, thats where I was afraid I might not have any reasonale umph if I started getting too wild with this motor, so it looks like I am in good shape, and wow, they even got good power at lower RPM with that bigger cam too, coo coo cachoo. I would love to see those specs that you spoke of!!! I did look at delta's web site but couldnt get any specs just info about HOW they do their work, so it looks like I am shooting for 264-268 advertised duration, with about .470 lift at the valves, and about 102-110 lobe seperation, does this sound pretty good to have low end grunt and some top end pull to about 4000-4500 RPM????? any other advice at all guys??? Oh on a side note, are mechanicals a LOT louder under the hood than hydraulics?? cause I think I want a smooth runner with good exhaust note, ya know????

Make a call to DELTA I found them to be very helpful. I had them do a 350HP 327 SBC grind for my 153 ChevyII in my T roadster. Good thing I got a 5 speed as there ain't a lot of low end grunt with that much cam in a small motor. What ever cam you use use plenty of cam lube putting it together and use a good diesel oil for at least the first 1000 miles ,like Rotela or Delo 400.

i had delta grind the cam i have in my new motor. a great bunch of guys to talk to.

dbane261,
Here are the links to the information that was mentioned in one of my previous posts. Note that both the McGurk Cam Sheet and the Racer Brown cam card show dual pattern profiles on their cams. Given the different flowpaths in the intake and exhaust ports and valve sizes, it is not surprising to see different profiles. As we know, there is a lot more to defining a cam profile than just duration, lift, and lobe separation. Acceleration ramps, profile asymmetry, "area under the curve", etc. need to be defined.

High lift and moderate duration is certainly advantageous for good torque at low to moderate speeds (2000-3000 rpm?). However, the 235 port design may result in lifts above about 0.450" of little value. See these articles from the 2001 12 Port News.Duggan article, page 1 Duggan Article, page 2 What little analysis and data that I have seen on flow bench tests of the 235 heads indicates that most of the pressure loss in these heads comes from the small siamesed intake port (about 1.375" diameter) and the two 90-degree turns that the flow must make to get to the intake valve. More than about 0.440" to 0.450" intake valve lift will not help much and put a lot more stress on the valve train. Read the May 1955 HRM article about going to the No. 82 cam.

yeah it looks like .470 might not be so hot, maybe I'll go a little lower to like .450 and get a 264 mechanical set up, and maybe that will work, hey is it possible to just take that specs for that racer brown cam and just make it a little higher lift like I am after and just make it a little longer on the duration to the aforementioned 264 duration? I am not familiar with this cam, is it a good cam, power results? the cam guy should know how to make it work if I give him this right? that motor from the duggan article looks AWESOME!! man I like that header, are those three holley two barrels? that sounds like a lot of carburetion, WOW! I wonder what kind of power results he got on that? does anyone know? it is a good looking piece though, must be a beast!!

hello again, so I was curious, and just got off the phone with clifford yesterday, and he said that I would pretty much be dumb if I didnt deck the head .100 of an inch, I asked him if that was ok with my 848 head, and asked if this would be too high of a compression ratio and he told it was fine, does this sound weird to anyone here, can anyone shed some light on this, he also told me that his cams are vastly superior to anything on the market, including howards or langdons, I am kinda skeptical, he aslo says that his intake and 390 holley will make 30 PERCENT MORE POWER than a couple holley webers, which rated like a 4 barrel is about 400 CFM, and this sounds very appealing but what do you guys think, does this sound fishy? ALSO HUGE QUESTION, he said to sink the intake valves .100 when I cut the head down, and that the intake valves have NO SEATS, so just cut into the head???? I am lost on this, help please!!

One of the biggest problems/issues I see with anyone Milling a head that much is what Happens if you over heat the motor and Need to mill the head to fix any warping that may happen???
Just my 2cent food for thought.

if a standard rebuild is going to put me at like 9:1 CR though, then wont milling the head that much make me have to use higher rated fuel? and are there really no seats on the intake side of this head and that the intake valves actually "seat" to the head itself? sounds like a lot of headache, having to chop the valve stems and bush the springs???? I just dont know.

dbane261,

Sinking the intake seats by an amount equal to the thickness removed from the head has been standard practice for the stovebolt six heads to maintain valve-to-piston clearance. This was described in the May 1955 HRM article. I would not to mill the head by as much as 0.100". Work through one of the online compression ratio calculators to see what the difference in the gain in CR is for 0.060" and 0.100" of milling the head.

Did Clifford offer any dyno or road test data to support his claims? We have a saying at where I work about performance claims that seem almost too good to be true: Trust but verify!

Clifford equipment was not around when I was running 235s and 261s. My stuff came from McGurk and Toros.

no he did not offer dyno data, all he said is that his 235 with holley 390 4 barrel and intake with hedders, cam and decking .100 with porting and polishing acheived 320 ft/lbs torque, and he also told me a 261 would maybe get a couple more hp but other than that it would offer no better power, seems kinda strange, but he kinda poisoned the well for me with my cam grinder, told me "yeah right!!! theres no way that guy can grind a cam anywhere near as good as ours" and laughed at me for wanting to use webers "you call me when you cant those to work" do intake valves have seats, or do they just grind and seat to raw iron from the head?????

It was common for the heads (iron) not to have seats (inserts) then because the lead in the fuel lubricated them enough that it wasn't necessary. I have never heard of an engine of that vintage coming with seat inserts (on the intake or exhaust) so unless someone put them in previously then no your's won't have them either.

Hope that helps.

Oh, yeah, while I might believe that an engine that is optimised for one displacement won't make much more HP with a displacement increase like yours, I would be amazed if the torque didn't increase noticably.

What he is telling you is what some people I have met consider salesmanship.

yeah this is what I am suspecting, because to my knowledge many people here at inliners use these webers with great success, makes me wonder why so many people would buy them if they created no power and had so many problems, because in all reality if a holley 390 made as much as 30 percent more, eveyone would use them hands down right, i mean thats the differnce between 150HP and 195HP straight up, so I think someone might be blowing steam, so I think that I am buying two holley webers when tom gets back from vacation. maybe I will buy their cam kit just to get the valve train parts and all, see when he said sink the valves I thought this was a huge process because they had to pull the seats out, cut in .100 and then reinstall seats and then cut them, maybe I'll get it cut like .070 or something, but I dont want to get too high if compression, or maybe my cam grinder can do just as good of a job and I am being led astray by these guys so they can make a buck off a sucker looking for a dream of unattainable power, any thoughts????

I haven't talked to or bought anything from Clifford in a number of years, but I have used their intakes and headers. However, I did NOT use one of their cams. In most of the old Clifford ads and catalogs from back in the '70's, '80's, and '90's, some of their claims seem a bit, umm, shall we say, overstated. I would tend to trust your cam grinder more than I would a salesman at Clifford, but that's just my opinion, not hard fact. I've never played with a 261, so I don't know about the intake valve thing, but I'm sure some of the guys running 235's and 261's can come up with the answer on that.

Well I pulled the trigger and sent my cam to delta cams after I talked to Scott for about 25 minutes on the phone, I actually feel bad that I took up so much of his time, but he told me something that sold me against the clifford cams and claims, this also involved the tom Langdon, it was actually about who to beleive between the two "I would take the word of the guy who builds them over the word of a salesman ten times out of ten" but the guys at delta cam were very nice, and it only cost like 72 bucks to regrind my cam, I went with 268 mechanical, with .450 lift at intake and .470 lift at the exhaust which was one of their profiles, and he told me there will/should be no valve to piston clearance, which is sweet. Then there is the engine part, I guess the block was already .030 over so they went to .060, which gives me like 270 cubes practically which is awesome, he didnt want to bore it much more than like .010 or .020 over stock provided that it was at standard, which kinda made me silently chuckle after the bore guy told me where they were at. Have any of you guys ever tried backcutting that valves in the head, machine guy says he will port and polish the head and backcut the valves for like 250 bucks, this a good deal, sounds kinda good, and this involves runners and ports, the full nine. And the deck on the head, he said that he isnt going to deck it because he said that he checked it and said that someone was into that before because the combustion chamber marks and the water pocket marks were not deep as usual so he thinks that someone decked it at least .025 before, can anyone tell me what this would get me for a CR with like a .010 deck on the head with a copper head gasket??? thoughts anyone, comments welcome!!

oh hey is it possible to advance the cam by pushing the cam gear one or two teeth or whatever ahead of TDC to advance it similar to having the cam reground at an advanced state from a cam maker, ya know like roll it foward one tooth to get like 2 degrees advance or something, anyone ever done this????

You advance the cam buy using either offset crank keys or purchasing a crank gear/cam gear combination directly from Cloyes with multiple choices. I'm sure you will be putting on new gears on with all this work. Using the cam you have selected and advanceing it 4 degrees will give you great bottom end and performance where you will use it the most. I can give you the Cloyes # after I get home. I run them in my 302 GMC which use the identical gears. The Tech guy on the phone had a raft of information on Chev/GMC 6's. I believe I still have the box. (one tooth is way too far)...Good Luck. JD

so here we are, I cant get the motor done in the next two weeks for the show, too many things to deal with involving time for the truck, so I roll with the stock 235, but I want to upgrade the induction to my offy triple, I was thinking about just blocking the middle hole and running webers on either end, this should be ok right? it should be able to run ok shouldnt it, I mean three is just too much I think for a stock as a rock 235, what do you guys think???? Oh if I could get that info on that advance gear from jimmy six taht would be great, is 4 degrees the best advance, what about 6???

any help with the carburetion issue? is the triple holley weber linkage a long straight bar that connects all three together for a unifying centerline, does anyone have pictures upclose of this set up? I looked in the rides section, but cant get a good close up, I am trying to see if I can use a triple linkage set up, and just not hook up the center carb bars and just connect the outside carbs with the triple linkage set up and just hook up a third when the need demands it, any help/thoughts???

ahhh come on guys, I know someone here has to be using this linkage set up, if not several people, I need some tech help here gentlemen, I am hoping to get this set up finished as soon as possible for the parade next week, SOS, por favor, please help me out here!!!! I see that like 450 people have checked out this topic, someone must know, thanks in advance.

dbane261,

The engine will run reasonably well with any of the setups described in the posts above, in my opinion. I forget, do you have an automatic or manual transmission?I have run a couple of 261s with three "non-progressive" Stromberg 48s on the street with no problems (other than an idle speed of 800 rpm) and five "non-progressive" 48s on a 278 set up for off-street. I have no direct experience with Holley-Webers. If each carb has the "progressive" second barrel, I would not be afraid of running all three, even on a 235. I also ran two in-unison BXOV-2s on a 235. Experimentation is the way to learn, as long as you are not violating any safety guidelines.

Good luck, in any event,

I just dont want to over carb it at wide openj throttle because those webers are mechanical secondaries and not vacume operated, so it I hit it wide open, say hello to all six barrels, and goodbye to all that gas mileage, it just seems more practical to me to just set two up on this triple intake, block the middle and put one at either end, but the question being, is will vacume just take care of it like it does when we run a single in the middle like in stock configuration, or is there going to be massive fuel distribution issues at large, plus I just dont want to have to worry about the headache and pricetag of triple everything inlcuding cleaners and adaptors, hello to 500 bucks, if I do the double, it will be more like 300 and something, and less plumbing, and can I use a triple linkage and just ignore the center set up and just put it in later, tech info on linkage gentlemen, I am pretty desperate here!!!