Inliners International Forums General Discussion Hi Performance Cam duration question

Hello, I have a cam question that I have never seen asked before. Take 2 cams that I have under consideration. Cam #1 Crane 200511 total intake duration 248@004. Cam #2 Clevite 229-1878 total intake duration 273@004. Thats quite a difference but at .050 the crane is 192 and the clevite is 194 almost the same. The crane opens and closes the valve much faster than the clevite. Other than faster ramps would there be any difference in performance? Would the crane have a big difference in duration at say 200 lift? Is this what is talked about when people say "under the curve"? It would seem to me that in this case that the clevite would be the better choice because it opens and closes the valve more gently or am I missing something? Is there some advantage to opening and closing the valve more quickly? If this post is in the wrong area please feel free to move it. Jay

What are the duration @.050 numbers, that's the only real way to compare the 2 cams. Also, without installing the 2 cams in an engine and plotting all of the O/C events its hard to also compare the @.200 numbers as well.

There are actuallly several such cams I believe are all pretty similar, but the "Advertised" duration is measured on the shallow part of the ramp so it looks like it varies a lot.
Im giving the .050 lobe durations, lobe separation, and lift:

Comp 240H (see lump port thread too)
192-200-108 .455 .455

Crane 200511
192-204-112 .467 .498

PAW/SSI Clv229-1878 (I have a new one before PAW went under)
194-204-112 .464 .490

I think all3 of those would run pretty much the same, you might notice a slight lumpy idle when its cold but not warmed up. I put the PAW grind in our 289 Ford and you cant even tell it has a "cam" in it, still gets 20mpg too but runs 15.80s at 87mph in a stock slushbox-3.00 car.

Probably the big advantage of the 240H is you could get away with just about any valvesprings.

Clevite 229-1551 is a little smaller, the stock 292 cam and I also believe the stock 230 HiPo cam from 1964
188-190-112 .406 .406
That gives you an idea of what the factory put in there, the stock 283-2v had a similar cam.

Thank you both for the replies. I guess that the "ramp" up to .050 has little to do with the effective duration when comparing cams at .050 lift. If cam A has 200@ .050 and cam B has 200@.050 they will act the same if all other factors are equal even though cam A has 35 degrees more total duration at .004 lift. I just thought that the cams with the "steeper/faster" ramps might open the valve higher/longer than the cam with a slower ramp. Please don't misunderstand me,I am not trying to split hairs just curious. I have crossed off the comp 240H from my list because it is just to "tame" for my "327/300" build. I have a set of single non stock valve springs for a sbc that i am getting tested for pressure ect. If these won't work I can buy the springs that I need. The Crane 200511, Clevite 229-1878, Schneider 02527, and Crower 03241 are most of the possibilties for right now. The most that I would consider is something like the Comp 252H although I like dual pattern cams better. It's sad that PAW has gone under after all those years in the market. At this level (190-200 intake duration@,050)does lobe seperation have much effect? Seems to me that tighter (108/110)is the way to go for this type of cam. Any advice on lobe seperation would be welcome. Don't know if this makes any difference, I am going to put 1.84 intake valves in my head. Thanks for the great info. I will be happy to contribute anything that I learn. Jay

The 108 LSA makes the 240H considerably hotter.

There are so many variables that can affect cams of like specs. Panic brings up a good point, even 2 cams with the same @.050 duration can have different LSA and be total different altogether in how they perform in the same engine.

Get David Vizard's book, "How to Build and Modify Chevrolet Small Block V-8 Camshafts and Valve Trains"

Commit it to memory and you will be just scratching the surface of camshaft design. Although there are cylinder head considerations, the dumb camshaft doesn't know if it's a Ford, Chevrolet or ?? V8, inline 6,etc.

To your original question:

Harvey Crane coined the term 'Hydraulic Intensity'. This is the difference between duration at .004" and at .050". The lower the number the higher the intensity. Those with a higher number will have lazy valve action and even though they have more off-seat valve time(ing) they are likely to produce less power over the entire operating range of the engine.

The area under the valve lift curve is much more important than the advertised duration. And as Panic and CNC-Dude pointed out, LSA will definitely change the characteristics of two cams with identical lobes.

This is a wonderful discussion! Panic what do you mean by hotter? Rougher idle? more top end? From my limited understanding of lobe seperation is the tighter the seperation the wilder and more narrow the rpm range will be. One thing that happens with a small LSA is the intake valve closes sooner so that compression starts to build earlier. Another thing is increased overlap allowing more of the intake charge to go out the still open exhaust valve at low speed. At these low duration numbers there's not much overlap to begin with. One thing that I noticed with the Comp cams is the low lift for a given duration compared to other brands. The Langdon marine is this way also. Does the 250 with a stock (or 2bbl intergrated in my case) head "like" a lot of lift? Do these engines also "like" dual pattern cams better with a full exhaust system on the street? A lot of people here are running a lot more cam than we are talking about, which is why I find this so interesting. Thanks again for the replies. Jay

Gearhead1 I think that you understand what I am talking about with "Hydraulic Intensity". What do you mean by "valve lift curve" ? Is this the area starting at .050 lift? Would a cam with a low Hydraulic Intensity (higher number) have a smaller valve lift curve area than one with a high Hydraulic Intensity if all other factors are the same? Jay

Jay,
I think you got to the essence of it on Lobe Separation (LSA) -
If you have enough gears, closer is usuallyl better and makes the wholce curve tighter. Tradeoff is a rougher idle and quicker falloff on top.

If the cam is small enough, as you noted, the idle isnt going to be rough no matter what - the stock six cam LSA are all under 110 but they idle smooth as we know. Monster cams (eg the 302-z28) will run a wide LSA like 116 just to get a decent idle on a street car.

On a bigger cam, a closer LSA will eat more gas too, so a wider LSA is a compromise.

On the intensity, higher intensity is of course always better, ideally the valve would just pop open to full lift and then pop shut again. Stuff like mass, geometry, metal strength and fatigue prevent that so again there is a compromise, the factory tended to go for longer life/reliability ie less intensity.

I always degree the cam and measure all the angles at lifts of
.006
.050
.100
.200
max lift
.200
.100
.050
.006
that is not only a double check on installing the cam but gives you a good idea, vs the stock one (which I also measure) of how much you're adding.

Crane's phrase is counter-intuitive: "high intensity" means mild action.

DeuceCoupe, thats why I want a tight LSA for the cam range that I am looking at. The amount of .050 duration is so low that I think that I can get away with no ill efects.(Who said a little rough idle is a bad thing?)Have you measured any stock 250 cams at the different lift points? Or the PAW cam that you have? The only non-stock 250 cam that I have any experence with is the Crane 203901 in my 79 p/u. The truck idled smoothly,pulled hard to almost 5k rpm and was a little weak in low speed torque.It didn't get going until 1500-1800 rpm IIRC. Huge power increase over stock. Looking back I should have made up for some of the low speed loss by upping the compression by milling the head ect. This time I have a lighter car and an auto trans so I am going after a little more low speed torque. Jay

Im pretty sure I've measured at least the stock 250 and 292 cams, I will hunt for the scribble sheets.

I havent measured the PAW-1878 cam its still new in the tube. I also have a new solid 292 cam from Oregon Cams, 206-206 at .050 I think, but I dont think I've profiled that either.

You could always advance or retard the cam for fine tuning too, that can really help with a tight converter.

When I taught H.S. Auto Shop, occasionally I would get a student that wanted to build a 'High Performance' engine. I would make them plot the valve lift (every degree) for both the intake and exhaust valves on graph paper. They could then slide the graphs over each other and open and close the lobe centers. Eventually, I made and Excel spread sheet that would graph the numbers.

My hope was that, over time, we could have some data to compare with real running engines. They would be able see the effects of overlap, intensity, lift and duration.

But, alas, video games and texting are a lot more exciting than plotting valve lift curves and building engines.

I miss the smoke and noise.

One of the reasons I retired.

Gearhead,
x2 on the videogames. I never took autoshop in hi school but at least we HAD one. I'd tell my other teachers I was gonna skip class to go to autoshop & use the distributor machine. I was getting A's so they'd say it was cool. Back then "cool" was getting good grades AND having a fast car you built YOURSELF. Today its about how much money you paid for your car. At least theres a few of us left.

ANYWAY
Jay here is a stock 292 (ok rebuilt by somebody so I ASSUME cam is stock), lobe lift and angles
The ** measurements I always take but they are on the shallow parts so I dont trust those numbers. the .050 .100 and .200 are the most trustworthy.

Intake #1
.006 16 btc**
.050 18 atc
.100 35 atc
.200 76 atc
.232 65BBC max**
.200 28 bbc
.100 11 abc
.050 28 abc
.006 66 abc**
.000 base (always make sure it goes back to .000)

Result-
190 duration at .050 (180-18+28)
156 duration at .100 (180-35+11)
113 LCI

Exhaust #1
.006 63 bbc**
.050 22 bbc
.100 5 bbc
.200 35 abc
.232 70 abc max**
.200 74 btc
.100 33 btc
.050 16 btc
.006 24 atc**
.001 base (yup, lost a mil somewhere, oh well- repeat test showed same numbers and came back to .000)

Result-
186 duration at .050 (180-16+22)
152 duration at .100 (180-33+5)
109 LCE

Engine was stamped F0106THH
So I'd call this one
190-186-111 LCI 113 LCE 109 ie 2 retarded
.232 x 1.75 = .406 lift, thats spec so seems very little wear

I had measured another 292 cam, same way, got
188-189-111 LCI=112 LCE=110 ie 1 retarded
154-152 duration at .100
.233 max intake
.227 max exhaust (a little wear)

I had also measured a stock 250 cam at
172-172-105 LCI=106 LCE=104 ie 1 retard
140-137 duration at .100
.221 max intake
.210 max exhaust
Spec is .222 lift on both

The 194 cam is supposed to be even smaller, I think I measured one but cant find it just now.

Typical is +/- a degree or so and a couple mils but thats good enough for me, its better than guessing!

Gearhead1 X3 on the videogames! DeuceCoupe, this is very good info to have! Did you notice that on the 292 cams at least that both the lobes are very close to the same on both sides of the peak lift. Also notice that all 3 cams are low intensity with about 40 degrees between .006 and .050. Look at the Comp cams for example the 240H has 24deg on each side of the lobe between .006 and.050 lift. The 252H has 23deg and the 260H has 24 deg. The Crane 200511 looks slower at 28deg but only at .004 lift. the Clevite 229-1878 is at 39.5deg again at .004 lift. The stock 250 cam is 49deg at .004 lift. There is a big difference in open/close speeds between stock and aftermarket cams. Until this thread I did not notice that the difference was so great! Now that we have some info on this I will buy a degree wheel and get the same specs on whatever cam I finially end up with.It may take some time for me to get it done as I am just rounding up parts right now. The factory reason for using slow ramps has to be low warranty claims and long service life. Most aftermarket cams won't be going 200k miles so a faster valve speed is ok. As for advancing or retarding the cam are you suggesting that I go bigger and move it a few degrees to try to have the best of both worlds? How big a consideration should lift be? From what I have read on this board the 250 likes a lot of lift even with a stock head but Comp cams with their low lift are popular also. Makes for a little confushion sometimes. Jay

I have e-mailed comp about the specs for their 240H and 252H cams at .100 and .200 lift. I then went to Crane with the same idea but instead found specs at .200 lift for all lobes used in all three cams they make for a 250. They are: 200511 intake at .050 192deg at .200 83deg. Exhaust 204deg at.050 114deg at .200 lift. 203901 204deg at .050 114@ .200. This is the same lobe used as the exhaust on the first cam. For 203901 exhaust its 216 @.050 and 127@ .200. Compare as this to the stock 292 cam the Crane200511 has about 5deg more duration @.200 lift. I also found from looking at the lobe charts the more radical the cam the bigger the difference in duration at .200 lift. Is 5deg at .200 a lot? I don't think so at the level of cam that I am looking at. IMHO the Clevite 229-1878 would fall somewhere in the middle between the stock and Crane cams at .200 lift. I will report back what I hear from Comp Cams. Thoughts anyone? Jay

You could call Jerry Cantrell at Schneider Cams in San Diego. If you tell him what you want the cam to do he can figure out a grind to do it. He has done my last two 261 chevy cams and he was terrific to deal with. In fact, I messed one of them up hand clearancing in between the lobes to clear the 302 rods I am using an he fixed it up quick as could be. What's nice is you get to speak to the owner who has been grinding cams for a very long time. Might save a lot of time on your part. Just a thought.

mdonohue05 - I am planning to talk to Schneider Cams about my GMC. I started the current post asking for GMC Cam Advice. Do you have any recommendations on recommend for my car. I enjoy racing my 40 Chevy which is powered by a 302 GMC. I like the way current Isky E2 cam behaves at low speed but would like a little more performance. I'm from Fallbrook so Schneider is close by.

I am probably not the best person to talk to about cams as I know just about enough to be stupid, lol. In fact, I will admit that many years ago I thought it was a good idea to run a Clifford (Erson I suppose) cam at 290 duration and 495 lift on the street in a 235 chevy, silly boy. After I bent the intake valves hitting the pistons, then clearancing the stock pistons so that would not happen again, got the motor running, I learned just how awful the wrong cam grind can make a motor run, lol. I still have that cam to remind me of that fiasco. That being said, i have owned my 57 for 36 years and ran chet herbert regrinds in my 235 and 261 motors for years, and they were all like 278-284 duration and to tell the truth, i loved the cammed up sound. So, herbert does not mess with the odd stuff any more, Howard's does not want to mess with anything other then what they have in their catalogue, Clifford is just too expensive, so I called Schneider. Jerry was very cool to deal with and ground me two cams for the 261 that took into consideration the weight of my 57 chevy, about 3500 lbs, the fact that I was running no accessories, manual trans, manual brakes, no air ect., knew that the veniolia pistons i was using had
sufficient clearance for .490 lift, would be a street car, knew that max rpm would be 5400-5600 rpm, and the fact that I wanted a lot of rumpty rump, and that I did not mind setting valves and could put up with a little ragged idle. All of the above is just because every time I get behind the wheel of my car I feel like a kid again. So I like a little rough around the edges feel. So the cam is .480 lift, duration is 280, 240 at .050 cam lift, lobe separation is 108. But that being said, Jerry will grind what you need, just tell him what you want to do with the car. Mike.

Sounds like Jerry would be good to work with. Got a reply from Scott Gilbert at Comp Cams. The only figures he had was at .200 lift. They are for 61-113-4 (240H) 192@.050/96@.200IN and200@.050/102@.200. For 61-232-4 IN and EX are both 206@ .050/109@.200. Looking more at Crane's lobe chart I think that the 83@ 200 for the IN of the 200511 cam is a misprint and should be 93@.200 after looking at other lobes on the chart.Does anyone have any experence with the Comp 252H? How does it run? IS it soggy on the bottom end? When I figure out how to contact them I will send an E-mail to Clevite and get the same info from them and post it. Mdonohue05 I know what you mean by feeling like a kid again as I worked on 78 Nova's at a Chevy dealer when they were new and almost bought a 79 Jay

Comp cam will put what ever grind you want.
You do not need to buy an off the shelf camshaft.

MBHD

Hank, I think that's right and there are probably one or two other grinders that will grind a cam for our inlines. Now this is no slight on comp cams, as I ran their cams on some of my SB motors over the years (momentary lapses of judgment) and they were excellent cams. Had one in a super comp 8.90 motor that ran like no tomorrow. And I called them for my 261 cams but the problem I had was getting someone on the phone who could make a recommendation. It was three or four transfers and they weren't even sure they could get a core, let alone make a recommendation which is understandable. If they had to make a living on 235/261 cams they would be out of business. So I ended up at Schneider out of happenstance who put me on the phone with the owner on the first call, had cores and made a recommendation. It was a very
good experience that thought others should know about as an option. I have no doubt that your experience with comp was excellent. Anyone else have a good experience with a cam grinder for one of our inline motors?

I bought an internet roller cam for my 300s sight unseen, of unknown manufacturer, unknown specs, on a chance that I could use it. With some detective work I was able to determine that it was a Schneider roller cam. I called tham and the fellow I spoke with was the second generation owner who said my cam was so old that they did not have computer records of it but he woud check with his father as he had written records of some of the older grinds in storage. They got back to me with the cam specs (short oval track and bracket racer grind - PERFECT!!!).

They weht through that trouble for me and didn't make a dime off me but I would definitely do business with a company that offers service-after-the-sale like this.

The cam is now in my vintage Logghe car and works great.

How much lift can a 235 take?

Secondly, when going with a high lift/high duration cam, is it necessary to go with stiffer push rods?

The 235 has pushrods that are almost 12" long. I would think there would be alot of deflection.

The intake makes contact pretty quickly, which gets worse with:
1. cam advance
2. more intake lift
3. more intake rocker ratio
4. more overlap
5. smaller LSA
6. head or block mill
The obvious cure is aftermarket pistons with valve reliefs such as shown in the Ross ad picture. Problem: $$$. The stock pistons can be relieved to some degree very carefully since the dome thickness isn't great.
The exhaust has plenty of room.

Yes, the stock pushrods are terrible. The problem is that even 5/16" tubes will rub the clearance holes to some degree especially with more lift (duration doesn't matter).

A couple years ago, I saw a flow bench test for a STOCK 235 head, for a stroker build to 255". At valve lifts over .450", there seemed to be a lot of unwanted turbulence around the valve if I recall. Most of the 235 cams I've seen offered are in the .400-.425" range - advertised lift with 1.5 stock rockers. In reality, the rockers seem to measure LESS - more like 1.4-1.45:1, from what I've read here on the board.Knowing this, I wouldn't try for more than .460 to .480 MAX, on a NEW BLANK. I don't think a regrind could safely get into that range, but is nearly HALF the cost of a NEW cam!

In 1978, I bought a RV cam from Clifford, ground by Sig Earson. Ether they filled out the cam card WRONG, or they used a 250 pattern on my 235 stick - adv. duration and lift was 264-.480"! I used stock springs, push rods,retainers with no issues - driving the PISS out of that mill as a dumb,heavy-footed ute in my 20's, driving all over hell in my '53 p/u - IT RAN GOOD!!!

I've been intrigued by DUAL PATTERN cams, ever since learning about Mcguirk using them back in the '50's. I asked Isky if he still has Frank's cam masters - he did, and remembered helping him develop those cams, as they were very close friends! I mention this, as SCHNEIDER offers dual-pattern grinds for the later Chevy sixes - I'm thinking about calling Jerry Cantrell about using one for my 261 build on a stock core, for my '57 car. Adding duration on the exhaust side has got to help those BAD ports breath a little better!

MAN, what a great thread this is... GREAT JOB GUYS!!!

- Tim

The largest cam I ever used on a street 235 is in the motor I just took out of my 57 (new 261 going in although that has been a fiasco all of it's own. Look for the thread chamfering rod bearings if any one is interested. I am still not done fixing the "new" venolias yet). I built the motor in 86. the cam was the most reliable cam I ever used and was a Chet Herbert regrind 280 duration and .480 lift. Did not hit the stock pistons, I did not shave the head or block. Used dual springs I got from Clifford (I never did figure out what they were actually from) and aluminum retainers (yikes!). I used trw pushrods, they were much better than stock, used a small block chevy 1.6 exhaust valve, clearanced the pocket for the larger valve and got rid of the little bump out on the chamber wall that stalls exhaust flow for a bit. Motor had a loopy idle at about 900 rpm, and made power from about 1800-1900 rpm to about 5300-5400 rpm where the head ran out of air. That motor was in and out of my 57 four or five different times as I replaced it with other motors but when the other motors quit or puked bearings or something, that one always stayed together. I never did clay up the pistons to see exactly what clearance I had. That being said, I would think a cam in the range of 268 - 278 duration with a lift of .450 -.470 would probably be a safe bet with stock pistons. As for the dual pattern grinds, i would love to try one at some point. Clifford did sell them, and may still offer them, but the difference in expense is just too great. The exhaust ports flow lousy no matter what and my all out 235/261 racing days are long over and anymore I am just happy finding a cam grinder to make me up a cam so single pattern is ok with me these days.

IMHO more exhaust duration within reason would help out on the street with a full exhaust system even a freeflowing one. What were the results on a 235/261 dual pattern cam over a single pattern cam?

The McGurk article from '55 seems to be the bible for the Stovebolt builds. Low lift and lots of Duration seem to be the key. I really like the cam grind he has in his #5 and 7 dyno runs. It has 245 duration and .421 lift on the intake, and 284 .410 lift on the exhaust. It peaks out on torque at 2000, but barely drops off all the way to 3500. It peaks out on Hp at 4500. Talk about a workhorse!

Even when he goes to a 264 .428 cam, torque still peaks at 2000 and goes strong to 3500. Hp peaks a little higher though.

I'm thinking something somewhere between the 245 and 264 would be ideal for a good street machine. Some more lift on the exhaust would probable benefit too.

In the CompCams catalog, their lobes have more lift than I like, given the duration. They must be more modern, small block grinds.

I was just trying to get some more opinions.

http://www.selectric.org/55chevy/soup.html

A lot of those old books are neat and cool, but so much has changed in the 60 years since they were written, that they really aren't even relevant any longer. Cylinder head porting technology and techniques has advanced more than 5 times compared to just 10 years ago, and compared to the 50 years prior to that, the gap between then and now is unmeasurable, as is cam technology. There shouldn't be any reason that you can't use today's technology and get 40-50% more power out of the same engine built in 1950 with 1950's technology. So by combining 21st century head porting and cylinder head machining along with the most current cam profiles, the Stovebolt can easily be like the Enterprise, and go where no Stovebolt has gone before.

Yes,modern porting is no longer about big holes,it's about velocity too. And the valve spends more time partially open than fully open so low lift flow rates are important.
Is there any reliable dyno data on a 235-261 done in the last 10 years?
There was some info here on a 302 GMC a few years back. I believe it was about 250 HP and 340 ft lbs of torque with a well massaged head and other typical modifications.
It'll take alot of dyno and or road testing and piles of money to get real power from a 235-261

The casting makes "too large" a port impossible.
There's no special secret master for dual-pattern, they just grind the same stick twice, and swap out the master for a different profile to do the exhaust. Which combination works depends entirely on who chooses which master, the parts themselves do nothing.

Tony,
Do you recall any hints to find that 302 GMC dyno test ~250hp?
Ive tried Search but cant find it.

Only recent Stovebolt dynos I know of are
HAMB about April 2011, "truckedup", 261 at 180hp
Chevytalk about Feb 2010, t=235371, 261 at 155hp
Even they were kinda vague but better than nothing.
Then theres the old 1950s dyno data.

There was one on here a few years back that made 339 HP@5400 and 346 Torque@4600. It was a 321 cubic inch 302 GMC.

Don't have any stovebolt dyno data, but I do have some updates from the cam mfg.s I have contacted. First Clevite can't tell me anything other than .050 data (which we allready have) because they got out of the car cam business 2 years ago. I am currently checking with Car Quest to see if any are still in a warehouse or something.Price $110. Looking into MBHD's statement about a custom cam from Comp, Scott Gilbert has told me that 2 standard lobes custom ground on a cam will cost me $192.73 about $47 more than a off the shelf catolog cam. This seems very reasonable to me for what you are getting. I have also E-mailed Schneider but have not got a reply as of yet.(Just sent yesterday). I did not send Crane any request because we allready have the info. When I was reading old posts here it looks like Crane may have shut down for awhile. Anyone know what happened? Their catolog cams are $245. From what I have read here the stovebolt stock head runs out of air at a certain amount of lift and having a higher lift cam doesn't help. Does the stock 250 head have the same limit? If so what is it? Sorry for the long post but I want to thank everyone again. Jay

THANKS MIKE, for your cam story! My 235 "turd motor" currently in my '57 is a stocker - except for the Clifford shorty headers and Crower 260/.450" cam (222 @ .050, lash is .014" across), provides 17" of vacuum at idle for my power disc brakes. Works well with the stock carb and intake, 3.08 diff and 3.11-low Saginaw 4-speed. Having been snakebit TWICE by CROWER parts (wouldn't buy a cotter key from OR recommend them), I proudly wear Schneider's IRON CROSS decals on the front fenders, and their shirts on my back, as their logo dates back to 1964!

CNC-dude - SO VERY TRUE!!! I've thought of having Isky grinding a Mcguirk pattern for me - but soon realized I would be leaving some power and driveability on the table, compared to what engine builders and cam people know TODAY!

As for HP, I recall on an old thread here (I think) that the BEST numbers Patrick was able to pull on his sixes were around .7 HP per CI - that may not mean much without knowing what combos of cams, carbs and intakes he has tried on the dyno, plus flow bench numbers for the head work. One can only guess how IN HELL Chevrolet came up with their factory ratings without calling them LIARS - a mild 235 build featured in HOT ROD DELUX with dual 1-bbl carbs and a mild Isky cam did no better than 125 on the dyno - a far cry form the factory's 140 rating for '57 and later engines. I WAS SHOCKED!!!

- Tim

Fudging dyno numbers was rampant before all companies switched to SAE Net performance testing proceedures in the early 70s. Before that advertised horsepower and torque numbers were SAE "B" curve numbers which meant no air cleaners (velocity stack "OK"), minimum exhaust backpressure (dyno headers "OK"), unconstrained coolant, air and oil temps, LBT fuel curve, MBT spark curve, no front end accessory drive (idlers only), etc. Maybe even SAE A numbers with a remotely driven water pump snuck in there.

Today SAE C performance numbers are published with the engine run "as installed in a vehicle" with exhaust backpressure restriction and accessories in place, and numbers generated by the average of several runs, not a flyer.

Even so there are ways to make some dyno tests "more equal" than others and for this reason I am always skeptical of dynamometer claims until I see the vehicle performance numbers to back it up, be it an e.t. slip, a land speed record, or lap times.

You should be too.

CNC:
I remember the 321/346hp gmc threads:
Ron Golden 346hp GMC 321cid
https://www.inliners.org/ubbthreads/ubbthreads.php?ubb=showflat&Number=47835&fpart=12

https://www.inliners.org/ubbthreads/ubbthreads.php?ubb=showflat&Number=47701&fpart=6

Trying to find any others?

Tony:
Cant recall a 302gmc/250hp dyno thread, might have missed it?


6bangertim:
I must have missed the Hot Rod Delux 235/150hp article (any hints? Issue date? test details?)
Most of what I have on the stovebolt dyno is way back from the 50s, a lot of the tests run with muffler[s] stuffed on the end, etc.

However, the Gonkulator does rate the 235/"140" at about 130hp SAE gross (more like FTF's B scale)

FTF:
x2 on that!
Your comments are why I began to write the DeuceCoupe / WerbyFord Gonkulator back in the 1970s.
Ratings got so crazy by the late 60s, some UNDERrated but most overrated, you couldnt compare anything to anything based on the "ratings". The ratings these days "jive" a lot better.

Jay,
I found some data from back when Tom Lowe did the 292 and 250 dyno series. The "Nova Six" with a 1.94 valve (either lump or nolump) does not flatten out at .400 lift. It tapers off but keeps right on gaining up to .600 lift, at least on the intake side.

Yes, Crane went bankrupt for a while there but now they are back.
Wow, this thread is up to 3 engine families.

Some of the impressive early tests for both GMC and 235 included, only in passing, that this was not pump gas, not av-gas, not alcohol, but in fact a light nitro blend.
Some reprints of that article left that part out...