I was talking to an old school Corvette guy the other day, we were talking about the old 097 Duntov mechanical camshaft how they were legendary, he mentioned running this camshaft with 1.6 ratio rocker arms, he said it gave the cam more lift and much needed low end torque. He called it a "Saturday Night Special". Has anyone ever done this before?

It sounds like it will work, whats your comments?

rustylugnuts

 

interesting, i guess i don't understand how more lift equates to more low end... i would think that would be a function of overlap...

Bill

 

Bigger isn't always better. HOT ROD did a dyno comparison about four years ago of the same engine with four different cams, running each cam with both 1.5 and 1.6 rockers. The best improvement they got at peak power was 4 hp; hardly worth the effort.

 

I dunno - Zora Duntov was pretty much a camshaft genius and I would be reluctant to screw with his original design. There is a reason the 097 is already "legendary". There was a service bulletin way back to tighten up the lash for 'weekend racing' but I never saw anything about changing rocker ratios.

 

......especially after you consider the mickey mouse drilling out the pushrod guide holes in the early cast heads and the extra wear put on the valve guides......

 

Slightly off-topic....am I crazy or wasn't there an old Rambler engine that had a hollow stud to deliver oil to the valve train ? Seems I traded one of these in during the '60s with a seized up valve train cuz some fool but a solid stud in the head...

 

yep!!...the one im familiar with were the y block v8's....the rear bolt for the rocker stand had a small hole in it for top end oiling...rambler made a hell of a good engine;...heavy though and a lot of them were used by gray marine along with single barrel side drafts used on the 6 banger vette too.......

 

Thanks! I have a bet with mechanic younger brother on this one..

 

Trying to visualize this, it appears to my mind that the lift, duration and overlap would all be increased going from 1.5 to 1.6 rocker ratio. No?

 

Thats the way I look at it! As for that 1.5 vs 1.6 in that four years back article, I'll bet the camshafts that were tested already had a sufficient amount of lift that it didn't make much of a difference. However the 097 Duntov has just under .400 lift, and this might be what he was saying. Something to consider, anyone have other inputs?

rustylugnuts

 

Mike
as i 'visualize' it, the lifter is going to come off the base circle of the cam lobe at the same point no matter what the rocker ratio is, and ramp down to the base circle at the same point as before.. yada yada yada...

so all i see is the valve lifting higher, not longer...
Bill

 

Nope, it will lift more (quicker / earlier), so the effective duration will be increased at the same time (with higher ratio rockers).

The cam ramp point at say .050" (measured point of effective valve opening) will be earlier.

Comp Cams has always stated that changing from 1.5 to 1.6 ratio rockers on a SBC will move the effective peak torque point up 200 RPM.

So to answer the OP's original question, no higher ratio rockers will decrease low end torque.

Plasticman

 

With the 097' cam's relatively short lift, the 1.6 rockers give the valve a boost to ~.425". Larger than stock but nothing like the lift of later 30-30 or LT1 cams, or even the 327/350hp cam.

The greater leverage on the lift also lengthens the 0.050" duration, but the total duration and effective dynamic compression ratio remains the same (lending some truth to the claims of more area under the hp curve and higher off idle torque).

The instrumented data of a 4hp gain is probably correct with the larger 327/350 hydraulic, the 30-30, and most aftermarket cams, because they are already over 0.450 lift (the lift where stock heads begin to flatten off and lose any airflow benefit from more lift). Put 1.6 rockers on a cam that is already pushing .500" lift and the typical Z28 stock springs lose control of the valve train. The results may be a step back in power at high rpm (the system approach goes out the window).

With the 097' cam you have not begun to come close to the heads flow/lift potential so the gains are likely to be more (but not much more than 8-10hp).

I run stamped steel 1.6 rocker (cheater) arms on my totally stock 340hp 327. There is not much difference in SOP feel, but I also did not need to open the guides with a Lewis tool (it was a drop in replacement for the stock rockers, for the same price). Considering the stock rockers are more like 1.43:1 ratio, the stamped 1.6 rockers are actually more like a 1.54:1 ratio rocker arm. The car runs 14.01 @ 101mph (340hp/4:11, spinning 215/75/15's) and performance did not change much with the rocker arm change. If there was a power gain resulting from the 1.6 rockers, it was free (no extra cost, nothing to lose).

YMMV

 

oh yeah..lest we forget....check your pushrod length too!.....another alternative to the 097 is the wolverine "blue racer"....adv. dur is 296 with 498 lift less lash....nice cam..........i dont know the .050 off # but if you are buying a new cam anyway you could run this with a good set of 1.5 rockers and it would be easier on the valve train of a street engine.....good luck

 

I used a Wolverine "Blue Racer" hydraulic in the 383 I built for my Grand Sport - WG1024 or WG1042 maybe, don't remember, but it was somewhere around 236/242 @ .050"; ran strong only pulling 2300#.

 

Eight to ten horse power increase, I'm there! If I went to the 1.6 ratio rockers, will this change my valve lash adjustments? I strongly believe it shouldn't but then this has been my off month.....ha ha ha....

I appreciate it, rustylugnuts

 

The lift change with a 1.6 rockers is a 6.7% increase.

If you want to start & stop the valve at the same degree point on the lobe ramps as the factory 0.008/0.018 lash, the theoretical 6.7% increase lash result is 0.00853/0.0192 (IMO, not enough to worry about or measure).

The 097' cam had factory lash recommendations of 0.008/0.018 (1963 & "competition") & 0.012/0.018 (56' to 62'). Use what works for you.

I have heard of circle track guys running this cam from 0.006/0.016 to 0.016/0.026 (and even 0.026/0.028). The long low-intensity ramps of the 097' cam allow room for lots of lash related performance modification (tighter improves higher rpm, looser improves low rpm... so they say). Considering the cam has been around for 50-years, and has been used in displacements from 221 to 435 cu. in. (including use with hydraulic lifters in ".420" lift rule" oval track classes), it has proven to be very forgiving (even when misused).

There is no promise of more power, but "cheatin" is never promising .

 

Very true, remember one doesn't need to be quicker then the tiger thats chasing you.........you just need to be ahead of the guy thats running next to you....

Thank you, rustylugnuts

 

What aftermarket cam would produce the extra 25 gross hp as the 097 cam? But....Not lose the 15 lb torgue that the 097 does? Seems like there would be a better cam nowdays, with computer simulation, improved lobe profiles etc., that keeps the low end but also gets the high end?
By the way, in GM's own published testing from 1957, the 097 cam 270hp only got 15 more NET hp than the powerpack cammed 245hp. Both engines have the same 9.5 compression ratio.

 

My cam is a Duntov 'replica' and I can't say much in this area simply due to a lack of knowledge...here are the grind specs and my dyno sheet for anyone interested. I'm real happy with the top RPM band on the car...the low end is a little 'doggy' but I think its more a factor of a tall gear (3.70) and me still learning to drive the car in its 'happy space'...
I was told by the engine rebuilder that the setup nets me about another 25-30HP for close to 300HP and that they dyno shows lower than the typical 'rated' numbers...

I don't understand the penciled in lash specs of .006 and .008 on the grind sheet...I've never had the courage to set lash at anything other than the factory specs.