Duntov Cam Performance

[Duke W.]

Re: Duntov Cam Performance

I can add to the input of the engine rebuild. The engine is a 302 cu. in. block bored 30 over with the stock heads, intake manifold, exhaust manifolds, "480" distributor, and 10.5 compression ratio. I appreciate all the replies, can I get some more input from people that have this Duntov cam ( 12/18 valve lash ) in their engines. At what RPM range do you feel the engine start to pull and what RPM does the cam pull to?

If it's an original 302 Z-28 engine the cam was the 30-30. Those 302 Z-28s barely qualified as a "muscle cars". With standard 3.77 axle and CR four-speed they ran the quarter mile in the low to mid 15s.

Short stroke and big cam = soggy bottom end, but they certainly loved to rev... to the point of bending pushrods and throwing rods. So depending on the block make it a 327 or 383.

My 340 HP (Duntov cam) SWC with a CR T-10 and 3.08 axle was pretty doggy down low and "came on the cam" in the 3500-4000 range. After I modified the spark advance map to 365/375 HP specs low end torque was much improved.

You mentioned a distributor number, but I don't know the specs. The spark advance map is critical to achieving the broadest torque bandwidth, and I recommend the aggressive 365/375 HP spark advance map as a good starting point for all OE mechanical lifter cams.

The Duntov cam's low lift can't take advantage of big port head's larger ports, which is why I would never recommend it for big port heads.

The LT-1 cam has similar low end torque characteristics as the Duntov, but more top end power, about the same as the 30-30 cam.

Duke

[Frank D.]

Re: Duntov Cam Performance

I own several stock Corvettes with an 097-cam engine: a '57, a '62, and a '63. They all have good low-end power. They all idle reliably at 750 rpm and make 13" - 14" of vacuum at that speed with .012"/.018" lash.

I prefer to drive the '57 and the '62 with 4.11 rear end ratios. The '63 has a 3.70 rear and I slip the clutch more when taking off. I don't feel the power "come on" at any particular rpm like it does with the 30-30. That cam is an absolute dog below 3,000 rpm, ESPECIALLY if you run less than .030"/.030" lash or have a rear that is lower-numerically than 4.56.

I found during hundreds of chassis dyno pulls that the peak power with an 097 cam is reached below 6,000 rpm with stock exhaust (varies a little with displacement). I know the cam can rev higher, even with stock (85-pound?) springs, but I see no reason to do it.

Agree totally... I had a 5 speed Tremec put in my 270hp 61 and was concerned about low speed cruising in overdrive with the Duntiov cam....however I found I coulld cruise in 5th gear all day long at 1500 RPM on flat highways just fine if I was easy with the throttle.

[John D.]

Re: Duntov Cam Performance

Hello to all. I am not getting involved with this post as I respect all of your opinions.
I hope the moderators don't mind me saying this. I would like to put a plug in for an old time NCRS member #1900 or so.
. My pal Jeff Reade from American Motors Memories in CA.
Jeff has an exact replacement ''097 cam if you want one. Now he used to have an ad in the Drive Line all the time for this cam but quit for one reason. He's having trouble getting American made lifters. Stay safe. John D.

[Michael J.]

Re: Duntov Cam Performance

I would agree, but frankly my '63 L84 would not be as much fun without the 4.56 rear end. And the '64 L84 I have with the 3.08, well that is pretty doggy until you get high in the RPM torque power band. None of these engines is as much fun as an L36 for low end punch.

[Don H.]

Re: Duntov Cam Performance

I have a 1960 F.I. with the 097 cam and have drag raced it many times over the years (I've held the NCCC Drag Record 3 times). My experience is the same as what Jerry Bramlett said. It will go over 6000 RPM but quit pulling about 5800 so that is where I shift. Don H.

[Michael M.]

Re: Duntov Cam Performance

Duke, what performance gain will I notice with the Duntov cam (12/18 valve lash) when I use 1.6 rocker ratio instead of 1.5 rocker ratio?

[E S.]

Re: Duntov Cam Performance

Hi-Don't forget the heads-62 and 63 L84's had 1.94/1.50 intake and exhaust valves, whereas 64 and 65 L84's had 2.02/1.60 intake and exhaust valves. (same size combustion chamber- 62.076 cc)
Part of the HP increase from 360 to 375?
E.J.

[James G.]

Re: Duntov Cam Performance

I didn't see it on the dyno & it was before video phones, I just paid the bills & ultimately I was happy with how it ran. The build wasn't really vintage, it was pretty exotic for 25+ years ago, it had a callies crank, 6" rods, short compression height pistons, with narrow wrist pins, zero gap rings only the top ring pack, 2.05 intakes.

[Duke W.]

Re: Duntov Cam Performance

Duke, what performance gain will I notice with the Duntov cam (12/18 valve lash) when I use 1.6 rocker ratio instead of 1.5 rocker ratio?

I don't have any experience with so-called 1.6:1 rocker arms, but I can tell you that NO rocker arm has a constant ratio. OE SB rockers start out at about 1.37:1 at low lift and reach a peak of about 1.44:1 at about 0.3" lobe lift, and these aftermarket 1.6 rockers probably have proportionate behavior.

Anecdotal reports I've heard indicate they might add 2-3 percent more top end power.

Duke

[Duke W.]

Re: Duntov Cam Performance

Hi-Don't forget the heads-62 and 63 L84's had 1.94/1.50 intake and exhaust valves, whereas 64 and 65 L84's had 2.02/1.60 intake and exhaust valves. (same size combustion chamber- 62.076 cc)
Part of the HP increase from 360 to 375?
E.J.

461 heads with the big valve set have about 64 cc chamber volume due to the inlet valve relief cut. That's why the advertised CR was dropped from 11.35 to 11:1

462 heads with big valves are about 66 cc. The added 2 cc is due to elimination of the small quench zone the spark plug side of the head.

Duke