Duntov Cam Performance

[Michael M.]

I need the cam experts on this forum to give me their opinion on the performance range of the Duntov 12 / 18 valve lash camshaft. I see from past threads that the 30/30 and LT-1 cam are not good choices for the small block Chevrolet engine. I am rebuilding a small block and need help with a solid lifter camshaft selection.

[Troy P.]

Re: Duntov Cam Performance

I have a strong opinion from one engine builder that if you have an FI engine you need to stick with the stock cam. His firm belief is that the vacuum signal provided by that cam is matched to the Fi unit. But if you have a carb engine you have more choices. Comments on that by cam experts?

[Jim L.]

Re: Duntov Cam Performance

I have a strong opinion from one engine builder that if you have an FI engine you need to stick with the stock cam. His firm belief is that the vacuum signal provided by that cam is matched to the Fi unit. But if you have a carb engine you have more choices. Comments on that by cam experts?

Troy this isn't wrong but it needs clarification.

For an FI engine to idle well, the manifold vacuum needs to be greater than about 12" Hg. Within reason more is better. Off idle, manifold vacuum doesn't matter because the Venturi signal takes over.

The Duntov cam easily produces about 14"Hg at idle with lash settings of 12/18.

The LT1 cam also produces satisfactory manifold vacuum that lets an FI engine idle well.

The 30-30 cam makes less manifold vacuum than either the Duntov cam or the LT1 cam and setting up an FI engine to idle with it requires a lot of attention to fine detail.

In general, therefore, if an engine is built with a cam which produces good manifold vacuum, it can operate with Rochester FI.

Jim

[Philip A.]

Re: Duntov Cam Performance

I need the cam experts on this forum to give me their opinion on the performance range of the Duntov 12 / 18 valve lash camshaft. I see from past threads that the 30/30 and LT-1 cam are not good choices for the small block Chevrolet engine. I am rebuilding a small block and need help with a solid lifter camshaft selection.

Interesting. My recollection of past threads is the exact opposite; that for small block solid lift camshafts the LT-1 is best and 30/30 second best.

[Duke W.]

Re: Duntov Cam Performance

The Duntov cam was designed in the small port/small valve 265/283 era. Those heads have an E/I flow ratio of about 0.75. The later big port heads with their larger inlet valves need a longer duration exhaust event via an earlier opening exhaust valve due the the E/I flow ratio dropping to about 0.65, but Chevrolet did not implement this strategy until the second design "300 HP" cam that went into production for 1967 Both the 30-30 and L-79 cams have the same lobe on both sides.

The ultimate small block cam is the LT-1 cam. It uses the L-72 lobe (on a smaller base circle) on the inlet side and the longer duration 30-30 cam on the exhaust side, phased earlier for less overlap - about the same as the Duntov cam so idle behavior is similar. I recommend the LT-1 cam for all 327 mechanical lifter engine rebuilds both SHP and FI. The 30-30 cam has too much duration and overlap for a sensible road engine. The LT-1 cam makes noticeably more torque/power at low revs with about the same top end.

The LT-1 cam might be a little too big for a 283. The L-79 cam would be a good choice - similar duration but less overlap to tame the idle and improve low end torque, and with proper valve spring setup valve train limiting speed is 6500-6800.

For 283s I've also recommended a "custom" Duntov cam using the Duntov lobes with the inlet retarded 2 degrees and the exhaust advanced six degree, which yields essentially a mechanical lifter version of the L-79 cam, albeit with less lift.

You should do a Web seach: Hinckley Wiliams small block valve adjustment and make sure it's the 9/08 revision.

Duke

[Michael M.]

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?

[Frank D.]

Re: Duntov Cam Performance

Well - I won't pretend to have Duke's knowledge on the topic but that's not what you asked...
My stock 270 hp dual quad 61 283 ci motor had the Duntov cam; it pulled hard to the redline any time I wanted...
And the myth that the cam didn't "go to work" until a high RPM just isn't true... From 1800 RPM up
it had a nice "seat of the pants" feel... A mild run - I wasn't really "pushing it" this day:

https://youtu.be/j0BdovAFjkQ

[Michael J.]

Re: Duntov Cam Performance

OK Duke, my memory needs refreshing. What would have been the stock cam in a '63 L84, and then a '64 L84?

[Mike M.]

Re: Duntov Cam Performance

duntov cam 57-63 high performance solid lifter engines..
30-30 in the 64 and 65 l-84's. mike

[James G.]

Re: Duntov Cam Performance

I built a .020 12:1 302 with a crower .636 gross lift solid roller, 268 intake 280 exhaust using the original heads with blended bowl transitions made 517 hp @ 6800.
It made over 300ft # torque by 3500 RPM and made 14" vacuum at 1000rpm idle. I could not believe how easy the car was to drive.

[Michael J.]

Re: Duntov Cam Performance

Thanks Mike, I had thought that was the changeover period from one to the other, and why the '64 L84 has more HP than the '63.

[Michael M.]

Re: Duntov Cam Performance

Frank, I like the fact that the cam started to come in at 1800 RPM. What RPM does the cam pull to?

[Frank D.]

Re: Duntov Cam Performance

Frank, I like the fact that the cam started to come in at 1800 RPM. What RPM does the cam pull to?

I ran the car at SEbring up to 6500 RPM on several sprints, always pulled strong....throughout the range...

[Duke W.]

Re: Duntov Cam Performance

I built a .020 12:1 302 with a crower .636 gross lift solid roller, 268 intake 280 exhaust using the original heads with blended bowl transitions made 517 hp @ 6800.
It made over 300ft torque by 3500 RPM and made 14" vacuum at 1000rpm idle. I could not believe how easy the car was to drive.

T = 5252(HP)/6800 = 399

There's no way in this universe that a vintage naturally aspirated 302 can make nearly 400 lb-ft of torque at 6800 no matter what CR and camshaft it has.

Duke

[G B.]

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.