Cam question

[Bruce B.]

I have a 327, 0.040 over with 11 to 1 pistons and stock cast iron GM heads with 1.94" 1.50" valves. My desire is to have 15" vacuum minimum at idle so I can use MAP to fuel my Hilborn injection.
I have spoken with a cam manufacturer and they recommend the following flat tappet (my preference) custom ground cam:
Duration @ .050 224/228
Lift with 1.5 Rockers .525/.525
LSA 115
Any input and opinions will be appreciated.
Thanks.

[Duke W.]

Re: Cam question

...might do it - not that much different than the L79 or L46 cams that pull about 14" @ 750, and setting the idle speed higher pulls more vacuum, but the high lift is going to require gorilla valve springs and possibly cause valve train durability problems.

Why not just go with the L46 cam? On 327s I recommend the L46 cam over the L79, but install it advanced 4 deg. from the OE indexing.

As with any other engine, the best bet for "more power" is massaging the heads. To get the full benefit of massaged heads and the Hillborn injection system, the engine needs to rev beyond the valve train limiting speed of hydraulic cams. The LT-1 cam would be the best choice, but it's only about 12" @ 900.

Duke

[Joe R.]

Re: Cam question

The LT-1 cam would be the best choice, but it's only about 12" @ 900.

Duke[/quote]

Isn't the LT-1 cam your only recommendation? IF it were not for the 30/30 64-65 camshaft the LT-1 would be the biggest dog of all time.

JR

[Timothy B.]

Re: Cam question

Why is the LT-1 cam the biggest dog of all time?

I think the 1970 lt-1 350 motor is the best small block chevy made. It's got all the goodies and will rev easily to 7000rpm.

[Stuart F.]

Re: Cam question

Tim;

Joe posted a few "testy" comments early this morning. All I can say to Joe is "don't hold back!"

While directing comments to you in this thread Tim, I was wondering about your PCV restrictor setup that you were going to send me pictures on: Aren't you concerned that you may limit vapor evacuation from your crankcase?

Stu Fox

[Joe R.]

Re: Cam question

Tim;

Joe posted a few "testy" comments early this morning. All I can say to Joe is "don't hold back!"

While directing comments to you in this thread Tim, I was wondering about your PCV restrictor setup that you were going to send me pictures on: Aren't you concerned that you may limit vapor evacuation from your crankcase?

Stu Fox

Stu,

At 65 one is allowed to take some "editorial" freedom and especially at 3AM when the old one cannot sleep.

JR

PS. The LT-1 can hardly get away from the stop light without a push! The torque of a lawn mower engine!

[Michael H.]

Re: Cam question

PS. The LT-1 can hardly get away from the stop light without a push! The torque of a lawn mower engine!

I have a feeling there will be a rebuttal coming from the west coast when Duke wakes up and reads this.

[Stuart F.]

Re: Cam question

Joe;

At 72 I well know the feeling, and I fully agree with you about both the LT-1 and the Fuelie Engines. I too have had a fuelie (58) and it was fun (had it in a 50 Chevy Coupe with a "whistler" 57 air cleaner). It torqued well from 3500 on up, but lacked the low end torque and sound of a good single or dual quad carbureted set up. Often times at the strip (back in the day), the low end performance (off the line) of the carbureted Chevies was enough to overcome the fuelies at the other end. I know I never had much problem with them. Same goes with my 63 L-76; I easily out ran 63-65 Fuelies on the road, but that was more a matter of gearing, i.e. my 3.36 vs, their 3.70's, 4.11's and of course the 4.56's. You remember those days with the C-2 bodied cars; take it right up to the point of rotation and take off! Yee Haa!!

Stu Fox

[Stuart F.]

Re: Cam question

Yes Michael, and it will probably be a long one. Oh well, us old geezers need to keep the blood pumping somehow.

Stu Fox

[Joe C.]

Re: Cam question

I have a 327, 0.040 over with 11 to 1 pistons and stock cast iron GM heads with 1.94" 1.50" valves. My desire is to have 15" vacuum minimum at idle so I can use MAP to fuel my Hilborn injection.
I have spoken with a cam manufacturer and they recommend the following flat tappet (my preference) custom ground cam:
Duration @ .050 224/228
Lift with 1.5 Rockers .525/.525
LSA 115
Any input and opinions will be appreciated.
Thanks.

Here are the specs on the L46/L82 cam (3896962):

LSA: 114
Dur @ 0.050: 222/222
Lift with honest 1.5:1 (@POML) rockers: .450/.460

Comparison of both cams shows that the custom grind has very slightly wider LSA, which, all else being equal, would produce less EFFECTIVE overlap, and thus marginally higher idle vacuum if both are idled at equal RPMs. As you might know, idle vacuum is a function of overlap, but must be looked at in terms of "area under the curve", or inch degrees. Because your custom grind has significantly higher lift than the L46 cam, and despite the slightly wider LSA, the increased lift will have the effect of more than cancelling the slightly lower (cam degree derived) overlap of the custom cam. The custom cam will have somewhat LOWER idle vacuum at the same RPM than the L46 as a result of its higher lift.

If we knew the custom grind's advertised (seat-to-seat), or J604d duration, then that would give us a more complete picture; assuming that it's not an aggressive profile, as is the vintage cam, I believe that the above analysis will give a realistic estimate of the custom cam's vacuum-producing characteristic. Of course, if it's more aggressive than the vintage grind, then the idle vacuum will decrease in direct proportion to the lifters' velocity/acceleration on the flanks as compared to the L46/L82.

The lift of your custom cam is considered relatively low by today's standards.......only .040" more than the "346", and .016" more than the second design "off road's" exhaust lobe. You wouldn't need an outrageously strong spring with this cam, although GM's "Z28" or "142" spring would not accommodate the lift on this cam before coil bind becomes a problem. Use of this cam would involve sinking money into your original heads. Screwed in studs would be a must, and enlargement of the spring pockets might very well become necessary. The LS1 beehive spring should be investigated as it is progressive and actually not very stiff as compared to a stock spring. It will, however, accommodate your desired cam's higher lift. IT IS ESSENTIAL THAT YOU HAVE YOUR HEADS FULLY PORTED TO TAKE ADVANTAGE OF THE CAM'S HIGHER LIFT, ALTHOUGH YOU MIGHT BE WASTING YOUR TIME DUE TO THE HEADS' SMALL VALVES. IF YOU UPGRADE TO 2.02/1.60'S, WITH THE REQUIRED UNSHROUDING, THEN YOU WILL PERHAPS GAIN A 30% TORQUE/HORSEPOWER ADVANTAGE.

If you do not invest the money to upgrade your heads, then a cam providing lower lift would be in order. You should also have that custom grind's LSA opened up by another 2 degrees in order to ensure a mushy smooth idle with your target vacuum as a "given".

[Joe R.]

Re: Cam question

I have a feeling there will be a rebuttal coming from the west coast when Duke wakes up and reads this.

Michael,

Yep, but all he has to do is copy and paste!!!!!

JR

[Michael H.]

Re: Cam question

IF YOU UPGRADE TO 2.02/1.60'S, WITH THE REQUIRED UNSHROUDING, THEN YOU WILL PERHAPS GAIN A 30% TORQUE/HORSEPOWER ADVANTAGE.
".

Is that your final answer?