Cam question 402BB

[Heff]

ok I'm rebuilding the 402 as follows .030 over, reconditioned rods, arp bolts, k/b forged -41cc domed pistons, and balanced rotating aasy. heads are stock 1971 open chamber 2.19 int. 1.74 exh. mild port and polish can't remember the casting # they are at my builder. rebuilt factory quadrajet with Cliff Ruggles kit. can use factory 71 low rise intake, or factory hi-rise from a 67 396. I will be using exhaust manifolds to 2.5" duals w/ crossover and flowmaster delta 50 mufflers. 12 bolt 3.55 posi rebuilt 400th w/shift kit. This will be a street driven car. i want to keep it looking completely stock under the hood but give it as much umph as I can. I will run a stall converter if the combo requires it. any help or experience in cam selection would be greatly appreciated.

[Mike 57]

I would call a at least three cam companies and give them the complete rundown of what you have and what you want it to do. they will be happy to give you some advise.

[wallaby]

You need to change valve springs too, if you want an aftermarket cam. Anything over (I think) .480 lift gives stock springs coil bind. Figure long-slot rockers also...unless you plan to use roller rockers.

I am currently running a Lunati 60202 cam. It has a pretty smooth idle...but the good part is it makes great vacuum for the brakes and makes big torque. It's not too bad with fuel economy either. It's a big improvement over a factory cam, but it really doesn't have the sound; the choppy idle some folks expect from a performance cam.

Here is the Lunati page: LINKY

 

[72MC]

Heff, if you stay with the stock heads, along with what Mark has stated, be sure to check and verify your max valve lift. With new valve springs, my stock heads on the 402 BBC I am rebuilding is only getting a .550 max valve lift number. - Dave

[Heff]

Thanks for the info I've already purchased the long slot rockers from summit (forgot to mention it in the first post)I will purchase matching springs w/ whatever cam I end up with. Wallaby the 60202 is a cam I was really leaning to until I talked to Cliff Ruggles, he said that cam was too small, and would build too much pressure with my set-up roughly 10.5 to 1 he suggested a cam in the 224to226/ 234to236 at .050 with a 113 lsa?

[wallaby]

Ok, i see you have a bigger dome on your pistons than I do...the catalog says 10.5:1 with a 119cc head chamber.

You will want to bleed off some of the low-rpm pressures to make it pump gas friendly. Now I always thought the way to do that was to increase the valve overlap; and that is done by increasing the duration...or decreasing the LSA. (the increase in overlap is what gives the engine the choppy idle and poor low speed performance).

I find it strange that he recommends a cam with more duration, and a larger LSA. It seems to me that puts us back where we started...I find it unusual.

But he knows more than I do.

 

I cruised the Lunati site, and found that even the 60203 (the next larger cam in the series) jumps to a 110 LSA. Nearly everything in the Comp Cams catalog is based on a 110 LSA, but they have something close in their marine section: LINKY

 

The only problem I have is the springs. I have used the Comp 911 springs and had nothing but trouble with them. I broke 3 before I decided to get a new set from Lunati, and have had no issue since. The experience realy soured me on the Comp Cams brand.

 

 

[Sam (Bones)]

a tighter LSA will also effect idle quality and narrow the power band of the engine

 

I understand what Mark is saying...I was thinking the same thing

 

watching at what degree the intake valve closes will also help

[Heff]

 

This is from comp's website on LSA (sorry don't know how to do linky)so more LSA would be better for my application I think? If so summit sum-1302 looks like a good choice 228/238 at 114 LSA

 

 

 

 

EFFECTS OF CHANGING LOBE SEPERATION ANGLE (LSA)

 

Tighten (smaller LSA number) Widen (larger LSA number)

Moves Torque to Lower RPM Raise Torque to Higher RPM

Increases Maximum Torque Reduces Maximum Torque

Narrow Power band Broadens Power Band

Builds Higher Cylinder Pressure Reduce Maximum Cylinder Pressure

Increase Chance of Engine Knock Decrease Chance of Engine Knock

Increase Cranking Compression Decrease Cranking Compression

Increase Effective Compression Decrease Effective Compression

Idle Vacuum is Reduced Idle Vacuum is Increased

Idle Quality Suffers Idle Quality Improves

Open Valve-Overlap Increases Open Valve-Overlap Decreases

Closed Valve-Overlap Increases Closed Valve-Overlap Decreases

Natural EGR Effect Increases Natural EGR Effect is Reduced

Decreases Piston-to-Valve Clearance Increases Piston-to-Valve Clearance

 

 

[Andy's Auto]

I am a big fan of this cheapie Summit Cam kit cam kit for 99% of the street driven heavy big block cars. Cheap, effective, pull like a train to 5200.

 

Andy

[Heff]

Thanks for all the info, I think I'll look into the Summit cam as mentioned above. looks like a better choice, and the money saved may go towards some roller rockers.

[Andy's Auto]

Thanks for all the info, I think I'll look into the Summit cam as mentioned above. looks like a better choice, and the money saved may go towards some roller rockers.

 

I put that cam in my own 72 402 Monte and it is a helluvalotta fun. Smokes the tires at will. I still use the stock convertor and a 3:31 Posi 12 bolt. When my daughter wrecked my 07 TrailblazerSS, that was what I put her in. She got in much trouble at school.

 

Andy

[72MC]

I am a big fan of this cheapie Summit Cam kit cam kit for 99% of the street driven heavy big block cars. Cheap, effective, pull like a train to 5200.

 

Andy

 

Hope your right Andy. That's the cam in my 402 I purchased from bobmc. He liked it as well. Guess I will find out how it is when I am done rebuilding and it goes in the El Camino. - Dave

[Heckeng]

Call Chris Straub, Comp Cams, and Lunati. They may back up what your guy said, or you might prevent making a big mistake and burning up some pistons!

[Andy's Auto]

Originally Posted By: Andy's Auto

I am a big fan of this cheapie Summit Cam kit cam kit for 99% of the street driven heavy big block cars. Cheap, effective, pull like a train to 5200.

 

Andy

 

Hope your right Andy. That's the cam in my 402 I purchased from bobmc. He liked it as well. Guess I will find out how it is when I am done rebuilding and it goes in the El Camino. - Dave

 

Hey Dave. Look what Bob drives. He obviously has good taste.

 

Andy

[Heff]

Hey Andy, just to update Cliff Ruggles e-mailed me back and said his cam of choice for my application would be the Summit 1302 also. Based on your real world experience, and Cliff's recommendation for the exact same cam I'm feeling good that I've made the right decision to go with the 1302. I'll let you know in a couple of months when I have it all together. It's also good to know I won't need a huge stall to make this work. Thanks again for everyone's input.