Cam selection for a 70's Malibu

[Christian Nelson]

Hey guys, feel free to jump all over me iff needed, but I have a cam question.

A friend of mine asked me for help picking a cam for his son's 70 something malibu.

It's got a stock 350 (as far as he knows) with vortec heads, with aftermarket intake and I think holley carb?

Anyhow, he found a bent pushrod, and thinks either his cam is bad, or lifter is shot, because a couple of his pushrods aren't even going up and down.

So, he wants me to help pick a cam to replace this one.

We both think the vortecs were just pulled off and installed.

He doesn't want to do any machine work to the heads, just wants to slap a new cam in, and pushrods. I am not wanting to just shoot him down, however I think he's gonna end up puling the engine apart, and so forth..

Anyhow.

Research I've done, I find people saying stock vortecs can only handle .420 lift, and that one should pick a cam with 8-10 longer ex duration than in.

Well, looking at Summit for cams, I am getting walleye vision with all the choices.

I've found a couple good low end torque cams, but really not finding anything that fulfills the kid's desire.

He has a stock torque converter, wants to feel the power in his seat, and would like a lopey idle.

I've not found many decent street cams that fit this bill. Couple of RV type cams seem to work, but most are too high lift, if indeed .420 is the hard limit.

Anyone have any good ideas?

My biggest question, just how firm is th .420 lift limit?
What cams do people like for good power, lumpy idle, with stock stuff?

 

[El Camino Man]

Im no cam expert but he should probably stick to something fairly close to stock. After you start getting too crazy with it, youll need to start changing things like valve springs and your torque converter... EEK!

Im sure with a little homework, he can find something with a bit of a lope and a hair more get-up but its not going to be spectacular on a stock motor. Iv seen it a few times now... someone slaps in a hotter cam without changing anything else and it ends up robbing power.

Hope I helped!

 

[Driver4r]

70 350 350hp Vette cam, adds a lope but still keeps the mpg in good standings.
Its what i have in my truck, but my trucks also a little more then factory.

 

[BigAl285]

Do the lifters move freely in the lifter journal, valves adjusted correctly? Hate to see something happen to the new cam. If I was doing this I would call the brand of cam you want to go with and see what they think. When I was shopping for my cam they asked me everything about my motor and what I expect out of it. If you go to big with the cam I have a nice 2000 rpm stall Im trying to sell.

 

[Swims350]

I always heard the vortec's were good for a bit more lift like close to 480 or so?

I'd say comp 268h. it's got a good lope, ut it's single pattern 218/218 duration at .050

and 454 lift on both sides.

they say to add a mild stall but I had a 2k stall and it sucked. I';d run a stock converter and be done.

 

[Driver4r]

I always heard the vortec's were good for a bit more lift like close to 480 or so?

I'd say comp 268h. it's got a good lope, ut it's single pattern 218/218 duration at .050

and 454 lift on both sides.

they say to add a mild stall but I had a 2k stall and it sucked. I';d run a stock converter and be done.

Ive heard of vortecs binding at 470.

 

[bucket]

Ive heard of vortecs binding at 470.

From my findings, .465 is the safe limit, but some can manage .485 on the vortecs.

 

[HotRodPC]

Man ohh Man is this ever a loaded question? Cam selection is easy. BUT, First you have to know what performance you want? Do you want alot of bottom end, mid range, top end? Economy? Torquey? Kid driving it, does he want him to have alot of power to roast the tires, does the state do emissions testing? What rear gear does it have? All kinda things to know before choosing a cam. I have a feeling he's going to be wanting something like an RV cam.

 

[bucket]

Man ohh Man is this ever a loaded question? Cam selection is easy. BUT, First you have to know what performance you want? Do you want alot of bottom end, mid range, top end? Economy? Torquey? Kid driving it, does he want him to have alot of power to roast the tires, does the state do emissions testing? What rear gear does it have? All kinda things to know before choosing a cam. I have a feeling he's going to be wanting something like an RV cam.

Wrong

Most people want a bottom-of-the-page rumpity rumpity cam. However, most people NEED an RV cam.

 

[philjafo]

All good advice here, but before even thinking about a new cam figure out why bent pushrods, why some not moving. Yank that motor apart and figure that stuff out, a cam swap is a lot of work and money to have to do it twice. Besides its easier if the motor is out. Then call your favorite cam grinder and have a discussion about the car and what you expect out of it.

 

[HotRodPC]

Wrong

Most people want a bottom-of-the-page rumpity rumpity cam. However, most people NEED an RV cam.

Well, you can get bumpity bumpity bump bump cam too, it just puts the power band range at the top of the spectrum so it takes off like a turd is all that will do, but yeah, it will SOUND badass with flow masters.

But, to my point, does dad want the kid to have some power or not. Not a good idea to turn a 16 yo kid loose with alot of bottom end and mid range, cuz they'll sure use it, and then loose it !!! Sounding like an RV cam candidate to me though.

 

[HotRodPC]

All good advice here, but before even thinking about a new cam figure out why bent pushrods, why some not moving. Yank that motor apart and figure that stuff out, a cam swap is a lot of work and money to have to do it twice. Besides its easier if the motor is out. Then call your favorite cam grinder and have a discussion about the car and what you expect out of it.

Not bad advice either to call a cam grinder, but there are so many options to choose from today, I bet he can find one without a custom grind. A cheap $59 Summit Cam will do the job well, and I think it's about $100 for a Summit Cam and Lifters.

If you have 2 pushrods NOT going up and down, that means you've likely got flat cam lobes maybe caused by someone over tightening the valves. Hard to diagnose bent push rods. In MOST cases, but not all, bent push rods come from over revving and floating valves. SBC's aren't zero clearance motors so that didn't do it.

 

[Christian Nelson]

I agree, finding out why bent pushrod, and why others don't go up and down is important. He thinks it may be because previous owner installed too high a lift cam in the engine, and wore out the lobes..

I don't know. He doesn't want to do a rebuild, doesn't even want to pull the intake manifold off. I say good luck, and I am pretty sure he will end up doing it anyhow. but I am just trying to give him my reccomendation.

I agree RV cam is best. Kid is 19. He wants to feel the power. No emissions. I just kept seeing the .420 and many othe rnumbers, and need an uper limit.

My thinking is, get a cam with as high a lift as I can find, with 10 longer duration on exhaust than intake, set up for rpm range between 600-3500 for power.

That, unfortunately will not give him as much of a rambunctious sound. This is why I mentioned before how I'd like to somehow figure out how to open a vacuum leak or something at idle to make them sound god, and actually have some decent performance when they wanna drive the thing lol!

Yeah, I am leaning towayrd RV type cam, but even moving the rpm up abit, say to the 1500-4500 might be nice.

But I really need to know the real limit of the vortec heads so I can see the highest lift I can get away with. One can get some good performance with low duration, high lift cams I hear.

 

[El Camino Man]

Your going to HAVE to remove the intake to swap the cam. Unless its got those fancy lifter catchers. If its just got vortec heads and not block, I doubt it has em but I could be wrong

 

[Swims350]

see there ya go comp 268h has only 454 lift, so it's under the limit and its bumpity bump somewhat.