Cam for stock ‘71 402 - Chevelle Tech
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post #1 of 35 (permalink) Unread Oct 17th, 19, 9:30 PM Thread Starter
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Tony
 
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Cam for stock ‘71 402

Hi folks, I have a low mile 71 Impala 402 convertible that needed some head work so it’s currently sitting with the heads off...and I thought, perfect time to replace the old nylon gear timing set...and while I’m in there, why not do a mild cam swap. What do you guys recommend for a 100% stock low compression ‘71 402? I don’t plan to make any other mods unless they are invisible.

Thanks!

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post #2 of 35 (permalink) Unread Oct 17th, 19, 10:03 PM
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jeff
 
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Re: Cam for stock 71 402

Here is a little reading on a 402 cam selection and some suggestions.. but his is more modified than yours.
https://www.chevelles.com/forums/13-...-opinions.html




I would look for something in the 218-224 duration at .050 if it was mine and I was just going with stock heads.
Yes I would probably at least change valve springs.

If my compression was low ..like below 10:1 I would tighten up the LSA on the cam to 108 unless MPG was very important and then i would probably opt for 110 or 112.

I like early closing intake sides to trap some cylinder pressure.. but I also like some added overlap especially with weak flowing heads.

If you want sound and not too concerned with pulling the last bit of MPG from it tighten the LSA.
Especially if it is low on compression. 106 or even 105.

Others will chime in I am sure. I am old school and like tight LSA cams.. they just work very well for me.
I know it is not about the LSA but the valve events.

Good luck to you.
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post #3 of 35 (permalink) Unread Oct 18th, 19, 2:02 AM Thread Starter
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Tony
 
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Re: Cam for stock ‘71 402

Thanks Jeff! That was about the duration range I had in mind. Any grinds you recommend?

Tony

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post #4 of 35 (permalink) Unread Oct 18th, 19, 7:46 AM
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Re: Cam for stock ‘71 402

https://www.summitracing.com/parts/i...make/chevrolet

I like Isky products for FT cams.

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post #5 of 35 (permalink) Unread Oct 18th, 19, 9:57 AM
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jeff
 
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Re: Cam for stock ‘71 402

That Isky in the above link looks like it would work well based on the advertised numbers anyway.
To take advantage of it you will really need to upgrade valve springs..Just about any cam really needs a spring upgrade.

If your heads are off it is not but a couple steps away from some easy bowl porting to pick up another 30-40 HP.

A corded drill and a hard stone is all it really takes.
You can spend money on all the other cutters but the majority of the power is in the blending and shaping.
It would be a shame not to do it. About the same power you will get from the cam swap. Talking small cams here.
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post #6 of 35 (permalink) Unread Oct 18th, 19, 11:04 AM
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Re: Cam for stock 71 402

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Originally Posted by badrad View Post
read my mind on that one

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post #7 of 35 (permalink) Unread Oct 18th, 19, 11:28 AM
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Re: Cam for stock 71 402

A 71 Impala is a Heavy car that is likely to have tall gears (2.56-2.73) and a tall tire. Real compression ratio on that engine likely isn't much more than 8:1.

Having said that, I like the ISKY 262 Supercam. 208/208 @ 0.050" on a 108 LSA. I think anything with much more overlap will be a dog off-idle in a heavy car with tall gears and no compression.

A '71 Impala sounds more "cruiser" than "racer" (to me), so focus on pumping up tq in the 1500-4000 rpm range and forget about power above 4500-5000 rpm. JMO.
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post #8 of 35 (permalink) Unread Oct 18th, 19, 12:04 PM
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Re: Cam for stock 71 402

Hey guys, could he use a shim head gasket to get his compression up to like 9.5 to 1?

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post #9 of 35 (permalink) Unread Oct 18th, 19, 4:15 PM
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Shane
 
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If heads are off , have them decked .060 or so ... simple answer would be xe268 . More in prefect combo but would run with stock parts and have a some rump/gains . 💨💪
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post #10 of 35 (permalink) Unread Oct 19th, 19, 12:17 AM
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jeff
 
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Re: Cam for stock ‘71 402

A camshaft with more overlap does not make an engine a dog out of the hole it is later closing intake valve that reduces pressures that kills the low end.
I Agree heavy cars with crappy gears are hard to get rolling.

I just helped a buddy with his 355" in a 4000 lb chevy truck..I told him get some Etech heads and he did and i ported them and took his 305H magnum cam and had it reground using the 280H masters and stuck it on a 106 LSA to close the intake valve much earlier.
The 305H magnum does NOT have the added +4 degrees advance ground into it I advanced the reground cam and installed it on a 102 LCA Not to be confused with LSA.

He has 2.75 gears and Hurricane intake with 750 edelbrock..yea it has a stall converter 3000 stall cheapy one in a TH 350.

That heavy chevy will flat move now.. I was quite impressed with the power even right out of the hole.
And he was nothing but giggles when he first drove it.

Lots of 1 tire fires.
Hard to hook it up.
Surely with the correct cam and some head work the BBC could match some little 355".
Etech 5089 heads were used and flowed 256 and 187 @ .500" lift.
Cast flat tops .030" down the hole and .039" head gasket.

Buddys truck is getting some 4.11 gears and a locker though for much more tire fire issues.
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post #11 of 35 (permalink) Unread Oct 19th, 19, 4:46 AM
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Bill
 
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Lightbulb The perfect cam for you engine is...

The 100% matched el-perfecto camshaft for your motor/usage/purpose.

Use a Cloyes timing chain & Crane anti-pump up (drain-hole) hydraulic lifters, with Comp beehive springs. Use the short poly-locks.

You WILL be pleased & amazed by these unseen mods, for sure.!


https://www.lunatipower.com/voodoo-h...k-250-256.html
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post #12 of 35 (permalink) Unread Oct 19th, 19, 8:25 AM
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Re: Cam for stock ‘71 402

SUM-K1302

One and done. Used this cam in my 71 496 Monte in the first incarnation and it sounded great and ran even better,

In 2009 when my daughter turned 16, I bought her a 72 Monte with a 402. Used the same cam due to need. Bought it with a wiped cam.

She loved that car.

Couple of junkers and a few clunkers.
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post #13 of 35 (permalink) Unread Oct 19th, 19, 10:52 AM
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Jeff
 
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Re: Cam for stock 71 402

Checkout this thread from the guy whos knows pretty sharp with performance engines.. Its on a Pontiac board but it applies to your set up...

https://forums.maxperformanceinc.com...d.php?t=834752
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post #14 of 35 (permalink) Unread Oct 19th, 19, 11:36 AM
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jeff
 
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Re: Cam for stock 71 402

Quote:
Originally Posted by hydro462 View Post
Checkout this thread from the guy whos knows pretty sharp with performance engines.. Its on a Pontiac board but it applies to your set up...

https://forums.maxperformanceinc.com...d.php?t=834752

That engine had 10.5 or 10.6 as was stated in compression and really good flowing heads with larger valves as was stated and the tight LSA put it into ping mode.


Some attention to details when building a high cylinder pressure engine.
NO sharp edges anywhere in the combustion space and NO stickups like casting flash allowed in the combustion space.
Smooth intake runners are a poor choice as they do not keep fuel atomized as well as a very rough intake runner texture.
The little things can make or break a build. There may have been some missed attention on that build.



I built a .030 over 396 years ago for a friend and it has 11:1 compression, a comp 280H that was made using the SBC masters so .544" lift and 234 at .050 duration. I had it ground on a 108LSA.
210-215 psi cranking pressure, it runs excellent with open chamber oval port heads from 1969, I ported those heads, they have 2.19-1.88 valves.
It has been together over 15 years and gets hammered on.
91 Octane from 7-11.
38 total timing. all in by 2200rpm. 4200lb truck with 3.08 gears currently. limited slip that usually has 1 tire hooking.
He had it in a 1969 3/4 ton for a few years and pulled his trailer and tractor with it.
Then a Moore Ok tornado stuck the house on top of the truck.
Engine is now in a 1/2 ton 1966 truck that is just as heavy.
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post #15 of 35 (permalink) Unread Oct 20th, 19, 1:21 PM Thread Starter
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Tony
 
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Thanks for all the help so far guys. This is a totally stock engine with 8.5:1 advertised compression, and 2.73 gears, so I’m a little hesitant to go too big on the cam. Andy, your cam looks great but I don’t think I have the gears for it. The Voodoo grind looks good but anecdotally people seem to have trouble with flat lobes. What about this Isky grind below?

https://www.summitracing.com/parts/isk-396286/

Tony N.
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