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Cam for stock ‘71 402

7K views 35 replies 18 participants last post by  novadude 
#1 ·
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!
 
#2 ·
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-performance/704641-402-bbc-flat-tappet-cam-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.
 
#5 ·
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.
 
#7 ·
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.
 
#8 ·
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?
 
#10 ·
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. :)
 
#11 ·
#12 ·
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.
 
#14 ·
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/forums/showthread.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.
 
#15 ·
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/
 
#17 ·
#22 ·
Re: Cam for stock ‘71 402



With 402" and no compression and a cruise rpm of ~2K, you don't really want--or need a split pattern cam, a single pattern will make better low end power.

Personally I would use the 10303 cam and install a decent 2 1/4" or 2 1/2"dual exhaust (retaining the manifolds), close the hood and cruise the wheels off of it.

Oh yeah, keep the QJet.
 
#20 ·
That cam calls for 9.5-10.5 compression. and some gear.
But is that because they want their cam to impress you so they do not get a bad rap.

That is the thing about camshafts. They will get blamed for bad performance ..when it could be the rest of the parts.

It is nice if someone ran the EXACT same combo you have and can tell you this is good and this is junk.

That is hard to do really.

My friend at the cam shop told me I change cams like he changes underwear :)
Yea I like to try things.
But one thing I learned when I was 18 or 19 I need to run ported heads.

That cam in the link is 224@ .050
I have ran 224 at .050 single pattern and it was a little down on power vs my 218@ .050 in a 350".
Made up for it past 4500 rpm and took me from 14.50 to 13.8 et.
But 350" with ported iron heads.

I like to swap cams and see what they do but most people do not.
My 4 door 57 that pulls my boat has 10.87 compression so it runs well with just about any cam I stick into it.

I quit playing with 8.5 compression when I was around 21.
I do want to revisit it but use a turbo in the process.
But even that low compression Turbo trend is not what some of my quick buddies are doing.
10.3 compression and 27 PSI on top of that and running into the 4's in the 1/8 mile!

Friend had stock heads 76cc on his 355" with thick head gasket and non decked block .. ran the 292H with stock springs. valve float at 5600 so he shifted at 5500. It was a turd that sounded awesome.

I raced him and smoked him by 5 bus lengths.
I told him I was shifting at 6900rpm and ran the 270H which was 224 @ .050 on a 110 LSA.
I told him he needs a much smaller cam and he said he did not want to rev it too much past 5500.

I seen him the next month and he installed the 268H which was 218@ .050.
He said it is the fastest engine he had ever built and it had the smallest cam he ever used.
Low compression and NON ported iron heads

Yep!
 
#23 ·
Re: Cam for stock ‘71 402

Isky MEGA_Hydraulic 264. Cam And Complete Kit [390264] - $650.00 : ISKY Racing Cams, Do It Right

PS. The "MEGA" series are typically tight LSA, while the CompuCam series are typically wider LSA. The wide will give a smoother idle and a bit more top end pull with a broad flat TQ curve. The tight (108) gives a slight chop at idle and a mid range hump in the TQ curve, sacrificing some top end. I personally would use the MEGA series.
 
#24 ·
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#25 ·
I just stumbled across the cam card from a rebuild I did many years ago. Same situation, stock ‘72 402 with measured compression barely over 8:1, stock converter, gears, etc.

At that time Harold Brookshire recommended the following two cams.

https://www.lunatipower.com/high-ef...t-tappet-cam-chevrolet-big-block-262-272.html

https://www.lunatipower.com/high-ef...t-tappet-cam-chevrolet-big-block-266-270.html

I went with the smaller of the of the two. Not much to say, it’s a very mild streetable cam that fit the combo and was a healthy bump over the stock 193/204 and .398/.430 lift cam.
My opinion is, unless you bump up the compression and do other supporting mods, stick in this cam size range for a street cruiser and be happy you gained power over stock with no real trade off.
 
#32 ·
Changing valve springs just got easier. :)

Good luck!
 
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