1970 CHevelle 350 Swap cam choices - Chevelle Tech
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post #1 of 23 (permalink) Old Feb 13th, 20, 7:48 AM Thread Starter
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1970 CHevelle 350 Swap cam choices

Thank you all with the help dedcing on the 350 vs 454 due to my parts.

Here is the deal - I have been asking people and researching and I am considering another cam. Here is what I a considering - what do you all think?

Here is my setup:
350 SBC 4 bolt main – stock bore and stroke
Summit Racing Headers SUM-G9001-SS Full-length Primary Tube Outside Diameter (in):1 5/8 in.
350 CHEVY CYLINDER HEADS #041 casting NEW GUIDES .500 SPRINGS
new stainless 2.02 swirl polished intake valves
new stainless 1.60 swirl polished exhaust valves
Heads are assembled with new .500 Z-28 lift valve springs
64CC of flow rate
Rebuild/overhaul master kit with moly rings
Edelbrock Single-Quad Performer Manifold and Carburetor Kit for Small Block Chevy 1955-1986 - Performer EPS Intake Manifold, 600cfm Performer Series Carburetor

I am looking at these cams. I want something that will run power brakes, or close to it, and I want something that is good from the bottom end – stop light racing and tire burning are fun in my book.

Which one of these would work best for me? Can I used my z28 valve springs?

COMP Cams Xtreme Energy 262H - COMP Cams 12-238-2
K12-212-2
https://www.summitracing.com/parts/cca-k12-212-2
K12-600-4
https://www.summitracing.com/parts/cca-k12-600-4
K12-246-3
https://www.summitracing.com/parts/cca-k12-246-3
K12-238-2
https://www.summitracing.com/parts/cca-k12-238-2
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post #2 of 23 (permalink) Old Feb 13th, 20, 8:37 AM
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What transmission and rear end gear ?
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post #3 of 23 (permalink) Old Feb 13th, 20, 9:42 AM Thread Starter
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Re: 1970 CHevelle 350 Swap cam choices

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Originally Posted by Reelysalty View Post
What transmission and rear end gear ?
Looking at a TH350 and 3.42 rear end. I open to stall converter suggestions.
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post #4 of 23 (permalink) Old Feb 13th, 20, 10:13 AM
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“I want something that is good from the bottom end – stop light racing and tire burning are fun in my book.”

You can have a lot of stoplight fun in your 350 Chevelle if you change your thinking....3:73/4:11 posi, Muncie close ratio 4 speed, 750 DP Holley, choose a cam w/operating range of MOL 2400-6500. If you need vacuum, get a vacuum pump. Don’t sacrifice motor for vacuum!
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post #5 of 23 (permalink) Old Feb 13th, 20, 10:50 AM Thread Starter
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Re: 1970 CHevelle 350 Swap cam choices

What about these two?

I am looking at these two now – wondering what might benefit me the most:

K12-238-2
https://www.summitracing.com/parts/cca-k12-238-2

CCA-12-600-4.

https://www.summitracing.com/parts/cca-k12-600-4

I don't want to go too wild on my first build, just right at the edge.
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post #6 of 23 (permalink) Old Feb 13th, 20, 11:24 AM
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Re: 1970 CHevelle 350 Swap cam choices

I ran this cam...

https://www.claysmithcams.com/hr-809...que-3600-3800/

With 3.31 gears and 2400 converter made good power, drove nice and sounded good.

'71 Malibu
3580 #, Carbed 6.0l LS swap in process
T-350, PTC 9" converter, 12 bolt, spool, 3.90 gears, MT ET R 275/60/15

355 [email protected]
125 [email protected]
388 Mud Motor- [email protected]
100 shot [email protected]
'72 Greenbrier Wagon: 454, 700R4, 12 bolt with 3.73
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post #7 of 23 (permalink) Old Feb 13th, 20, 11:38 AM
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Re: 1970 CHevelle 350 Swap cam choices

If there was some bowl porting done to the heads I would say the XE274 would be the one I picked and a good 3000 stall converter.
You did say ragged edge though and that would make me want a really good converter like a coan in the 4000 stall area.

Watch these 2 videos same long block in both vehicles First is a 47 dodge 3376 lbs with me in it.
3.25 rear gear 2500 stall 268H cam on a 106LSA long block is standard crank and standard bore 601 heads ported with 1.84-1.50 valves and Z springs in it at this time Stock Delco HEI, RPM intake and 750 edelbrock 1407 carb.

The tires are 28.5" tall TH350 with that 3.25 gear first gear runs to 70 MPH.. so what Reelysalty stated about a gear change is truth. Sorry kind of crappy video all I own is a 3.2 MP sony camera.







Now the same heads and block and transmission into a much heavier vehicle with my 250 lb son in it with me the
weight is 3900 lbs.
But it has 4.56 rear gear and a Coan 4500 stall which at the top end slips less than the 2500 stall in the much lighter vehicle. Quality converter vs old GM bent vane deal.
Intake is now a tunnel-ram and 2 edelbrock 1405 600 cfm carbs Single point distributor.
And the cam was changed to the 280H because I was getting beat on the top end with the smaller 268H.

I broke a couple Z springs and this one has Pac beehive Trick flow brand 313 rate same 110 seat pressure as the Z springs.
I like driving this set up way better. Gears and converter a big yes.




Notice the idle and driving away from idle speed the 4500 stall does not act like a cheap 4500 stall.
Quite streetable.
Currently I have a tight 1500 stall in the car and RPM intake with a 1407 carb and 3.70 gears.
Not as much punch but pulls my pontoon much better.

I would have kept the tunnel-ram but when i went to the store shopping I kept thinking someone is going to steal those carbs or air filters.
30 years ago I was not worried about people taking stuff.
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post #8 of 23 (permalink) Old Feb 13th, 20, 11:46 AM Thread Starter
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Re: 1970 CHevelle 350 Swap cam choices

Wow! Very nice

I am thinking the XE274 buuut - I won't have a converter right away, will have stock. The rear I have is a 3.42. Do I need to switch springs? I guess I am just confused, I am trying to understand all of this stuff lol. What is the main difference between the thumpr and the XE274 - I see the numbers and understand some of it, but not getting a performance picture in mind.
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post #9 of 23 (permalink) Old Feb 13th, 20, 12:08 PM
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Re: 1970 CHevelle 350 Swap cam choices

The thumper is for a lot of sound and idle vacuum will suffer because of the Overlap.
Which is the result of a lot of duration on the exhaust side and the 107LSA.

Buddy ran the thumper cam in a boat with 355" and ported 993 heads ..sounder horrible through hull exhaust dumped into the air.
Not an even steady chop.. more broke up like it was sick.
It was prop driven and did hit 67 MPH in a 21 foot boat though.Never thought it would go that fast GPS verified

It was a turd out of the hole and did not want a lot of prop. just could not make the TQ needed for a 24 pitch.
Had to get it on the top end.

I have ran the 260 and 268 and 270, 280 268XE and out of those I like the 280H best.
I have ran others and seen dyno tests with the 280 vs XE274 and the XE beats it.
I had a friend use the 274 in a stroker and it was fast as I was told. I moved away and never seen it run.
He loved it and 7000+ rpm shifts were the norm.

The only heads he could come up with that were not cracked were swirl port.
I ported them and they worked fine
RPM intake 750 Edelbrock 700R4 3000 stall and 3.73 gears in a Monty.


You do not need to switch springs it is just I have had too many Z springs of different manufactures break on me years ago.
But I am hard on my stuff.. that last video is how I always drive.

Stock converter for now will be just fine.
Yea it will like more but won't be a deal breaker. I had a 3000 stall and my stuff still felt like it wanted more.. that is why when I put my tune on kill I stick in the 4500 Coan and I would bet even more would be sweet.

Id does not take more than 2 hours to swap it out. Keep the old one for long trips to the next state and stick the high stall in for fun times.


It is tough getting the performance picture in your mind.
I started small 268H 72cc ported heads 350". Later I wanted more.

You will always want more.
You need to know or learn how to tune also. Mufflers and bends in the exhaust make a little difference also.

You may not know but the engines in the above videos run stock pushrods and stock rockers.
I have not seen any gains with 1.5 rollers My valve spring open pressures do not hurt the stock pushrods either.

Stock studs in those 305 heads also.
Not pinned either.
Things not needed.
But head porting is a big deal for me ..It is a must do. Take all those cams you chose and run every one of them.

In a stock gm iron head you will not see a lot of difference.. there will be trade offs in low end and top end slightly.

I bet there would not be a 1/4 second difference in them.

Port the heads and gain 40 HP.. it will be more than switching to a different cam.
Now test those cams in ported heads... that is when you start seeing bigger differences in cam swaps.
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post #10 of 23 (permalink) Old Feb 13th, 20, 12:24 PM
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Thumper Cams, the ultimate “Poser” ?
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post #11 of 23 (permalink) Old Feb 13th, 20, 12:46 PM
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Re: 1970 CHevelle 350 Swap cam choices

The 280H may be a bit to hot for good vacuum. Do you have power brakes? The https://www.summitracing.com/parts/cca-cl12-211-2 which is a 270 and I have run that cam is a little hotter then my L79 cam and almost identical to the Lunati 290 i mentioned earlier. I do like that. The 280 would be fine in a stick though. You mentioned you have .500 Z28 Springs which are just stock Chevy springs but use them. Using heavy duty springs on a cam that doesn't need them just uses more HP and buys you nothing. Unless you are planning on a beefy bottom end 6000 redline should be a redline target max and the 270 falls there.. I have heard the newer design cams with fast ramps do put more strain on the drivetrain which may need screw in studs.
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post #12 of 23 (permalink) Old Feb 13th, 20, 4:42 PM
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If it were me, I'd go with the XE268. You're not building a race car, but it'll operate your power brakes and also be a blast to drive. If you're out for the most you can get, then I guess go big. I think the cam I mentioned will give you what you're after. You should get a higher stall converter, but Comp cams says a stock one will work.
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post #13 of 23 (permalink) Old Feb 13th, 20, 7:23 PM
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Re: 1970 CHevelle 350 Swap cam choices

Engine Idle vacuum.



Cylinder head runner size plays a huge roll idle vacuum.
Those 041 head runners are not very large under 160cc usually when stock.
My 186 double hump castings were 158cc after porting.
My 601 305HOP heads come in at 175cc after porting.
None of those heads will have any issues with idle vacuum and the 280H cam unless you idle it at 600 rpm.
DO NOT do that. Flat tappets need splash oiling or or other trick oiling stuff.


Now I ran the 292H in a buddies 78 Nova and 601 heads Idle was 1000 rpm and it had 12.0 vacuum. and brakes worked fine No extra vacuum cans. 357"



The largest cam I ran in my personal 78 Nova was with ported 186 heads and it was a herbert solid flat tappet circle track cam .
[email protected] .050 .500" lift both sides and 108LSA.. brakes worked fine. 350"



Fast forward to a 355" in a 76 step side truck 601 head casting same porting 175 cc runners.
This cam was a tweaked crane 110921 picked it to beat the Nova with the 292H.
Tweaked as in exhaust lobe was used on intake and exhaust side .
[email protected] .050 106LSA and 1.6 rockers were used.
https://www.summitracing.com/parts/crn-110921


It beat the Nova and the Nova clicked off 11.94 et's like clock work at 115 MPH.


Guess what Power brakes worked on that truck just fine 11.5" idle vacuum.
those 2 vehicles were close on compression 10.3 and the other 10.4.


You stick those cams in a SBC with 200cc intake runner heads and you should expect much less idle vacuum.
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post #14 of 23 (permalink) Old Yesterday, 3:35 PM Thread Starter
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Re: 1970 CHevelle 350 Swap cam choices

Quote:
Originally Posted by Reelysalty View Post
Thumper Cams, the ultimate “Poser” ?
This is what Comp told me LMAO. Almost word for word!
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post #15 of 23 (permalink) Old Yesterday, 3:41 PM Thread Starter
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Re: 1970 CHevelle 350 Swap cam choices

Quote:
Originally Posted by Johnny Bravo View Post
If it were me, I'd go with the XE268. You're not building a race car, but it'll operate your power brakes and also be a blast to drive. If you're out for the most you can get, then I guess go big. I think the cam I mentioned will give you what you're after. You should get a higher stall converter, but Comp cams says a stock one will work.
Quote:
Originally Posted by jeff swisher View Post
Engine Idle vacuum.



Cylinder head runner size plays a huge roll idle vacuum.
Those 041 head runners are not very large under 160cc usually when stock.
My 186 double hump castings were 158cc after porting.
My 601 305HOP heads come in at 175cc after porting.
None of those heads will have any issues with idle vacuum and the 280H cam unless you idle it at 600 rpm.
DO NOT do that. Flat tappets need splash oiling or or other trick oiling stuff.


Now I ran the 292H in a buddies 78 Nova and 601 heads Idle was 1000 rpm and it had 12.0 vacuum. and brakes worked fine No extra vacuum cans. 357"



The largest cam I ran in my personal 78 Nova was with ported 186 heads and it was a herbert solid flat tappet circle track cam .
[email protected] .050 .500" lift both sides and 108LSA.. brakes worked fine. 350"



Fast forward to a 355" in a 76 step side truck 601 head casting same porting 175 cc runners.
This cam was a tweaked crane 110921 picked it to beat the Nova with the 292H.
Tweaked as in exhaust lobe was used on intake and exhaust side .
[email protected] .050 106LSA and 1.6 rockers were used.
https://www.summitracing.com/parts/crn-110921


It beat the Nova and the Nova clicked off 11.94 et's like clock work at 115 MPH.


Guess what Power brakes worked on that truck just fine 11.5" idle vacuum.
those 2 vehicles were close on compression 10.3 and the other 10.4.


You stick those cams in a SBC with 200cc intake runner heads and you should expect much less idle vacuum.
Jeff, Johnny, and all
Thank you so much for all the information! I ended up with https://www.summitracing.com/parts/cca-k12-242-2
I spoke with Comp and they said that it was a step below XE274 and would allow me to run my stock stuff. I figured this would be good for now as I have no idea when I will have space to update more stuff at once - probably this fall. What do you all think of this choice? I do not currently have power brakes - but I am a click away from buying the kit! LOL, I don't mind the manual drums BUT I am not going fast by any means. I mean honestly, other than possible fade from the heat, Drums are pretty good, right? And if I can stand manual brakes just fine - my first car was a 1967 Newport with a 440 and manual brakes so I learned from age 16-19 how to deal with them in daily traffic.

I am starting to second guess my choice now that I have read your posts. Should I have gone bigger and gotten a converter too? I just didn't want to spew the cash out for a new converter plus I would like to upgrade the transmission at the same time and often the company will not honor the warranty if you do no use their approved converter. HMM.
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