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Pure American Muscle
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684 Posts
Discussion Starter #1
Hello everyone,
Well as some may have noted from my project journal I have torn down my engine to get ready for my new heads. I have everything else I need and got it narrowed down to two cams but can't figure out which would be best for me. I just gotta get it figured out so I can order it before the heads come!

Here is what im working with...
355 2 bolt main/ 2pc rms
4 valve relief pistons
stock bottom end
eld. perf. intake
holley 650 DP
1 5/8 headers
MSD ing system
The CR should be between 9.1 to 9.8

This is going in a 71 Chevelle that to the best of my knowing weighs around 3500lb it has a TH350 with shift kit and stock rear non posi.

Now I bought my AFR heads and in two weeks they should be here. *hopes* they are the
195cc straight plug 74 cc chamber heads.

My question is which cam should I go with the XE268H or the 270 H magnum cam. I know the magnum is more agressive but it is also a single pattern cam. I just wonder if the 268 dual pattern is needed with the heads. From what I understand the dual patterns work great for more stock heads but not as well on high flow aftermarket?

If someone could help me figure this out :confused: that would be great! Sorry for the long post :mwink:


Chris
 

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It just takes time and money
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225 Posts
Chris,
When I rebuilt my 355 (now 357) I called AFR tech support and asked them for camshaft suggestions. I have the 180 heads. I decided on a Comp Cams 12-239-3 262h-11 dual pattern. It is in a 2200lb car with a 700R4 and 2400 stall converter.
AngliaBob
 

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1,161 Posts
i'd go with the 270 magnum.i myself have the 280 magnum and have used it in a 60 over 350 and now a 406 and both were originally for a 72 nova that i am restoring the motor blew in my GMC VANDURA G-2500 and thats where i have been usingmine for a couple of yrs now.with that 700r4 you would be able to use the 292 also if you wanted with no gear changes.an 11" 2800-3200 would not be very loose or create much heat and yet be very fun.go with a converter company near you though in the same state or maybe one state away.that way what ever converter you chose you canhave adjustments made tto it ,more or less stall,and later before it is completely trashed they will rebuild it for you cheaper than buying a new one and again you can have changes made to it if you want to.good converters are a must cause power is no good if you can't transfer and increase it.good luck.
 

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Pure American Muscle
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684 Posts
Discussion Starter #4
I have a trans shop I go to about 20 mins away from me and I let them do the work for me I figured on giving them a call once I knew what cam I wanted and let them get the conv. for me mainly because they warr. all their work and parts.

So you think I would be safe with the 270 mag. GoneNova? I just don't want to over cam it to some extreme. So if I went with the 270 which says it opp. RPM is 1800-5500 then I would need what speed conv. the AFR heads say they are from 2000-6*** thats why I figured I could use the cam because it would put me in a very good powerband.

I looked at the 262 but it almost seemed a little small thats why I went to the 268.


Chris
 

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http://teamrfc.gospelcom.net
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The 270H is a long way from too big for your combonation. It matches your parts pretty good, and will give you good torque. I had a 355 in a 1972 nova, with vortec heads, and a 268h cam with a 1900 stall. The cam worked really well, but if I had it to do again, I would have gone with the 274H and a 2400 stall. The 268 had A LOT of bottom end, but could have used some more on the top end. If I was in your situation, I would actually go with the 280H With around a 2500 stall. The 2000-6000 powerband of the 280H matches your heads perfectly.

Adam
 

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Pure American Muscle
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684 Posts
Discussion Starter #6
Yea I noticed that but I think the 280 would work better with a little higher CR more towards to 9.8 side. It always makes me wonder because when you go to the comp. cams website and look up the 270 and 280 they note them as having a mild to rough and rough idle. Yet it seems that so many people run them without problem. I wonder if it better to start your cam before the heads hit their beginning RPM or right at.


Chris
 

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http://teamrfc.gospelcom.net
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If you look at the comp website http://www.compcams.com/Technical/CurrentCatalog/HTML/128-169.asp And look at the other Magnum cams, they recommend a minimum of 9:1 compression with the 286H cam. That being the case, you should be fine even if you ran that cam as far as compression goes, so the smaller 280H should just be that much more acceptable with the 9.1:1-9.8:1 compression that you will be running. Another thing, just because a cam has a little bit of a rough idle, doesnt mean that it cant make good low end power. Although there is a defanite trend that way, a little bit of a lope is not a bad thing. If you still arent sure, I would call comp and see what they recommend for your situation.

Good luck
Adam
 

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Pure American Muscle
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684 Posts
Discussion Starter #8
Yea that is true about the CR. My main things I worry about are 1. drive-ability 2. Performance

Well I think im pretty set on the 270 then I will stay a little on the small side (better to under cam then to over right lol) away from the 280 hopefully for a little more low end and a great street car.

So you think I should go with a stall of around 2000 something?

Thanks so much for all the help!

Chris
 

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If driveability is the main concern run the smaller cam. Bigger cams only make more power if you have the cylinder pressuer to support them. The fact that your heads are flowing more, will make whichever cam you have act as though it is bigger.

I went with 2,400 on my car. My car is extremely streetable.
 

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Pure American Muscle
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684 Posts
Discussion Starter #11
Thanks everyone for your help I will get the cam ordered and talk to trans shop about conv.
I noticed looking at the specs of the cams that the 268 has a 224 intake and 230 ext. while the 270 have both 224 (single pat.) and both have a 110 lobe sep. Only diff is the 270 has slightly more lift .480 the 268 .47 something... Pretty close if you ask me lol.

Again thanks everyone for your help i'll be sure to post pictures once the engine comes together and inform everyone how that new seat of pants feel is!
:evil:

Chris
 

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http://teamrfc.gospelcom.net
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Your motor should run really good and have a good 450 hp. One thing to think about in the future that will make a noticeable difference in hp: get a hyd roller cam. There is of course the gain in hp due to the lack of friction, but also the AFR heads flow just as impressively at higher lift as low lift, so getting a roller with around .530-550 lift will give you a noticeable gain in hp (around 50 hp) with about the same power band.

Good luck
Adam
 

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Pure American Muscle
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684 Posts
Discussion Starter #13
Also I had asked awhile back and was told it was ok to use the valve springs the AFR heads have on them since they can take a .550 lift or so. I had asked about thr 280 cam and was told it was ok with those springs. I assume that the springs will be ok with this cam.

Thanks


Chris
 
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