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yet another cam choice...
https://slantsix.org/forum/viewtopic.php?t=33928		 Page 1 of 2
Author:  zorg [ Sun Feb 22, 2009 8:37 pm ]
Post subject:  yet another cam choice...
After searching old posts for the last few weeks, rereading the Erson thread multiple times, the engine matrix thread, etc. I know the range I want to be in. However, this is my first build, so I would love the voice of experience to weigh in. I was planning on having my cam reground locally for around $50, so am hesitant to just call Erson for a recommendation...

Would like something close to the Erson 270/270 or Doc's RV15, which is 260/244 (or is it 266/244?).

'76 225
engnbldr O/S valves/340 springs
minor port/polish/gasket match
Shave head/block for roughly 9:1 CR (that is open to recommendation, as I want to still run 87 octane. *CCing stock head tonight, for starting point)
super six w/ BBD
headers and 2 1/4" exh, Borla turbo muffler
double roller t-chain

Daily driver, looking for some spunk. 833OD, rear gear is another can of worms. A few years from now I'd like to have my 3.55 geared 8 3/4" narrowed to fit, but until then? That could be it's own thread if we have to go there?
Author:  Dart270 [ Mon Feb 23, 2009 4:54 am ]
Post subject: 
For 87 octane and 9:1, and with a stick, I'd run the 280/270 Erson. Doc will probably tell you to go smaller.

Also, I recommend spending as much time/money head porting as you can. This is where most of the power is made and there is no downside on a 225.

Lou
Author:  zorg [ Mon Feb 23, 2009 7:56 am ]
Post subject: 
Good info, thanks. I would love to run a big cam, but am trying to be realistic. Doc's thought would be smaller cam = more low end power = more fun around town?

I will be teaching myself on the porting, so I'll give it my best shot.
Author:  Dart270 [ Mon Feb 23, 2009 8:10 am ]
Post subject: 
Doc just likes smaller cams than I do. I tend to like to bleed off a bit more cylinder pressure for lower octane gas, which gives up a little low end, but that's not such an issue if you have a stick.

280/270 is still my pick.

Lou
Author:  sandy in BC [ Mon Feb 23, 2009 10:34 am ]
Post subject: 
That cam is kinda the Ultimate Super6 cam. It has great low end . My CR is 9.5 and I can run regular in the right situatons. It is a far better cam than the Comp 264 it replaced.

What you are looking at is a fat torque curve that keeps building. You shift when the BBD runs out of steam....

Spend the money on the headwork....be prepared for recurving .
Author:  runvs_826 [ Mon Feb 23, 2009 11:03 am ]
Post subject: 
What is the exact specs on the 270 one? That one is my vote and I think I'm going to have to get one over Spring Break. I thought it was a RPD pattern design but the specs are really what I wanted in the beginning.
Duration
270
Lift
.465
LSA
111
Advance (?)
4 deg
Is this what I install it at with the bushing?
Author:  Doc [ Mon Feb 23, 2009 11:15 am ]
Post subject: 
Quote:
Doc just likes smaller cams than I do. I tend to like to bleed off a bit more cylinder pressure for lower octane gas, which gives up a little low end, but that's not such an issue if you have a stick.

280/270 is still my pick.

Lou
I could not have said it any better myself...
For street cars I use a smaller cam and carb just to give the combo better street "manners".
(I give-up some top end HP for low RPM "drive-ability")

The RDP grinds I worked-out with Erson include an important feature, that is a long lash ramp on the exhaust side. (the MP 244's profile) That allow quiet operation in the .020 to .022 lash range. Many of the other soild lifter profiles quiet down in the .012 - .016 lash range and then heat expansion starts to impact the idle quality.

I really need to find a cam grinder that has the latest CNC cam granding equipment so I can get a new exhaust lobe profile (master) worked-out. A profile with the long/easy lash ramp, like the stock and the 244 cams but in a 260 duration.

BTW, what is commonly called the "Erson 260" profile (RV-15) really comes out at 266 degrees when checked at .015 lash. My guess is that it is real close to 260 degrees at .018 lash.
DD

Image
Author:  68barracuda [ Mon Feb 23, 2009 4:54 pm ]
Post subject: 
love this profile doc - plumbed it int my my dyno sim FLAT torque peak of 300lbft from 2000 3000 rpm 226hp at 4500 - running the ported engine builder, 9.3 cr dual header plus my dual long ram high torque weber setup - just whish the blasted thing had a timing facility :?
Author:  Doc [ Mon Feb 23, 2009 5:30 pm ]
Post subject: 
Yes... I also like this grind.
I have used this cam in 3 different engines so far and all have run well.
( I would have said "all are running well" but Twiggy blew a head gasket and is currently sitting on an engine stand... waiting for a new plan... )
DD
Author:  zorg [ Tue Feb 24, 2009 2:09 pm ]
Post subject: 
Quote:
BTW, what is commonly called the "Erson 260" profile (RV-15) really comes out at 266 degrees when checked at .015 lash. My guess is that it is real close to 260 degrees at .018 lash.
Ok, thanks. I was a little confused there, yes.
Quote:
280/270 is still my pick.
So will I be under-carbed with a BBD and this cam? I like to build on the max end of my use, so you have me on the hook here, Lou. I only see a straight 270 or 280 on the Erson .pdf. Anyone have the spec sheet for the cam Lou is referencing? I need to get my cam to the grinder in the next couple days, while I am in the area. Thanks.
Author:  Dart270 [ Tue Feb 24, 2009 2:20 pm ]
Post subject: 
You will have to ask Erson to make this special. They have done this for at least Menko, Sandy, and I (their 280 int lobe and 270 exh lobe at 108 deg LSA).

People have run 15s and even 14s with a BBD, so it has some legs if you want to play with it.

I have never played with a BBD, but my new Slantkota has one on it, so I've done a little now.

Lou
Author:  sandy in BC [ Tue Feb 24, 2009 2:31 pm ]
Post subject: 
I run this cam (280/270) with a BBD. Yes it runs out of steam on the top end. What you get though is a strong vacume signal and great low end.

You need a lot of motor before you need a 4 Bbl......
Author:  zorg [ Tue Feb 24, 2009 10:18 pm ]
Post subject: 
Quote:
You will have to ask Erson to make this special.
As stated above, I am using a local cam grinder (to save $100+)... So looks like I am out of luck on that grind? Or I guess I'll see what the grinder can do. Otherwise, I have the sheet for Doc's RV15 here somewhere.
Author:  Dart270 [ Wed Feb 25, 2009 4:58 am ]
Post subject: 
Your local grinder should have some profiles to use. Just spec 230 @0.050" int and 220 @ 0.050" exh with about 0.460-480" lift. If this is Oregon Cams, they have a good rep and can help you properly.

I plan on getting them or someone similar to grind some custom cams for me sometime soon.

Lou
Author:  Custom Coupe [ Wed Feb 25, 2009 10:20 am ]
Post subject: 
Quote:
The RDP grinds I worked-out with Erson include an important feature, that is a long lash ramp on the exhaust side. (the MP 244's profile) That allow quiet operation in the .020 to .022 lash range. Many of the other soild lifter profiles quiet down in the .012 - .016 lash range and then heat expansion starts to impact the idle quality.

I really need to find a cam grinder that has the latest CNC cam granding equipment so I can get a new exhaust lobe profile (master) worked-out. A profile with the long/easy lash ramp, like the stock and the 244 cams but in a 260 duration.

BTW, what is commonly called the "Erson 260" profile (RV-15) really comes out at 266 degrees when checked at .015 lash. My guess is that it is real close to 260 degrees at .018 lash.
DD
I'm trying to wrap my brain around cam speak - something I have a little trouble with is "ramp" and how "lash" setting relate to the cam specs. Is there a good explanation guide somewhere I can read ?
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