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  #1  
Old Oct 11th, 05, 10:50 PM
Importtech Importtech is offline
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Default Cam gurus..need some help (circle track)

Well Just got back from a rules meeting for next year. They surprised us with a new cam rule. We have always been limited to .450 lift but they have decided it was too difficult to check so additionally we must pull 12" of vacuum at 1200 RPM which they say they ARE going to check every week on top 2 cars. I've looked at a oval track cams and most of the .450 lift rule cams I've seen are ground on 106 centers. Will these cams pull 12" of vacuum in a 350? Any alternate cam recommendations. I'm not real worried about the lift rule but the most of the techs know how to read a vaccum guage..
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Old Oct 11th, 05, 11:41 PM
Tom Mobley Tom Mobley is offline
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Default Re: Cam gurus..need some help (circle track)

use a locked distributor at full advance all the time. this will help with vacuum at 1200. if you have trouble with it starting (kicking back against the starter) run a separate ignition switch so you can get it spinning with the starter before turning on the sparks. seems like I recall there was trouble getting the inches with a 106 cam in 350. This has been awhile back, there's probably better stuff available today.
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Old Oct 12th, 05, 1:03 AM
Wolfplace Wolfplace is offline
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Default Re: Cam gurus..need some help (circle track)

Quote:
Originally Posted by Importtech
Well Just got back from a rules meeting for next year. They surprised us with a new cam rule. We have always been limited to .450 lift but they have decided it was too difficult to check so additionally we must pull 12" of vacuum at 1200 RPM which they say they ARE going to check every week on top 2 cars. I've looked at a oval track cams and most of the .450 lift rule cams I've seen are ground on 106 centers. Will these cams pull 12" of vacuum in a 350? Any alternate cam recommendations. I'm not real worried about the lift rule but the most of the techs know how to read a vaccum guage..
=
Short answer,, no
Any cranking compression rule? Carb? Solid lifter?
12" at 1200 should be a piece of cake with some compression but not at 106 separation unless you run a very small cam which won't work power-wise.

I can tell you a 400 will make 13-14" at 850 RPM with a 270 adv/242 @ .050 solid on a 112 center with a locked distributor & about 10.5 compression though,,,,
It should make about 12" in a 350
If you don't have a cranking compression or compression rule this will help a bunch,,,
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Old Oct 12th, 05, 8:01 AM
Importtech Importtech is offline
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Default Re: Cam gurus..need some help (circle track)

Thanks for the replies..

Hydraulic cams
rochester 2 or 4 barrell
flat tops and 882 or equivalent heads so I'm thinking 9.1 or so at the most.


I found a couple last night...think either one of these might work?


449 450 224 232 112

434 434 244 244 108

Jack
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Old Oct 12th, 05, 10:55 AM
Tom Mobley Tom Mobley is offline
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Default Re: Cam gurus..need some help (circle track)

skip the 112 version, that's like a blower cam or something. you can give the 108 a try, but it might not make it. You need to be looking at modern, aggressive lift rate cams. see what you can find with 110 or so, with less difference between seat timing and 050 timing. the seat timing will affect your idle quality and vacuum readings at low RPM. Look for cams that have no more than 50* spread between the two duration figures.


Say, you know there's no way for them to tell you're running Rhodes lifters...... really help with the vacuum. Do they check after the race? When the oil is really hot?
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Old Oct 12th, 05, 1:24 PM
Wolfplace Wolfplace is offline
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Default Re: Cam gurus..need some help (circle track)

Quote:
Originally Posted by Tom Mobley
skip the 112 version, that's like a blower cam or something. you can give the 108 a try, but it might not make it. You need to be looking at modern, aggressive lift rate cams. see what you can find with 110 or so, with less difference between seat timing and 050 timing. the seat timing will affect your idle quality and vacuum readings at low RPM. Look for cams that have no more than 50* spread between the two duration figures.


Say, you know there's no way for them to tell you're running Rhodes lifters...... really help with the vacuum. Do they check after the race? When the oil is really hot?
Tom,
I don't understand the "50deg spread thing, could you explain??

Jack,
I highly doubt you will make the vacuum with that 108 cam. In fact I can almost guarantee it.
The first one on a 110 would probably make it if the seat timing isn't stupid long.
I used a hyd cam similar to that a few seasons ago & it worked very well but don't remember the vacuum.
You need some duration to fill the cylinder & the only way to get vacuum is to widen the centers & kill some overlap
Vacuum is not just related to seat timing, it is also directly related to overlap as is idle quality.

And do not believe you can't make power with a wide lobe separation.
I have a "few" restricted 2bbl engines with 180 cranking compression 14" vacuum rules & one in particular has reset the track record twice this year along with winning the championship & generally ****in off most of the other drivers in the class.
To the point I have gotten a number of kinda rude phone calls about my "cheated up" engines" This is with a 114 separation.
BTW, these same lobes went from 110 to 112 to 114 & the car lost nothing according to the driver, just got faster. The engine was within 6 or so HP with the 110 & the 114, this I know for a fact,,, can't tell you the vacuum at 1200 though as we had to make it at 850.
It did lose some mid range torque but this I think actually made the car better off the corner due to tire rules & made the thing a bear down the straight,,,
Go figure,,, Gotta love restricted racin',,,,

Also, you are restricted to the 882 head but is there a cranking compression or compression rule?
The heads can be brought down to the mid 60cc range without too much work. About .100" angle mill will do it.
Flat top .010 out with 65cc's is about 10.3,,,
You can get more with attention to detail.

While I am not a fan of Rhodes lifters most of the time, this is one place where they are a win-win deal & as Tom said, try to make sure the oil is hot like 200 at least if possible & run a lighter grade oil like 15/40. Don't use crap oil, use a race oil or one of the good synthetics like Amsoil or what ever you like except Mobil 1 shelf stuff. The race stuff is ok but the shelf stuff has the Zinc & prosperous either removed or lowered a bunch just like all the "for gasoline engines only' dino oils or anything with the Starburst on the container.
If you want to run Mobil 1 or cheap oils add some GM EOS or Crane Break-in lube every other change or so,,, it has lots of the 'good stuff" in it,,

Also, do not restrict yourself to just the hyd lobes.
There are a number of solid lobes that work very well with .002-.006 hot lash.
Your rule states hyd lifters,,,,
no one said you had to know how to adjust them,,,
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  #7  
Old Oct 12th, 05, 1:36 PM
dave_silva dave_silva is offline
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Default Re: Cam gurus..need some help (circle track)

We have a 500 lift rule with a 17" vacum @ 1000rpms. I typically would use the Summit cams that come in a kit. We also used the Rhodes lifters.

sum k1104
Summit Cam and Lifter Kits
Cam and Lifters, Hydraulic Flat Tappet, Advertised Duration 282/ 282, Lift .465/ .465, Chevy, Small Block, Kit

sum k1106
Summit Cam and Lifter Kits
Cam and Lifters, Hydraulic Flat Tappet, Advertised Duration 292/ 292, Lift .488/ .488, Chevy, Small Block, Kit

We always ran up front, if not won, and set fast times with these cams. We had fuelie heads 462s and a 350 or 383 (all cast) flat tops.

Also is that a 450 lift at the valve? We can get a way with a lot here with a little lash or just the rockers not being exactly 1.5.
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Old Oct 12th, 05, 7:15 PM
Tom Mobley Tom Mobley is offline
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Default Re: Cam gurus..need some help (circle track)

wolfplace, I meant the spread between the the advertised seat duration and the duration at .050. Sorry if I confused.

Keep in mind that if you angle mill the heads .100 two other things will enter in: valve-piston clearance and angle milling the manifold too. Not a show-stopper but it needs to be taken into accout if there's a budget.
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  #9  
Old Oct 12th, 05, 8:25 PM
1968 hot rod 1968 hot rod is offline
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Default Re: Cam gurus..need some help (circle track)

Another way to cheat vacuum would be to run an adjustable vacuum advance with a electric solenoid in line with your vacuum line.
Energize the solenoid when checked to run your total up to 50 or so.
Switch it off for your race & qualifying.
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Old Oct 12th, 05, 9:28 PM
Importtech Importtech is offline
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Default Re: Cam gurus..need some help (circle track)

Tom, Mike

Both cams I listed are from Howards cams line of circle track cams..

The 112 LSA cam is a 450 lift rule cam and is the only one I've found with that LSA. I'm assuming that profile was aimed at a vacuum rule.


I had thought about the Road's lifters but I've have no experience with them and the few people I've talked to that had differing opinions. What are the pro's and cons?

I had been using Kendall racing oil. I had heard it still had zinc in it...

There is no stated compression rules...I think they try to control that with
4 relief flat tops and 76 cc heads. I'm sure milling is a viable option. We don't
have a claim just a teardown if someone puts up the dough which rarely happens in this class. I hear a bunch of guys are running oldmobile rods? Im not reallly concerned with cheating er that is running in the grey area just getting through tech. Anybody consistantly running up front has a edge somewhere.

Dave the lift is checked at the rocker.. I've never seem it happen though I know most guys are running 1.6 rockers.

The whole vacuum rule makes no sense anyway. Supposedly they implemented the new vacuum rule because a few of the cars were running obviously much faster and they think the vacuum rule will put an end to it.
ALL car's must weight 3400 lbs....Buuuttt herein lies the real probem... they allow big body cars (pre 78 monte carlos etc ) to run 400sbc but metric chassis cars like mine can only run 350's. How's the vacuum rule going to change that
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Old Oct 12th, 05, 10:12 PM
Doug F. Doug F. is offline
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Default Re: Cam gurus..need some help (circle track)

I dynoed the exact same cam a year ago with 108, 110, and 112 LSA. It really didn't make much difference in power. I was a little surprised. The few 106 LSA cams I messed with for sure didn't make much vacuum.

I'd add more .050 duration easily before I'd go lower on the LSA. IE run a 240@.050 on a 112 vs a 230@.050 on a 108 assuming they both meet the vacuum rule.
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Old Oct 12th, 05, 11:29 PM
Wolfplace Wolfplace is offline
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Default Re: Cam gurus..need some help (circle track)

Quote:
Originally Posted by Tom Mobley
wolfplace, I meant the spread between the the advertised seat duration and the duration at .050. Sorry if I confused.
Quote:
Originally Posted by Tom Mobley

Keep in mind that if you angle mill the heads .100 two other things will enter in: valve-piston clearance and angle milling the manifold too. Not a show-stopper but it needs to be taken into accout if there's a budget.

=
Thanks Tom, I figured but you gotta be careful of some of the stupid advertised numbers,,,
If you can get them at 004-006 or measure them, not a problem but some of the stuff on my stand makes no sense as far as the advertised numbers go. On some I don't have a clue where they come up with them.

I recently profiled an Ede 5062 "Torquer Plus" for a Rat deal & the cam was advertised as 302/304 but measured 285/288 at .006. The rest of the numbers were right on..527/.553, 224/232, 114 lsa, 109 icl.
I never did see the 302/304 numbers,,,

The head deal is not a problem especially with the lift rule & these short cams & I never cut the intake manifold but you are correct, it ain't free
I always correct the intake side of the head & the top of the block so any manifold will fit without issue & I have rolled them almost a full degree on occasion.
They do get a bit "iffy" here as the sine of 7" is damn near an eighth inch,,,

John,
What's with the Olds rods??
Unless someone thinks there is power in a longer rod or something which is crap especially in this venue,,

Also, with 15+ inches of vacuum you don't need any switches in the vacuum line, just run it to the intake & be sure it isn't working below about 6" especially with a 2bbl
Works great at idle but does nothing at WOT,, plus it drives the competition nuts seeing a "stock" HEI complete with vacuum advance on a race deal,,,,,
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Old Oct 12th, 05, 11:42 PM
pdq67 pdq67 is offline
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Smile Re: Cam gurus..need some help (circle track)

Mike,

I bet that old-style E-brock Torquer + BB cam would be a real dandy with solids on it set at .006" AND watched real close!!

Probably would be a REAL torque cam then, imho...

pdq67
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Old Oct 13th, 05, 2:12 AM
Wolfplace Wolfplace is offline
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Default Re: Cam gurus..need some help (circle track)

Quote:
Originally Posted by pdq67
Mike,

I bet that old-style E-brock Torquer + BB cam would be a real dandy with solids on it set at .006" AND watched real close!!

Probably would be a REAL torque cam then, imho...

pdq67
=
Probably be pretty noisy at .006,,
Made decent torque in a 489 with Ede roval heads though.
An honest 550 at 4000 about 500HP at 5000 or so.
over 500 from 2800 to 5000 & idled like a kitten,,
This with no tuning, all Ede stuff, cam, heads, carb, intake,,,, great "tow truck" deal
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Old Oct 13th, 05, 2:44 PM
70GS455 70GS455 is offline
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Default Re: Cam gurus..need some help (circle track)

20 degrees of overlap (@ 0.050") will be about the biggest cam you can stand and still have 12" vacuum in a SB. Overlap can be had by many combinations of LSA and duration. Overlap is (intake dur + exhaust dur)/2 - 2*LSA .

Many cam companies have lift rule profiles: Isky's "Lift Rule Oval Track", Bullet with .300" lobe lift, and Reed's "DH" are just some examples. Usually these types have very fast valve action. Example the Reed "DH" are only 44 degrees from 0.006" to 0.050" . Bullet has some that are 42 deg. !!
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