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Old 07-15-2006, 10:42 PM
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help with a cam choice

I'm at the point where I'm picking a cam for my wifes '70 mustang and could use some help.
Here is the pertinant info:
1970 351 4V cleveland with closed chamber heads.

Silvolite #1159 .030 over dish pistons. These are the later 351 pistons and I estimate they will give roughly 10.4 or 5 to 1 CR with our heads.

Stock intake and exhaust manifolds
650 holley. I have a vac secondary and a double pumper, I'll try both of them. I also have a 700 DP and a 750 Vac sec but I don't think those are needed.

Stock close ratio four speed with 3.25 rear end. It has a fairly large fywheel and an 11" clutch. Someday it may get a set of 3.70* gears.
This is not a daily driver, we used it for coast road cruising and mountain runs.

The stock motor specs say it makes 300 HP at 5400 rpm.
I thought that spinning it up a little higher was in order but still, the max rpms it should ever see is under 5800.

I called Crane to ask about the 278 energizer cam, #113132,(see the spec card here:
http://www.cranecams.com/index.php?s...32&lvl=2&prt=5) and the tech guy recommended a crane 523802 powermax instead. Here is that cam listing:
http://www.cranecams.com/index.php?s...02&lvl=2&prt=5

The tech said it had a 114* LSA

My concern is that it has not enough overlap and a bit too much duration and it will make a detonation machine out of that motor. The Crane tech guy said it would not be a problem.
He also said it was a grind that took better advantage of the bigger dia ford lifters, as opposed to alot of the more popular chevy grinds on a ford cam, whatever all that means

The heads and intake and exhaust are not going to get changed.

Also- are the screw in stud conversions that install without machining worth using in this application or should I go with the real ones that require some time at the machine shop. I think you use BB chevy rocker arms with either setup unless i get a set of harland sharp rockers.

Any suggestions? Criticism? Mockery?

Thanks for reading this ,
Mikey

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Old 07-16-2006, 11:13 AM
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I didn't look up the piston numbers, but you can't put a Windsor piston in a Cleveland. The valve notches are in the wrong place.

I would seek for low 9s compression with a flat top piston (not dished), for pump gas, and be able to use a cam with decent velocity numbers. Unless you want a lopey idle, I would stay on the conservative side. A Cleveland with 10.5 compression will be a bear to run on pump gas unless you are blowing it out the valves, which in itself will limit low rpm torque even more.

We all know that the 4bbl C has excessively large ports. Australian heads would be much better. If you can't get the compression down with those heads and a flattop, I would consider Cleveland reverse dome pistons, definitely not a full dish piston which ruins the quench.

I'd stay with a 600-650 vacuum secondary.
I'd think the heavy flywheel and the 3.25s are a good combo.

The entire valve train depends upon the cam. If you have springs above 300 pounds, then you need screw in studs and better rocker arms. I would think that a good cam will keep you in the 250 range and eliminate the necessity of removing/machining heads.

Another thing that you need to consider is that with stock heads the valve lift is limited by valve guide height.

Off hand I would suggest that a 110* LSA will give you some lope and compression blow down, and come into a decent midrange. Then you might need the 3.73 gears.

Since you admit that you do not understand camshaft dynamics, I would suggest you pick the cam company of your choice, be brutally honest about what you want and what you have, and allow them to choose the cam for you.

If you talk to Crane, Isky, CompCams, Lunati, etc. you will see that opinions vary from person to person, and company to company.


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Last edited by xntrik; 07-16-2006 at 11:20 AM.
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Old 07-16-2006, 12:19 PM
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Thanks, X.
Those aren't windsor pistons that I listed. The number came from the silvolite website.
I know they are cleveland pistons because they have been in the motor for 30,000 miles.. I am re-ringing it and freshening it up because it sat for several years and I had the heads redone because of some cracks.. Those pistons have a 6cc dish. The heads are off the motor.

I already have a set of 4V open chamber heads and a set of 72 2 barrel heads. Even though they would be better performers ,I am not using these on this car. I am not buying any other heads. I said that in my first post.
This is the original motor that came in the car so it will stay as is. The 600 holley Vac secondary was my first choice and I would only try the others for my own education.

I did call tech at crane directly and WAS brutally honest about what I wanted to do with the car. I told him it was a weekend car that saw a fair amount of hiway and I would like a better sounding idle and some more midrange and top end over stock. I questioned his recomendation while I was on the phone with him and he was not listening.
If I wanted something that had low end I would not use anything with a cleveland. Or I would put 4.86 gears in it and let it rev.



I know enough about cam dynamics to question the crane tech guy's recommendation regarding the wide LSA that he suggested . I think that powermax cam would make that motor detonate like crazy

That is why I posted here. Posting here is not an admission that I don't understand cam dynamics, so you don't need to offend me by saying something like that. (at least you could have put a smiley there to show you were joking)

I posted this to see if someone would verify what I believed to be right. You did that ,thanks. I won't use that cam as suggested.



I am trying to get a cam that will work with my current heads and pistons. I don't mind a little lope or a little low end misfire. I know one exists. I wouldn't mind running the stock cam (if I could find one), except it does not have enough overlap, lacks midrange and top end power and sounds crappy at an idle. A boss 351 cam would work but I think that has some of the same problems.

I posted this here looking for info, Cam company tech guys want to sell you a cam, not info.
But as you suggest, I will call isky, comp and lunati.

Unless some one else would like to add something.
Thanks for reading this,
mikey
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Old 07-16-2006, 05:06 PM
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Quote:
Originally Posted by powerrodsmike

Posting here is not an admission that I don't understand cam dynamics, so you don't need to offend me by saying something like that. (at least you could have put a smiley there to show you were joking)

I posted this here looking for info, Cam company tech guys want to sell you a cam, not info.
But as you suggest, I will call isky, comp and lunati.

Unless some one else would like to add something.
Thanks for reading this,
mikey
Some of the things I wrote were to expound for readers who might not be on the "same page" as us.

First I wasn't trying to be offensive or funny. I apologize that you were offended.

You stated you did not understand the concept of the lifter diameter and how it affects cam dynamics, so it was easy to conclude that you might not understand the other events, as sometimes people are just repeating rhetoric. I did not want to turn this thread into a lesson on cam dynamics, so I suggested calling cam lines.

I think that you are correct. CompCams recommends a 110* LSA (8* tighter at the piston) which at the same duaration and intake closing would add lope to the idle, bleed off some of the low rpm compression, and increase the mid range torque, while pulling the power peaks closer together. (Also closes up piston/valve clearance) Those 3.73s might be good afterall.

You can probably get the dynamic compression down to 8.5 but the fully dished pistons are losing quench and increasing the possibility of detonation.

I stick to all the suggestions I wrote previously.

I have seen people put W pistons in Cs. They just didn't get it.

I haven't done a C in 7 yrs, there just aren't many to be done.

Have a great Mustang !!


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edited: I also doubt that the 2V heads would be better performers. They have smaller ports but horrible open chambers that require an additional full compression number reduction. The Aussies are the best.

Last edited by xntrik; 07-16-2006 at 05:22 PM.
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Old 07-16-2006, 07:14 PM
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Thanks X
I knew you did not really think I was an idiot.
You are right, no one does clevelands anymore.

I posted some of this on the 335 forum and I guess no one took me seriously. I guess because I wasn't buying the latest AFR heads and wanting to spin up 9000 rpm's.

This is a 99% stock car that is somewhat collectable (ragtop) as well as special to us. My wife bought it in 77. I really just want it to behave and perform as it should.

I know that keeping the LSA smaller (I was thinking 108 or 110) will bleed off compression and the extra scavenging will add a bit of cooling to the chamber. I could not get anyone to verify it up until now.

In its stock state with the flat tops and stock cam it was impossible to keep it from detonating on any kind of pump gas available at the time.

After I put the 6cc dish pistons in it that helped alot. I also had a supposedly stock replacement cam that turned out to be a smog dog cam for a '74 2V 351. (at that time I had NO clue about cam dynamics) It was a dissapointment to drive.



I'm just not sure about how a 220* @.050 will act with the big valves and giant ports.
It just seems like too much.

I guess my question is will a split pattern 220*intake / 230* ex with the 110 LSA and lift in the .530" (@ valve) range work with the 10.5 CR and closed chamber heads without detonating itself into oblivion and making decent midrange/ top end?

And as for my second question regarding the screw in studs: There is a set that require no machine work. Crane sells them. They look like cheese to me. I was wondering if those were really junk or what.
Thanks for reading this.
Mikey
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Old 07-16-2006, 08:19 PM
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I' d go here and look at the 2000-6000 rpm power range of cams and the choppy/rough idle... compression above 9.5 will still be a challenge on pump gas. You should consider a water injection system. It works well and is cheap to do. I ran one in the mid 80s on a '70 - 350/350 SBC.

http://www.compcams.com/technical/Ca.../86-91_231.pdf

I don't have a specific recommendation, yet.

If you jot down the part # like 32-208-3 etc. you can go back to the index page and click on cam cards and the specs will get you to overlap. 45 is slight lope, 60 gets pretty rough.

The cam card for 275 DEH part # 32-208-3 (most like what you spec'd) says 60* overlap, 219/232*, .515/.541 lift, 110* LSA, and a power range of 2-6,000, needs a 2800 converter. That is going to have a rough idle.

How much lift will your valve guides support? Have they been machined down?
The screw in studs are good, but you have to pull the old ones out and thread the bosses on a special press, use ARP studs only, this is not a place to save $ 20.

Shout if I can do anything else. Maybe we can kick around some more ideas.

edited afterthought...... You can also have your existing rocker studs "pinned" so they won't pull out. Just a cross drill and a hard pin inserted.

Last edited by xntrik; 07-16-2006 at 09:15 PM.
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Old 07-17-2006, 07:56 AM
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First of all, tighter lobe separation (108 to 110) doesn't bleed off cylinder pressure. Overlap does not have anything to do with building cylinder pressure since the engine is not making cylinder pressure during overlap.

As far as cam timing events, the intake closing point is what effects cylinder pressure. And a later intake closing point will lower cylinder pressure ("compression bleed off").

And, wider lobe separation makes the intake valve close later. So, wider lobe separation angle (112 to 116) will reduce cylinder compression as compared to tighter LSA (106 to 111).

Secondly, you have a slight mismatch in your engine setup. 10.5:1 cr with 3.25 gear is not a good combo. Plus you have stock heads and manifolds and want to limit rpms to 5800. So, you will need a short duration cam with wide lobe centers and should use more exhaust duration due to stock manifolds and heads.

I think a cam around like this would do well. 218 intake/226 exhaust with 114 LSA.

Use the 750 vacuum secondary carb.
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Old 07-17-2006, 09:36 AM
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Thanks for replying, 454c10.
I realize that 10.5 CR and 3.25 rear end gears are not optimal. . The car came stock with 11.0 CR and those 3.25 gears. The 10.5 CR pistons that I have are actually a later dish piston.
I really don't want to change pistons at this point. Lower gears are being considered, but not just yet. If I have to I will.


I always thought that overlap did have an effect on cylinder pressure at, (higher rpms anyway), as it helped pull the new charge in and aided in cylinder filling.

The idea is to get a cam that will work with what I have.
Maybe my use of the term bleed off was wrong, but I am trying to use the extra overlap as a way to keep detonation down. I've seen it work on another motor. I have spoken with my machinist and posted here and now I think it is worth a try. It will also make it sound a little better.

Also, with the exception of 3 drag race cams, every cam that comp cams has listed for a cleveland has 110* LSA. There has to be a reason for that.

I found a dynamic compression ratio calculator online that I can use. Although I am 90% sure of my numbers, once I really get down and cc everything and have some hard numbers I will plug some intake closure numbers from different cams and see what happens. I know the heads are about 65CC but I have not checked the deck ht or measured the dish yet.
I think X is right about trying to get dynamic CR down around 8.5. We'll see what works.

I looked at the cam that Xntrik, (Thanks X), suggested (Comp, dual energy 275DEH) and also the one just below it ,the 265DEH with 211*/223*. Both of those have the 110 LSA. They look good as far as the reccomendation in the catalog. I would be inclined to go with the 265 because of the gears I have now.


The only thing that keeps me wary of comp cams is hearing about the failure rate. I also hear that is a result of lack of oil additives, so I don't know.



The cam you suggested sounds just a little less than the Crane H278-2 cam that was recommended by the tech guy at crane. It has the 114 LSA. I did a search in the 335 forum a while back and saw that several people used that cam with good results.


I believe the stock heads are more than adequate for even higher rpm than 6000 if I wanted to go there, if I spend some more money on the valve train and maybe some headers and intake. Although I want to keep the car as stock as I can, so that is out for now.

You can't make good low end with those heads so I'm shooting for the top to be in 5500-6000 range and trying to make a compromise between what it should have and what I can afford.


After I get the motor together I will play with my carb collection. I have a pile of them.

.Thanks for the reply,
Mikey
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Old 07-17-2006, 11:40 AM
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First Mike, I did NOT suggest that cam. I used it as an illustration of the cam that you specified. As I stated with that cam link..... quote
"I don't have a specific recommendation, yet."

Second, as you say 454, although increased overlap in itself does not directly affect cylinder pressure, per se, it does allow the intake stroke to draw in more exhaust gases that do have an EGR effect on detonation/ reducing the combustion temperature and pressure (BMEP). The same dynamic cranking pressure build-up using some unburnable gasses does makes less combustion power. As rpm increases the inertia of the air makes itself more prominent and the effect is reduced substantially. I apologize for not being more clear.

The wider lobe separation does NOT make the identical intake lobe/valve close later unless the intake lobe is phased to do so (retarded). If the cam is timed to the same intake event centerline (using the same lobe) there is no difference. Please also note that later intake closing also necessitates later opening which reduces the effective time that the intake can suck, and the delayed closing is into the power stroke farther allowing the piston to begin to push reversion. This is the reason that advancing the cam increases dynamic pressure.

I apologize for not writing a more detailed explanation of cam effects.

I suggest looking at the ISKY site and reading their tech info tips about the subject of split durations and phasing.

Regarding cam failure rates, it is reported that there are only 2 cam blank manufacturers that are used by almost everybody. It is not likely that Comp got bad blanks and other companies did not.
Also I will point out that CompCams probably sells the majority of cams today. So any failures will seem like more, because there are more.

There seems to have been some bad foreign lifters for a short period of time. CompCams uses only top quality American made lifters.

IMO 99% of all cam failures are due to the installer, the break-in procedure, and poor oil. Break-in springs are highly recommended but very few assemblers use them because of the 2 hour hassle of changing springs again. As I have stated on other threads, most engine guys are stuck in the 70s.

If it were me I would consider blending and polishing the combustion chambers, and at the risk of being redundant, water injection which increases power and reduces combustion deposits further limiting detonation,

and I would look into the "head grooving" that has been introduced on this site by automotivebreath. It works.

X

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Old 07-17-2006, 11:47 AM
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Yes, narrow LSA helps fill the cylinder. This is especially helpful with carbs. EFI engines tend to have wider LSA because cylinder filling is easier for efi and computers typically don't like overlap which messes with manifold vacuum sensors. However, a lot of stock carb'd engine came with 114 to 116 LSA.

Yes, I also like 110 LSA for a carb'd engine. However, with todays gas and your 10.5:1 cr and 3.25 gears, some changes need to be made to a typical cam profile. The extra LSA will allow a smaller cam to be used with higher compression. Then with stock heads and no headers, that is where more exhaust duration comes in handy. The reason for more exhaust duration on the cam is to make up for poor flowing stock exhaust ports and poor flowing exhaust manifolds.

But no, more overlap doesn't make an engine less likely to detonate. It is the closing point of the intake valve that determines that. If you have two identical cams, except one cam has wider LSA. The wider LSA will be less likely detonate due to a later intake valve closing point which allows the engine to capture less air in the cylinder. You will see this when you use the dynamic compression calculator.

Wider LSA will make the idle smoother and a wider torque band. But peak torque will be a little less. Works better with a wide ratio gear pattern and efi. Narrow LSA is just the opposite.

Maybe you should consider going efi on that engine. More compression can be used with better fuel and timing control.
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Old 07-17-2006, 12:04 PM
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Just a couple questions.

[QUOTE=454C10]

EFI engines tend to have wider LSA because cylinder filling is easier for efi

The extra LSA will allow a smaller cam to be used with higher compression. .

But no, more overlap doesn't make an engine less likely to detonate. It is the closing point of the intake valve that determines that. If you have two identical cams, except one cam has wider LSA. The wider LSA will be less likely detonate due to a later intake valve closing point which allows the engine to capture less air in the cylinder. You will see this when you use the dynamic compression calculator.

Wider LSA will make the idle smoother and a wider torque band. But peak torque will be a little less. Works better with a wide ratio gear pattern and efi. Narrow LSA is just the opposite.

QUOTE]


EFI cylinder filling is easier? Please explain why. How do the pistons know the difference?

Extra LSA allows a smaller cam?.... Then why do they all use bigger durations?

So you advocate a retarded intake event and an advanced exhaust event?

Just asking.
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Old 07-17-2006, 12:14 PM
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Thanks X, Now it's my turn to say I'm sorry. I misread your post and took that cam # as a suggestion. It actually looked alright to me although I would, as I said be inclined to go with the lesser 265DEH.

I had also given some thought to polishing the chambers. It couldnt hurt either as it would open up the chamber some too.

Grooving is something I had not thought about but I will look into it. Might open up the chamber further still as well as help the flame.

I have not had any cam failures myself. I do know how to break in a cam, and I dont think the spring pressure will be so excessive that I would even need to bother with changing them for break in. If I remember right the recommended spring for the cams I'm looking at are less than 120 closed/330 open. (the stock spring is 95/299). Not exactly astronomical spring pressures.

Thanks for the explanation of overlap and cam timing.
I certainly won't say that I know all there is to know about cam technology but I understood enough about overlap prior to starting this thread to realize that it might be able to help with the detonation problems present in my mismatched /obsolete/generally undesireable combination of parts.

I do have a basic grasp of why and how cams work. I always appreciate when someone explains it a little differently.
Especially someone who has done it.

The isky cam website is the next stop.
Thanks guys
Mikey

EDIT: EFI is not an option.
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Old 07-17-2006, 12:32 PM
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The difference is with EFI, the gas is sprayed under high pressure directly into the intake port. As opposed to a the carb that needs a stronger signal from the engine to pull gas out of the carb and through the intake and then into the intake port. And as you know, at a certain rpm, the exiting exhaust helps pull in the next intake charge which is more helpful to a carb. EFI is less sensitive to this due to the fact gas is already in the intake port. I'm not making this up. Just knowledge I have picked up reading countless tech articles.

This 10.5:1 cr engine is not optimized to the 3.25 gear due to poor gas quality. Typically a 3.25 gear would use a short duration cam to maximize torque. And a 10.5:1 cr engine would use a long duration cam to make high rpm power which also has the side effect of having a later closing intake event to keep dynamic compression ratio pump gas friendly. So as compromise to this situation, yes, I think a retarded intake and advanced exhaust timing event will be helpful. If the car had a 4.11 gear and headers and a better intake and a 6500 red line, then picking a cam would be much easier and a much simpler selection.
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Old 07-17-2006, 12:37 PM
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This is fascinating. We have three really bright guys discussing the mechanical brains of an engine. The camchaft. It really, really is fascinating.

I note that 454 believes that incresing LSA will result in later valve closing and thus lower dynamic compression. I agree with him. X notes that changing LSA doesn't matter a bit (as I interpret him) if you still time the same lobe to the same event (intake lobe centerline, I assume). I agree with him too. I think 454's comments are based on widening the LSA bilaterally from the split line (where the intake and exhaust are equally open).

But please, keep it up. I am learning, and that's why I love this site.

Pat
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Old 07-17-2006, 12:53 PM
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Quote:
Originally Posted by 454C10
If the car had a 4.11 gear and headers and a better intake and a 6500 red line, then picking a cam would be much easier and a much simpler selection.

Here is a small aside. strictly fantasy though.
Don't think I havn't thought about all that at one time or another. I was thinking more on the lines of 5.86 gears, tunnel ram with dual 600 holleys, fenderwell headers and 8500 rpm redline.

That would stray significantly from the current plan and I don't think my wife would want to drive it anymore.

Now back to reality.

I would really just like that car to be able to be driven without rattling itself to pieces and act like a 1970 mustang with 4V cleveland and a four speed should. If I can get the right cam in it I think it might. Thanks for helping,
Mikey
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