Selecting a cam: the soul of the engine

Personally, I think that's still right on the edge or too aggressive. I think the numbers Paul posted are 2v grinds and they are full duration. So subtract about 20 degrres to get to .050" timing and 20 degree to convert to 4v....and that says you want 220 dgrees. for street. His 280, is your about 240, requiring higher compession.

Remember too that your heads now flow 100% more air at .050" lift. That had the same effect as adding about 10 degrees duration to the cam.

 

I missed that they were 4v.....I'll have to double check the total v .050 number I've been using.

Anyway, I guess because your exhaust is 220, and you are only upping the duration on the intake, you could average the numbers to see where you fit on the chart.

I'll say one more time, that you will now have 100% more flow at .05" lift than you used to as the duration the can has becomes much more effective. Typically an engine with well ported heads wants about 10 degrees less duration for the same power band as an engine with stockish heads.

 

I just checked the specs aon a few crane cams 4v cams and it looks like for their stuff, the conversion from total duratio to .050" duration is around 50 degrees.

Here's and example:
http://www.cranecams.com/?show=browseParts&lvl=2&prt=5&Vehicle_Type=Sport-Compact&Cylinders=4&Engine_Make=TOYOTA&Year=2007&Engine_Size=2189-2366%20C.C.&partNumber=704-0012&partType=camshaft

 

Sorry to get off subject again Russ....

Can I ask, is the 20hp gain with the same everything else, ie flow, valve size, seat ID, ect? I've just never gotten a 5 angle seat to flow within 2% of a radius - ok, semi-radius seat. I've always had to open the seat id to get the flows matched, then the peak hp matched but the lowend was off a touch due to the larger port/seat...but that is a sample of 1 engine years ago, and I've just done it that way since, I've never tried again. Maybe I just didn't spend enough time picking the angles?

I know getting the piston to head clearance/angle right made a BIG difference on hp on a couple engines I messed with it on....which could be the same fuel puddling effect and getting the fuel mixed. I honestly never understood why it was so critical, but it sure was. The 2 different engines I tried liked the same set-up, so I've used it on everything since. I'm wondering if it a "more than 1 way to skin the cat" kind of thing.

 

thread here. It's a new thread Newman vs. mk e.


http://ferrarichat.com/forum/showthread.php?p=136886318#post136886318

 

Mk e,

I am going in a different direction as I am designing a package that is a bolt on without major mods to the heads, intakes or carbs. Knowing this will leave a fair amount of torque and HP left on the table, I see this as the direction that most of the 3x8 owners would rather go when making mods to their cars.
I have yet to find a currently available cam that does what I want it to so I am working with a cam designer I have used for 25 yrs in coming up with a new profile to do this.
I am currently working on the 2V engine with the goal being street use. My experiance with the 4V engine has been limited to the 3.4 and full race use so it doesnt factor into this conversation of streetable cams. I will give the 4V engine a try after the 2V effort is sorted out and I have a mule on the road.

I agree with your thoughts on the blow through. Too much exhaust port is a well known issue. Any more duration given the currently available cams will only agrivate the situation in my mind. I have to admit that my engine design experiance with a forced flow system is quite limited.
Forgive me but I have not followed your build, have you ever check exhaust temps near the head and down at the collector?

Sinking valves out of necessity is a whole different thing. Depending on the port design, there are a few situations where a venturi effect is gained and the flow increases. My experiance shows that this is the case with a flat head design with the combustion chamber in the piston but I have yet to experiance it with a hemi style chamber. This in no way says it doesnt happen, I just havent run into it. Having been deeply involved in racing from both the drivers seat and the pits for over 35 yrs, only a fool would say "this is a fact that cant be changed". I have had my backside handed to me on the track enough times to know better.

The need for the light weight shims and followers is completely dependent on the cam profile used. I would guess with the currently available cams the need is limited but I have seen pictures here of some pretty beat up shims and cams! That said, who knows how the engines were built, used or broken in. Again, too many variables to make a blanket statement regarding the causes.

We all have to remember that building the ultimate Streetable engine is not just about torque and HP numbers, it is about driveabilty and longevity. Having 2 dozen folks trying that many different ideas just makes it more interesting. Now having (2) 77 GTB's, I am going full ahead to make one into what I believe they can be. The other will be used for "butt-o-meter" base line refferance purposes.

Dave

Dave

 

No...I know, shame on me

I will though. Thanks for the responce.

 

I’m going to put this here, Dave may delete it, but after thinking about it, I personally think something important has been removed from this thread.

The debate (ok name calling argument) that Paul and I were having (that went on way too long) I think points out just how unsettled the debate is over how to install a valve to achieve maximum performance is. The same is true about the debate for port shape, combustion chamber shape, piston shape, and cam selection.

It’s been my experience that none of those things are independent of the others. That means that once one is selected, like the seat design, the ideal port and combustion chamber will almost certainly take a difference path than they would have had a different seat been chosen.

The other thing that was in my head, but never made it to the debate is that the purpose the engine is build for also dictates the correct, well lets say best, choice on a lot of parts. If it’s a mild street hop-up and the pistons are not going to be changed and the heads not milled, sinking the valves any more than absolutely necessary is usually a losing plan. But when is a hot street or race hop-up, high head flow is the goal and all else will be dealt with accordingly, I’ve never seen it not help. The same with port size and cams duration, bigger ports/cams flow more but on a street engine are not generally the best choice.

The third thing is that terminology is anything but standard, In this case a “radius seat” might mean a full and complete radius or it might mean a seat that uses radii. That carries over into most areas of the engine, terms are mixed and can lead to debate when there in fact was no disagreement in the first place.

Anyway, I think that the debate over “right” is anything but settled and I think the thread lost that bit info.

 

One other seat related note is that both Russ's and my heads are pretty much done at this point. A Buddy of mine, Vic, is doing them. I didn't do my own for a couple reasons, first is Vic just always seems to get a couple more CFM than I do, the second is that I sold my flow bench 2 moves ago and Vic's is now 5 hours away. We (Vic and I) have shared results and equipment back and forth for over 20 years now.

The moral being, we have both just spent a lot of money having the valves sunk a bit and the seats are radius (or semi-radius if you prefer), so any debate about how it should be is a bit mute. We'll see what dyno says when the engines get back together.

 

mk_e

The 20+ HP (actually 26) was with the same size valves, same port volume, etc.
Airflow was within a couple of cfm, either up or down at various lift points from .100" to .700".
The differences were primarily the shaping of the short turn, guide bosses and chamber, the valve job and the location of the spark plug.
Each angle of the valve job is a shear point for the fuel as it enters the chamber, and you can see it atomizing as it passes over the seats.
The air/fuel mixture is much heavier and acts differently than just air, this is why traditional SAE airflow measurements are limited in their ability to predict actual engine performance.

Jack

 

Russ,

Everything you state agrees with my research. That said, if you come across Kermits numbers I would love to review them and verify they agree with mine. Never can have too much data, and all the better if its from different sources. Thank you for the offer!
The theoritical flow limit with the 32 MM venturi's I have found to be conservitive and can be messaged a bit. In my case it is more about velocity and working towards correctly tuning the intake track thus boosting the torque numbers.
I have put longevity as my number one issue as I know no 3X8 owners that are willing to double or tripple up on maintaince. That said, keeping with the stock redline is my objective while picking up the torque numbers.
Oxygen being a good thing for combustion, is short on supply at our altitude so shooting for HP gains in the OE redline range is unrealistic. With our twisty mountain roads it is torque that is really needed regardless.
The other problem I am trying to deal with is the fuel quality. Alcohol is here to stay and dealing with that is proving a bigger chore than the cam design. At this altitude the alcohol boils in the float bowls when at a stop light!
As Mk e so correctly stated, it all has to be viewed as a "package". I figure if I can get it to work here it should be a real hoot when used with oxygen.

Dave

 

Here are the spec's for the cams that were in my motor that ate the shims up pretty badly:

Intake
.406 Lift
Duration @ .05: 230 deg

Exhaust
.350 Lift
Duration @.05: 232 deg

Had good torque all the way from 2k and peak was at 5500 rpm . . . according to the accel g's on my data acq system, for optimum accel when shifting from 1st to 2nd seemed like you'd want to go past 8000 rpm, but all other gears you didn't have to rev so high and I guess this is because of gear ratio difference between gears?

I wanted to do a shim under conversion and will on another motor . . . got tired of waiting for parts for this one and I still think the standard shim/bucket setup will work (and others say it should) with the right spring pressure and/or coating on the cams like what's applied on the shim under style buckets.

I'm putting stock cams and springs back in this motor for now and I'm very curious what it will run like with the high comp pistons and efi, etc.


Edit: I had the cams profiled so I have other data points for them if anyone's interested.
Sean

 

I posted some pic's in another thread called "excessive shim wear with big cams" or something like that . . . I don't know how to post links or I'd do it . . . I just found the thread though.

The intakes saw most of the damage. It was Norwood's spring and retainer kit. I might have time next week to go up to Web Cam for them to check things out and also see the spring guy that has all the shim under parts and get his opinion on things.

Anyone had to buy a set of stock springs lately? I need a set.


Happy to share BTW.


Sean

 

I just pulled this info off the cam profile data sheets I have for both the custom cams and some stock cams.

Peak accel values are about 5% more on the big cams
Peak decel values are about 30% more on the big cams

Just using basic physics F = ma assuming same valve train weight you'd need 30% more spring force which I did not have. Had Ti retainers but no way 30% weight savings.



Sean