I'm sure this has been discussed many times, but I'll ask again. Is it any or all of the following: carb size, cam selection, balance (of rods, pistons, and crank), stroke, friction (oil viscocity, roller lifters, etc). Of these, which puts the biggest limit on rpms?

Here's my set up: Edelbrock 500, Offenhauser 4 bbl, Clifford shorty headers, 280 deg .465 lift cam, head milled .100, ported, big valves. It is not assembled yet and I was wondering what I can still do to get the rpms up (balancing the rods and pistons, etc) Also, what redline would you guys give this set up?

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Stephan Nelle

A stock cammed and carbureted 225 has a hard time hurting itself with too much RPM because it doesn't breathe well enough to reach harmful speeds. With your modifications you'll have the breathing capability to possibly hurt the stock bottom end.

Generally speaking the rod bolts are the first thing to fail which is why lots of folks use ARP rod bolts. Light weight pistons reduce the rod and rod bolt loading which will allow more engine speed before these parts become over stressed. Reducing the engine stroke lowers piston and rod acceleration which will allow more engine speed before the rods, rod bolts and piston become over stressed.

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Joshua

The biggest and most important thing you could do at this point would be to install ARP rod bolts into your rods ( have a good machine shop do it).


Balancing is a good plus also, the smoother these parts rotate, the less stress on them and the more power you will get. Not alot of power to gain from it though unless its so far out it would shake itself to death anyway, but durability is better. A out of balance engine will wear the bearings a lot quicker.



These things want get the RPM up, but it will stay together if you do get them up.



What is the rest of the specs for your cam ? There is a very good chance it will respond very well to advancing it depending on the center line and @50 duration numbers. With the rest of the specs I coudl figure how much advance to use and what RPM it should peak at. Also what are the valve lash specs on the cam.



You have every thing you need to turn a few RPM as far as size/specs ect,ect..... Now just add the durability ( Rod bolts and balancing) and get it all tuned right and you will probably be ready for around 5500 RPM peak HP with a shift at about 5800 to 6000 RPM.


Close attention to tuning can really make the diff between a dog and a good running engine. Things like header collector lenth, camshaft install, Distributor advance curve setup and jetting the carb right are very important to how your engine comes out. With the rest of the specs of your cam I can figure the collector lenth and what to set the cam at, the rest is through testing to find what works best.



As far as what limits your RPM, with the range you will be able to reach
the cam and the head ports will be more of what limits it. Having good valve springs to work with the cam is needed. But at these RPM ranges roller lifter and rockers and such are really not need, although the right setup may make more power ( mainly a roller cam would have possible more power). The gains are very minimal at these levels and getting the basics right will be your best bet for gains. Maximize what you already have. If money was no probelm and I wanted to do the one thing that could help, it would probably be a set of roller rocker. ALthough IMHO to make the best use of them you need 1.6 intake and 1.5 ratio exhaust and I dont know any company that is offering them that way. T & D might make them if they where asked. The other thing I could suggest would be a custom cam made for your setup. BUt you already have a cam so for now I would run it, some changes can be made in degree setting and valve lash to maximize the one you have now, then latter if more is wanted you will no more about what type cam you would want after running what you already have.



Jess

Jess,

Thanks-that's exactly the kind of info I was looking for. Thanks for offering to figure how much advance, etc. I should run. I'll get the numbers up tomorrow evening. I've never done a performance rebuild and I will be needing all the help I can get with understanding (and actually performing) degreeing the cam, advancing timing, etc.

Stephan

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Stephan Nelle

Duration @ 50 deg is 230 for both intake and exhaust and .310 gross lift at cam for both intake and exhaust. Here's the other numbers straight off of the cam card. I'm not sure what these refer to or mean, so I'll copy them exactly as they are and let you interpret for me: these are all under BDC, starting at "exhaust closes" in the upper right corner, working counterclosewise: 26, exhaust closes, 60 overlap, 34 intake opens, 66 intake closes, bdc, 74 exhaust opens, and back to 26 exhaust closes. Now for what's under TDC: again, starting at "exhaust closes" in upper right corner, working counterclockwise: 1, exhaust closes, 10 overlap, 9 intake opens, 41 intake closes, bdc, 49 exhaust opens.

I hope these numbers make sense. If not, I can scan the card to my computer and post a picture of it here.

I've read all about degreeing a cam, but am still at a loss as to what it does. You can only put the cam on one way, right (unless you drill a new hole in the cam sprocket and put in a new dowel)? Does all this have to do with distributor timing?

Sorry for all the elementary questions. I appreciate all the help.

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Stephan Nelle

Errr... not really... Cam timing indexes the camshaft to the crankshaft, so your 'valve opening' events are indexed a certain way to the position of the piston... if you read a few more articles on this you can' retard or advance' a cam a few degrees one way or the other from it's 'centerline' and change your cam timing to either make more peak torque or more peak horsepower depending on the grind and what you are hoping to acheive...

Distributor timing changes the event when spark (determined by load, driving, carb, air fuel mix...etc...)

-D.Idiot