I want to get the most out of my Rajo 4 valve head. It's got HUGE intake valves and I'm running a big intake manifold and two super fast U&J carbs. I've got Ford Windsor 351 valves for the exhaust and a dual exhaust manifold. Between the engine and my Chicago and 3:1 Ruckstell, she accelerates like a scalded dog. But I want whatever the best this thing has to offer and I don't think I've quite found it yet. I know it's not an 8 valve or OHC but I want to maximize what I've got.
Currently I have a Stipe .280 cam, but I'm thinking to really get the most out of what I'm working with I need a custom, dual pattern cam shaft. I've got a bronze Dan McEachern cam gear. I emailed Mr. Stipe but never heard back from him. Does anyone know who might have a good idea about what I need and could make it for me? Thanks!
Just food for thought- 4 valve rockers (stock ones anyway) are 1:1 so you're not going to gain much there over what you have. Bill's cams are already dual pattern AFAIK. To really design a cam to get the most out of the head, you need to put the head on a flow bench and get a lift VS air flow curve for it. I have curves for several heads, but not for a 4 valve.
I haven't seen pictures of your car from all sides so when you find the time how about posting some. They may have been on here in the past and I missed them
Hey Dan, that's good info to know. I guess the next question is where I can get the head tested like that?
I'm not expecting there to be this sudden massive change where the engine comes alive because I have a few more degrees duration or my separation angle is a little different. But a few horse power here and there makes a huge difference with so little weight (and already so few horsepower).
I ran a 4 valve with one to one rockers on my speedster for several years. While it ran fine, there were two changes I would have made beyond what you have stated for your engine. First and foremost increase the compression with high top pistons, secondly find/adapt or make a set of 1 to 1 1/2 rockers. My car ran OK but was no hot rod. Increasing compression and changing rockers would certainly have helped. Why didn't I do these things? The engine ran fine with the existing pistons and I didn't have easy cheap access to modified rockers. Instead, I happened across a Fronty that was a good deal and went that way.
Mine already has domed pistons!
Modified rockers is a good idea, I don't think those will be very hard to make, though they'll end up looking kind of new compared to the cast ones I have now.
Seth, you need to find a good race engine shop. Your in the south, you should have no trouble finding someone around in a motorsport rich area (although you may have to travel a little to get to one). But Dan is right, without proven head data, anything beyond what you have done is a crapshoot.
No sense making or retrofitting rockers that promote more valve lift if the ports in the head can't support it. That is one reason why people port heads. But that is also a tricky game as you can make a good head bad in a hurry.
Engine performance is based on air flow---more in and out equals more power. But other real world things like drivability also come into play--not just a number on the dyno.
One thing I often wondered is where does the dual port exhaust manifold compared to a tube header. Would building a header with a good scavenging collector might help your combo out more. As will tuning the length of the pipe on each port. The downside is, something not as period looking.
I believe your intake is probably as good as it will get, so will there be anything to gain by porting the head? Porting the block for the exhaust? Opening the valve more? Keeping the one or both valves open longer? More or less overlap on the cam or changing the centerline? Those are questions that really can't be answered without more concise data.
By the way, if your cam is advanced, you can always try retarding it some to pick up more top end. I believe those cams are built with some advance in them, that is where checking the centerline with a degree wheel comes in.
I forgot to add, When trying to find a shop, you need to ask them if they have a flow bench for the head. You could also try building one yourself if you feel inclined. It's been done and your not necessarily chasing a number, but looking for data on where the head port stalls. I would imagine there are how to's on the net for building a bench.
Next time I have the head off I'll see about getting it on a flow bench. With the updated info I have I agree that there's not much point to a different cam or rockers without testing the head. And, a tubular header would probably help over the current manifold.
I guess I mainly want to see if there's any relatively low hanging fruit left. Obviously a supercharger would help! Haha, just looking to confirm that it's all detail things like tubular header, raising the compression by shaving the head but then relieving the block for the exhaust, porting the intakes and exhaust, wee bit different cam, etc. If those are all that's left, then ok.
Iím in the process of making aluminum roller tip rockers running on needle bearings on the shaft for my Gemsa head. I am certainly prepared to share my experiences with you if you decide to go down this road. The actual cost of the stuff Iím having to buy is quite reasonable. I had the rockers themselves water jet cut from 6061-T6 aluminum by the same shop that laser cut the head gaskets I think I supplied
Maybe devise a way to duct cool outside air toward those carburetors? Seems like they're on the hot side of the engine right below the exhaust manifold,....??? Just a thought,....harold
My Mercury had a 4v when I got it. I found that they don't perform as well as a good flathead until you wind up the motor. The high compression piston should help since the 4v has such a large chamber.
Have you considered the hi performance roller rockers available in the aftermarket? I have found some that should work with my SO Fronty. 1 and a 1/2 to 1 with needle bearings at the rocker shaft.
If you want a modern aftermarket aluminum rolletized rocker arm, there are a few places that will custom make them. Harland Sharp is one such place.
I know Les enjoys making his own parts, but it sounds as if they would be similar to most modern aluminum rockers.
Just curious, how do you change the ratio of your rockers when the locations of the pushrods, rocker shaft & valve stems are a constant? Do you relocate the rocker shaft closer to the pushrods?
Jerry, that's exactly it. In order to change the ratio I'd need a different set of rocker towers that would move the rocker shaft towards the push rods, giving the valve side of the rocker a longer arm and thus more travel.
Why not supercharge? It works.
Hmmm, I've got ideas now for my wife's Dyson!!
One of the Hot Rod Magazines had a gas powered leaf blower into the corvette fuel injection!!! Better than a Dyson since you don't have to plug it in!
BBC rockers would fit lengthwise but a couple of issues;
1. They are stud mounted, so;
They actually mount on a ball and so depend on a push rod guide to keep them straight.
They also depend on the stud mount for lash adjustment.
Lubrication is a bit complicated as they are designed to be fed from the push rods
Certainly all manageable issues. It just seemed easier and cheaper to go with shaft mounted and use adjustable studs for the push rod tips.
I had been waiting on one of the custom rocker arm suppliers in California for 4 months, but no progress was forthcoming. It was reaching the stage where this was the last significant issue!!
Each to there own