Max lift with stock valve length?

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gzig5

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It's time to start putting my '71 340 back together so it will be ready when the body/chassis work is done. Might not make sense but I'm doing an iterative build over time with different cam/head/intake/carb combinations in hopefully increasing levels of HP. I'm retiring and an ongoing project like this will help keep me out of the bars during the winter. I will be doing the majority of the work myself and I hope to learn from success and failure.

I want to start off with the stock 2.02" J-heads that were on the motor. They look to be pretty low mileage but I'll go through them and make sure the guides are good, etc. I'll be porting the heads myself and will freshen up the valve job. It was running a stock 340 cam, but I will be starting out with a solid flat tappet cam that is 242/247 @.050", .540"/.549" lift, and 109 lobe separation. With the correct head prep to lower the seal seats, will the stock length valves support this amount of lift? Springs appropriate for the cam will be purchased, maybe I need to figure out what those are first so I have the setup specs? I'm not against going to a longer valve, but to get the project rolling, I would prefer to use what I have.
 
You can net .600 lift with stock length valves IF a you can find the right springs.

With lifts much over stock you’ll need to correct the geometry.

EDIT: I forgot to mention that one of the limits we are stick with is the 5/16 hold down bolts. That limits how much RPM, spring load and lobe aggressiveness.
 
ehhhh......the clearance you have to watch for is retainer to guide. I think some have contact with less then .500 lift so be careful. Of course different retainers and valve keepers can also help.
 
Rat Bastid said:
With lifts much over stock you’ll need to correct the geometry.
Click to expand...
Geometry correction is in the plan. In the beginning I'm going to try to adhere to the KISS principle where I can to reduce the number of potential problems. I'll start with a good set of 273 adjustable rockers and then see what difference a PRW 1.6 rocker will make. I was considering machining the shaft bases flat and making offset blocks optimized for each set once it is running well. Other than comitting the head to that setup, I don't see a down side? In my mind's eye it would be a more stable setup and making blocks is pretty simple once you know your offset. If there is room, I thought a pin or two from the block to the head would help stabilize the base. Would do same to the ProMaxx's that will be waiting in the wings. The guy that did some chassis/body work for me that was too big to handle, has a chassis dyno and I'm going to see if I can work out a deal with him to evaluate performance after each major change. Car will be street driven so that will limit how hairy a cam I can get to, but I do plan to spin it up and realize that will take more than the stock parts to live at the higher rpm range. Keeping the stock valves in these heads will allow me to put a little more $$ towards better stuff for the next set of heads.
RustyRatRod said:
ehhhh......the clearance you have to watch for is retainer to guide. I think some have contact with less then .500 lift so be careful. Of course different retainers and valve keepers can also help.
Click to expand...
I'm writing this without while at work without the heads in front of me so I'm at a bit of disadvantage visualizing how much room there is. I'll be pulling them down soon to check them out and then can measure spring heights, retainer clearance and such.


I'm an engineer, and I envision this whole process as a big DOE (Design of Experiments) to see what does what. A lot of you guys have been doing this your whole life, but my day job and family commitments precluded me from being able to, so I'm going to try to learn as much as I can as fast as I can and I learn best by doing. Thanks for the guidance.
 
Rat Bastid said:
You can net .600 lift with stock length valves IF a you can find the right springs.
Click to expand...
That may be a problem with this cam. I just got off the phone with Comp Cams asking for the spring spec for this cam. Lift will be .540/.549 @1.5 ratio and .576/.586 with 1.6 rockers. I told him up to 6500-7000rpm max, thinking of the future. He said it needed 150-160 lbs on the seat and 380-400 open. The problem is the relatively short install height on the stock length valve of 1.650-1.700" in the J-head and he said they didn't have a spring that would work. @Rat Bastid any suggestion? I looked in the PAC catalog but the way the data is laid out makes it difficult to go through for me and nothing jumped out.
 
gzig5 said:
That may be a problem with this cam. I just got off the phone with Comp Cams asking for the spring spec for this cam. Lift will be .540/.549 @1.5 ratio and .576/.586 with 1.6 rockers. I told him up to 6500-7000rpm max, thinking of the future. He said it needed 150-160 lbs on the seat and 380-400 open. The problem is the relatively short install height on the stock length valve of 1.650-1.700" in the J-head and he said they didn't have a spring that would work. @Rat Bastid any suggestion? I looked in the PAC catalog but the way the data is laid out makes it difficult to go through for me and nothing jumped out.
Click to expand...

Let me get the Crane book out and then I can see what crane spring works. I bought my springs from Doug Herbert. I’m 1.700 installed height and I’m at 145 on the seat and could easily shim it a bit to get where you want to be.

Hang on and I’ll see if I can find out what you need.
 
This below doesn’t solve your problem unless you find 16 of them in what you need. Hopefully this will help some.

B8954CCC-9DB8-4B9A-9F5E-123DBF98D82B.jpeg
 
@Rat Bastid IIRC, Crane supplied the cams and valve train components for MP for years. Someone gotta make something!
 
Look at the 26995 beehives from comp…you can be a touch lighter with the smaller retainers and improved design. I ran the 26918 with +100 valves up to 7000 rpm and 600 lift, cam was 246/260 @050. Smaller top/retainer clears rockers way easier too.
 
gzig5 said:
It's time to start putting my '71 340 back together so it will be ready when the body/chassis work is done. Might not make sense but I'm doing an iterative build over time with different cam/head/intake/carb combinations in hopefully increasing levels of HP. I'm retiring and an ongoing project like this will help keep me out of the bars during the winter. I will be doing the majority of the work myself and I hope to learn from success and failure.

I want to start off with the stock 2.02" J-heads that were on the motor. They look to be pretty low mileage but I'll go through them and make sure the guides are good, etc. I'll be porting the heads myself and will freshen up the valve job. It was running a stock 340 cam, but I will be starting out with a solid flat tappet cam that is 242/247 @.050", .540"/.549" lift, and 109 lobe separation. With the correct head prep to lower the seal seats, will the stock length valves support this amount of lift? Springs appropriate for the cam will be purchased, maybe I need to figure out what those are first so I have the setup specs? I'm not against going to a longer valve, but to get the project rolling, I would prefer to use what I have.
Click to expand...


Ok, I finally found my Crane catalog.

The part number of the spring for what you want is
99838.

The catalog says it’s good for .690 lift. At 1.650 it’s at 112 pounds and 1.600 it’s at 131. At .600 (1.000) lift it’s 383 pounds. It coil binds at .950 so if you net .600 lift you’d be .050 away from coil bind which is pretty spanky.

It has a spring rate of 438 lbs/inch and an OD of 1.465.

Crane didn’t make their own springs. This is really close to the spring I use that I found from Doug Herbert. Someone made this spring for Crane and I’m sure someone still has it.

You’ll just have to dig around and find them. If Doug Herbert is still up and going I’d try them first.
 
I actually lowered my installed height to 1.625 for the springs I used coil bind was .950 so I had p)entry of room for my .550 lift solid cam. I will try to find the spring no.
 
dusterbing the peace said:
Look at the 26995 beehives from comp…you can be a touch lighter with the smaller retainers and improved design. I ran the 26918 with +100 valves up to 7000 rpm and 600 lift, cam was 246/260 @050. Smaller top/retainer clears rockers way easier too.
Click to expand...
Those are a little lighter than what the comp guy said, and he did say they didn't have anything that would cover it. BUT, I think he was being a little bit over cautious on the upper end of the RPM range I gave him. I doubt these J-heads will be making much power above 6k rpm so I won't need to spend much time there. They may be a viable option. I think I could shim them a bit to increase the load a bit too? They support about .640" lift and I'm not going to use it all.
 
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gzig5 said:
Those are a little lighter than what the comp guy said, and he did say they didn't have anything that would cover it. BUT, I think he was being a little bit over cautious on the upper end of the RPM range I gave him. I doubt these J-heads will be making much power above 6k rpm so I won't need to spend much time there. They may be a viable option. I think I could shim them a bit to increase the load a bit too? They support about .640" lift and I'm not going to use it all.
Click to expand...
I shimmed mine within 050 of bind for that little extra pressure, FWIW. So if you can get a 030 locator under then it should put you pretty close to where you want to be with 550 lift.
 
gzig5 said:
I can’t read the specs but I’ll see if I can look them up. If I can’t I’ll ping you.
Click to expand...
Hey gzig5, any progress with your build? I'm about to go through a similar process of finding the right roller cam and springs to work with my stock heads with stock length valves, and curious if you found some good springs.
 
CopperheadDart said:
Hey gzig5, any progress with your build? I'm about to go through a similar process of finding the right roller cam and springs to work with my stock heads with stock length valves, and curious if you found some good springs.
Click to expand...

If you are talking about a solid roller you’ll be hard pressed to find a spring that will take much lift at that short installed height.
 
Rat Bastid said:
If you are talking about a solid roller you’ll be hard pressed to find a spring that will take much lift at that short installed height.
Click to expand...
That's what I'm starting to figure out... I thought there would be some newer beehives or double springs that would fit the bill for a smaller lift solid roller cam. May have to re-think my build if this is the case.
 
CopperheadDart said:
That's what I'm starting to figure out... I thought there would be some newer beehives or double springs that would fit the bill for a smaller lift solid roller cam. May have to re-think my build if this is the case.
Click to expand...

If you can finagle a 1.850 or even 1.800 installed height you can find some pretty good springs That will take some lift.

The problem is you will need to correct your geometry with a kit from B3 Racing engine. You’ll probably need to do any way.
 
Rat Bastid said:
If you can finagle a 1.850 or even 1.800 installed height you can find some pretty good springs That will take some lift.

The problem is you will need to correct your geometry with a kit from B3 Racing engine. You’ll probably need to do any way.
Click to expand...
He'd need to do it on a stock engine, I'd bet.
 
CopperheadDart said:
Hey gzig5, any progress with your build? I'm about to go through a similar process of finding the right roller cam and springs to work with my stock heads with stock length valves, and curious if you found some good springs.
Click to expand...
I’m currently on the slow boat but hopefully picking up the pace in a few months.
 
The Comp 26918 Beehive will do nicely. Coil binds @ 1.100". Normally installed @ 1.800" with 125 lb seat. With your valve lift, you could reduce this to about 1.750" to increase the seat pressure to about 140. Beehives require less tension because of their lower weight & design.
 
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