Re: [Amc-list] V8 Cylinder Head Questions - 2nd Follow up ( read )

[Greg Taylor <amundaza@xxxxxxxxx>]

Hi Nick,
  Thanks for getting back with me on the heads.  I was just toying with the idea of putting the ported/polished heads on my 360, to pick up some HP/torque and utilize the roller rockers and porting I've done to them.
   
  I am basically building up the Jeep for much better fuel economy, utilizing hydrogen-boosting and water injection for supplementing the gasoline.  While I was fixing the timing cover leak, I was going to install a new double roller set, new cam/dist. gears, high flow water pump and an HEI distributor.  I'll also be installing the Hydrogen unit at this time.  The water injection and Hydrogen allow the timing to be adjusted much higher and the fuel to be leaned out.  
   
  I'm running a Holley Street Dominator intake on the 360 and will be swapping from a 600-cfm Holley (4160) to a 670-cfm Street Avenger Holley carb (4150).  I will also be modifying the carb to pull mild vacuum off the bowl vent tubes, to help improve fuel atomization ... another trick for improving gas mileage.
   
  I am simply considering swapping to the other 304 heads that I had worked on and had modifed for Chevy valves ... IF ... they would improve performance (HP, torque an MPG's) over the basically stock 360 heads.  The Grand Wagoneer is an occasional driver and would be an occasional offroader.  I wouldn't expect it to see over 5000 RPM, and that on occasion.  It is currently a dog from off-idle and I'd like to improve that (carb & HEI for starters).
   
  As for the valves slated for my ported 304 heads (per Performance AM Style specs), I did the math and the 1.94" Chevy intake valve is 6% smaller than a stock 360.  The 1.50" Chevy exhaust valve is 20% smaller than the stock 360 ... I could also machine the heads for a 1.625" Megaflow valve (6.5% smaller than 360).  These Milodon Megaflow Chevy valves have the 5/16" undercut stem in the runners, making them 1/16" smaller than stock 360's 3/8" valve stems.  On a Chevy they run 40% more flow at low rpms and about 15-20% at mid-range (top end is null between the two).
   
  I checked my 1989 TSM for the GW and it shows that the '89 heads have a 58.62-61.62 cc chamber size (nominal of that would be 60.12 then), so it appears that some of what Rick Jones was discussing was correct ... all but the actual CC size (he was thinking ~65 cc).  I can see now that this mild change from the earlier 360 size of 57.92 would account for the compression drop from 8.4:1 (57.92) to 8.25:1 (60.12).
   
  As a side note, what do you think the 1970 small chamber (52 cc) 304 heads would be worth, fully rebuilt/remanned and ready to bolt on?  I don't think I'll use them since they have the much smaller stock 304 valves, but am curious what they'd be worth selling for.
   
  Thanks for the additional feedback, Nick.  I appreciate it.
   
  Sincerely,
  Greg Taylor :)  <><

Nick ALFANO <71amx@xxxxxxxxxxxxx> wrote:
  Greg,

There is a lot to chew on here. I think the best place to start would be exactly what do you want to accomplish with the engine/vehicle. I get customers that start out like this and all they do is confuse them self and contradict their initial intention which is easy to do. 

Knowing that your engine was rebuilt by someone unknown and in the .020-.030 over range, it is most likely that the compression is not exactly what it was from the factory. Available pistons at the time, gasket thickness, whether the heads or the block were decked etc all play a factory in the actual compression. A general rule of thumb you can go by for compression increase when only swapping heads and everything else remains the same between the two stock chamber sizes is a 0.7:1 increase from the 51cc to 58cc head or the reverse from the 58-51 head. 

Valve size increase on an AMC head. You can comfortably fit a Mopar 2.08 intake and 1.74 exhaust valve in the 360-401 heads. Unless you have a very healthy cam, I would stay away from increasing the exhaust valves. A 1.65 valve with the dogleg design works very efficiently at removing the exhaust gas. In addition, unless you only want a power band under 5000 rpm, I would not put the 304 heads on a 360. It is really going to choke that engine at wide open throttle. When you say huge rpm, that is really a subjection statement. To a rock crawler, huge rpm might be 4500rpms. To a racer or even performance minded street guy, that is not even close to redline on most stock AMC 360-401 engines. Buzzing a 360 to 5500-6000 is not uncommon when you are at wide open throttle even messing around on the street. My Dodge Ram will go up almost 6000rpms before it will shift if I have the pedal to the floor.Same goes for a 727 behind a 401.

Matching your components correctly is the best way to get the kind of power you want. Too many times a guy will put the wrong cam, carb, intake, gearing and stall speed together just because they think all are interchangeable and each one will increase power on their own. When in reality, putting a cam that should give you more power in a car with not enough or too much compression will end up with less usable torque and horsepower. A way you can add a larger duration cam to a lower compression engine is to advance it increasing the cylinder pressure in essence increasing your bottom end.

I know you are gathering a lot of info that may be confusing so again, I think the best place to start is think of how do I want to use this engine and what kind of performance do you expect when finished. Then you can work from there.

Nick

Alfano Performance
4849-76 st.
Kenosha, WI. 53142
262-308-1302
262-942-8271 after 6pm central and weekends 
       
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