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Cast crankshaft and connecting rods for racing |
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74jmill_jav
AMC Fan Joined: Feb/20/2020 Location: Baltimore Status: Offline Points: 28 |
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Posted: Feb/23/2020 at 6:02pm |
Is anyone running the cast crankshaft and connecting rods on a javelin and doing well racing? I’m about to rebuild my 304, and curious if I should invest in forged connecting rods, or if the cast ones will work just fine for track courses and autocross? Curious to everyone’s thoughts! Thanks!
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304-dude
AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Stock class? I thrashed on my stock 304 running max RPMs (4600 to 4700) limited by stock valve springs. Only ate on valve on a max rpm blip / shut down. Never had a problem, after changing my head only. If changing to solid lifter or roller cam, then be careful and have it balanced and yada, yada, yada. I would not push beyond 6500 for long term racing use on cast rods. Buick and AMC have some good stuff in their basic v8 blocks. Key is getting the work done for race perposes. Mild porting, Chevy 305 valves, should being some good results without spending extra for whatcha got. Though cost wise, it is cheaper to go to a 360, as it weighs the same and allows for more effective power with a little extra cost, mostly in obtaining an engine.
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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74jmill_jav
AMC Fan Joined: Feb/20/2020 Location: Baltimore Status: Offline Points: 28 |
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Thanks for the tips! What exactly did you do to your heads and block? And how much horsepower do you think you were pushing from your engine? I understand that I can’t buy aftermarket aluminum heads for the 304, but I can for the 360. I’m still deciding what to do—- buy the 360 or work on the 304 that came with the car. There is something cool to me about being competitive in a smaller engine car....
I’m not sure of what class... I just know that I want to have some track fun with my 74 Javelin and be as competitive as possible with it.
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304-dude
AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Mine was a stock engine, with dual exhaust, Holley 650 spread bore with some mods for 304 engine drivability, which were smaller jets, higher plenum (used 1" ported spacer) an Offy spread bore 360 (rare to find these days). Engine was factory rated at 150hp. I assume I got 220 out of it. Though I changed to a Mopar 8-3/4" rear out of a Cornet 500 with 2.76 gears, for highway cruising speeds. Topped out above 138MPH. A Ford Probe GT has a factory speed limit at 138MPH could not pass me as my RPM was maxed at 4700 in drive. Oh I did have a cowl hood, no rear spoiler. Cowl hood added, extra aero, and nose stability. Never floated at any speed. Very stable, considering I used factory 14" X rally wheels with G60 tires.
Edited by 304-dude - Feb/23/2020 at 7:16pm |
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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74jmill_jav
AMC Fan Joined: Feb/20/2020 Location: Baltimore Status: Offline Points: 28 |
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What’s the deal with Chevy valves? Why are they better than the stock amc?
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304-dude
AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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If your racing, for higher than stock rpm use, the 305 valves are a wee larger, for better breathing. A cam and lifter set, will require the head work done. Also if you go with a hugh lift cam, if your heads, have bridged rocker arms, you will need to run LS rockers on machined pedistals, or obtain early 304 heads (70 - 72) with stud mounted rockers. |
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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PHAT69AMX
AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5919 |
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It might be that the Chevy Valves are just lower cost due to production volume.
Same Stem Diameter and nominal overall Stem Length, and pretty much head diameter basically. IF having heads re-worked, my logic was new valve guides, so go smaller to 11/32 stem dia., valves are lighter, and there are 'undercut' available once again due commonality with sbc stuff. Although I long ago that is the logic I went with at the time and deviated and got / used 1.68 exhaust. At the time Si Valves had both available and reasonably priced, 2.02 & 1.68, 11/32 stem, 4.910 Long iirc. Rods... understanding is it is a matter of cycles and a fatigue failure... the stock AMC parts are pretty good, but it comes down to how many cycles are on them. But others here are much more better informed and experienced on that than I am.
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74jmill_jav
AMC Fan Joined: Feb/20/2020 Location: Baltimore Status: Offline Points: 28 |
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Ok- so I bought a new “Sealed Power” performance cam for the 304. It came with new lifters and rods. Should I just buy the Chevy 305 valves, or get the stock ones polished? It sounds like the Chevy ones might be the way to go... any suggestions on what exactly to buy since I have no clue the compatibility differences between my 1974 304, and a Chevy?
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304-dude
AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Being sure to get quality springs for the lift requirements of the cam. Too light on pressure will cause dropping of the valve, from valve float. Stock 304/360 springs, are not that good for performance. Though I was able to barely run them with stock setup. Probably would have gotten more hp, if I had bumped the spring pressure to 15# by a wee shim or two on the stock cam. As for Chevy valves... the engine guy will oversize the valve seats, while doing minor porting. Don't go ape poo, just clean up and smooth. There are tricks of the trade with contouring, which if not familiar with amc heads, could ruin your set, even though they look cleanly done. |
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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mramc
AMC Addicted Joined: Jul/12/2007 Location: United States Status: Offline Points: 3219 |
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The Chevy valves is an old engine trick, as the Chevy valves are one once lighter then the AMC valve , so you get one pound off your valve train. The Chevy valves are also cheaper and easier to get. LRDaum
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LRDaum
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