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| At what point are oversize valves effective? https://www.slantsix.org/forum/viewtopic.php?t=17207 |
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| Author: | AnotherSix [ Sun Apr 23, 2006 10:05 pm ] |
| Post subject: | At what point are oversize valves effective? |
I am going to make some changes to a stock 71 swinger. I have built up various engines before but this is my first slant. Boy is that a long stroke and small bore! It has a 225 with a 904 and I assume (the car is not here yet) 2.90 something gears. So far I have a new (bare) unleaded head casting, a super six setup and am deciding what cam to use. I would like to stay with the stock converter so that limits it some. That may change. Most likely it will be something with around 210 to 215 degrees at .050" I plan on milling the head to a real 9-1 ratio and porting the head as well. This head has hard seats and if I cut it to fit 1.70 and 1.44 valves I will lose that and am not sure if inserts for the 1.44's are a good idea. So the real questions: do the larger valves really help a low rpm (4500 peak ?) engine like this and if so how much? Do they hurt the low end torque? If I go to oversize valves are seat inserts a good idea? If I do that and step up to a cam around 220 degrees at .050 is the little two barrel still enough? ( at that point I am looking at a converter and gear change as well). My first line of thought is to get all the flow possible because of the long stroke. But being a little motor I don't want to kill the low end torque. Any thoughts would be appreciated. If you have a setup just like this I would love to hear about it. |
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| Author: | Dart270 [ Mon Apr 24, 2006 6:34 am ] |
| Post subject: | |
Yes, large valves will help with a low-end motor. The head was designed for a 170ci motor, so more is better on a 225. 1.70/1.44 is the easiest and probably best for a stock bore (or small overbore) motor. I have run 14.90s in a Valiant with 3.00 gears, 2800 stall, mild/medium cam - a motor I shift at 5200. That's mostly due to a ported head that Mike Jeffrey did for me. Lou |
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| Author: | sandy in BC [ Mon Apr 24, 2006 7:31 am ] |
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I have 1.72 / 1.50 valves in the Valaint with a Comp 264 cam and Super 6 manifold with BBD....9.25 CR The head work makes more difference than the cam....Low end (800-2000 rpm) is better than stock....top end is thrilling. The BBD on this motor works just fine. Only downside is it shrieks like a banshee at WOT.....oh....mebbe thats not a downside. My 225 is bored 60 and I radiussed the chambers for flow around the valves. I decked the block instead of the head for compression so I would not have to bore notch. |
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| Author: | AnotherSix [ Tue Apr 25, 2006 8:55 pm ] |
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Thank you for the input. Good point about the head starting out on a 170. The 225 is over 30% more displacement, that makes a lot of sense. Decking the block instead of milling the head sounds good too. Even if it does not need a bore notch it should help the flow at least some by giving the valve a little more room to breath. I plan to pull the whole engine and do whatever is needed but at the very least re-ring it. It has about 95,000 miles on it. Any thoughts about having exhaust seats for 1.44 valves installed? Is there enough meat in the head to do this? I am sure it can be done but I am concerned about reliability. I don't want to cause a crack or have the seat come lose. This must be an old subject but I have not found a definitive answer. |
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| Author: | Dart270 [ Wed Apr 26, 2006 4:30 am ] |
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You can do hardened seats on 1.44 valves no problem. I have them on my head with 1.50 exh valves and I just pulled it apart at 50k and they are fine. I have seen them come out (on Ford 351), but not sure how much was due to machining errors...? That said, I'm not sure I would bother. The installed hardened seats I just looked at had about as much wear as other Slant heads (30-50k mi) with no hardened seats! The Slant head has very hard material anyway, so unless you are generating lots of sustained heat in your driving (road racing, mountain roads with low octane and high timing advance...), then I wouldn't bother. Lou |
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| Author: | argentina-slantsixer [ Wed Apr 26, 2006 9:49 am ] |
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hey lou how much is bored over std to allow the use os 1.5" ex valves and what size are you using on intake valves? |
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| Author: | Dart270 [ Wed Apr 26, 2006 12:36 pm ] |
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Std bore and 0.030" over require a small bore notch to clear the 1.50 exh valves. I made my notches by stuffing an oily rag into the cylinder, grinding, then removing and checking cyl for debris (motor in car and assembled). 0.060" or more overbore does not require notches. I have 2 heads with 1.72" int valves, and the one from Mike Jeffrey (full boogie) has 1.76" int/1.50exh. Lou |
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