Milled heads and bad geometry
10-25-2005, 04:08 PM
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Milled heads and bad geometry My heads are milled .030. I've doing something thinking and talked with a buddy of mine, and I'm pretty sure that I'm losing some juice due to the valves remaining open. My buddy said he's read that some take some preload off the lifter by tightening the rockers, then turning them back one turn. I'm not sure if that will work with .030 though. What would be the best way to fix this problem. Adjustable rockers? something else?
10-25-2005, 06:19 PM
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A friend of mine just recently had the same problem you speak of. He did a head and cam swap and had too much lifter preload giving him only a 10RWHP gain! He first did a compression test to see where that was at and it was low (140's). He took a 1/2 turn out of each rocker and redid the test and he was seeing 210's across the board. The main culprit for his problem was the fact that he was using stock legth pushrods with heads that were milled .016. My heads are milled .030 and I am using the 7.350 length pushrods and I never had any problems. I would do a compression test and see what you get for starters.
10-26-2005, 09:08 AM
#3
With stock rockers, backing off the bolt does nothing for you since youre just tightening the pivot against the rocker boss. They are NON ADJUSTABLE. The most correct way to fix it is with a shorter pushrods. Another option is to shim the rockers up higher with a washer underneath. Youll still tighten to 22 ft. lbs. but now the rocker will be .015 higher (or whatever you shimmed to).
10-26-2005, 09:21 AM
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I was asking this a while back. I have 7.40 pushrods, 6.0L heads milled .030 with LS6 valves (which I believe are longer than stock, correct me if I am wrong). I couldn't decide which to length pushrods to go with. Last time I figured it, I think I needed somewhere in between a 7.35 and 7.40. Any opinions? Is there a calculation I can use to figure this out?
10-26-2005, 09:33 AM
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Originally Posted by Hugger
I was asking this a while back. I have 7.40 pushrods, 6.0L heads milled .030 with LS6 valves (which I believe are longer than stock, correct me if I am wrong). I couldn't decide which to length pushrods to go with. Last time I figured it, I think I needed somewhere in between a 7.35 and 7.40. Any opinions? Is there a calculation I can use to figure this out?
10-26-2005, 09:36 AM
#6
you might want to try some 7.350. i think that LS6 valves are a little longer not for sure though i think i heard that somewhere. if they are LS1's milled .030 then you prob do need shorter ones. what cam are you running? also you cannot just loosen the rocker bolts. first off the bolts would come loose and there is nothing that will align them cause they have to be tight again the head mount to stay straight.
10-26-2005, 09:49 AM
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I did have a good valve job done on the heads when I had them milled. I have a 228/228 .571/.571 on a 113. I guess I need to do a compression check to see for sure. The car doesn't feel down on power though.
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10-26-2005, 09:52 AM
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To clear up any misconceptions my friend backed off the rockers a half turn for troubleshooting purposes. He ordered the shorter pushrods to correct his problem.
10-26-2005, 11:29 AM
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AFR's are not the same as stock heads with respect to required pushrod length when they are milled. Of course the cam base-circle comes into play but mine are milled .030 and I run 7.4 as recommended to me by LG. Vinci used to have this AFR Head/Pushrod info on their web-site.
10-26-2005, 04:44 PM
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Well according to the handy pushrod calculator I am ok. The calculator says that I need 7.4095. I would have thought it would be less than that. Does anyone know offhand how much longer and LS6 valve is than a stock LS1 valve?
-Josh
-Josh
10-27-2005, 05:19 AM
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All comp cams use an LS6 blank billet which is 0.7mm shorter in radius. Assuming you mill the heads 0.030", that equates to approx. 0.7mm so you are OK. If you then use LS6 valves, you will increase preload since they are 0.6mm longer than stock LS1 valves. That's about 0.025" so in theory you would need a 7.375" rod. However, the difference in performance, I would have thought, with that additional preload, would be irrelevant. In that case you could shim the rockers up 0.025" and be done.
10-27-2005, 05:37 AM
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Originally Posted by MNR-0
All comp cams use an LS6 blank billet which is 0.7mm shorter in radius. Assuming you mill the heads 0.030", that equates to approx. 0.7mm so you are OK. If you then use LS6 valves, you will increase preload since they are 0.6mm longer than stock LS1 valves. That's about 0.025" so in theory you would need a 7.375" rod. However, the difference in performance, I would have thought, with that additional preload, would be irrelevant. In that case you could shim the rockers up 0.025" and be done.
10-27-2005, 01:35 PM
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Originally Posted by MNR-0
All comp cams use an LS6 blank billet which is 0.7mm shorter in radius. Assuming you mill the heads 0.030", that equates to approx. 0.7mm so you are OK. If you then use LS6 valves, you will increase preload since they are 0.6mm longer than stock LS1 valves. That's about 0.025" so in theory you would need a 7.375" rod. However, the difference in performance, I would have thought, with that additional preload, would be irrelevant. In that case you could shim the rockers up 0.025" and be done.
10-27-2005, 06:56 PM
#18
Originally Posted by Mirek
AFR's are not the same as stock heads with respect to required pushrod length when they are milled. Of course the cam base-circle comes into play but mine are milled .030 and I run 7.4 as recommended to me by LG. Vinci used to have this AFR Head/Pushrod info on their web-site.
