JMortensen Posted April 20, 2006 Share Posted April 20, 2006 With a cam' date=' I bet you won't have to retard timing at all.If you do, I'll buy you a shot of tequila next time I'm in San Luis Obispo:) FWIW, I ran my 3.1 with a stock N42 head shaved ~.010", stock cam, and 2mm head gasket, ~10.3:1 CR, at 35deg advance, with no pinging for years.[/quote'] Keep in mind the 91 octane oxygenated crap gas they have there Dan. Remember Bastaad's NA engine? N42 head with flat top block, 91 octane, Schneider "Stage III" (I guess that's the 3rd stage of puny) cam, and he only ran 26 degrees total as well due to pinging. Maybe since Jessie went with a larger cam he won't have that issue. Hopefully. AK-Z, the chambers are the same on the N42 and N47, so any mod you've seen in this thread should be the same for you. 2003z, for a dished piston block there isn't much point to using a P90 head. Even if you mill the crap out of it you'll only get it back to about stockish NA compression. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 20, 2006 Share Posted April 20, 2006 Jessie, I'm going to try one more time. My bro in law Matman has a couple P79s and I think a P90. I'm sure he'll sell you one cheap. If you're going with flat tops, I'd really consider it. Quote Link to comment Share on other sites More sharing options...
Mack Posted April 20, 2006 Share Posted April 20, 2006 Ill still toss in my vote for a MN47. If sompression ratio is a problem, UNshroud the valves and take a little out of the cahmber to make it bigger. I would think that would be a lot less hassle than shaving, shimming and all that garbage. With a felpro gasket (.8mm) and flat toips, you will be under your perfect .035" required for optimum quench. while its true the MN47 does have small intake valves, I have personally made them flow as well as a regular P79 or P90 valve and intake port. its not that hard. and as an added bonus, with the smaller intake, you get lotso velocity. torque city. Quote Link to comment Share on other sites More sharing options...
JessZ Posted April 20, 2006 Author Share Posted April 20, 2006 Well I spoke with Stephen today and his shop is running a little behind schedule. I will research the P-head more tonight and get back to you Jon; this does sound like an option I will condiser. Dan if I go with the N42, I drink Patron--and lots of it... Quote Link to comment Share on other sites More sharing options...
oinojo Posted April 25, 2006 Share Posted April 25, 2006 when shaving the p-79 head to .080", do you need to shim the valve springs as well? on the zgarage website it says to do so but i havent heard of anyone actually doing it on this site. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 25, 2006 Share Posted April 25, 2006 If you were to just shim the springs .080 that would get exactly the same amount of preload on them. But in this case it's not likely that Jessie can do that because he's installing a new cam, which most likely will require new springs. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted April 25, 2006 Administrators Share Posted April 25, 2006 when shaving the p-79 head to .080", do you need to shim the valve springs as well? on the zgarage website it says to do so but i havent heard of anyone actually doing it on this site. Shaving the head has no affect on valve springs, (unless you shave into the vale spring pockets which would be impossible). You can shave the head as much as you want and the valve spring pressure with the valve on its seat and over the nose of the cam wont change, so there is no need to “shim†the spring just because of surfacing. You shim the springs for other reasons such as sinking the valves deeper into the head, etc. or for any other reason that the installed spring height isn’t where it is supposed to be for that particular spring. Now you will need to shim the cam towers if you shave al to of material off of the head to keep cam timing within the range of the factory adjustments on the cam sprocket. Spring shims and cam tower shims were mentioned and pictures shown as well in this thread about what is involved in building a custom L-series cylinder head. http://forums.hybridz.org/showthread.php?t=108398 Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 25, 2006 Share Posted April 25, 2006 In this particular case Paul, the guy suggests shaving the P90 .080 and swapping in the N42 or N47 valves. The lash pads don't need to be adjusted if you do this, and the shims restore the original seat pressure, because the new valves are .080 longer than the P valves, since the P heads have the deeper combustion chambers they have shorter stems. But if you go with a cam over .460 lift, then you have to change the valve springs and the lash pads anyway. The benefit is that you get a more efficient combustion chamber design with a reasonable compression ratio for a hot engine that can still run pump gas. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted April 25, 2006 Administrators Share Posted April 25, 2006 WOOPS!! My bad. You are absolutely correct. I wasn’t paying attention to the details within this thread, (I just lightly skimmed through it), and I just assumed he was asking about how/why just the act of shaving a head would need to have the valve springs shimmed…. DOH!!! Sorry fellas. Please forget my previous post. Paul Quote Link to comment Share on other sites More sharing options...
oinojo Posted April 25, 2006 Share Posted April 25, 2006 In this particular case Paul' date=' the guy suggests shaving the P90 .080 and swapping in the N42 or N47 valves. The lash pads don't need to be adjusted if you do this, and the shims restore the original seat pressure, because the new valves are .080 longer than the P valves, since the P heads have the deeper combustion chambers they have shorter stems. But if you go with a cam over .460 lift, then you have to change the valve springs and the lash pads anyway. The benefit is that you get a more efficient combustion chamber design with a reasonable compression ratio for a hot engine that can still run pump gas.[/quote'] so how would i go about shimming the valve springs. I have both an N42 head and an extra P79 head. The N42 head has been through some overheating on top of the head so it might be done for. I was thinking of freshening up the P79 head by doing the suggested mod to it. Now my question is, could i take the shims on the N42 head and combine them with the ones on the P79? or would i need two sets per valve to be placed on top of the original p79 to fill the 0.080 slack. Being that the stock shims are (0.040" in size) Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted April 25, 2006 Share Posted April 25, 2006 Patron? Don Julio (anejo) fer me. Actually, I usually cheap out and get Sauza Hornitos, but it's only good for Margaritas. I need to be rich enough (or enough of a drunk) that $60/bottle doesn't faze me... Anyway, I wouldn't have any qualms about an N42 head at 10:1 with a mild cam, even with 91 pump gas instead of 93. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 25, 2006 Share Posted April 25, 2006 so how would i go about shimming the valve springs. I have both an N42 head and an extra P79 head. The N42 head has been through some overheating on top of the head so it might be done for. I was thinking of freshening up the P79 head by doing the suggested mod to it. Now my question is' date=' could i take the shims on the N42 head and combine them with the ones on the P79? or would i need two sets per valve to be placed on top of the original p79 to fill the 0.080 slack. Being that the stock shims are (0.040" in size)[/quote'] Just go to a machine shop and buy enough shims to finish the job. I didn't think that the stock shims were all the same size, but if they are that's great. If not you don't want to mix them up. Basically you're going to pull the valve springs, set the extra .080" of shims in there, then put the valve springs back on. If the new valves are .080 longer and the shim is .080 taller, you should end up with exactly the same seat pressure. Quote Link to comment Share on other sites More sharing options...
AK-Z Posted April 26, 2006 Share Posted April 26, 2006 What gasket height are your suggestions reffering to? As in shaving the N42 head for ideal quenching. wouldn't it be easier to just get a thinner head gasket? Oh BTW whats the OEM gasket height? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 26, 2006 Share Posted April 26, 2006 Stock gasket is .050. 1mm gasket is .040. Shaving the N42 changes the shape of the chamber in addition to increasing compression. Quote Link to comment Share on other sites More sharing options...
oinojo Posted April 26, 2006 Share Posted April 26, 2006 Just go to a machine shop and buy enough shims to finish the job. I didn't think that the stock shims were all the same size, but if they are that's great. If not you don't want to mix them up. Basically you're going to pull the valve springs, set the extra .080" of shims in there, then put the valve springs back on. If the new valves are .080 longer and the shim is .080 taller, you should end up with exactly the same seat pressure. Sorry if this is a dumb question, but what if i just transfered my valvetrain from the N42 head to the P79? Would i still need to shim up valvesprings? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 26, 2006 Share Posted April 26, 2006 Dunno. Quote Link to comment Share on other sites More sharing options...
Guest norm[T12SDSUD] Posted April 26, 2006 Share Posted April 26, 2006 Yes if you swap your N42 valvetrain over you will have to shim the valve springs since the roof of the P79 is higher you will have less spring pressure until you add the .080" extra valve spring shim. Quote Link to comment Share on other sites More sharing options...
DATZ Posted October 9, 2022 Share Posted October 9, 2022 On 4/19/2006 at 8:46 AM, Guest norm[T12SDSUD] said: Yes the ideal quench distance is .035" and that is exactly what I have on my 10.7:1 stroker motor with dished pistons and .070" shaved N42 head. I also read in HotRod magazine where reducing CR with a lower piston deck height and a resulting larger quench distance will result in INCREASED pinging! You gotta get the squeeze for mixture turbulence! If you’re running dished pistons you have no quench. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.