absolute minimum p/v clearance on intake valve
04-03-2005, 10:36 AM
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absolute minimum p/v clearance on intake valve Hi guys I did a search and can find recomendations but what is the absolute min. p/v clearance is anyone running without problems? I am checking it with pusher springs and a dial indicator and at tdc I have plenty of clearance but at about 6-8 atdc it drops down to about .056 is this to little for the intake valve? The exhaust valve is fine. also if I retard the cam 4 deg. (it has 4 deg. ground into it) I can get the recomended clearance, but how will this affect my power? also does pushrod length affect this measurement? I am tightening rocker arm just until I get zero lash otherwise it just opens the valve, so it is still loose will this throw my measurement off?
thanks for any help you got, Richard
thanks for any help you got, Richard
04-03-2005, 11:27 AM
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Originally Posted by SiL3NtXWS6
From what i've read, .080 is about the lowest you WANT to go.. but lots of people push the limits.
04-03-2005, 02:19 PM
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I have a post in this section basically asking the same question. We need to know what your circumstances are, also when you check, the rocker must be set a zero lash with a weak spring or your results will be skewed. What cam do you want to run? Check your valve drop at TDC with a dial indicator and report the results. Let me know if you don't know how to get that measurement.
04-03-2005, 07:33 PM
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the spec on my cam are 221/221 in./ex. dur., .559/.559 lift on a 112 deg. lsa, it is a MTI T1. I installed cam straight up and verified my 108 deg. ICL which the cam card says will make it 4 deg. advanced. to awnser your question my valve drop at tdc from fully seated valve, to piston contact, is .159 my heads are also milled .030. intake valve size is 2.02.
thanks for the help, Richard
thanks for the help, Richard
04-03-2005, 08:37 PM
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Those numbers appear to be very close. Is the cam installed and running in the engine now? If I were you I would call MTI tomorrow and see what they reccommend. For every 2* that you retard the cam you will probably pick up .005-6" of clearance and move your RPM band up 200 RPM.
04-03-2005, 08:46 PM
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No motor has not ran with this cam. I am in the middle of the "mother of all mod fests" if you will. I am installing, heads, cam, intake, throttle body, 12 bolt rear end, headers, cat back, pulley, converter, shift kit, and everything else assosiated with any of these parts. I desided to just pile up parts and do it all at once. Not sure if that was a good idea or not but past the point of no return now. I have not posted much on here but I referance this site more than my service manual ( not joking!). I have got a TON of info on here, and my research on here has led me to my current set up. when complete I will post results. Any dyno tuners around Wyoming? I got a mail order tune coming but I would like to get it on a dyno.
thanks, Richard
thanks, Richard
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04-03-2005, 08:59 PM
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Whose heads do you have? I'm surprised your numbers are so tight with only 2.02 intakes. I'm getting ready to install a Comp 228/230 .588/.592 112+2 and am somewhat concerned because I will only have .072 clearance. This is with .177 valve drop and what Comp says is .105 lift at 110ICL. I have heard of cams being run at .060, but what I don't know is how dangerous that is.
04-03-2005, 09:22 PM
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They are absolute speed stage 2's. I did mill them .030, I'm sure that is not helping my clearance. but with this "little" cam I didn't think clearance would be an issue. I read on here about all of these monster, lift and duration cams, I almost didn't even worry about checking it, sure glad I did now. that is why I would like to hear from someone who has ran this little of clearance with or with out issues so I know what to do before I complete assembly of the engine. I also am running comp's 918 springs. would titanium ret. help? I did read a post on here I believe it was from chris @ APEnginnering that said .050 would fly on intake if you had good control of your valve train. but I would like to verify this with real world "been there done that".
thanks, Richard
thanks, Richard
04-03-2005, 10:06 PM
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Are you sure you don't have 2.04 or 2.55 intake valves. Jay set my heads up for a TR 224 on a .563, so I can understand where I woud be tight with a 228 .588 and 2.04 valves. Are you degreeing the cam, something just doesn't seem right. With that size cam the tolerences should not be near that close. Do you know what cam the heads were originally set up for? What springs are you running, install height?
04-03-2005, 10:36 PM
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I had the Speedtek F1 Cam in my 99TA stock heads Comp 918's and after I pulled it out to swap to a friends car I had marks on all the pistons where the intake valve had come in contact with the piston. No valve train damage occured but I was pretty freaked out by it. Specs are 230/226 at .050 and .591/.569 lift 112lsa with 4 degrees advance built in. According to Speedtek's website this cam can be used on heads that have been milled .030 and have 2.05/1.60 valves in them. Just FYI.
04-03-2005, 11:14 PM
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Yeah not sure when it happened but I had let friends drive my car and I am sure that 6800 rev limiter and a missed shift happened a time or 2 with out my knowing. I would think that they would at least warn you of some remote chance of it happening with the stock pistons. I would have had them flycut or something. I am not fond or having to remove the heads on an F-body. Especially for something that could be remedied easily. But I did love that cam mad 372hp 372tq with LS6 intake stock TB and MAC midlengths ORY pipe and Borla cat back with a pig rich tune.
04-03-2005, 11:30 PM
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I am using comp's 918 springs. I bought the heads used and the guy said they had 2.02 intake valves. he also said he was running a 228/228 cam from texas speed and perf. but that was before I milled them .030.
thanks, Richard
thanks, Richard
04-04-2005, 01:53 AM
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.080" is a very safe clearance to be at. You can definitely run the intake valve tighter, but you need to be VERY careful and I would not recommend it on a street driven setup.
I have run them as tight as .045" (intake) in some personal setups without any problems. If it blows up, that's on me.
I did have some PtV issues at .035" during some previous cam testing though on the intake valve. 
The exhaust valve is a little more critical as the piston chases the exhaust valve up. If you have any valve float/valve bounce, this is where you running into issues. The exhaust valve also runs hotter, so thermal expansion is greater than the intake valve. Another reason why you need slightly more clearance on the exhaust side.
You just need to be sure the clearance you are stating is exactly what you have. How are you measuring this?
I have run them as tight as .045" (intake) in some personal setups without any problems. If it blows up, that's on me.
I did have some PtV issues at .035" during some previous cam testing though on the intake valve. The exhaust valve is a little more critical as the piston chases the exhaust valve up. If you have any valve float/valve bounce, this is where you running into issues. The exhaust valve also runs hotter, so thermal expansion is greater than the intake valve. Another reason why you need slightly more clearance on the exhaust side.
You just need to be sure the clearance you are stating is exactly what you have. How are you measuring this?
04-04-2005, 10:08 AM
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Yes I believe my measurement to be VERY accurate. when it ended up this close I triple checked everything. After degreeing the cam to verify 108 ICL I checked p to v clearance on the exhaust side the closest it gets is like .175 which is plenty. but on the intake it gets down to .056. I am checking this with the indicator that came with the degree kit on the flat portion of the retainer with lightweight checking springs and gor the indicator as close to perfectly straight with the valve as possible. I used the degree wheel to check it literally every single degree, and .056 is the absolute closest it ever gets and that is at 6-7 deg. atdc.
thanks for all help and info, Richard
thanks for all help and info, Richard
04-04-2005, 10:11 AM
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Originally Posted by Jason99T/A
.080" is a very safe clearance to be at. You can definitely run the intake valve tighter, but you need to be VERY careful and I would not recommend it on a street driven setup.
I have run them as tight as .045" (intake) in some personal setups without any problems. If it blows up, that's on me. I did have some PtV issues at .035" during some previous cam testing though on the intake valve.
The exhaust valve is a little more critical as the piston chases the exhaust valve up. If you have any valve float/valve bounce, this is where you running into issues. The exhaust valve also runs hotter, so thermal expansion is greater than the intake valve. Another reason why you need slightly more clearance on the exhaust side.
You just need to be sure the clearance you are stating is exactly what you have. How are you measuring this?
I have run them as tight as .045" (intake) in some personal setups without any problems. If it blows up, that's on me.
I did have some PtV issues at .035" during some previous cam testing though on the intake valve. The exhaust valve is a little more critical as the piston chases the exhaust valve up. If you have any valve float/valve bounce, this is where you running into issues. The exhaust valve also runs hotter, so thermal expansion is greater than the intake valve. Another reason why you need slightly more clearance on the exhaust side.
You just need to be sure the clearance you are stating is exactly what you have. How are you measuring this?
this cam you ran at .045 on the intake. Do you recall the specs? Seeing that you did this eases my mind about running my .056 and it is an auto car for now so overreving should be minumal.
thanks for the input, Richard
04-04-2005, 11:06 AM
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Originally Posted by bigdsz
It's like pulling teeth tonight to get some of the guys that are really in the know to comment. They must have better things to do.
isnt that the truth? I have put up a thread, PM'ed 2 guys that were recommended, and still haven't gotten squat. BTW I've got a comp cam 224/230 .567/.573 on a 112 and I have AS stgII milled .030 and not having any problems, and I want to get a bigger cam, but dont know if i can. So if anyone can help me please go to my thread so I don't hijack this one anymore.
https://ls1tech.com/forums/generation-iii-internal-engine/294992-new-heads-now-searching-new-cam.html