853 head question
06-23-2016, 01:53 AM
#1
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853 head question Hey guys sorry if im posting in the wrong section, but my question is i got a 02 5.3 and the mileage is unknown. I pulled the heads and the intake/exhaust valves were in pretty rough shape filled with gunk and rust they are 706 castings, i have another pair of 853 heads just sitting there, should i just stick the 853's on the way they are or get them milled for boost? I'm using a vs racing 78/75 turbo if that helps. I'm trying to post pictures but it won't let me
06-23-2016, 07:22 AM
#2
LM7 is already 9.5:1 with the stock ~61cc head. 853 heads stock should be about 70cc and IMO even for a turbo setup yield too low of a CR. Out of boost it would perform poorly. Good news is you will gain the larger LS1 intake valve. So mill..at least .030" I think, but if you have the opportunity now, do the math and come up with your ideal SCR and mill for that.
EDIT: 70cc is wrong. 66.7cc as indicated below.
EDIT: 70cc is wrong. 66.7cc as indicated below.
Last edited by Mercier; 06-23-2016 at 09:48 AM.
06-23-2016, 08:53 AM
#3
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66.7 cc 853 cylinder head volume.
06-23-2016, 09:46 AM
#4
You are absolutely right. Good catch. I was thinking 317 and that's actually more like 71. My bad.
So OP wouldn't have to mill as much but I think probably would still want to in order to maximize the combo. Still about .030" I think to get back to mid-9.x CR?
So OP wouldn't have to mill as much but I think probably would still want to in order to maximize the combo. Still about .030" I think to get back to mid-9.x CR?
06-23-2016, 10:10 AM
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So i should mill .030 off the 853 heads to get me to almost stock compression ratio correct? I just don't want it to be a dog out the gate and i would like quick spooling if possible, i was thinking of just switching valves from 853 to 706 heads but I'm afraid of the rumor of the 706 heads cracking real easily, my goals is around 600whp in a 86 nissan 300zx im swapping into
06-23-2016, 11:05 AM
#7
Go to the link below to download a neat program from Cam Motion to calculate your compression ratio. You will need to be on some sort of PC to make this work.
http://www.cammotion.com/engine-calculators.php
The 706 head deal is hit or miss. AFAIK, Only *some* 706 heads made by Castech were prone to cracking. So *some* 706 heads are perfectly fine and functionally the same as 862s. This cracking seemed to occur under normal operation so if you have an older engine with some miles on it, you probably are OK IMO. Look up "Castech 706 crack" on google and there is a lot of info available to you.
The 862/706 heads have enough meat in the valve seat to be cut out to accommodate the 2" LS1/2/6 intake valve without changing the seat. I was quoted locally "about $50/head" by a reputable machine shop. They'll also charge you about that to mill heads as well. So it's a toss-up strictly in that context. Milling gets your valves closer to your pistons but .030" is usually safe.
http://www.cammotion.com/engine-calculators.php
The 706 head deal is hit or miss. AFAIK, Only *some* 706 heads made by Castech were prone to cracking. So *some* 706 heads are perfectly fine and functionally the same as 862s. This cracking seemed to occur under normal operation so if you have an older engine with some miles on it, you probably are OK IMO. Look up "Castech 706 crack" on google and there is a lot of info available to you.
The 862/706 heads have enough meat in the valve seat to be cut out to accommodate the 2" LS1/2/6 intake valve without changing the seat. I was quoted locally "about $50/head" by a reputable machine shop. They'll also charge you about that to mill heads as well. So it's a toss-up strictly in that context. Milling gets your valves closer to your pistons but .030" is usually safe.
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06-23-2016, 01:22 PM
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Oh okay so to run the 2' valves on the 862 heads i need to get the valve seats worked on right? I don't want to run into ptv issues, i was planning on running the lil jon motorsports stage 3 turbo cam, sorry to sound so noobish since this is my first time building a engine at 21 years old lol and thanks for the link from cam motion I'll check it out!
06-23-2016, 01:40 PM
#9
Yes.
You still may not run into PTV depending on that cam, even with milling of the 853s. That vendor is likely the best source of advice on that. It doesn't look like you would hit, especially with the dished piston of the LM7 and the reasonable lift and duration, but I can't check for you over the internet.
You still may not run into PTV depending on that cam, even with milling of the 853s. That vendor is likely the best source of advice on that. It doesn't look like you would hit, especially with the dished piston of the LM7 and the reasonable lift and duration, but I can't check for you over the internet.
06-23-2016, 01:49 PM
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Ok i understand if i have anymore questions I'll let you know buddy thanks for all the advice and information! I'll get some prices on a valve job, I made up my head and I'll just swap valves from the ls1 853 heads to the 5.3 706 heads and let her eat
06-24-2016, 12:00 AM
#11
Oh okay so to run the 2' valves on the 862 heads i need to get the valve seats worked on right? I don't want to run into ptv issues, i was planning on running the lil jon motorsports stage 3 turbo cam, sorry to sound so noobish since this is my first time building a engine at 21 years old lol and thanks for the link from cam motion I'll check it out!
06-24-2016, 01:08 AM
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I personally think your best bet is to pick up a set of used 243 or 799 heads for $400. Bigger valves stock and much better airflow stock. 64cc chambers.
06-24-2016, 03:41 AM
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06-24-2016, 12:13 PM
#15
Well I guess I shot down the idea of using 862 heads , which was not my intent. Going back I assumed you just trying to decide between 5.3 heads and the 853 that you already have . Now we talking bout purchasing 243/ 799 heads . What is your budget for heads and what CR are you trying to get . For a turbo I would consider 317 if want to lower CR and get good flow #s The 317 is the only head that I would consider milling .
06-24-2016, 05:18 PM
#16
Well imo I would not go 2" without chamber work to unshroud the valve. I would go with Rev . Manley or Ferrea no bigger than 1.95 , If your on a budget you may be able to have the 2" turned down . The stock smaller valves do have some advantages in no head work required and they are lighter too. Worst case if don't want to touch the chamber work . Just spend your money on a back cut on stock valves , good valve job and bowl blend.
And as far as 243/799 goes, agreed..superior top to bottom. Just didn't think it was in the budget.
06-25-2016, 01:55 AM
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Once you start talking porting, valve jobs, milling, etc, the 243 head swap becomes the budget option since it already has the 2" valves and better ports. Then later on if you decide to do port work you've got a better foundation.
06-25-2016, 11:06 AM
#18
No question in that context. If spending $450 get 243s. But we started talking about ~$100 of work on heads already owned with either milling the 853s or taking the valves out of the 853s for the 706s. No matter I suppose if OP has the cash for 243s.