keep blowing headgaskets/ cam too small ?
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From: SpringCity Tn
keep blowing headgaskets/ cam too small ? So I have seem to run into a problem this yr. basically I started out 5.3 stock 862 heads comp cam .614lift .230 duration dual plane intake 76mm turbo 14psi pump gas. then I wanted to make more power and I went 862 heads ported polished. bigger valves. single plane intake race gas 18psi and basically picked up no et at the track at all. And I have also blown 2 sets of cometic head gaskets with arp studs. and it doesn't seem to pull much over 5600rpms... I'm leaning towards cam being too small not allowing the valves to be held open long enough and causing it to build cylinder pressure. am I on the right track? any suggestions?
I Dont think it has anything to do with the cam at all if its a 67/76mm turbo then the drive pressure is nearly 3 to 1 and the test I am referring to was done on a 4.8 This test was done by FOOSE04. It will be worse on your 5.3. The problem is the turbine side is too much of a restriction and youve hit your limit increasing the boost wont do any good if it cant flow any more past the exhaust all turning up the boost will do is lead to increased exhaust back pressure. So based off the 4.8 data your exhaust side pressure would be nearly 54 psig since your motor is 10% bigger your probably more likely to be at 60 psig plus which is retaining more heat and pressure from the onset, leading to increased cylinder pressure, most likely causing you to blow gaskets.
Option 2: The heads could possibly be warped have them checked, also have the short block deck checked. If they are straight then you have too much back pressure.
Bottom line is you need a turbo with a bigger exhaust wheel to go any faster.
Here is a link to the thread/test I am referring to. FOOSE04 posted it up on our local board but I don't think it made it here to tech. It pretty much proves these turbos are not sized any where near correctly for any LS motor including the 4.8 not saying it wont work. FOOSE04 went pretty fast on it I had one and ran a 6.38 with it on my 6.0 but there was nothing else left in it at that point turning the boost up past 14 psi gave me nothing. I got rid of it and swapped to a S480 and havent looked back and it was a world of difference and isn't laggy at all.
http://www.carolinahorsepower.com/fo...ad.php?t=13109
Hopefully this helps.
Option 2: The heads could possibly be warped have them checked, also have the short block deck checked. If they are straight then you have too much back pressure.
Bottom line is you need a turbo with a bigger exhaust wheel to go any faster.
Here is a link to the thread/test I am referring to. FOOSE04 posted it up on our local board but I don't think it made it here to tech. It pretty much proves these turbos are not sized any where near correctly for any LS motor including the 4.8 not saying it wont work. FOOSE04 went pretty fast on it I had one and ran a 6.38 with it on my 6.0 but there was nothing else left in it at that point turning the boost up past 14 psi gave me nothing. I got rid of it and swapped to a S480 and havent looked back and it was a world of difference and isn't laggy at all.
http://www.carolinahorsepower.com/fo...ad.php?t=13109
Hopefully this helps.
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Thread Starter
On The Tree
Joined: Mar 2010
Posts: 153
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From: SpringCity Tn
Well mine is a 5.3 base bored .120 over so basically a 5.7 the exhaust side on turbo is .96 ar and cold side is .80 I'm not real familiar with exhaust pressure side of the turbo. but I do know going up 4psi never made a difference in et. never checked it in hp. Temps norm runs 190 degrees it will run up to 205-210ish after a pass. but never over 210. this last time I blew the head gaskets it blew it in the water jacket side and torched my head. the heads were brand new 2 months ago my machinist always does a mirror finish on the heads.
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I Dont think it has anything to do with the cam at all if its a 67/76mm turbo then the drive pressure is nearly 3 to 1 and the test I am referring to was done on a 4.8 This test was done by FOOSE04. It will be worse on your 5.3. The problem is the turbine side is too much of a restriction and youve hit your limit increasing the boost wont do any good if it cant flow any more past the exhaust all turning up the boost will do is lead to increased exhaust back pressure. So based off the 4.8 data your exhaust side pressure would be nearly 54 psig since your motor is 10% bigger your probably more likely to be at 60 psig plus which is retaining more heat and pressure from the onset, leading to increased cylinder pressure, most likely causing you to blow gaskets.
Option 2: The heads could possibly be warped have them checked, also have the short block deck checked. If they are straight then you have too much back pressure.
Bottom line is you need a turbo with a bigger exhaust wheel to go any faster.
Here is a link to the thread/test I am referring to. FOOSE04 posted it up on our local board but I don't think it made it here to tech. It pretty much proves these turbos are not sized any where near correctly for any LS motor including the 4.8 not saying it wont work. FOOSE04 went pretty fast on it I had one and ran a 6.38 with it on my 6.0 but there was nothing else left in it at that point turning the boost up past 14 psi gave me nothing. I got rid of it and swapped to a S480 and havent looked back and it was a world of difference and isn't laggy at all.
http://www.carolinahorsepower.com/fo...ad.php?t=13109
Hopefully this helps.
Option 2: The heads could possibly be warped have them checked, also have the short block deck checked. If they are straight then you have too much back pressure.
Bottom line is you need a turbo with a bigger exhaust wheel to go any faster.
Here is a link to the thread/test I am referring to. FOOSE04 posted it up on our local board but I don't think it made it here to tech. It pretty much proves these turbos are not sized any where near correctly for any LS motor including the 4.8 not saying it wont work. FOOSE04 went pretty fast on it I had one and ran a 6.38 with it on my 6.0 but there was nothing else left in it at that point turning the boost up past 14 psi gave me nothing. I got rid of it and swapped to a S480 and havent looked back and it was a world of difference and isn't laggy at all.
http://www.carolinahorsepower.com/fo...ad.php?t=13109
Hopefully this helps.
Just look at the data in the thread I posted it also has a video explaining it while it was running down the road. Sorry about the heads, your best bet if you want to maybe go faster is take the boost back down to 14psi and add some more timing to take advantage of the octane but it will probably only net you .1-.2 tenths best case scenario.
Sorry for the bad news though, good news is a S475 is cheap and can be had new for around 600.00 cheaper if you can find them used. I would check out the yellow bullet classifieds, all said and done you should be able to swap over for about 300.00 out of pocket and I guarantee you will go a second faster when you get it full tilt.
Sorry for the bad news though, good news is a S475 is cheap and can be had new for around 600.00 cheaper if you can find them used. I would check out the yellow bullet classifieds, all said and done you should be able to swap over for about 300.00 out of pocket and I guarantee you will go a second faster when you get it full tilt.
This turbo is very common on here because it is cheap, and for a hot street car it performs well and is very responsive on automatics and 6 speeds. It will do 600rwhp all day long but when you lean on it you run into the above posted back pressure issue. You really don't even have to get the converter right because the exhaust is undersized and it spools so quick.
To answer the second question yes he did swap but hasn't posted the data he still has the rig so I will ask him if he ever got around to testing it, he stays pretty busy as he is active duty.
Last edited by Preston99WS6; Dec 18, 2012 at 08:34 PM.
You got one hell of a car for that class as it will be pretty competitive because it is lighter than most of the fox bodies running that class, and its LS powered. Which means its going to hurt a lot of peoples feelings when you get the right power adder on it. You know what to do from here.
Last edited by Preston99WS6; Dec 18, 2012 at 08:41 PM.
I have a PT7675 for sale and Jax04 has a S475 for sale for cheap. Either of those used turbos would make a night and day difference on your combo. You spent money on cam, heads, etc. Now spend it where it counts.
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Joined: Nov 2007
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3:1 drive pressure ratio is absolutely asinine. 2:1 at most is where you would like to be. I shoot for 1:1 drive pressure to manifold pressure.
youll find that the car actually spools faster when drive pressure isnt so high.
youll find that the car actually spools faster when drive pressure isnt so high.
