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TDI Power Enhancements Discussions about increasing the power of your TDI engine. i.e. chips, injectors, powerboxes, clutches, etc. Handling, suspensions, wheels, type discussion should be put into the "Upgrades (non TDI Engine related)" forum. Non TDI vehicle related postings will be moved or removed. Please note the Performance Disclaimer.

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Old January 10th, 2018, 12:04   #1
jpderv
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Default Tdi head stud question

Hi folks have a small question for you.
At the moment I'm getting head lift pressure in the expansion tank with 2.7bar boost but when it lower the boost to around 2.2/2.3bar everythings alright no pressure in the system.
Pd130 with gtb2265 firad 120s with pd150 headstuds.
If I was to fit ARP head studs now could info back upto 2.7bar without head lift.
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Old January 10th, 2018, 16:21   #2
Mongler98
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quite a few of us who go to ARP studs have this issue. in reality, the head is probably warped or the gasket is on its way out. i had this issue same as you, so i did a full head job, port polish, valves, seats, decked it from a good shop, undercut valves, helper springs, cam, the works!

I still have this issue and after talking with some folk around here, i highly suspect the head to be warped again due to higher EGT's and a few low coolant overheat events.
you need to check for block flatness against the crank journals, you can do this against the pistons as long as they are not bent at the rods or anything. A properly built set up with normal head studs should take 40PSI before issues come up. im running 32 myself and dont have the $$$ to fix it so i only autocross it as it only acts up when i go for a long pull. short busts and highway driving has no issue.

my advice, dont waste your money on the headstuds, take the head off and have it decked by a good head shop, get a gauge block so you can measure the TDC on each piston and measure it against the surface of the block. You can do a block deck with the engine in place but it takes time and care.
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Old January 10th, 2018, 21:17   #3
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Lower the compression while it's apart.

with ARPs torqued to 140ft/lb and ARL pistons mine was lifting at 40 psig, so that's 3800 mbar absolute or 2800 mbar gauge
Even at only 13 deg start of injection timing it was pressurising the cooling system. Completely ignorable, being that it wasn't losing any coolant, but concerning nonetheless.
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Old January 10th, 2018, 21:54   #4
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Just curious, what you would do to lower the compression on the head work? i already have a 3 hole sized (largest) head gasket.
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Old January 10th, 2018, 22:55   #5
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Quote:
Originally Posted by Mongler98 View Post
Just curious, what you would do to lower the compression on the head work? i already have a 3 hole sized (largest) head gasket.
You do not want to run wider piston/head clearance, this only wastes air where the injector can not reach it. Same with valve reliefs, only make them as large as your camshaft requires, or you're wasting air that could be burned.

Cut the bowl larger to lower compression, on mine I just used an edge-trim router bit to cut the lip off, then used a roundover bit with a 1/8" radius to smooth the edge. No idea where it'll leave the compression ratio. looking at the difference between 19.5 ALH and 18.5 ARL bowl sizes, it looks like maybe they'll end up something like 16-17:1? No matter, what does matter is if it still leaks.
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Old January 11th, 2018, 03:29   #6
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Why the hell do you want 2.7bar boost?

Stock 2260VK can do over 300bhp with 2.2 - 2.4bar boost level. Flow is not same as boost, look EMP gauge to find out right boost level for your setup.
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Old January 11th, 2018, 05:11   #7
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I used run stock pistons and 35psi blew the the head gasket. I run .120 flycuts and delipped pistons. ARP studs torqued to 140ftlb. I’m at 40psi don’t have the drive pressure gauge hooked up yet it just came in. I’m at 40psi now. I used run stock pistons and 35psi popped head gasket twice. .
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Old January 11th, 2018, 07:45   #8
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im pretty brave but not brave enough to re cut the bowls on my tdi. Are there pistons with this done to them already?
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Old January 11th, 2018, 08:14   #9
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No I had my machine shop do it they came out perfect. They were brand new asv pistons.
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Old January 11th, 2018, 12:41   #10
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Thanks for the help folks seems strange to me you would think that if it pressurised once then no matter what pressure you ran then it wouldn't it all the time.





Quote:
Originally Posted by Yucca View Post
Why the hell do you want 2.7bar boost?

Stock 2260VK can do over 300bhp with 2.2 - 2.4bar boost level. Flow is not same as boost, look EMP gauge to find out right boost level for your setup.
I highly doubt a gtb2260 would make 300bhp at 2.2bar unless you have some head work and cam perhaps.

The reason I'm running 2.7bar is because I can lol in my case less boost ment less power on the dyno so that's were it's at atthe moment.

EMP seems stable at the moment max 50psi at about 2700rpm then almost matching boost to about 4700/4800rpm.

I wanted to see what would blow the pd130 up after a couple drag events and maybe 40/50miles per week of excited driving nothing has given yet apart from the head.

Before next drag event Il probably get the pistons machined a little should help a bit with cylinder pressure atleast this time the head studs will be done the correct way.

I did change to ARL head studs using the one at a time method perhaps this hasn't helped the situation any although even darkside developments recommend this method so doubtful.
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Old January 11th, 2018, 13:45   #11
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Sure you need good ported head and cam.

I dont know what is good boost level with stock head and cam. It is good to hear that you have also measured EMP.
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Old January 11th, 2018, 15:03   #12
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Getting the necessary trapped air mass for a given power output and lambda by volumetric efficiency improvements (e.g. head porting and cam) is almost always preferable over boost from mechanical (PCP, EMP), thermal stress and efficiency standpoint.

A similar analog in the fuelling side is that it is preferable to get the necessary fuel quantity for a given HP / lambda by injection flow rate (hole size and pump pressure) rather than simply extending the injection duration.
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Old January 12th, 2018, 15:48   #13
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Question is where can we get an H11 or similar ALH stud these days?

A1 who made Whitbreads is no longer in business.

Does anyone know of another motor that has a similar stud that can be made to work for an ALH in H11 or similar?
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Old January 12th, 2018, 19:00   #14
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just measured a stock head bolt and they're 110mm under head length, standard M12 pitch
Call up ARP and they'll probably make you some for a hideous price.

On the other hand, I think the limitation is the aluminum head rather than the 8620 studs. There's just too much space between the bolts and the deck isn't thick enough to bridge the gap.

Easy solution on most peoples setup is limiting torque. Tiny turbo and okay nozzles it's easy to make some ridiculous torque figures far too low in the revs to be of any actual utility.
400 ft/lb sounds mean and certainly is a workout for the bits in your bottom end, but when it equates to 110hp, who really cares? Bump the revs up from 1500 to 4000 and that same torque's suddenly 300hp.

Last edited by [486]; January 12th, 2018 at 19:09.
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Old January 12th, 2018, 19:47   #15
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Poor understanding of properties of materials result in wasted money at best, or no significant improvement.

The metal stretch of a bolt (strain) is related to the stiffness of the material (Young's modulus), applied force, cross sectional area and length - the latter because strain is expressed as a percentage of the total nominal length). If you are dealing with a ferrous-based material, the Young's modulus doesn't vary outside about 210 GPa +/- 5%, regardless whether we're talking plain carbon steel, alloy steel, tool steel or some other exotic grade of steel, therefore not much to be gained there. Ultimate tensile strength (PSI or MPa at breakage) is rather useless in the discussion of bolts, but yield strength is more relevant. The higher the yield strength, the more stress you can apply (and the more strain/stretch by extension) before it stretches permanently longer than the original, unloaded state. But in and of itself, a higher strength bolt does not increase the degree of stiffness or resistance from stretching whatsoever.

SImply installing higher "strength" fasteners of any kind - bolts or studs - with all else being equal (diameter, and torque) will give you a goose-egg zero additional clamping force.

You need either to increase the bolt diameter, along with increasing the tightening torque, but then by doing the latter you can damage the aluminum head.

Installing higher strength fasteners and seeking more clamping force (within what the cylinder head can withstand), while not a bad thing in and of themselves, are very poor Band-Aids for the root of the issue, which is the need to manage peak cylinder pressures (PCPs).
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