Making a stock AHU survive

Making a stock AHU survive 30-35psi

This might be a bit premature seeing as how I'm probably a good 2-3 months from this being a reality, but hey I like to plan.

I have a stock AHU block with 300k km on it that I'm using in a swap. I also have a vnt-15 and a td04-13 that I'll be throwing on in compound. VNT-15 will be going on as a single first just to get the swap moving and work out the bugs then the td04 will go on. I know they're not perfectly matched but I should be able to run 20-25lbs@ 3k rpm with both turbos in their peak efficiency so it'll make a good towing setup for the truck. The td04 should be able to flow something around 25lbs of air. I've been playing around with the not2fast turbo calc and based on what I've got from there I'm hoping to run 20psi at 2krpm if I can get it and ramp it up to 35lbs at 4750 where the LP should just start to choke.

Whitbread had suggested that I use a k03 instead of the vnt to simplify tuning so I'll be slightly heeding his advice in that I'll be running an external waste gate with the vnt-15 with the vanes in a tbd fixed position. Might run a pushpull cable on the vanes just because I like to tinker. Boost will be solely controlled by the waste gate.

Thats just a bit of back ground. The real question is how do I make the stock block survive?

My plan is:
-head studs/12.9 Cap screws
-Minimal timing on the low end.
-Maybe reduce cr? (Remove the bowl lip)
-Rod/main bearings?
-Larger than needed nozzles to keep the injection even short -> less timing needed.

Head studs or 12.9 cap screws will be in order for sure as well as being careful with the timing. I have the ability to remove the lip on the piston bowl so I'm really not opposed to doing that if its needed to keep the engine alive. I'm contemplating dong the rod bearings while the engines out but don't really want to. Upgraded rods are out of the question for a year or two. I just cant afford them.
Any thoughts/opinions? Am I missing something important or am I just nuts?

I know its a high mileage engine so I'm not expecting too much out of it and I fully expect to grenade it at some point but I'd like to make it last as long as possible within reason.

Have no problem tuning for MK4 N75 valve equip VNT AHUs

Reliable and 30+ PSI do not go together.

- no need for head studs below 25 PSI.
- If the bottom end isn't giving you issues, leave it alone, rebuilds are expensive and don't always go as planned.
- Boost should taper down past 4K on a stock head, they do not flow that well up top, and that turbo isn't suitable for that much boost. Cam and port is another story.

I'd run a k03 or k03/k04 hybrid, GT2052, or just do a VNT setup.

TD04 (measurements taken from here http://forums.tdiclub.com/showthread.php?t=255310)
Compressor
Inducer = 38.19
Exducer = 50.95

Turbine
Inducer = 47.40
Exducer = 40.00

Common turbo sizes for comparison from darkside


Similarly sized to the 2052, but the GT2052 is a newer/better turbo.

Past 25-26 PSI, get your wallet out, port the head, build the bottom end, consider a crank girdle, and still potentially risk catastrophic failure. If money is even a consideration, it'd be best to stick to a reasonable tried/tested setup. A k03/k04 or gt2052 will be plenty, k03/k04 is good for 20-22, 2052 is good for ~25 or so. Those are "conservative" safe boost levels, and you'll want a diff by that point anyway. Would be a nice compound setup, but doing so on a budget is a gamble.

look up "fix_until_broke"s compounds and "486"s compound thread too if you havent already.

#1 I'd highly recommend stronger dual valve springs.(aftermarket gasser ones,or Some TDI aftermarket ones if available)

#2 don't pull the cyl head if its never been off since new.Just add head studs/12.9 cap screws and swap one by one.

#3 don't worry about stock compression ratio/rods.The rings will eventually be the weak point with lots of heat before the rods and pistons.

#4 replace balance shaft bearings.

I have ran a 12mm pump with hflox warp 5 nozzles for many years and just last year ran a gt2052w with hx30w and had no issues keeping coolant in.Low oil pressure is my main concern and I have ran my engine hot a couple of times resulting in lower compression.

I plan on replacing the balance shaft bearing on the timing belt end of the block to help restore oil pressure.

Thanks for the input guys

@Owain:

The tuning issues I mentioned with the vnt has more to do with getting the vnt mech to play nicely with the wastegate bypass than with getting the ahu ecu to control a vnt. I have no doubt that you guys could get to to work perfectly. However since I'll be doing the tuning for this and I'll need a bypass for the turbine anyways Im gonna give it a shot like this.

I'd love to run a gt2052 since that was my original plan but i was pretty much given these turbos so i'm going to work with what I have.

@ketchup, I swear I've read over both of those at least 3 times. Lots of great info in them. Thanks

@andy:

Good to know you think that stock cr will be fine, and you more or less echoed my thoughts on the studs/head. I had been thinking it would be best to not disturb it.

Good point on the balance shaft bearings. Good cool flow to the oil squirters will be the key to keeping this alive I think. I'll be running an extra oil cooler on top of the stock exchanger and an oil temp gauge will be used as well.

I'll look into the valve springs, just gotta find some place in Canada that sells them.

Dual springs from the 8V or 16V gas motors work fine. Those are what I have in mine, which incidentally was running 28psi from a GT2052v on a completely stock AFN bottom end (block is the same, I think the AFN has sputter bearings though). Full boost was 2500-5000rpm with a ported head and PD130 inlet.

I ordered a tool and the springs from concept1 years ago,

http://store.concept1.ca/Valve-Spring-Compressor-Kit-C-1TL-A2116/
http://store.concept1.ca/Autotech-HD-V.-Springs-8v-AT10.109.600K/

With the piston at TDC I didn't need to add air to the cylinder as the valve doesn't drop far enough to prevent removal or installation of the keepers with the springs fully compressed.I didn't bother changing the valve seals either as they still had adequate drag on the valve stem.

cut your pistons
running into issues keeping the head down with stock (18.5:1) ARLs and 35/40 PSI (int/exh), lots of fuel and ARPs at 140 ft/lb

stock compression's fine if you don't put the fuel to it to use the air, but I've gone all the way down to 13 degrees of timing and still pressurizing the coolant

ETA: still running stock 140k mile valve springs, probably run into trouble once the emp starts coming above imp though

I can chime in, but my results are confusing since I am having some strange smoking issues that are currently not diagnosed.

I have a stock AHU with a ported head, dual valve springs, ARP's at 125 ft/lbs. I run a holset he211w at 35psi with race 520 injectors and lots of fuel. and the engine has perfect compression, gets 48mpg and hauls butt.

However, it has been making strange smoke at idle for the last 5000 miles, and the abuse I have given it has not been ruled out as a cause.

I also have a mega external oil cooling inline with the stock oil heat exhanger. The oil cooler has flow regulated thermostatically and the fans on the oil cooler run with the radiator fan. It really helps keep the oil dead steady when beating the hell out of it. Before the cooler, oil temps climbed fast.

I block the oil cooler with cardboard in the winter to help oil warm up. Removing the cooler completely would be better.

Hmm, I think I'm just gonna go with the studs and maybe valve springs for now because I know that if that head comes off to rework the pistons I'll be opening up a whole new can of worms with regards to porting, aaz cam ect. If/when I have issues with the head gasket then I'll cut the pistons, port the head, cam ect. Who knows, by that time I might be looking at a larger lp turbo wich would mean rods and arl's anyways.

The rad in my ranger has a oil heat exchanger built in so I'll be running that as well as the stock one. Might look into another external cooler if that proves to be insufficient. Should I be monitoring the sump temperature or the temp after coolers? I'm thinking sump temps.

careful trying to use the trans cooler as an oil cooler, maybe just run the turbo feeds through it or something, they usually don't flow well enough for a full flow oil cooler.

Oddly enough this Is actually a proper oil cooler it would seem. It's a 5pd truck and the exchanger was plumbed in the oil system so I'm inclined to believe that it should flow enough. I will definitely check the flow/pressure drop from it though.

Exenos said:

Oddly enough this Is actually a proper oil cooler it would seem. It's a 5pd truck and the exchanger was plumbed in the oil system so I'm inclined to believe that it should flow enough. I will definitely check the flow/pressure drop from it though.

Click to expand...

Huh, only seen that on chevies so far, ford seemed more a fan of the plate exchanger on the oil filter adapter.

[486] said:

Huh, only seen that on chevies so far, ford seemed more a fan of the plate exchanger on the oil filter adapter.

Click to expand...

Ok, I take that back. Only a trans cooler on my spare rad. Dont know why I remember disconnecting oil lines from it.