My v6 Drag Week build

[foxbrand]

What is the dish in the 74 pistons. I know greater displacement helps bring the ratio back up but I know there are people avoiding running the 75 block because they think it has thin cylinders so they have 75 cranks in 74 blocks and I wonder if they even know what their compression ratio is!

not entirely true, one guy I know on a different forum who is in Austrialia got his Pajero 6g75 block sonic tested and his 6g74 block sonic tested
http://3000gt.com.au/car/74%20vs%207...all%20test.pdf
http://3000gt.com.au/car/74%20vs%207...all%20test.pdf
if you are having problems reading the handwriting, same guy was able to read it

The 74 varies from 235-289 thou with the majority around 270 thou
The 75 varies from 230-275 thou with the majority around 260 thou

so at least with these specific 6g75 and 6g74 blocks, it appears the cylinder walls have nearly if not the same wall thickness, the 6g75 was revised for the bigger bore while retaining the same wall thickness, but this might not be true with every 6g75 and 6g74 block due to core shift and different versions of 6g74 and 6g75 blocks (such as JDM 6g74 blocks and MIVEC 6g75 blocks might have changes), it is worth investigating independently to be sure

from what I have read, people use 6g75 cranks (and maybe other components) in 6g74 blocks because
A: the 6g75 block is busted (it happens more than anyone ever wants)
B: if they have a 3000gt or a Stealth, it requires a large amount of fabrication to get the 6g75 block to work (no mounts for half shaft hangers and what not for the 3S platform), a JDM 6g74 block (at least from my reading) is much closer to a drop in with a few modifications

[Vigo]

I really do wish that people would get off this goofy idea that manufacturers bore one block with stupid huge wall thickness and just bore it by various amounts for different bore sizes.

Thanks for that info!

[foxbrand]

since I have been doing my comparisons between the two engines, that has practically become a pet peeve of mine (but if I can, I will edit this out of forum postings I have on other forums if possible from before I did the comparison), for modern(er) engines, why would they produce only one block with, as you said, stupid huge wall thicknesses? If anything (and this is a running theory of mine), they would cast the blocks as is, and without liners/sleeves, then machine the block for the proper outer diameter for the sleeves that are going to be used, but that is only a theory of mine since there are different block castings and, the block and sleeves are more likely cast as one
Also there are very obvious external differences between the 6g75 and 6g74 blocks, so they can't be the same block or at least the same casting

glad to help, I'm waiting on the machinest at a local shop to come back from vacation before I get my blocks tested for secondary confirmation

[Ondonti]

since I have been doing my comparisons between the two engines, that has practically become a pet peeve of mine (but if I can, I will edit this out of forum postings I have on other forums if possible from before I did the comparison), for modern(er) engines, why would they produce only one block with, as you said, stupid huge wall thicknesses? If anything (and this is a running theory of mine), they would cast the blocks as is, and without liners/sleeves, then machine the block for the proper outer diameter for the sleeves that are going to be used, but that is only a theory of mine since there are different block castings and, the block and sleeves are more likely cast as one
Also there are very obvious external differences between the 6g75 and 6g74 blocks, so they can't be the same block or at least the same casting

glad to help, I'm waiting on the machinist at a local shop to come back from vacation before I get my blocks tested for secondary confirmation

I didn't say they were correct in not boring their motors. I think its just the fact that nobody in america tested things (or made results well known) and there are a few "visual inspection guesstimation rumors" which have led people to make 20,000 dollar build decisions. I know some of it is also due to the passenger side motor location they rely on.

[Sundance 6g72]

and im just sitting here with a good ol 3.0

[Irocelectric93]

Good info. Joe- I'll probably stick with my 3.0 for a while if not for good there are other car/engine swaps out there that id be more interested in outside of a 6g75 to be honest. The 3.0 makes great power with boost anyway.

[Ondonti]

since I have been doing my comparisons between the two engines, that has practically become a pet peeve of mine (but if I can, I will edit this out of forum postings I have on other forums if possible from before I did the comparison), for modern(er) engines, why would they produce only one block with, as you said, stupid huge wall thicknesses? If anything (and this is a running theory of mine), they would cast the blocks as is, and without liners/sleeves, then machine the block for the proper outer diameter for the sleeves that are going to be used, but that is only a theory of mine since there are different block castings and, the block and sleeves are more likely cast as one
Also there are very obvious external differences between the 6g75 and 6g74 blocks, so they can't be the same block or at least the same casting

glad to help, I'm waiting on the machinest at a local shop to come back from vacation before I get my blocks tested for secondary confirmation

What exactly do you mean buy block failures? The 3000gt guys are usually buying brand new cranks as they only cost about 1000 dollars and will have no history of abuse. Ray Pampena has also been grinding some of them down to fit into 4 bolt 6g72 blocks but keeping large fillets to keep things strong.

Block failures is a bad thing and kinda makes wall thickness a mute point if something else will fail. I have only heard of people spinning mains from junk oem TTY fasteners that become lose.

Normal 75 blocks are fine for dodges since we have our transmission on the driver side. Junky blocks are not fine for us though.

[foxbrand]

blocks being unusable (ie broken) not from power, but because of how the car that they are out of was totaled, the passenger's side engine mount bracket was broken and the bosses on the block were either, broken off or cracked, I actually have a triangular part of the block that I nearly pulled off the block itself (due to how deep the crack was) where the engine mount bracket bolts to. The crank is OK, I could easily spin it by hand (after I put some oil to the walls and into the pump) when I had the engine on my cart, I have read at least 2 other instances of killed 6g75 engine blocks that have fully workable internals on the forums, one case, a new 6g75 block was purchased (if I'm remembering right), another used a 6g74 block, I'm going with the later (unless the 6g74 block doesn't check out)

a project I want to do in the distant future (year plus or so) is using my MIVEC block in a dragster, if not, it will make one awesome coffee table

[c2xejk]

This weekend I tried bolting the 6g75 oil pickup onto my 6g74 engine. Ran into 2 problems. One easily solvable, the other would take some work. The pick-up tube hits the windage tray. A little grinding and it clears. The bigger issue is that it sits a little further down in the pan. Putting the pan on, there is more than an 1/8" gap all the way around the pan... Not sure how different the two pans are, but for the moment, I am using the 6g74 oil pick-up tube...

[Ondonti]

Friend of mine welded a custom pickup tube to fix a similar issue but I remember at first he was paranoid there was a leak in his weld and that he would lose oil pressure. I don't think he wanted to pressure test it and find out. :P

For now keep your oil level on the high side. I don't know that I would bat an eye at bending the thing a little as long as it didn't spring a leak.

[Vigo]

Any news on this?

[c2xejk]

The trailer is done.

Back to working on the car. I still have a fairly long punch list of items I would like to get to before Drag Week... Trailer hitch is next. Then I need to dig into some issues related to the turbo. A "replacement" turbo arrived today. I ordered it just in case I can't fix the current one...

[c2xejk]

Ok guys, I need your help. Less than a week till Drag Week and the Shadow is giving MAJOR fits...

Since I rebuilt the engine I have been having trouble with the turbo leaking oil into the compressor and turbine. The result is a lot of smoke out of the tail pipe. At idle there doesn't appear to be any leakage. Once warmed up you can rev the engine in neutral and get some. Drive it down the road and you get a LOT...

At first i thought it was some changes I made to the PCV system, but I have undone those and the problem persists. And the new turbo I put on does the same thing...

My current thoughts are:
-excess blow-by. (about to start doing a compression check and maybe a leak-down check.)
-The oil I am using (rotella 5w-40)
-???

Any ideas guys?

Thanks in advance. (PS. Right now I will listen to even hair brained ideas, so toss them my way!)

- - - Updated - - -

Compression test results

#1 160
#2 165
#3 155
#4 160
#5 160
#6 165

[Sundance 6g72]

any chance your spirit's turbo will drop in to triple check?

Compression seems "normal" ?

How exactly is the PCV system hooked up? Do you have a catch can and how is that tied into everything?

[c2xejk]

any chance your spirit's turbo will drop in to triple check?

Nope, the Spirit has a T3 flange, the Shadow has a T4.

Compression seems "normal" ?

Yes, I was worried I was going to find something very wrong... Glad I didn't, but the mystery remains...

How exactly is the PCV system hooked up? Do you have a catch can and how is that tied into everything?

Right now it is back to stock. I have a vacuum gauge hooked up to the tube that runs between the heads. Tomorrow I plan on checking the reading with the engine running.

[Vigo]

I dont know how easy it would be to find one that fits, but i would consider running one of those breather-type oil caps like Brent has run on his motors.

The other thing i would consider is adding a restrictor to the oil feed line to the turbo.

[Sundance 6g72]

You are running a stock pcv valve routed into the stock locations? DONT DO THAT. Thats something we rarely talk about and I dont know why because it caused me huge issues. With boost I was overwhelming the pvc valve and actually forcing pressure into the crankcase causing all sorts of things like oil leaks and oil out the exhaust.


I run my rear valve cover to a catch can and then the catch gun runs pre turbo. The turbo supplies vacuum to the catch can in order to provide suction on the heads/crankcase during boost. I leave my pcv valve undone.

If you want, you can google the DSM fix for pcv valves. They use an additional check valve. you may already know all this but I just want to be sure!

[c2xejk]

Just did a test. I hooked a vacuum gauge to the line between the front and rear head. With engine warmed up, I get 2-3" Hg vacuum. Then I took the car for a drive. I kept the throttle mild and did not go into boost. Quickly I had 1-2 psi of pressure.

I have an electric AIR pump that I put on the car earlier (part of what I undid.) I hooked that up also between the two valve covers and took that for a spin with the pump always on. If I kept my foot light (like before) I could maintain 2-3" and had less smoke out the tail pipe... If I dug into the throttle a little more, vacuum moved to 0"...

Right now I highly suspect that the #3 cylinder rings may not have seated...

[Vigo]

Thats under the plenum, isnt it? GRR. If it wasn't id say you might be able to attempt some stoogery with brake cleaner but it would probably require so many repititions that it's not feasible with taking the plenum off every time.

[Sundance 6g72]

Im curious what the results would be with a catch can hooked up the way I do it

Valve cover ran to catch can, catch can ran to pre turbo. This has always worked well for me. I would be able to blow oil out my rear valve cover without the can, after installing the can it completely stops.