New here, Entertaining idea of building 12v 3.0 3000gt

[Mdoe8]

Hello all,

I've peaked around thieseforums for a few months now without registering, but figured it was time so I could post my situation.

I'm currently building a 99 3000gt base. The original plans were to build a DOHC for obvious simplicity reasons. However, many of my plans regarding this car are to make it unique to the 3s community. I've strongly considered building and turbo'ing the SOHC that's in it already. These motors are not proven on our platform due to the TT motor swapping right in, just entertaining the idea of doing something different.

I've already got the AWD conversion started, so drivetrain strength isn't an issue. Also, fabricating the turbo kit/etc. is not an issue either.

When it comes down to it, I'm just not familiar with this motor like I am the DOHC. However, the idea of having a completely unique build really entices me.

After research, I'm still not completely sure about a few things.

- Do they make any forged pistons for these motors yet? Or would I still need to get them custom made?

- Is Megasquirt still the best solution for tuning? How is it for tuning ease and driveability?

- Whats the story on ignition? Just the coil needs upgrading?

- Aside from all basics (bottom end/fuel/tune/etc.), what else do these motors require to break the 500whp mark?

If I were to begin going at this right now, it would look something like this...critique away!
-Forged crank
-Stock rods
-Forged pistons (need some info on rings here as it seems to be a weak spot)
-ported heads
-cams
-DSM head bolts (i think I read these were stronger) and metal headgasket
-fuel (are the fuel rails ok on these?)
-over trans turbo kit built my me
-3000gt tt drivetrain


I'm strongly considering building this! Would be one confused 3000gt! Let me know!

[Sundance 6g72]

on the other site, when i said dsm headbolts, i meant to use them as main girdle bolts. Brent will chime in on this, he is the one that has done this.

the forged crank is not needed but for reliability, i think it would be a nice addition. 500hp is alot of stress and if you can get a forged crank without bending over backwards then by all means do so.

About the fuel rails, now that you say it.. i dont think Brent had stock rails (custom made) on his 500hp motor but dont quote me on this.

for the heads, i assume youl go with the stiffer 3.3 behive springs, ls1 locks/retainers? I think that helps let the cam have more lift (but im not sure)

[MC#4]

I think this is a pretty cool idea. I love the lines on a 3S and I love the simplicity of a SOHC.

I can't answer most of these questions from personal experience but I've been absorbing info on TM TD and 3Si for the past year and half.

Forged crank - Nice to have although I don't think its 100% necessary.
Forged pistons - I've still never heard of anything off the shelf but custom can be done my many piston manufacturers. You send them a stock piston and ~$800 and they send you back 6 forged units. Venolia has made them and others can I just can't think of any names atm.
Stock rods - I think these have made crazy power w/o issues.
Ported Heads - Can be a DIY project but Ed (kmperformance) does this for cheap and he has a flowbench and years of exp. doing it.
Cams - Alot of uncertainty around cams it seems. Turbovanman has 3 stages of cams to choose from from $350-$400 a pair. I'd stay away from crower after reading horror stories of crap quality control
Head Bolts - Stock are quite strong, I think DSM's are a slight upgrade due to slightly more thread engagement. Arp's are believed to be a downgrade for these motors.
Fuel - I don't know anything about the rails limits sorry.
Turbo header - Ed does these cheap as well. crossover mounted as well as over the rear valve cover.
AWD - LOVE IT! Traction issues solved!

I'm sure more knowledgeable members will chime in. Good Luck with the build!

[Mdoe8]

Thanks for the replies!

I'm building my own turbo kit so that's not an issue.

I've checked out kmperformance before and that's where I got my ported head prices from, very affordable! I would simply go to them and tell them what my goals are and let them decide what I need

Also, do MAFT's work for these engines? Obviously if I go megasquirt it's not necessary, but they are very nice to have otherwise.

[Sundance 6g72]

Not sure on the maf translator. I would just go megasquirt for reliabilty reasons (spark control, overboost. And ms3 has a setting that cuts spark if you run to lean)

The dsm headbolts might work for our heads but brent used them as main girdle bolts after his girdle bolts stretched from detanating at high horsepower.

Ooo and for anyone else, ed does not do 3s manifolds... I these engines are flipped. Eds rear header would be on the front for these cars

[MC#4]

oh yeah, totally forgot about the motor being flipped in those. The crossover manifold would still work though right?

Also are you going 5-speed or 6-speed? How far along is the AWD swap?

A note on piston rings. You'll have to go file fit to get them right. General rule for Turbo motor is .005 for every inch of bore. Our bore is 3.59. I'd go .020+ to keep the ends from butting on a radical build.

[Mdoe8]

Thakns for the tip on the rings

As for the AWD setup, I've got the 5 speed and transfer case already. Rear subframe and subframe mounts i'm cutting off a car this week!

[Mdoe8]

Wow, somehow missed the "above and beyond" sohc mod bible that ondonti wrote....what a great post! That's helped me a lot, thanks!

[Sundance 6g72]

yeah get some dodge cam gears

[Mdoe8]

SO FAR, here's what I'm thinking. Obviously, this will continue to change as I learn more but this is where I stand so far.

Buy another junkyard 3000gt sohc motor (what other motors are identical (not Flipped)? Diamante?) and work on it in my garage while car is still driving.
- Disassemble Engine completely
- Rebuild with new gaskets, oil pump and pickup, and rings (appropriately gapped).
- Send cams for regrind
- Send Heads and new cams to KMperformance for port/polish/assembly
- Port Throttle body and intake manifold a bit
- Build over transmissions turbo kit (66mm turbo, 44mm wastegate, 3" exhaust, etc.)
- Massive in tank fuel pump and big injectors for E85
- Megasquirt
- Ignition upgrade of sorts

Then take this motor and run it at lower boost for a while. While this is running and enjoying 400whp, begin building the forged piston setup if I want or just have a backup motor in case.

[RoadWarrior222]

I would...

i) Build top end on spare motor while driving...
ii) Install to car on old motor, getting a good DD tune on low boost while...
iii) rebuilding the bottom end up fully of the spare motor... then
iv) tune hard, for medium boost and make all your mistakes NOW that punish pistons, rings and bearings...
v) swap in built bottom end when you thoroughly know what you're doing or figure you've "peaked" what you dare put on the stock bottom, or break the stock bottom..
iv) if you broke the stock bottom while below ~400HP, even though the new one will "survive" it, then reconsider your approach, ask advice, before going for broke on the new built bottom.

[Sundance 6g72]

I would get a 3.0 from a van. Cheeper and more than likely not beaten on as much.

[c2xejk]

I would get a 3.0 from a van. Cheeper and more than likely not beaten on as much.

Since he is running a Mitsu, there are several issues that would have to be delt with. Oil filter and dipstick placement being the first to come to mind...

[MC#4]

You should be able to snag a SOHC from an old base model stealth for cheap. I picked up a 93 SOHC stealth a few years ago for a 5 speed swap in a R/T. I only paid $500 for the whole car. I'm not sure if any other cars had the reverse mounted 3.0 besides 3S and maybe diamante? I would really try and find a mitsu block for ease though. The spare motor will make things so much eaiser.


Your plans so far look like a great start to me. Hopefully it all comes together for you.

[Mdoe8]

roadwarrior - i like your plan, though part of the reason to rebuild a stock motor is to gain the ring gap size and simply to get me familiar with the motor. Rather learn the hard way on stock internals.



Here's another question for you guys. I've got a 99 sohc, what years will be identical? I'm sure some changes werre made throughout the 9 years.

[RoadWarrior222]

Yes, good point, hear so often about how much the stock bottom end will take, I forget about the ring problem.... which won't let you get very far.

[MC#4]

I can't think of any differences between a 91-99 SOHC. There "may" have been slight changes in some sensors and wiring but I'm pretty sure the block and heads are identical for all. Shouldn't be a problem for your plans.

[Mdoe8]

Will the longblocks all be identical for all 3.0's? Even the non-reversed?

If so, I may just buy an older longblock from the junkyard with the 8.85 pistons and rebuild that. These pistons are supposed to be better for boost, i believe due to the intake valve reliefs and ring locations being slightly different.

I can then refresh that motor and pull all the accessories from my 3000gt and slap em on. Should I go with a pretty big ring gap? 22 or 24?

[Sundance 6g72]

they all have reliefs. the 8.5:1 have the ringland placed better.

all blocks should be close to the same.. oil pumps might need to be swapped along with the pan. the dip stick will not be the same though. brent ran a diemente block in a dodge and it was on the firewall side.

[Mdoe8]

Right, I thought I read somewhere that the valve reliefs were different on the older models...I could be on glue though.

do all these engines have electronic distributors?