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Another 3.8 Mivec swap... More fab! Less parts!

117K views 486 replies 65 participants last post by  billyfrancis40 
#1 ·
I guess My fender flare thread wasn't enough to stir the hornets nest... So to really introduce myself, I'm gonna stuff a 3.8 mivec into the stealth.

I was drinking one night thinking about my first girlfriend back in Jr High school.... Then I grew a wild hair up the butt and said, I'm doing the 75 Full Mivec Engine swap. That ends that love story.

It has been done many ways already and I'll be doing this my way. This time around. I'll post up pics of progress as I go along just like the fender flare thread. I know I'm pushing some kind of limit here but it should be interesting to be 4th or 5th known to have done this swap. So far, its Been Itallo, Bdranck, and MichealMR2 that are known to be running Mivecs.

Unicorn engine aquired.




 
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#9 ·
Sigh. I want another block just to do this with.
 
#11 ·
This should be interesting. Subbed!
 
#12 ·
The car afformentioned in the inspirational pic is Bdranck's car. My build is a bit more budget friendly, using what I already have stashed in the basement lol
 
#13 · (Edited)
First and foremost... The front engine mount, I plan on utilizing as many factory locations whether adding or fabricating brackets as needed. Since the Transmission on mounts one way to the chassis I won't go into any detail on that. But The OEM bracket that bolts to the 72 block does fit onto the 75 block with some creativity. That takes care of that issue.



As you can see in the next pic, the 75 motor mount bracket comes about as close as getting the hot chick in Chem class' phone number... needless to say you're gonna have to get crafty to get her digits.

 
#14 ·
The Valve coves are great!, they can be swapped back and forth. That should'nt need much explanation, But attention must be given to the timing marks on the front (red) valve cover. Once you swap them, the mark will be on the transmission side. The rear head timing mark is a notch on the stamped metal sheild behind the cam gear cover. Also the lower intake manifold needs to be flipped 180* The boss that is used to bolt the gusset over the water pump will need to be trimmed 1/2" to clear.
 
#17 ·
not sure what the stock 75mivec can handleto be honest. But I do plan on keeping the 10.0:1 compression and twin TD05 16G's. If my plans are correct it should lay down plenty of streetable power at very low boost levels. When I mean streetable, I mean fast ramping with a very flat torque curve.
 
#18 ·
The 75 Mivec has a returnless fuel system utilizing pulswidth modulation of the fuel pump to regulate rail pressure. Well...my Stealth isn't that smart even with AEM. So without diving into the wallet just yet I took apart the 75 fuel rails to convert it to a return style. Although the shape is odd and it looks very restrictive, The inside cross section measures out to just a C-hair less than 1/2"! Not bad at all! The injector bosses on the other hand are lacking...

At a measely 1/4" the openings had to be bored out. They may have been sufficient for the 330cc stock injectors and NA but not enough for 1150's and Boost. I also added -6AN fittings to the ends to make it a 2 piece fuel rail with a detachable fuel loop to aid in disassembly and user friendliness. I'll add more pics as I go along.



The top is 100% stock 75mivec, the bottom is the 180* flipped and being modded. Notice the stock rail is all 1 peice and stamped/extruded/brazed steel. the bottom rails will be modular.
 
#21 ·
72 in my car will be parted out soon and turned into a coffee table. ETA is unknown, I spend an hour on it every day lol
 
#22 ·
And for today's updates we tackle the Returnless fuel rail... True to the "more Fab, Less Parts motto" I converted the OEM mivec fuel rail to a return style setup. It doesn't really need much explaining.

DIY fuel loop -6AN


Feed and Return also -6AN


 
#23 ·
I'd love a mivec 3.8! Awesome build!
 
#24 ·
Subbing! Love engine swaps;).

Don't run those stock 3.8 rods with any boost. You'll have a mess on your hands. They 5mm thinner than 74 rods. Read one of my old threads if you want to see what happens at just 15psi with td05s on a stock 74. I was warned by Matt M and Ray P. Now you've been warned by proxy from both plus me. Don't do it. Don't do it. Don't do it.

That said. Do the full swap. Love it!


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#30 ·
^^^^ this. You will not get far on those stock rods.

However the stock crank seems to be made of unobtainium, i believe thatbis what Italo Grasso is running in his car (3.8L MIVEC 6G74 Stroker 1305awhp)

That being said, if you want to try it go for it! Just hate to see you get so far and destroy a fresh engine.

There is a 4G eclipse guy running twin 16Gs on a stock 75.. Last i saw it broke 400whp with 6 psi. This was years ago so i dont know of that car still runs and if so if its faster.
 
#26 ·
Sorry for the inactivity as building a vegetable garden has taken priority. Recent updates have been mounting up the 72's Timing belt idler pulley bracket and idler pulley as well as the Power steering bracket from the 72. I'll take pics as soon as I get a chance. Stay tuned fellas!
 
#28 ·
I love displacement, so the idea sounds like a good one.

How will you control the MIVEC part of it? Or will that happen automatically?

I'd love to turn a 6G72 or 74 into a 3.8L engine and run highish compression with lowish boost for a really nice street car. If I keep the car long enough, that's the plan.
 
#29 ·
subscribed.
 
#32 ·
The 6g75M is a 10.5:1 compression motor. I will not need that much boost to make power on the street. Mivec will be actuated through AEM, I just have to add a few wires to facilitate the operation. No one really knows the limits of the 75M in stock factory form so I'm also going to be the lab rat for a 10.5:1 boosted swap. My Tuner has accustomed himself to E85 high compression(10.5+:1) turbo builds with Evos Mainly. A 10.5:1 boosted mivec build will be cake for him to tune. If it hits 400whp but has 500wtq I'm done. If it makes more, we will have a good baseline of what we can throw at the 6G75M as a whole.
 
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