Now that I've tidied up a bit......next stage in "bored and stroked"
Finally come up with a workable plan to make a 3.5 bigger on the cheap.
Following on from what I did to the last 3.5 crank to make it fit the 6G72 block...it should be doable.
RB30 conrods.
Pauter make the aftermarket rods and have the specs on their site.
Starting off with a 6G74 crank which has a 55mm big end diameter and the rod is about 153mm long with a 22mm pin.
Reduce the big end of the crank to 6G72 size which is 50mm. If it's fully offset ground, that can increase the stroke from 85.8 to 90.8 or maybe 91 by going more undersize.
The RB30 conrod is slightly shorter at about 152.4, has the correct big end size (50mm at the pin, 53 mm in the rod), it's slightly too wide and the pin is only 21mm.....nothing that can't be fixed.
Stock RB30 rods are fairly strong and cheap.
As a "plan B"....you can get custom made 4340 conrods out of china for quite a good price...like $100 each.
I've got one 6G74 pajero block that I don't have a crank for.......so it wouldn't harm to see how far out I can get the bores?
A 91 stroke will give over 3.8 with 6G75 pistons........still stuck with the CR too high..........fix that later.
I've still got the 6G75 SOHC heads here....big combustion chambers for low CR, maybe I should use them? The exhaust ports are different, need custom pipes.

Meanwhile the 72/74 hybrid is still waiting to get bored.It's got to go out by 8 thou inch in total which includes 4 thou inch clearance.

Also made a bit of progress with the dyno.
Put a spigot bearing into the flywheel, broken input shaft of old gearbox, put a pin in it to fit the spigot bearing, put the clutch all together with spare bellhousing from broken gearbox.



I've applied a special friction coating to both the flywheel and pressure plate.....FeO for short. Although probably a mixture of FeO, Fe 2O3 and Fe3O4



On the flywheel I sanded some of it off because the coating was a bit too thick.
The gearbox shaft, I cut it so it's just 1st and 2nd gears.......Need a drivshaft on it, so ......universal joint, shaft, universal joint.....flywheel.I've got a full GTO driveshaft/ propshaft.........transfer case to rear diff. I'll cut it up.



Got to do some mods to the hamster wheel next. The tensioner is all wrong, wrong height and it spins in the wrong direction. It needs brakes and I think I can actually make a magnetic brake for it??? AKA and eddy current brake, then I can also hold the revs steady.......later on.


From Barry's workshop.

Wow, your a bit like the geek for GTOs. I should of come to you to look at my car when I was having all that trouble with my clutch peddle, all those years ago, that no one at the time could figure out. I ended up having to take the gearbox and clutch out, only to find that it was the plastic piston in the master cylinder that was causing all the trouble. I originally ruled it out because I had it resealed and thought it was fixed because I had that done, only to have it looked at again to find out that the resealing had not fixed it, and that it needed to be completely reconditioned with a new steel piston.
Anyway I better not go on too much about it, or I'll get told off like a little child by he who must be obeyed, for daring to go off subject.

Yes, those clutch master cylinders, they all fail........got that problem on my black GTO right now, just couldn't be bothered fixing it just yet.
I can still drive it........just got to keep on pumping the pedal to get up pressure to get it into gear.
I've already done the "pick a part" master cylinder fix on the red GTO......piston from a Galant.

dammit steve, dont you dare put that damn sohc head back on haha
youre the dohc mivec guy, and making the job easier for me down the track haha

Lol.....The problem with using a pajero 3.5 block is that I can't fit mivec heads anyway without a custom longer belt which isn't happening.
But having left over parts means it's handy for mocking up and test fitting.
No, I don't really want to fit the SOHC heads as I'd need to custom make some (turbo) exhaust manifolds, which I couldn't be bothered doing. I've made a few sets for V8s in the past but they all end up either cracking or warping the flanges, usually both........so it's a waste of time.
I've run out of mivec heads too......only got 4 sets with a 5th set minus valves and cams.
But fitting some DOHC N/A heads is do-able, still end up with CR a bit too high.

My 6G72 4 bolt block is now bored and honed ready for test fitting etc.......that's the one with the destroked 84 ish mm 6G74 crank.

In the meantime I've made a start stroking another 6G74 crank, this time to fit into a 74 block, giving it an extra 5mm of stroke by cutting the big ends down from 55mm to 50mm, all the cutting done on the inside rather than the outside.....like here.


https://www.youtube.com/watch?v=GYnDJBou07c

A bit later on

https://www.youtube.com/watch?v=621kt42 ... e=youtu.be

More photos.
This time it's back to the 72 block with the 74 crank.
Looking at the original post at the top, was going to use 6G74 pistons, using forged ones now, it's still a bit under 92mm bore (it's 91.6mm)
The piston at TDC, there's 3.8 mm of it sticking out of the top. That's to be expected because it's an aftermarket piston. with a 72 crank it should sit flush with the top of the block or maybe just a bit down. A factory piston sticks out the top by about 0.5 mm.
Because it's been stroked by 8mm and with a stock rod, that's 4mm extra at the top and 4mm extra at the bottom.

(edit, The un modified JE piston sits flush with the top of the block at TDC with stock crank)




The piston on the right, I've cut about 1.5mm off the top. Got to do all the others the same. With that one in the block, it only sticks out by 2.3mm.
Need 1mm min piston to head clearance. So 3.3 mm minimum HG thickness. Stock TT gaskets are about 1.4 ish mm.
A spacer plate sounds like a good idea. Scruffy thinks so too?....Later on though.


91.6mm x 84mm should make 3321cc. It's not a 3.5 but it's still an extra 10%.

Wow, imagine putting this engine in a much lighter car than a GTO, just to see what it's performance would be like. 0-100kph in 2 to 3 seconds maybe? I've always wondered about what that would be like. Some say it would be no good, but surely having 5 to 6 hundred kgs less to have to pull would make it go faster.

Like in a 4WD mirage?
There's even a vid on U tube somewhere of an Evo in Russia with a 6G72 in it.

Meanwhile there's yanks putting 4G63s into 3KGTs for an upgrade????


In the meantime, the crank that's going out to 91ish mm stroke, I've got all the big ends the same at just over 50mmm where I've paused.
Need rods and bearings first.
I've just hit the buy now on a set of RB30 conrods on TM.
It might take me another 6 months to figure out how to narrow them then bore out the small end to fit the pin.
I can't do any more to the crank without bearings.

magn1t wrote:

Meanwhile there's yanks putting 4G63s into 3KGTs for an upgrade????

Absolute dumbest thing ever.

ravensierra wrote:

magn1t wrote:

Meanwhile there's yanks putting 4G63s into 3KGTs for an upgrade????

Absolute dumbest thing ever.

Yes.


Anyway, I'm doing a bit more planning ahead. A few posts above I've got pics of the 3.8 which is going to be RWD. So far that's got multiple HGs to lower the comp a bit. But it's still too high for boost. A spacer plate seems to be a good idea......so that might be next week.
The 3.8, the way it is right now, if a spacer plate was added there would be problems with the water crossover between the heads.......the bolts won't fit.
OK that's easy, just slot the holes. The same problems with the lower intake manifold except the ports will also be out of line between lower plenum and head, again nothing that can't be fixed.
So........Part of the plan is to stroke the 6G75 crank in the same way as the 6G74........needs a thicker spacer plate.Then I dug out my old on hold intake manifold from a few years back.The manifold has been put away for a while 'cos it got too hard and CBF came into it. That's when I got hold of a factory one.
I was also looking at toyota 4 AGE ITBs last week.....6 of them would be doable (but NOT on a GTO). I might be able to come up with something that'll work?





At the moment, that manifold is just 9 pieces, there's 6 short bigger tubes pushed over 2, 3 port manifolds and a box.

95mm x 95mm should make about 4040

The 6G72/74 hybrid, I've got all the pistons cut down to the same height now, they fit the block and have about 2.3mm (I think?) sticking out the top. There's still about 5mm of piston above the top ring.That means the top ring is still 2.7mm inside the block.
Next week, I'll hopefully have a pair of spacer plates, maybe 3mm thick.....we'll see what turns up. I'm thinking lower compression will be better for more boost on 95RON.
OK so a spacer plate to lift the heads a bit (headlift mod?) The lower intake won't fit too well. I've got that worked out too....more later.

The 6G74, 91mm stroker........a set of RB30 conrods (and used bearings) turned up today.......trademe special. I got the pistons too but they're too small for anything.
The big ends are the correct diameter (for 50mm crank pin) but about 1mm too wide. Fully floating gudgeon pins (same as the '74) but 21mm diameter instead of the 22mm required. About 0.5mm shorter than the 6G74 conrods.
Next week I'll figure out the best way to narrow 1 rod to start with, also bore out the small end.....then I can finish the crank. The best way has to be free and done by me.


There you go......Holssan RB parts to make the mitsi go quicker...lol.

Barry

Had a play on the lathe today, I've got no idea what I'm doing of course but started off with just a bit cut off the top, did some mods to save weight and at the same time lower the CR a bit. This is for the '72/'74 hybrid.

Here, all 5 are different, just been playing around to see what's what. No 6 is still filling in a hole in the block.



Made a lot of shavings.


Getting closer.


They're thinnest in the middle so that stays as is, cut the most out where the valve reliefs are.
I've still got to cut no 6, then maybe weigh them, maybe even measure the dish CC? Try to get them all the same.

edit......3 of them weigh in at 362g, other 2 at 363g, the uncut one 372g. Then I shaved a bit more off them all.


U tube is good, it's got everything.
Was watching how to make a fly cutter for a lathe, I'll give that a go to narrow the Holssan conrods for the '74 stroker.

I see there's a thread going on 3SI.....apparently our bearings aren't wide enough?

Found it here
http://www.3si.org/forum/f1/finally-sol ... gs-744417/

Anyway one of the advantages of Holssan rods is that the bearings are a couple of mm wider.The rods themselves are too wide, the rods need narrowing as already mentioned but the bearings themselves are NOT too wide. If someone REALLY wanted to , they could modify 6G72 conrods to fit RB30 bearings or even modify the RB30 bearings to fit the rods......not that there's any point.
One thing to be aware of is that jap engines are all built in mm, in whole numbers.
When it comes to crank sizes, Mitsubishi, Toyota, Subaru all finish the crank on the whole number, eg 50.00mm. The inside of the conrod is usually 3mm bigger, eg 53.00mm. The inside diameter of the bearing determines the clearance, eg 50.05mm which would give 0.05 mm clearance or about 0.002 inch.
With Nissan and Mazda, they finish the crank, instead of eg 50.00mm, it's 49.95mm, the inside dia of the bearing would be 50.00mm to give the same clearance.......so using a 50mm Nissan bearing on a 50mm Mitsubishi crank you'll end up with about a zero clearance.......but that's easy fixed...so long as you know..............Just more useless information.


3 conrods, RB30 in the middle. To me , it looks stronger than the Mitsubishi rods.


edit, I've now got all the pistons down to 358g.

The latest episode and more useless information, maybe not quite so useless?
The 72/74 hybrid.
I put all the pistons onto the rods, just loosely, just for a trial fit in the block.
I've already done the trial fit with just crank out of the block, conrod and piston........there's no clearance problems............so it should clear in the block?
No.
So why's that?
Somethings not right..more measurements to do. No1 and no6 pistons hit the counterweights but only on one side of the piston skirt.

Right...so changing subject a bit.
The RB rods for the 74 stroker, got that sorted too.
The bronze bushings are too small at 21mm ID and 24mm OD, they come out, the small end gets bored to 25mm but offet to shorten it 0.5mm and also retain strength, then it gets a 25mm OD bush which has a 22mm ID to fit the pin.......6 bushes = $25..........bargain?



Then I came across a stroker thread on 3SI which I had previously missed.

http://www.3si.org/forum/f35/ray-pampen ... it-329013/

It's a "must read" for everyone.....if you've any interest in strokers.
If you're going to read it you should also brush up on your maths skills.
The more reading you do the better....it's called education.......then you know who's full of sh**.

All I'll say for now is that this particular 3.7 has never been built, nor has the 4.5.....because it's NOT POSSIBLE.
Here's the challenge.......from the info given........what will the stroke be?
Yes, it's easy to work out .
Yes, DR and others have built 3.7s but not with any of these dimensions , just a 75 crank in a 74 block..the easy way.


Now while we're at it........http://www.3si.org/forum/f1/heres-anoth ... er-545471/
The 4.0 uses a 3.75 inch stroke.........that's 95.25mm..........which is doable starting with a 6G75 crank(cut the BEs down to 50mm or just a bit less with a full offset grind.

http://www.3si.org/forum/f4/custom-bill ... re-704490/

The 3.5 pampena 72 uses the BC 84mm crank so it's NOT 3.5...only 3.4 ish.

Today's episode.
For scruffy.......I weighed some conrods.
6G72 (lightened a bit)..with rod bearings..........664g.
6G74, no bearings...........744g
RB30 stock, with bearings..........714g.(edit, RB30 rod, no bearings 685g, so a pair of bearings......29g )

A bit of a surprise there but I guess the extra weight of the 74 rod is mainly due to the 55mm big end size where the others are 50mm.
I'll need to weigh some bearings later?

Just for comparison, a Pauter '72 rod, from their own website weighs 619g.
A pauter '74 rod weighs 650g
A Pauter RB30 rod is 651g.
Weight is strength?
Design is strength?
Material is strength?
But nobody ever has any data on how strong a stock rod is?
Maybe that's because nobody would buy aftermarket ones if real tests were done?



Yesterdays episode with piston skirts hitting counterweights but only with it all in the block??????
It's only no 1 and no 6 because they're the biggest counterweights, only hit one side which is the outside, not the inside valley side.......both of them.
I just ended up taking another couple of mm off both counterweights, they were a bit close to the girdle too so that's fixed now.



Cant beat lots of sparks.


Vid.
https://www.youtube.com/watch?v=uqve5YVzlnE

I think I've dummy assembled this thing more than 10 times now, still haven't measured the bearing clearances or ring gaps. Haven't even taken the rings out of the box yet and I'm still using second hand but good bearings.


The golden rule with engines is to never throw away any parts until the job is finished.
Projects never get finished so you end up with lots of spare useless parts.

Next......need to measure the piston dish.
I already know they stick out by 2.5mm
Getting some head spacers organised....don't know thickness yet, maybe 3mm, maybe cut down a bit from that?
Need to measure the combustion chamber size on 30M head
Work out..... or make it.....a reasonable CR for boost.
Got a pair of unused cometic gaskets for 6G72, they're 2 mm thick, will also use second hand 30M HGs at 0.4mm.............RTV of course.

Cut and pasted from elsewhere.
................................................................................................

Sometimes the piston design is "set" and the compression height can't be shortened. In a case like this a "deck spacer" can be used and as long as the top ring stays under the deck of the block and minimum piston to head clearance is maintained , everything is fine. Jon Kaase raised a 351C block up to 9.500 ( from 9.200) with a custom .300 thick copper "head gasket" as a spacer was not legal for the competition he was in.
The engine won the competition and a maximum thickness rule was placed for the following year
...............................................................................................................................
Stay tuned.

I lit the fire today....was getting a bit cold.



It's just warming up slowly.

OK so no point in rushing things...my 91mm stroker..........finished the big ends, it was one of my old spare cranks that previously spun the no4 big end, there's no problem with the big ends now.
But the other thing that happens is that the mains always get pulled out of line, by that..........you clock it up on the machine or just place on V blocks, the 2 centre mains go out of alingment, towards the no 4 crank throw. About 0.20mm, about 0.008 inch(the no3 main adjacent to the no 4 BE gets the most bend, the no 2 main, less at 0.12mm). Normally you'd just grind it straight, it'll clean up at the first undersize.
If you're going to get a crank nitrided, it goes into a furnace, heats it up for a while (with nitrogen or whatever?), cools down, if there's any internal stresses like caused by a big end failure, if it goes in reground straight, it'll come out bent.Then it'll need regrinding again.

So the proper way is to put it in the furnace first (send to Auckland) to stress relieve it (send it back), grind it to how you want it.....then get it nitrided which is a second time in the furnace.
This is just going on what I've been told, whether it's right or wrong???...got to send it away twice. But it makes sense.

It's now in the fire (stress relieving)....I'll give it full throttle and warm up the house a bit.......re measure the bend next week. Grind it straight. Someone else is narrowing the RB rods for me, the counterweights will need cutting down a bit too but won't know how much until the pistons are on the rods and on the crank.


When I had the other crank in the fire last year, I had a visit from one of my nutter women friends, she went telling everyone how I had car parts in the fire / oven (actually I tried the oven first but it wasn't hot enough).....they all think I'm crazy .....but they're the ones who go to church every sunday and sing songs with their crazy friends.


Just remember that according to the gurus........you have to buy a new crank, can't fix them.


From Barrymods

magn1t wrote:

When I had the other crank in the fire last year, I had a visit from one of my nutter women friends, she went telling everyone how I had car parts in the fire / oven (actually I tried the oven first but it wasn't hot enough).....they all think I'm crazy .....but they're the ones who go to church every sunday and sing songs with their crazy friends.

I had a little chuckle about this.

Why wouldn't it straighten out again when you heat it the first time?

Is it really internal stresses that cause it to distort in the fire or is it just how it's sitting? Seems like you could bend it by having it sit in an awkward position in the "furnace?

Think about what happens when you spin a conrod bearing and you keep on driving.....just turn up the stereo and pretend that it's all OK.
It goes clunk, clunk, clunk, once the bearing gets a bit chewed up the piston goes too far up and hits the head too.
All that clunking chews up the crank, don't forget about the conrod either..but as well as the crank throw, it puts a lot of stress on the adjacent mains pulling them out of alignment.
If you keep on driving, the wear will be too much to grind out, often the crank will crack as well, like in an above photo of my 30M crank.
All of my spare cranks have had spun bearings........that's just normal. According to the usual gurus, you have to buy a new crank which of course is total bullshit, you've just got to make sure there's no cracks, then grind it back to spec and use undersize bearings which are available for pretty much everything.
The theory is that cranks can get stresses built up over time, the stresses pulling the mains out of alignment are real because you can measure it.
I can't remember 100% with the first one but I did a lot of reading. The oven isn't hot enough....not sure , maybe 300F which isn't a lot compared to cranking up the log burner where you can get the insides glowing.

You can find all sorts on google if you waste enough time.

https://books.google.co.nz/books?id=AfT ... ft&f=false

That link says that for nitriding, the temp has to be 500 to 580 deg C...so if it's not stress relieved first by bringing it up close to that temp, it'll stress relieve its self when being nitrided, if it's going to warp, it's going to warp....so I can grind it straight first....after the fire but before nitriding. You don't really want to grind it after nitriding because you might grind it all out....don't know the depth.

But I've made measurement before the fire....I'll take more afterwards, see what difference if any there is.
It might even end up straight by its self?

I suppose I could have just put the crank on a stand and attacked it with the gas burner like you do to straighten a bent head but doing it this way, I think it's a bit more gentle and can be done over a longer time, heating slower and cooling slower.

https://en.wikipedia.org/wiki/Nitriding

https://www.highpowermedia.com/blog/346 ... rankshafts

https://www.highpowermedia.com/blog/350 ... rankshafts

http://www.dsmtuners.com/threads/the-cr ... ks.309281/
That link is OK apart from cast iron cranks which don't work harden when ground.....cast iron is ALWAYS harder than steel, test it with a file. Any cast iron machine base.

http://www.nitriding.co.uk/crankshaft-case-study

There's even a 3SI link...lol. No they're NOT nitrided in the factory.........All Mitsubishi manuals say..."in the case of"..they're all the same
http://www.3si.org/forum/f42/re-nitridi ... nk-280627/

There's mention of bearing widths there.
From the link 0.606 inch...that converts to 15.39mm which compares well to my own measurement of 15.33mm. The RB bearings are 17.40mm wide.
Also from here.
http://www.3si.org/forum/f1/finally-sol ... gs-744417/
The BMW bearings are 18mm wide.

None of the aftermarket billet cranks or reworked stock cranks from Pamapena , 3sx, or anywhere else are nitrided.


Last of all.......this place here.......that's where it goes to. Hopefully they know a bit about cars?
http://www.heat-treat.co.nz/

This week's chapter......the crank is still in the fire, we had a bit of a cold snap last week, it's been too hot to light it up again.

In the meantime been thinking about measuring the combustion chamber CCs...BUT....doing several all at the same time.Not just combustion chambers but intake ports and exhaust ports.
Why?
Because say if you were into SBCs, the most popular engine in US of A, there's lots of different aftermarket heads, they're often identified by the volume of the intake ports, if you port them, the volume goes up. If they're all different after you've ported them....you cocked it up.
Mine are all standard.

I've got another Pajero 3.5 complete engine, bought it 5 or so years ago, it's just been sitting around....time to strip it. It's got the 3A heads on it, small intake ports, by eye, the combustion chambers appear to be the same size as 3N, 3T, 30M. The cams are P and K so the timing specs should agree with my "degreeing cams" topic.
I bought the engine as a good runner but all second hand engines are duds unless you strip them. I've stripped it so I can measure the heads.
BTW the stock head gaskets, they're composite, 94.3mm hole in them, between 1.3 and 1.4mm thick measured with dial caliper. I've saved them to use again....lol.

In the meantime I've done some quick rough calculations for volume.......first of all the 30M....
nominal 10 to 1 CR, 495cc per cyl........that makes 55cc total combustion chamber volume, roughly flat top piston, zero deck(0cc). 0.4mm head gasket (2.66cc).....so the head should be about 52.3cc.
Next is the pajero 3.5 (3A head) 10 to 1 CR, 583 cc/cyl, 64.76 cc total combustion chamber vol, nearly zero deck, slight dish piston (close to zero cc), 1.4 mm head gasket (9.7cc), should give about 55 cc in the head.
The numbers we'd expect from measuring would be maybe between 45 and 55cc?


Then some compulsory reading.

http://www.club3g.com/forum/3g-eclipse- ... ber-s.html

6g72 DOHC TT- 48cc
6g72 24v SOHC- 43cc
6g72 24v SOHC PnP- 44cc
6g74 SOHC N/A- 43cc
6g75 SOHC(M?)- 65cc
and evo pajero, 6G74 mivec, 46cc?


They'll end up measuring up at about 48cc.......that's the 30M and the 3A?..maybe?



http://www.3si.org/forum/f35/who-has-cc ... ost2529170



Some proper measurements coming up soon






The pump wouldn't turn, it does now




Mint crank, need to check it for bend, may as well stroke that too?


The block, I'll see how it looks with a 95mm bore. Will be fitting oil squirters too. That'll be another first.


Mint runner, the usual 67,000Ks on the clock.

The numbers are in at last
Only for the 30M heads so far

The combustion chambers are 46 cc, all 3 of them.
The intake ports are 126 cc
The exhaust ports are 86 cc

The only problem was that the heads don't have sparkplugs in them, got plenty of sparkplugs but no socket because a normal socket doesn't fit. My specially modded one is at home.......got to grind 2 sides flat so it fits down the tube. Playdough is the answer.


OK so what about all the other numbers in the post above?
A perfect match with the evo Pajero numbers which came from Australia.
The other numbers........I won't comment until I've double checked, I'll assume for now that they're ALL wrong.

What's also required is some accurate measurements of the various pistons, the bowl or dome, depending on which one...later.
The nominal 10 to 1 CR from Mitsubishi could really be anything from 9.5 to 10.5?

Yeah I don't trust Mitsi's nominal CRs either cuz I've done the calcs and they never match up with the measured volumes.

I've just been digging through the "Ross" pistons PDF catalogue", only because 3SX sells sells Ross pistons with various CRs but no bowl/dome/head data, not that they'd have any clues anyway.

From the Ross catalogue the 3.5 (the 3A head) has a volume of 46cc and the TT head has a volume of 51cc......... will get some of my own numbers on that later.


So in the case of taking a stock 3.5 pajero engine at 10 to 1, dumping the 3A head 'cos they're junk anyway, fit 3T / 3N heads, you're going to drop the CR a bit which has got to be good?.......how much????
Start with a nominal 10 to 1 CR, 583cc/cyl, 64.76 cc total in the head, add 5 cc...makes 69.76............drops to 9.3.


As it becomes more obvious with progress...........it's pretty essential to measure everything properly when boring and stroking otherwise it ends up totally cocked up.

Another thing which is now easier, knowing that 46cc is the number, my present engine in the black car, it's a 2 bolt TT block, 30M pistons, TT gaskets, 30M heads.The 30M gaskets are 0.40mm, the TT gaskets are 1.40 to 1.50 mm, lets say 1.40.
495cc/cyl, assuming a 10 to 1 CR, 55 cc total head vol (head + gasket + bowl), the head is 46, the gasket at (let's say) 92.5 mm and 0.4mm is 2.67 cc, that means the piston bowl should be 7.33....but it's a flat top ( a slight bowl)........so something else isn't right.....maybe it was a typo, the 1600cc mivecs are all 11 to 1.
I've added 1mm in gasket thickness (6.72 cc) so IF it started as 10 to 1 , the 55 cc total has gone up to 62.33 to give (495 + 62.33)/ 62.33 = 8.94 which is my present estimate of 9 to 1.........but if the original 10 to 1 wasn't right, neither is my 9 to 1.

OK ramble?????


Another quick calculation............Start off with a stock TT, swap heads( Box?...30M) lose 5 cc.........495cc/cyl, 8 to 1, 70.71 cc total head vol (head + gasket + bowl), that becomes 65.71 or (495 + 65.71)/ 65.71 = 8.53......which should be a step in the right direction.

I've now done some measuring no the 6G75 SOHC head and also the 3A head.

The 75 head is from an Ozzy mitsubishi 380, the 3A is found on all of the DOHC Pajeros and probably the Debonair too......well all of them that are 3.5 DOHC but not GDI and not Mivec.

6G75 combustion chambers........68 cc
6G75 intake ports...................117.5 cc
6G75 exhaust ports.................76 cc......these BTW are a different shape from all the others, needs different ex manifold.

3A combustion chambers..........46 cc
3A intake ports......................107.5 cc
3A exhaust ports....................84 cc

So cut and paste the 30M numbers for comparison

30M combustion chambers...... 46 cc.
30M intake ports are ............126 cc
30M exhaust ports .............. 86 cc

The '75 number of 68 cc compares quite well to the quoted '75 mivec number of 65 cc and the 3A number of 46 cc is spot on with the numbers from "Ross pistons"

Coming up later will be 3T and 3N2, the 3N2 being the 2nd gen N/A.

I like to guess just for fun.........so.........I'll guess that the exhaust ports will all be about the same at 84 to 86 ish, I'll guess that the chambers agree with Ross pistons at 51 cc, both of them. The intake ports of the 3N will be close to the 30M at 126 ish cc (they're visually the same), the intake ports of the 3T will be more because the divider in the middle is cut right back, won't guess at a number though.


The '75 head








The 3A head

Was wasting more time looking for something on the interweb and got sidetracked again.

I came across this one .......well worth reading due to the BS content,,,in particular the maths. http://www.3si.org/forum/f35/my-6g74-3- ... ge-240131/
BUT
This post here. post 203
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I cc'd 3 seats of Heads, NA 6g72, TT 6G72 & NA 6G74. They have identical combustion chamber size.

The 6G74 heads are set up to use a CAM angle sensor behid the CAM gears just like a 93+ 3S. You can remove the cam cover on the other side of the head and use a 91-92 CAM sensor, that is what I am doing.


P.S. If you are doing this swap just buy a JSPEC 3.5L and make sure it has all fo the parts listed on my webpage. Getting the alternator bracket, powerstering bracket and P?S idler pulleys were the hardest part of my swap.
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Solidworks models of 3S engine parts: http://www.wrenchmonkey.com/Images/Solids/3000gt2005/
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So does does that mean they're all 46cc???
Will find out later.