7m head on 5m block?

[andrew_mx83]

After killing my 7m at winton over the weekend i am now in the process of planning a high rpm build. it is well known that the 7m's long stroke makes the piston speed too high for reliability at revs. i want to build something that will rev to 8k and be reliable sitting above 5k for extended periods of time.
the car now only sees track days so power/torque under 3000 rpm is not an issue. while i am always a fan of more cubes = better, in this case i am more going for revs for driveability on the track.
motor runs a super light flywheel/clutch, no fan etc and is already very responsive and will be balanced/blueprinted etc. i am in the process of converting it to triple 40mm dellortos which will definately want to make it scream up top and it will also get a cam grind.


7m: 83mm bore 91mm stroke
5m: 83mm bore 86mm stroke

with a set of 60thou over pistons the motor would nearly become square...very desirable.


has this been done before? im assuming the bore centres and head bolt/oil gallery locations are the same.

[Radar]

5MGE = BHG Poo.
7MGE = Still BHG Poo.
2JZGE = more power than the car will handle
1JZGTE= ^^as above^^

*not raggin on the idea* just for reliable torque up to 8k cant look past the jz motor for ease...

[amichie]

After killing my 7m at winton over the weekend i am now in the process of planning a high rpm build. it is well known that the 7m's long stroke makes the piston speed too high for reliability at revs. i want to build something that will rev to 8k and be reliable sitting above 5k for extended periods of time.
the car now only sees track days so power/torque under 3000 rpm is not an issue. while i am always a fan of more cubes = better, in this case i am more going for revs for driveability on the track.
motor runs a super light flywheel/clutch, no fan etc and is already very responsive and will be balanced/blueprinted etc. i am in the process of converting it to triple 40mm dellortos which will definately want to make it scream up top and it will also get a cam grind.


7m: 83mm bore 91mm stroke
5m: 83mm bore 86mm stroke

with a set of 60thou over pistons the motor would nearly become square...very desirable.


has this been done before? im assuming the bore centres and head bolt/oil gallery locations are the same.

5m and 7m have different head gaskets. Some of the passages are in different places. You can see pics of both in the ACL catalogue.

A propoerly put together 7M using new OEM bearings etc should handle a 7500 rpm all day. I beleive the 7MGTE oil pump is a doable upgrade.

[gianttomato]

^ What he said. Then there are issues with the crank nose/timing belt gear - maybe a 5MGE crank would be an easier starting point. Too much headfucking for a bastard motor with less capacity. Legalities of putting an earlier motor in a later model car might be an issue (still an issue with LPG?).

Just build a 7M. Clearance it properly, run 7MGTE oil pump and go from there.

Or buy a 2JZGE/1UZFE for half the price of a 7MGE build and spend change doing a conversion. LPG and you already have the IGN only ECU?

Your triple carb mod would translate easily to a 2JZGE and I can tell you from experience (in EFI ITB format) that it's a nice drive.

Food for thought...

[neal]

LPG!! Its a race only engine isn't it?.

Andrew: What sort of times were you pulling? Another cheaper alternative could be changing your diff ratio's to suit the 7M. Also what did you break?

I have a mate who has done close to 500+ laps at winton with a standard RB30 and he just can't break the thing, his times are 1:50.

[andrew_mx83]

not really interested in going jz....i have a real soft spot for the 7m. going boost or v8 would put it up a class for racing so that puts that out too. plus i have a lot of supporting mods for the 7m id rather not have to throw out and buy again for another series of motor (button clutch, superlight flywheel, bellhousing, extractors etc etc) plus i have a fair bit of experience/knowledge with the 7m now. BHG is not, and has never been an issue in my book.

lpg was a once only thing, this weekend was its first track outing since being pulled off daily duties and did not have time to get the carbs on and running (its dedicated lpg atm)

motor is already clearanced properly, .5thou mains .75 big ends and and .5 piston to bore (when it was built anyway) significant oil system upgrades will be mandatory in the new build -baffled or dry sump, shimmed pump, cooler, temp guage, bigger filter etc.

diff change wont really do what i am looking for, it already has fairly short ratios in the box and want i want is to be able to hold gears for longer without breaking the motor.

ill sus out the acl pics and see how far off the passages are....also have to look into the timing gear issue too.

im going to start pulling the motor out tonight and check for sure, but basically it lost oil pressure on the back straight of the last lap of the last session. my assumption is it cooked the oil (no oil temp guage only pressure) and spun a bearing. im aware that what i have suggested wont change this, but if i am going to rebuild it i dont want to have to stress about breaking rods etc if i am holding over 5000rpm all day again.

i babied it into the pits and dumped the oil (hadnt lost any) and refilled and the pressure came back however there was already a hint of death rattle. did not get far down the highway before it was becoming more evident and the oil pressure started playing funny buggers again. rattle got worse and worse, around seymour there was a nasty sound of something breaking and falling (sounded like it dropped a bunch of bolts onto the road) and ever since can hear what i think is a bearing shell clunking around in the sump.
no oil pressure since i got off the hume to my house (outer east) and the motor would not idle once i got off the freeway. the drive home took over 6 hours, spent most of it at 40k in the emergency lane keeping the revs and load as low as possible so it would make it home. fun times.

only good part about it was the water temp never budged.



edit: best time of 1:59 with almost zero rear traction all day but there is definately a lot more in it with better tyres

[gianttomato]

I would keep it 3 litres. Dropping the stroke to 85mm by using a 5M crank (I'd suggest a 5MGE crank) will result in a lower comp ratio and negate so many of the positive modifications you have already made.

Definitely look at better oil control in the sump - check some of the threads on sump baffling. Consider an Accusump to iron out the blips.

I know you don't want to go 2JZ but it's a whole generation better. The clutch is the same - you'd just need to source a front sump, bellhousing and flywheel. You could mount it using JZX81 mounts, and you can buy ebay extractors for the fuckers. It is a square motor already, base head flow craps on the 7M, the buckets are 31mm (rather than 28mm) so you can get a shedload more cam profiles to work with it. If you're keen, you can get a VVTi variant and get that to work with your standalone (if it allows). With just ITBs, my peak power moved from 5000 to 6600 - made 148 rwkW.

I have a pile of 2JZGE intake manifolds you can have for nada so you can mock up your triples.

[crowncustom]

As it is with the 5M crank it runs a small diameter nose compered to the 7M.The stroke is 85mm and the 7M is 91mm.The 5M doesnt have the extra water jackets on the inlet side of the block like the 7M has.The 5M has a blank on the inlet side of the block facing where the 7M has the same but it is not blanked off,I pressume by what I can see is that it is an extra oil drain.The 5MG crank is basically identical to the 7M except that it runs a 22mm wide No.1 main bearing where the 7M and 5M runs a 25mm wide No.1 main bearing,and is also a 85mm stroke.M,2M,4M and 5MG run the 22mm wide main bearings from 1 to 7,5M and 7M run these from 2 To 7.
If you need any more specs I have complete 4M,5M,5MG and 7M in my collection.
Cheers Brett.

[andrew_mx83]

well i have decided to at least give it a go, will be grabbing ryley's old 5m short block in the next couple of weeks.

once i have the 2 motors side by side will have a look and see what i can use, ideally i would bolt my head onto the whole short block but if they are not easily compatible i will look at getting the 5m crank/rods in there.

compression wise im shooting for 11-12:1 either way so will likely have to go custom pistons (depending how far down i can deck the head & block). will have to cc it all up and see what it comes out with then decide where to go from there.

will investigate dry sumping it otherwise just baffled & pump upgrade +cooler etc

gotta start calculating choke & venturi sizes to get the powerband right and also getting the intake length setup for top end (probably shorter than i had originally planned)

thanks for the offer gianttomato, but i really wanna see what i can do with the 5/7m. i also like the idea of having something different and fairly unique. also i am running the small diameter m series clutch so would have to replace that too.


at this stage i will be looking at 84.5mm bore and 85mm stroke = 2.9 litres.

[gianttomato]

Maybe get the block tested...see if you can take it out to 86mm bore. RB30/2JZGE/3SGE pistons could work then.

Compare the specs with 7M pistons in the ACL catalogue.

[RyleyMA61]

keen to see how this goes!

GT when I get my ITBs I'll come knocking for an old dunger 2JZGE intake runner set

[gianttomato]

Just checked catalogue - RB30E piston could work very nicely. Deck height 32.10mm vs 7MGE deck height 32.40mm. Also just a nice little high top to bump up the compression a taddle. Only problem is the gudgeon pin diameter 21mm vs 22mm - I suppose you could bush down the small end.

Also gives capacity of ~ 2962cc

[andrew_mx83]

i believe even 85 is a stretch, but i will certainly look into it. 86 would probably bring it back out to nearly 3 litre. plus im sure i would be able to find a set of rb30 forgies for cheap

thanks for the tip!

actually ill just grab an rb30 jobie off a mate and have a look.

im getting a bit excited to make this happen now, still have to get the dead motor out over the weekend and sus it out. even if i can get away with just putting big end shells in it i will put it back in and build up the hybrid separately, as i have a spare 7m head just sitting there anyway.

[andrew_mx83]

thanks heaps for that info GT, i couldnt find that data with a quick look through the acl catalogue. bushings and machining etc is not really a problem as the old man is a pretty switched on engineer and we have a lathe and a basic machine shop in the shed to make things in.


will def look into a big overbore and will get a piston to sus out.

[amichie]

Have you considered maybe building a big valve 7M ported head with bigger cams etc and running that on a healthy 7M bottom end. It would most likely yield better results.