7AGZE bottom end question

[nick.parker]

Hello,

If low comp factory 4AGZE pistons are used in a 7AGZE hybrid (7AFE bottom end) onto of standard length 7A rods, do the pistons line up flush with the top of the block deck?

Some time ago, IIRC I saw a picture some time ago showing that standard 7AFE pistons sit 0.5mm below the block deck in a 7AFE, but I'm not sure about the accuracy of that memory as I cant imagine that would help with having a proper squish area....

Cheers, Nick

[Bazda]

Sits more around 0.7mm. Because of the larger stroke if you have the piston right at the top the compression is going to be alot higher than it was in a 4age.

4agze 8.0:1 piston will be around 8.2:1 with a stock gasket at 0.7m deck height in a 7a. If you made it sit flush its going to be around 8.6:1

[nick.parker]

Thanks for the info. Was trying to calc what CR I would expect. The numbers dont seem too far off :-

bore 82
head vol [cc] 38
gasket [mm] 1.9 (1.2 + 0.7 piston below deck)
stroke 85.5

piston dish [cc] 12.5
swept cyl cap [cc] 451.53
gaskt vol [cc] 10.03

total volume 512.06
Piston @ tdc volume 60.53

CR 8.46
Total Cap 1806.11

[mullett]

You're still at it man? Awesome...need to put up a thread of the MR2!

-RM

[oldeskewltoy]

4/7AF combustion chambers are 38cc???? They seem much smaller than a 4AGE (36.25cc)

[nick.parker]

Yeah Robin, getting a bit itchy to do some more 'tweaking' on the AW. And that 7AFE I bought in a moment of insanity is still sitting around!...since that time a fair few people have proved the 7A a worthy workhorse! I plan to put up a members ride for the AW soon - its been on my mind.

oldeskewltoy - I'd use a 4AGE 16v small-port head.

[PrettyCoolWagon]

Building a 7agze at the moment - just finished stripping down the 7a block. I have a choice to use either early 8:1 GZE pistons or the later ceramic coated 8.9:1 GZE pistons.

It's going into an AE95 corolla 4WD wagon with over sized wheels & slight suspension raise.
Think snowboarding & camping. Not a daily more of a weekender, but driven hard on take off, long drives on highways & freeways, then happily thrashed on bushtracks - mud & snow.

The kerb weights around 1210kg & the 7A engine will be heavier than the original 4afe too. Add to this also I've got a custom alloy bullbar made up that weighs another 28kg's.
Then add in myself plus the occasional passenger(let's say 160kg's together) & some luggage & we're talking roughly around 1460kg's TOTAL ...At other times I'd also be towing a small trailer as well.

Just trying to figure out which piston & head gasket combo I should be aiming for to get the most suitable compression ratio for my needs?

I want the head studs/gasket to last - 'set & forget'

I'm using a clutched SC14 & forged 7A rods. Could possibly fit SC12 pulley...

Depending on the gasket used I've been told:
early 8:1 GZE piston would = 8.5:1 in 7A
&
Later 8.9:1 piston would = 9.3:1

Any recommendations?

[Bazda]

Id go with the 8.0:1 pistons after reading what your wanting to do with the car.

[mullett]

Likewise...I think that would make a perfect engine for what you've got planned, and if you were stuck in the bush you could put 91RON in it. Your biggest issue after that will be gearbox strength! Where did you get the forged 7A rods from?

[PrettyCoolWagon]

cool..

OK.. & what about head gasket thickness & using the SC12 pulley? Any pros or cons there?

I have a 1.65mm gasket from a complete 4agze set
or
1mm Multi Layered Steel
or
0.75mm steel

...

Mullet: Yeah.. I'll set up a switch so I can shut of the super charger altogether if I want to ... so standard fuel would be possible but I'd rather not... I plan on running 98 Octane & carrying extra fuel.

The most affordable forged 7A conrods I could find were from SPOOL imports.
Toyota 7AFE Conrods

There's no issue at all with gear box strength. (AE95 gearbox code is E57F) (rear axle is similar to AE86 but not LSD & uses 4 X 100 stud pattern)
E-series gearboxes are tough as.. shared by many Toyota alltrac makes & models from Rav fours & camrys through to MR2's & the 1994 world rally winning Toyota Celica GTfour ST205,
That had a 2Litre turbo 3S-GTE in it with a compression ratio of 8.5:1.

In 1999 through to 2007 they increased turboed CR to 9.0:1 (Caldina GT-Four ST246) ...So I think the typically over engineered E-series gear box will hold up absolutely fine.

Seeing Bazda's engine build & reading Billzilla's notes on 7A's makes me feel confident the 7A blocks are actually pretty good.
The celica CR's makes me think maybe the 8.9:1 ceramics(9.3 in a 7A) might be ok if I use the 1.6mm thick gasket.....
What CR would I end up with then???

It's probably worth mentioning too that 1st gear ratio is 3.833 ..a very low ratio spread to all four wheels that wouldn't put too much load on the drivetrain
??

[Sam_Q]

There are quite a few reports on Spool rods being extreemly close to their specifications. I can personally vouch for them in having good service.

Although 520 grams is quite heavy you will know they will never ever fail. However it does beg the question of need, a Toyota supercharger is physically incapable of making enough boost to stress these rods so it all comes down to how hard you rev it. I think if your not going to go over 7000 then you will be fine, although an expoert I am not.

I from memory think the compression height on the 7afe pistons is lower so some of the height below the deck is taken up when changing the pistons. In terms of combustion it's always a good idea to have a nice tight quench area so as for I personally suggest the earlier model ZE pistons flush to the deck, a standard 4age gasket and then you should have close to 9:1

[PrettyCoolWagon]

Just heard from the machine shop as I'm getting dowels machined in the flywheel & crank plus oil squirters in the block.
They weren't big fans of the spool rods - calling them 'cheap chinese stuff' apparently the small ends were a bit tapered & required machining. The big ends were about half a thou over size.. so they machine down the flat areas where the big ends bolt together, thus reducing the big end diameter and then re-machine to exact size.
For my needs I think spool rods are fine. Sam- you're right about the revs.. I don't know if I'll rev it above 7thou but you never know..

I ummed & aahed about which pistons and have decided to use early 8.0:1 only because I bought NPR rings for them not realizing you can only get the 8.9:1 rings from Toyota.
I would've liked to have used the 8.9:1's with a thicker head gasket because they're forged, ceramic coated and also have the notches in the skirts to clear the oil squirters.
Now I might have to file these notches into the 8.0:1's and carefully weight each one to ensure even balance

[Sam_Q]

sounds like a good plan

surprising about the spool rods, others have reported extremely tight tollerances

[PrettyCoolWagon]

Yeah.. not sure about this dude (engine machinist) ..found him real pushy, claiming a first timer shouldn't be honing their own block etc. and everything had to be crack tested, balanced etc. handing me an estimate of works just short of 2k...

He might've been right but he didn't explain things in a way I appreciated

See full breakdown of costs here..

http://www.toymods.org.au/forums/tec...e95-sr5-5.html

[oldeskewltoy]

$2k is a lot of cash. I paid a bit more ($2600), but I had a known successful, experienced 4AG engine builder do all the machine work AND very effective porting (my 4age is 145whp & 112#/ft) Sometimes shops will excess quote someone to purposely either lose the job, or make a large profit. I'm not saying either is happening here... but it is something to be aware of.




This should be checked before use... but it may offer some thoughts/solutions...

7A-G, bigport pistons, stock deck height, 7A-FE head gasket = 10.3:1
7A-G, bigport pistons, block decked .024" (0.6mm), 4A-GE HG = 10.3:1
7A-G, bigport pistons, stock deck height, 4A-GE head gasket = 9.7:1

7A-G, smallport pistons, stock deck height, 7A-FE head gasket = 11.3:1
7A-G, smallport pistons, block decked .024" (0.6mm), 4A-GE HG = 11.3:1
7A-G, smallport pistons, stock deck height, 4A-GE head gasket = 10.6:1

7A-G, 8.0:1 early GZE pistons, stock deck height, 7A-FE head gasket = 8.8:1
7A-G, 8.9:1 late GZE pistons, stock deck height, 7A-FE head gasket = 9.8:1

7A-GE with stock 7A block, silvertop pistons and head, 7A 0.6mm HG = 11.55:1
7A-GE with stock 7A block, silvertop pistons and head, TRD 0.8mm HG = 11.48:1
7A-GE with stock 7A block, silvertop pistons and head, 4A 1.2mm HG = 11.35:1


7a @ TDC (using 7A pistons) is in the neighborhood of 0.6mm BELOW the top of the deck.