7AG - a few questions

[eightsixboy]

Hi all,

I have been thinking about going a 7AGE for an "easy" torque increase with my smallport instead of going turbo, main reasons being cost and less cop bait.

I have read the threads on here about building a 7AG but there isn't any real data (so to speak) or info on exactly what C:R you get with stock 7A pistons, and a lot of the info is conflicting. Some say under 9:1, some say around 9.5:1 etc etc

From the threads on here I have gathered that when using stock smallport pistons you have to use a headgasket over 1.0mm or the C:R will be upwards of 12:1 or higher.

This has me thinking, why not just use a stock 7AFE bottom end with stock 7A headgasket (0.6mm?) and shave the GE head and/or deck the 7A block?

The only issues I can see with this might be, insufficient piston to valve clearance and that the pistons aren't designed for the head.

Thoughts?

[xero]

this is a 7afe piston:


this is a stock smallport piston:



if you decide you suddenly need a 7a now there will be minimal compression change. at best you MIGHT get 11:1 compression, at worst the same as before.
using a thinner headgasket wont give you a massive increase in compression, hell you could deck the block and head 1mm with a TRD 0.8mm HG and still not get near 12:1 compression ratio if you went with a 7a.
in reference to the headgasket thickness this will have a poofteenth of effect on the compression ratio, HOWEVER if you use a factory 4age (1mm) or 7afe (0.7mm) thickness gasket you will now have an INTERFERENCE engine. this means that if your timing belt snaps or skips you will bend valves.
piston and valve design with the head are nothing to worry about, the 16v and 7a head have very similar combustion and valve chambers meaning which ever pistons you used there will still be clearance (interference not-with-standing)

i suggest you go back and re-read the 7a info out there as this has all been covered many times and in 5 mins of googling i confirmed all your questions.

[eightsixboy]

this is a 7afe piston:


this is a stock smallport piston:



if you decide you suddenly need a 7a now there will be minimal compression change. at best you MIGHT get 11:1 compression, at worst the same as before.
using a thinner headgasket wont give you a massive increase in compression, hell you could deck the block and head 1mm with a TRD 0.8mm HG and still not get near 12:1 compression ratio if you went with a 7a.
in reference to the headgasket thickness this will have a poofteenth of effect on the compression ratio, HOWEVER if you use a factory 4age (1mm) or 7afe (0.7mm) thickness gasket you will now have an INTERFERENCE engine. this means that if your timing belt snaps or skips you will bend valves.
piston and valve design with the head are nothing to worry about, the 16v and 7a head have very similar combustion and valve chambers meaning which ever pistons you used there will still be clearance (interference not-with-standing)

i suggest you go back and re-read the 7a info out there as this has all been covered many times and in 5 mins of googling i confirmed all your questions.

Are you sure the top pic is 7A pistons? They look like small port pistons, same as the lower pic. I am 99.9% sure all 7A pistons are dished like a ZE piston.

From all the info I have seen if you bolt a 4AG head straight onto a 7A block you will end up with around 9.0:1 C:R and if you use 4AG pistons in 7A block you will end up with around 11.5:1 with a .5mm head gasket, over 12.0:1 with BT pistons.
http://forums.club4ag.com/zerothread?id=6433

I'm more trying to find info on using stock 7A pistons and getting them to work, as some people say smallport pistons fit fine with no mods needed while others say they need machining to fit the pressed in type pin the 7A rods use, some just use aftermarket rods completely.

I'm thinking along the lines of shaved 4A head and possibly decked block to, but not sure if the valves with touch the pistons or not.

[oldeskewltoy]

don't guess.......... DO THE MATH!!!!

high comp(10.3 to 1) pistons have a dome(+) of .2cc,
low comp pistons have a dish(-) of 3.8cc.
stock bore 3.189
stock stroke 3.366
4AGE chamber stock 36cc


now here is where the numbers get vague... when you use a 4A piston on a 7A rod, the piston is about .6mm below the deck of the block. You can either use a very thin gasket (.4mm)... OR get the block machined so the piston is flush with the top of the block. Then you use a 1mm gasket. Either way... using a low comp 4AGE piston in an otherwise stock 7A block, with 1mm of squish and you have a 10.7 static compression ratio.

Squish = final distance between piston edge and flat area of head when the piston is at TDC.

Here is an ITM 4AGE piston low comp with a 3.8cc dish


7A pistons

ITM


Other 7AF piston... similar to compare

DNJ - http://www.rockauto.com/info/190/P933.jpg

So although I don't know what the 7AF piston volume is... I do know it is a LOT more dish(-) volume then a low comp 4AG piston with a 3.8cc dish volume.

[xero]

don't guess.......... DO THE MATH!!!!

high comp(10.3 to 1) pistons have a dome(+) of .2cc,
low comp pistons have a dish(-) of 3.8cc.
stock bore 3.189
stock stroke 3.366
4AGE chamber stock 36cc


now here is where the numbers get vague... when you use a 4A piston on a 7A rod, the piston is about .6mm below the deck of the block. You can either use a very thin gasket (.4mm)... OR get the block machined so the piston is flush with the top of the block. Then you use a 1mm gasket. Either way... using a low comp 4AGE piston in an otherwise stock 7A block, with 1mm of squish and you have a 10.7 static compression ratio.

Squish = final distance between piston edge and flat area of head when the piston is at TDC.

.

THANK YOU OST!!

so there you have it, with a smallport piston on a 7a rod you will have just over 11:1 compression which is still very much on the safe side of compression (no more than a BT20V).

the wrist pins on both a 7a and 4a are press in.

[eightsixboy]

THANK YOU OST!!

so there you have it, with a smallport piston on a 7a rod you will have just over 11:1 compression which is still very much on the safe side of compression (no more than a BT20V).

the wrist pins on both a 7a and 4a are press in.

AFAIK all 20mm 4A pistons are fully floating pins, only the 7A pistons are pressed in. This is why I was asking about using 7A pistons instead.

OR if you need to modify the 4A pistons take take the pressed 7A pin or not.

This is what I meant by some people saying they fit without machining and others say they dont need machining to accept the pressed pin.

[trdee]

I thought 4A pistons are floating type from the second gen bigport onwards?

[eightsixboy]

don't guess.......... DO THE MATH!!!!

high comp(10.3 to 1) pistons have a dome(+) of .2cc,
low comp pistons have a dish(-) of 3.8cc.
stock bore 3.189
stock stroke 3.366
4AGE chamber stock 36cc


now here is where the numbers get vague... when you use a 4A piston on a 7A rod, the piston is about .6mm below the deck of the block. You can either use a very thin gasket (.4mm)... OR get the block machined so the piston is flush with the top of the block. Then you use a 1mm gasket. Either way... using a low comp 4AGE piston in an otherwise stock 7A block, with 1mm of squish and you have a 10.7 static compression ratio.

Squish = final distance between piston edge and flat area of head when the piston is at TDC.

Here is an ITM 4AGE piston low comp with a 3.8cc dish


7A pistons

ITM


Other 7AF piston... similar to compare

DNJ - http://www.rockauto.com/info/190/P933.jpg

So although I don't know what the 7AF piston volume is... I do know it is a LOT more dish(-) volume then a low comp 4AG piston with a 3.8cc dish volume.

I did the math if using 7A pistons on a undecked 7A block and unshaved 4A head (assuming 36cc). And the figures reckon what the consensus is of around 9.0:1 or prob just under.

I know some people who have done this ie;completely stock 7a bottom end with 4ag head, and no issues regarding interference.

BUT, I am more concerned with one with a shaved head and potentially a decked block as well. With a fair amount taken of the head you could get comp to around 9.5:1 or slightly higher and decked block over 10.0:1 which is probably ideal. My only concern is Piston to valve clearance.

If the 7A pistons are similar to low comp 4AG ones, why not just use the 7A pistons? If I were to use 4AG pistons it would have to be smallport as I have to motors I can take them from. Really the only issue I have with using 4A pistons is just unsure if you need to machining them to take the pressed pin or not. The other option is to go spool rods, but that blows the budget completely.

BTW the 7AFE pistons are meant to sit .6mm below flush as well, from what I have searched, but have a dish of -12, so I would assume similar to GZE pistons?

[eightsixboy]

I thought 4A pistons are floating type from the second gen bigport onwards?

Yes they are, so the only 4A pistons you can use in a 7AGE are fully floating, the early bigport ones are 18mm and can't be used.

But 7A pistons are pressed in, and 20mm pins like smallport, ST and BT pistons.

[oldeskewltoy]

because the wrist pin is fixed inside the rod of a press fit, you can use floating pistons in a press fit application.....

I'm doing it right now... I'm rebuilding my AE82 4AGE, it uses the "small" 40mm rod journal crank. I've had the small end of the rods (18mm) enlarged so now it accepts a 20mm press fit. I'm using aftermarket (Rock auto) 4AGE high comp(10.3 to 1) pistons. So we are using a floating piston on a press fit rod.

In my engine, because of the weakening of the rod to fit the bigger pin, I'm only running stock cams and stock engine management

I did the math if using 7A pistons on a undecked 7A block and unshaved 4A head (assuming 36cc). And the figures reckon what the consensus is of around 9.0:1 or prob just under.

What is the volume of a 7A piston then???? WHERE did you get this information???

When you do the math in a compression calculator... negative and positive get reversed So if calculating a high comp 4AGE piston you put in negative .2, if using a low comp 4AGE piston you put in a positive 3.8


F head volume is 30cc

[eightsixboy]

because the wrist pin is fixed inside the rod of a press fit, you can use floating pistons in a press fit application.....

I'm doing it right now... I'm rebuilding my AE82 4AGE, it uses the "small" 40mm rod journal crank. I've had the small end of the rods (18mm) enlarged so now it accepts a 20mm press fit. I'm using aftermarket (Rock auto) 4AGE high comp(10.3 to 1) pistons. So we are using a floating piston on a press fit rod.

In my engine, because of the weakening of the rod to fit the bigger pin, I'm only running stock cams and stock engine management



What is the volume of a 7A piston then???? WHERE did you get this information???

When you do the math in a compression calculator... negative and positive get reversed So if calculating a high comp 4AGE piston you put in negative .2, if using a low comp 4AGE piston you put in a positive 3.8


F head volume is 30cc

OK awesome, this is what I wanted to know about the pins. As I would be doing it all myself (bar head shave) I just wanted to be able press the pins in the pistons if I used my smallport pistons.

I got the info after googling 7AFE compression or something. There seems to be a lot og guys in the U.S who must have these motors in celicas and stuff, there was a guy building one up and he had actually Toyota literature with most of the info and he also took measurements.

From the measurements he took the dish was around .12cc and the piston had a deck height of -.6mm.
http://www.6gc.net/forums/index.php?...4&#entry961144

After using a whole bunch of different compression calculators I can't get any of them to show stock 9.5:1 with stock 7A measurements, I think most of them are inaccurate.

After reading one of the guys threads on AE86club I might stick to using Smallport pistons, I think any lower comp then around 11.0:1 will be a bit fail with a 7AG. I was hoping that wouldn't be the case but he only made around 78rwkw with around 11.4:1 comp (stock ecu, stock BP head).

[oldeskewltoy]

the link you posted doesn't seem to work....... now does... nevermind

simple math shows piston volume for a 7AF to be close to a 16cc dish.

BIGGEST problem with 7AG engines is getting cam timing correct. you need either a re-grooved drive/crank sprocket... Or you must use a piston stop to confirm TDC. This is because you CAN'T use the factory timing marks because they are wrong when you mix the 4AG sprocket and the 7A crankshaft

the local race shop who does some of my valve jobs... regularly make 260 crank hp(about 220 @ the wheels) with their 7AGs... they run about 11 to 1 compression in their builds, run cams about 275 degree, and run a full on Atlantic head.

As to checking if the press fit is good... you want the wrist pin .001" larger then the small end of the rod... heat the rod, cool the pin and put them together. once they equalize the pin will not move

[trdee]

you're never gonna make decent power with a stock top end and stock ecu. wont happen. you need cams and aftermarket management.

[eightsixboy]

you're never gonna make decent power with a stock top end and stock ecu. wont happen. you need cams and aftermarket management.

What in your opinion is decent power?

I'm a little confused to be honest with the numbers people are getting with there 7AG's. Was reading last night some guy got around 78rwkw just by bolting a stock 4AG head (think bigport) onto a stock 7A bottom end. While this guy in the link with a much much higher comp and better moded/built motor only made 82rwkw. I know he is only running stock ecu but that's not much more power then a stock smallport.
http://www.ae86drivingclub.com.au/fo...-HAWWWWT-STUFF

I am yet to see any accurate torque figures as well, the dyno graphs I have seen of 7AG only show kw/hp but not the all important torque.

[trdee]

I think you misunderstood me. My post was in response to you sounding disappointed that a stock bigport head on a 7A with a small bump in compression made only mildly more power than a stock bigport. It sounds like you expect the 7A to give you a big bump up in power with nothing else done to support it. It wont. If you want to make significantly more power than stock (if you want a number, then lets say 100 or more kw at the wheels) then the only way that is going to happen is with cams, compression, and an ecu.