7A block/bottom end. Relative vs abolute strength. Options

[Jehuty]

I'm interested in the 7AGE setup, and there is some good info out there, but it's vague in some spots...

Specifically, about strength of the block and bottom end of the 7AFE. Most refferences to the strength of these parts is stated relative to the 4AGE. For example, the fact that the 7A block has less ribs than the 4A, or that the flywheel bolts up with less studs. Yeah, great. It's not as good as the 4A, but what does that mean? I want to know what the actual rev and boost limits are.

Reason is that altho the (7A) block, crank, rods and pistons are all stated as being weaker than the 4A counterparts, the only parts that looks really "weak" (in absolute terms) to me are the pistons. The rest looks like a pretty stout little engine. Am I correct?

So if anyone knows where I can find some info about the rev and boost limits of the 7A (or the 4A for that matter!) please help me out! First hand experience from anyone who's blown a few would be nice too. Heck, I'd even appreciate a little heresay. ;)

[playr158]

PM frouto he knows about it alot...

but i'm goin to guess if you replace the pistons with forged low compression pistons and have a really good fuel managment and components then you can rev o maybe 8k?

[Kwanza26]

I've blown up a 7AFE before. I've blown up 4AGs before also...


The 7AFE is not as strong as the 4AG by a whole lot. If you just compare the size of the rods, you'll see the 4AG rods are significantly beefier in relation to their journals sizes. The 7A rod is slightly larger than the 4A rod, but it doesn't have as much actual "meat" as the 4A rod (with respect to the journals). I personally feel the stock 7A bottom-end is however, strong enough to make a reliable 7AGE and spin at 7500 rpms reliably. It's a well designed bottom-end with a decent rod-stroke ratio. Things such as flywheel bolts and and ribs doesn't make a huge difference. The weakest part of the 7A is the rods. Forget what Toysport says about hybrids (they don't know what they're talking about)... The rods is what will fail first if you try to rev that block too high. They tuners on toymods.org.au will say the 7A block can only do around 7200 rpms stock... but I personally would push as high as 7500 rpms. The Euro spec 7AFEs fuel-cut at 7000 rpms... so It's fair to say, a little above that should be ok. To be safe... 7200-7500 rpms is the stock limits of the 7A bottom-end. With re-worked stock rods, 8000 rpms is do-able.

As for boost... it all depends on tuning. I wouldn't try do more than 15psi on the stock rods and pistons, but with upgrades, it can handle it. It's all about tuning. When it comes to boost, the weakness of the pistons is more obvious. 15psi is really really pushing the envelope on stock bottom-end, but I feel with good tuning and proper fuel upgrades, the 7AFE can do it. I wouldn't do it as a daily driver, but it can hit 15 psi for some weekend fun. Regardless, anytime you look to do a 7AGE, you're gonna want to replace the pistons with 4AG pistons. The later model 4AGEs with 20mm wrists are direct swaps into the 7A bottom-end. With 4AGZE forged low-comp pistons, boost levels can be significantly increased...

Again, anytime you're looking to do a 7AGE, you'll have to use 4AGE pistons. The reason being, the 7AFE pistons are dished so compression will suffer when the 7A bottom-end is mated to a 4AGE head. When 4AG pistons are installed along with the 4AG head however, the increased stroke ratio of the 7A block will increase static compression of the 4AG pistons. Say for example, 4AGE pistons rated at 10:3:1 (smallport 4AG) in a 4A block will make 10:3:1... but when in the 7A block with the longer stroke, it's estimated to be as high as 11:5:1. Big difference. The 7AGE is a decently well documented set-up, so search a bit and learn. Frouto is the only Celica guy to do it (his is turboed) and as I warned him before about the wiring, I'll warn you. Try to get either a JDM AE86/AE92 MAP harness, or a 92 USDM Geo Prizm GSI MAP harness. It'll make tuning the engine a WHOLE lot easier. frouto didn't do this and now he's redoing a bit of his wiring because the stock AFM set-up is not very tuneable.

This post has been edited by Kwanza26: Jan 5, 2005 - 9:59 PM

[Jehuty]

Yeah, I found myself at odds with Toysport's advice. Reminded me of Mazdatrix back in the day... "No that's not feasable. Leave your car alone."

Anyhow, thank you thank you thank you for all the advice. I tried the search and I didn't quite find what I was looking for. I did, however find the conversation between yourself and Froutou when he was considering is head swap.

He was plannig to use an emanage and you recommended against it. However Im still not quite clear on why. The emanage will allow use and tuning of a map sensor on the 4a head, correct? Or is the 7A ecu too limited? Maybe I should go find that thread and read it again....

One more question... you mentioned "reworking" stock rods. Are you reffering to a standard strengthening process, like shot peening?

Thanks again for taking the time with your replay. The reason I'm not entertaining the idea of a straight swap is that I hope to one day have my own firsthand knowledge like that. I want to build and tune an engine myself. I'm tired of paying other people to do this sort of stuff. I understand the principles anyhow, I just need to DO it. I figured building a 7AGE hybrid on a stand over time would be a good place to start, since it's about the epitomy of a standard hi-po dohc. Not too pricey either. =)

[Kwanza26]

Yeah, I found myself at odds with Toysport's advice. Reminded me of Mazdatrix back in the day... "No that's not feasable. Leave your car alone."

Yeah... they're just guessing about the 7A...

Anyhow, thank you thank you thank you for all the advice. I tried the search and I didn't quite find what I was looking for. I did, however find the conversation between yourself and Froutou when he was considering is head swap.

He was plannig to use an emanage and you recommended against it. However Im still not quite clear on why. The emanage will allow use and tuning of a map sensor on the 4a head, correct? Or is the 7A ecu too limited? Maybe I should go find that thread and read it again....

I was actually warning him against using the AE86 harness in general, as he did. I was trying to tell him even with eManage, he won't be able to tune his car, and that's what happened... The donor harness he used was the AE86 Corolla GTS harness, which is AFM based. It's one of those odd ones that don't read out voltage in the "piggyback range" or a range where piggybacks can intercept. It's all said and done now... no use going over it again.

One more question... you mentioned "reworking" stock rods. Are you reffering to a standard strengthening process, like shot peening?

Yes... production casting creates weak spots in the rods and cleaning up those spots will essentially strengthen them. A google search can probably explain it better than I can.

Thanks again for taking the time with your replay. The reason I'm not entertaining the idea of a straight swap is that I hope to one day have my own firsthand knowledge like that. I want to build and tune an engine myself. I'm tired of paying other people to do this sort of stuff. I understand the principles anyhow, I just need to DO it. I figured building a 7AGE hybrid on a stand over time would be a good place to start, since it's about the epitomy of a standard hi-po dohc. Not too pricey either. =)
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No problem... good luck. If it's a well placed question with decent research done... I have no problem with going into detail... ;]

[doGGy]

you can find lots of and lots fo good info about 7AGE project on www.club4ag.com These guys do this conversiont into they AE86, so there was lots of documentary..

[frotou]

Yeah , the weak point of the 7a is the rods. Kwanza is right , don't rev over 7500 and something around 12-15 lbd of boost , for safety shot peened oem or get pauter (this is my negligence on my engine). It was my mistake to try my hybrid run with the afm ecu but never I was told that this ecu wasn't compatible with any piggyback. I'll do a lot better this year.

Claude

[FallenHero]

it's been a while since I took over another persons thread....

Hey guys. Do you forsee any problems in the 7ag if one were to use formula atlantic valves? Would the torque numbers suffer at all?

Just thinking outloud.

[Kwanza26]

it's been a while since I took over another persons thread....

Hey guys.  Do you forsee any problems in the 7ag if one were to use formula atlantic valves?  Would  the torque numbers suffer at all?

Just thinking outloud.
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Bigger valves = more induction = less velocity = more top-end power = slightly less low-end grunt. This applies only for an n/a set-up though.

[FallenHero]

so the small port head would still be a good thing. But the big port with the HUGE valves would make hella high RPM power... Low end.. with the mods planned would still be better than it is now i would think...

[Jehuty]

it's been a while since I took over another persons thread....

Hey guys.  Do you forsee any problems in the 7ag if one were to use formula atlantic valves?  Would  the torque numbers suffer at all?

Just thinking outloud.
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I don't think it would be driveable, really. I think Formula Atlantics are like 240 hp, so the engine must be getting up arond the 11000 rpm level to spin that kind of power out of 1.6 liters. Not that that means anything in and of itself, but the profile of a 1600 making that on the track is radically different than your average -or even buil-t 7age setup. To acheive breathing at that rpm the cams, inlet valves, exhaust vales, induction system, and exhaust would be tuned way out of spec for a "normal" engine. Not to mention things that could be different like compression. Heck, those things might be set to idle at 2000 rpm for all I know. (meaning the ECU would possibly be lacking maps below that range.) Throw in the fact that the tuning most likely has no accounting for emmisions...

On the other hand, I have heard of Spoon making 1600 bseries taht can turn 11 and subsequently make 240hp and are supposedly streetable. But they have the big advantage of VTEC to work with. And Im sure they're still no peach to drive on the street.

[playr158]

1.6 lite
its a 1.8 7afe so you know cause 1.6 is the 4age
and it think you wouldn't wanna rev that high cause the bottom end can't take it as we said 8k rpm at a good build.....

and small port is better IMO don't get the vavles

[FallenHero]

the 7a I am parts gathering for will have a fairly well built bottom end. I guess keeping the valves at the stock size would yield more drivability. A good set of cams will be involved though.