4AGE Blacktop Rods, Do they really break easily, or is it mistreatment?

[wiso]

I ask because I am finally putting a new 4age 16v bigport together properly rather than doing a slapper like i previously did. I aim to keep it very close to stock but want to do some tasteful mods to try and maximize the the drive ability from the stock engine.

I have searched around about found some people who have broken them from limiter bashing. So of course everyone now says they are weak and break and should not be used.


I am building this 4age 16v with 0.5mm oversized 9.4:1 pistons, stock head (with the casting marks smoothed out) stock valve train, TRD0.8 headgasket, stock crank but using a blacktop stock flywheel (about 5.7kg).

I intended to use a set of blacktop rods that I picked up in an effort to try to make it lighter. Now obviously with the setup I am using its never going to break 8000rpm, hell 7700 is rev cut on stock ecu (which I don't intend to change out) and will only have less than a 10:1 compression ratio.

So realistically am I likely to see any real issues in using these rods? the car is intended for weekend/club racer, so most likely only really a half dozen track days each year. I have never ever limiter bashed a car so I don't see that as an issue coming up.


the engine builder I have doing the work looked at me in horror when I gave him the blacktop rods vs the stock late bigport rods. But the car is NEVER going to see boost or anything crazy power wise. I am trying to keep it stockish to keep it quite reliable, but going for drivability rather than power

I also intend to get the rotating assembly balanced.

cheers for any advise

[kiwi]

Blacktop rods are fine. While lighter I would say they are ok for your usage. Know a guy with a blacktop in a 82 which hits 8,200rpm daily and its been over a year on stock engine including 5 or 6 track days with no rod issue.

Was thinking about blacktop rods in my silvertop but decided against it as purchased a pre-tuned engine.

[dnegative]

I took my 16v rods to 8200rpm quite a few times, no issues but that's on the limits limit for the bolts.
Its the bolts that give before the rod breaks as far as I can tell, 20v blacktop rods are good for 8200rpm from the box, they will do 7800 no worries.

[Sam_Q]

As above, the rods should handle your rev limit all day. However they have a larger big end than your crank allows so you can't use them unless I am missing something.

[wiso]

yes you are missing something. its a aus delivered AW11. and they all got the 7rib bigports with 42mm cranks and 20mm pins.

thats a bit of a load off my mind. there are a few threads out there with broken rods but they seem to come from bolts going. there is alot of hear say about them cracking around the pin but i couldn't really find any threads where this had happened.

[Billzilla]

As above, the rods should handle your rev limit all day. However they have a larger big end than your crank allows so you can't use them unless I am missing something.

This.
Bigport crank is 40 mm, 20v blacktop crank is 42 mm so they won't fit.
I'd rather lighten the 40 mm crank a little, get it balanced, and use the 40 mm rods.

[oldeskewltoy]

I'd rather lighten the 40 mm crank a little, get it balanced, and use the 40 mm rods.

lightest stock internals...(over 2 kilos lighter!) Fully capable of 8200 rpm (with a proper crank pulley)







And by getting "cheater" wrist pins you save almost an ounce per rod on reciprocating mass

[BLK_20v]

the rods are still strong enough to punch a hole in both sides of the casting...

[Sam_Q]

nice pic but I don't think it means much, I am sure even aluminum con-rods could do that if the engine had a few revs behind it

[wiso]

I do remember seeing a thread with an engine that looked alot like that, if I recall the engine was limiter bashed as it was used for drifting, it was also a backyard slapper. If I recall the cause of the rod going was the nuts came loose or the bolt snapped or something.

[bermy]

This.
Bigport crank is 40 mm, 20v blacktop crank is 42 mm so they won't fit.
I'd rather lighten the 40 mm crank a little, get it balanced, and use the 40 mm rods.

I don't know about Aus but here, late 1987 to 1989 MR2 use a bigport 7 rib block with a 42mm crank, no oil squirter though...

Come on, use a lighten 40mm crank in a 7A-FE bloc with E15ET rods and start having fun