Stock rods break before a 7AGE reaches the rev limit of a 4AGE.......... throw them away and buy aftermarket ones.
With a dead, ancient, SC12 in my AW11, I've been entertaining the idea of using a 7AFE engine to give me some extra capacity and just going for a small turbo (TD04) to try and retain some of the low RPM torque characteristics of the positive displacement supercharger equipped 4AGZE.
From what I've found on the net, the 7A rods are considered to be pretty weak. Just as wide as the 4A rods, but not as thick as the 4A rods. They are also quite longer than the 4A rods.
So does anybody have any genuine idea of the power limits of the 7A rods when the engine is leant on with some boost pressure?
Obviously keeping knock under control is a prerequisite, and that will be straight forward enough, but rather than wreck a block and a crank with a flailing, broken rod, what would be a safe number to stay below?
My target is a nice and tractable 160ishKW at the wheels. Believable on factory rods?
"Don't worry what people think, they don't do it very often."Originally Posted by oldcorollas
Daily: Glorified Taxi (F6 Typhoon). Out Of Action: Twin-charged Adub. Ongoing Nightmare: Over re-engineered (not) Alfa Romeo 75.
Stock rods break before a 7AGE reaches the rev limit of a 4AGE.......... throw them away and buy aftermarket ones.
Do you have any information that is more specific about rod failure other than "Stock rods break before a 7AGE reaches the rev limit of a 4AGE.......... throw them away and buy aftermarket ones."?
I'm not after revs, I'm after torque. That means I'm after combustion pressure(force).
With a rev limit between 6500 and 7000rpm, can the rods take the force of enough combustion pressure to make my target 160RWKW?
"Don't worry what people think, they don't do it very often."Originally Posted by oldcorollas
Daily: Glorified Taxi (F6 Typhoon). Out Of Action: Twin-charged Adub. Ongoing Nightmare: Over re-engineered (not) Alfa Romeo 75.
Nothing technical, no, but in my mind if they cant handle an extra 1000rpm reliably without failing catastrophically then I would think the chances of them withstanding over twice their "rated" power would be even slimmer.
it' revs not boost that kills these rods, they do seem to be stronger that what people give them credit for. I can't see any issues if you have a 7000 rpm rev limit
Hmmmmmmm, 2 conflicting opinions, I didn't expect that
If I found out that the 7AFE used snap ring retained gudgeon pins, I'll just get a set of Spool rods and put standard pistons in there and go from there. If the pistons use press fit gudgeon pins, I might lower my target (rather than just pointlessly breaking an engine) and build a second bottom end with better rods and forged pistons.
Maybe even Spool's stroker crank and an over bore and a bigger turbo and............
In the mean time, I just need a decent little donk.
"Don't worry what people think, they don't do it very often."Originally Posted by oldcorollas
Daily: Glorified Taxi (F6 Typhoon). Out Of Action: Twin-charged Adub. Ongoing Nightmare: Over re-engineered (not) Alfa Romeo 75.
A very wise tuner once made the comment when asked about the strength of some component:
'It will take a fair bit of horsepower and a little bit of abuse'.
When asked about an uprated forged component the response was similar:
'It will take a lot of horsepower and a little bit of abuse'!
If you are looking for nice tractable power on the street then you will most likely not be intending to build a high rpm screamer so not much abuse from rpm...
As long as you can creep up on the tune carefully or intend to leave it to a professional then you can limit the abuse on that angle too...
I cannot imagine you have too much to loose from what you describe as your goal.
Cheers,
Jason
3TC Compound Turbo 1976 TA23 - Members Ride Thread HERE
479RWHP on 50psi and 70psi hasn't broken her at the track!
from what I have worked out, as samQ says they aren't as weak as people think. everyone says they fail. but from what I have read it doesn't appear they fail from the shaft bending or breaking. it looks like bolts that join the cap onto the conrod stretch/shear/strip etc at higher rpms. because unlike 4age rods they do not have the bolt and nut holding them through, they just have a bolt from the cap into a tapped rod
to get around the 160kw mark your gonna running up around the 17-18psi mark? I honestly don't know how it will take that so I can't help
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00' MR2 ZZW30... Hers
Its not that expensive to uprate the rods. We have custom made rods to suit. At the end of the day if you throw a rod its gona cost you alot more to rebuild the engine. i would rather spend the extra to get it right and last you in the long run.
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1988 Toyota Levin GTZ 10.88 @ 209.57 340kw
Now 9AGTE 410kw atw
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As wiso said their weakness comes from the rod bolts, not the rods themselves. Boost "shouldnt" be anywhere near as much of an issue for the rod bolts as revs would be, but I dont think you will find anyone here that can give you a real quantifiable answer beyond "you shouldnt rev them past 7000rpm or badness happens"
Basically you will have to try it and see.
What Sam Trdee Wiso and Bazda have said are all true as per the forum research I've done, common consensus - it's the bolts not the rods. Keep the rev limiter set to 7AFE standards and you'll be fine.
I researched like crazy before starting a 7AGZE build.
I bought forged rods through spool but would've happily bought through Bazda had I known he was selling them at the time, as the price difference is negligable and he's been good to deal with on other items and... also can give you first hand advice on such a build as well.
Personally I'd say.. Forged rods is good insurance..
If your determined not to fork out for forgies..
There's a thread somewhere with comments from Billzilla (Bill Sherwood) saying they were using stock rods in races over in Asia somewhere to some fairly high revs IIRC they were shot peened though..
I've heard they 'can' break but have never heard of any first hand accounts.., but I have seen first hand accounts (forum threads and photo's) of shearing the 6 flywheel bolts and also ripping out the entire centre of the flywheel. (Same guy over in the states both times)
Press fit hardened steel dowels in the crank to flywheel are used to combat this.
Edit - AND.. ARP flywheel bolts!
Last edited by PrettyCoolWagon; 03-08-2012 at 09:41 PM.
4AFE/gearbox issues, 4AGT/ZE replacement changes to fully blown 7AGTE project...
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If the rod bolts are the issue, then you shouldn't have an issue running boost through it if you keep the rev limit down. Although its true that a decent set of rods is cheaper than a bottom end rebuild, if you're only going to get a used 7A motor thats not going to set you back too much. I'd probably leave it as stock, get the rest of your setup working on a mild boost level, and then save your money for the bits to wind up the revs and boost.
The rods are similar to the blacktop 20v ones.
Fine to swing to 8k or so
There is more load on the rods compared to a 4age. Because of the increased stroke the angles are not really ideal.
1988 Toyota Levin GTZ 10.88 @ 209.57 340kw
Now 9AGTE 410kw atw
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Turbonetics|Custom Coilovers|4/6 Piston custom brake kits|Twin/Triple custom clutch setups|+ MORE
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any know if it's true that the bolts pull out because their not a nut and bolt design?
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