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Thread: 4AGTE compression ratio

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    Default 4AGTE compression ratio

    Looking to see what compression ratios people are running on their 4AGTE's. Looking for reliability over peak performance.
    I've got a small port with stock internals asides from ceramic coated N/A slugs. Using a Microtech lt-9c for management with yaris cops, gt2560 running 16 psi. Recently blew the head gasket and I want to give a cometic mls gasket a run. I just need to know what ratio I should be aiming for so I can determine the gasket thickness I need.

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    Olde mechanic Carport Converter oldeskewltoy's Avatar
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    Default Re: 4AGTE compression ratio

    Quote Originally Posted by Murvz View Post
    Looking to see what compression ratios people are running on their 4AGTE's. Looking for reliability over peak performance.
    I've got a small port with stock internals asides from ceramic coated N/A slugs. Using a Microtech lt-9c for management with yaris cops, gt2560 running 16 psi. Recently blew the head gasket and I want to give a cometic mls gasket a run. I just need to know what ratio I should be aiming for so I can determine the gasket thickness I need.
    While very good for setting squish gap, the Cometic can "leak", it happens more often with boost. You might look at a "stopper" type gasket. You can ask Barry @ MRP - https://www.mrpltd.co.nz/product/cus...s-gasket-4age/ (read description)

    You are planning on running N/A pistons? They have a flaw.... (see piston on right)



    If you want to keep compression high, I'd recommend a custom piston, if you can tolerate a lower compression, the 2nd gen 4AGZE pistons, along with a thinner gasket, and machining the head can get you close to 10:1.
    Information is POWER... learn the facts!!

  3. #3
    Junior Member Backyard Mechanic
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    Default Re: 4AGTE compression ratio

    I think you can run a bit higher static compression with e85. What fuel do you plan to use?

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    broken down ex guru Chief Engine Builder feral4mr2's Avatar
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    Default Re: 4AGTE compression ratio

    9.5-10 is the norm for 4agte's now days, higher safer with e85.

    Using a mls headgasket the surfaces need to be prepped correctly, i've never had any issues running the trd 0.8mm ones that are readily available. https://www.mrpltd.co.nz/product/trd-4age-16v-0-8mm/

    Even though over the years i've had no issues with stock head bolts, ARP head studs are the go and I use them on all my builds now.
    https://www.mrpltd.co.nz/product/arp...head-stud-kit/

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    Default Re: 4AGTE compression ratio

    I was happy with power I was making on pump fuel (180kw atw) so not looking at e85 anytime soon. I didn't build the engine and I've been going through the receipts I got with it. It seems old mate had the deck shaved and put a standard head gasket back on thus raising the compression ratio. My theory is this is why the head gasket failed. I'm on a bit of a budget and don't really won't to strip the block. My plan is to run arp head studs and a decent head gasket. I'm just worried about knock if the compression ratio is too high. 10:1 is around the standard ratio for small port if I'm not mistaken? What additional risks do I run keeping the n/a slugs?

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    broken down ex guru Chief Engine Builder feral4mr2's Avatar
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    Default Re: 4AGTE compression ratio

    Shit, 180rwkw is alright. My old smallport 4agze based gte (8.9:1 c/r with a 0.8mm hg = ~9.4:1 c/r) @18psi from a gt2554r only did 142rwkw.

    Yeah 10.3:1 is na smallport 4ag c/r. If tuned right it shouldn't matter what your c/r is imo for detonation. Margin for error is a lot less though.
    Stock 4agze hg with arp studs has been proven to work well with boost, less prep needed on mating surfaces too. https://www.mrpltd.co.nz/product/4ag...e-head-gasket/

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    Default Re: 4AGTE compression ratio

    Well I'm starting to think now that as it was tuned already with the stock head gasket without knock issues, it may be worth keeping the same gasket thickness. I'll measure to make sure the mating surfaces are all still within tolerance. One question I have, to the torque specs change when using arp studs or do you still torque to the same oem tolerance?

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    broken down ex guru Chief Engine Builder feral4mr2's Avatar
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    Default Re: 4AGTE compression ratio

    Quote Originally Posted by oldeskewltoy View Post

    You are planning on running N/A pistons? They have a flaw.... (see piston on right)


    Is that piston on the right an oem smallport piston oldeskewl? I don't remember my oem smallport na pistons having a slot like that.


    One question I have, to the torque specs change when using arp studs or do you still torque to the same oem tolerance?
    ARP have their own torque specs.

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    Junior Member Backyard Mechanic
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    Default Re: 4AGTE compression ratio

    ARP product usually comes with both the assembly lube for under the heads and the torque specs or procedure included, and its also in a library on the arp site.

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    Junior Member Backyard Mechanic jondee86's Avatar
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    Default Re: 4AGTE compression ratio

    Quote Originally Posted by feral4mr2 View Post
    Is that piston on the right an oem smallport piston oldeskewl?
    For the curious, here are a couple of pics of a 100% genuine Toyota smallport piston as pulled from a low mileage JDM import engine...





    Didn't remove the rings but you can clearly see the slots on the inside.

    Cheers... jondee86

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    Default Re: 4AGTE compression ratio

    Cheers for all the feedback. With regards to arp heads studs, do they make m10 kits that screw straight into the standard bolt holes or do you have to drill and tap to fit the m12's?

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    broken down ex guru Chief Engine Builder feral4mr2's Avatar
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    Default Re: 4AGTE compression ratio

    The ones i linked above are to suit the standard block/head.


    Thanks jondee86, it's been a long time since i had my hands on the smallport slugs.

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    Olde mechanic Carport Converter oldeskewltoy's Avatar
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    Default Re: 4AGTE compression ratio

    Quote Originally Posted by feral4mr2 View Post


    Thanks jondee86, it's been a long time since i had my hands on the smallport slugs.
    thank you too..
    Information is POWER... learn the facts!!

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