12.5:1 CR GSR as a DD??

ASSISTANCE Hybrids & Advanced Aftermarket Engine Performance
1

Bought this DA GSR as a DD. i was ignorant and still am for the most part about a modified engine and its needs.

Its supposedly running 12.5:1 CR. Head and cams are stock. I have no receipts or boxes or a part # to reference as to tell if its really running that high of a CR. Is there away shy, of removing the oil pan, and inspecting the bottom of the pistons to tell if i have that high of a CR engine?

Can i run a compression test on it, and get a rough estimate? i know 1 bar is equal to 14.7 psi. so in math if i did a comp test i should have a PSI/cylinder of 183.75. is this a reliable way to find CR?

i am running 410cc injectors a high flow AEM fuel rail, stock FPR, stock fuel pump, (will change out fuel pump to aftermarket if i do decide to run E85)

Another BIG debate. Part 1: 92 octane pump gas is somewhat easy to find here. This being a DD should i run pump gas 92 octane and tune it on that. IF I CAN what should i not do while driving it, no wide open throttle, do i stay out of High RPMS etc?

If i CAN run 92 do i NEED timing gears to account for the lack of octane?

Ok here is Part 2 of the question if not 92 what about E85? there are only 2 pumps in a 20 or further mile radius that dispense it, in my area. would this be a better fuel to run the engine on vs. 92?

If this is not a good choice as a DD engine, i am not opposed to selling it and going with something different.

Sorry if this post is somewhat all-over the place. Im just confused, as to what the engine needs to run and last a long time, and as needing a DD what my needs are and how they may differ from the needs of the engine are etc.

any help is much appreciated once again sorry if this post is kinda crazy, my head is so full of things ive heard that contradict each other, etc.

2

[QUOTE=jtkc;2312741]Bought this DA GSR as a DD. i was ignorant and still am for the most part about a modified engine and its needs.

Its supposedly running 12.5:1 CR. Head and cams are stock. I have no receipts or boxes or a part # to reference as to tell if its really running that high of a CR. Is there away shy, of removing the oil pan, and inspecting the bottom of the pistons to tell if i have that high of a CR engine?

Can i run a compression test on it, and get a rough estimate? i know 1 bar is equal to 14.7 psi. so in math if i did a comp test i should have a PSI/cylinder of 183.75. is this a reliable way to find CR?

i am running 410cc injectors a high flow AEM fuel rail, stock FPR, stock fuel pump, (will change out fuel pump to aftermarket if i do decide to run E85)

Another BIG debate. Part 1: 92 octane pump gas is somewhat easy to find here. This being a DD should i run pump gas 92 octane and tune it on that. IF I CAN what should i not do while driving it, no wide open throttle, do i stay out of High RPMS etc?

If i CAN run 92 do i NEED timing gears to account for the lack of octane?

Ok here is Part 2 of the question if not 92 what about E85? there are only 2 pumps in a 20 or further mile radius that dispense it, in my area. would this be a better fuel to run the engine on vs. 92?

If this is not a good choice as a DD engine, i am not opposed to selling it and going with something different.

Sorry if this post is somewhat all-over the place. Im just confused, as to what the engine needs to run and last a long time, and as needing a DD what my needs are and how they may differ from the needs of the engine are etc.

any help is much appreciated once again sorry if this post is kinda crazy, my head is so full of things ive heard that contradict each other, etc.[/QUOTE]

Have you looked at the ecu to see what type of aftermarket engine management is in the car?

The 92 octane should not be an issue if tuned correctly and for that fuel.

If I were you, the first thing I would do is bring your car to a reputable local tuner and have it looked over and then if everything is okay and in good working order, have it dyno tuned. That way for your peace of mind its tuned correctly and for the fuel you want to run. You have no idea what the previous owner did as far as tuning goes and that is the single most critical thing to have done properly on a modified engine.

3

[QUOTE=TurboG2teg311;2312773]
If I were you, the first thing I would do is bring your car to a reputable local tuner and have it looked over and then if everything is okay and in good working order, have it dyno tuned. That way for your peace of mind its tuned correctly and for the fuel you want to run. You have no idea what the previous owner did as far as tuning goes and that is the single most critical thing to have done properly on a modified engine.[/QUOTE]

I concur. You NEED to get this engine tuned by a professional - especially since you’re trying to run that high of a compression ratio. I’d call your tuner, tell him what the engine is and the history of it, then ask him if you should come in for a tune immediately or if there are any parts you should install first in order to prep the car.

Doing a compression test will NOT give you the compression ratio. Do you know what components are in the engine? If so you can calculate the compression ratio - however, the variable here is if the block/head has been milled, if so and you don’t know by how much then there’s no way to calculate the compression ratio and you’re just guessing. This is why I would pretty much never buy a built motor. I broke this rule recently since the buyer was a friend of a friend and it was supposed to be an OEM rebuild. I ended up getting completely screwed. From here on out I’ll never buy anything but 100% stock engines.

4

[QUOTE=TurboG2teg311;2312773]Have you looked at the ecu to see what type of aftermarket engine management is in the car?

The 92 octane should not be an issue if tuned correctly and for that fuel.

If I were you, the first thing I would do is bring your car to a reputable local tuner and have it looked over and then if everything is okay and in good working order, have it dyno tuned. That way for your peace of mind its tuned correctly and for the fuel you want to run. You have no idea what the previous owner did as far as tuning goes and that is the single most critical thing to have done properly on a modified engine.[/QUOTE]

The ecu that was in the car upon purchase was a chipped socketed pr4.

5

[QUOTE=Colin;2312774]I concur. You NEED to get this engine tuned by a professional - especially since you’re trying to run that high of a compression ratio. I’d call your tuner, tell him what the engine is and the history of it, then ask him if you should come in for a tune immediately or if there are any parts you should install first in order to prep the car.

Doing a compression test will NOT give you the compression ratio. Do you know what components are in the engine? If so you can calculate the compression ratio - however, the variable here is if the block/head has been milled, if so and you don’t know by how much then there’s no way to calculate the compression ratio and you’re just guessing. This is why I would pretty much never buy a built motor. I broke this rule recently since the buyer was a friend of a friend and it was supposed to be an OEM rebuild. I ended up getting completely screwed. From here on out I’ll never buy anything but 100% stock engines.[/QUOTE]

Block has acl race series main n rod bearings. Cp rings. And a balanced and micropolished crank. Other than that its oem. When pistons were installed. The entire engine was torn down and fully rebuilt back to stock specs minus pistons and the other above mentioned items.

6

Well, clearly it’s not “stock specs” because it’s 12.5:1. And you haven’t even told us what engine you have in the car… b16a, b17a, b18a, b18b, b18c…etc.

  • What cylinder head is being used?
  • Has the head been milled?
  • Have the combustion chambers been modified?
  • What cylinder block is being used?
  • Has the block been milled?
  • What crank is being used?
  • What is the bore of the cylinders?
  • What pistons are being used?

If you know the specific answers to those questions then you can calculate your CR using the calculators available online. Without knowing the answers to all of those questions you can’t accurately calculate your compression.

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[QUOTE=Colin;2312789]Well, clearly it’s not “stock specs” because it’s 12.5:1. And you haven’t even told us what engine you have in the car… b16a, b17a, b18a, b18b, b18c…etc.

  • What cylinder head is being used?
  • Has the head been milled?
  • Have the combustion chambers been modified?
  • What cylinder block is being used?
  • Has the block been milled?
  • What crank is being used?
  • What is the bore of the cylinders?
  • What pistons are being used?

If you know the specific answers to those questions then you can calculate your CR using the calculators available online. Without knowing the answers to all of those questions you can’t accurately calculate your compression.[/QUOTE]

Sorry i didnt actually mention the specific engine.

  • What cylinder head is being used - B17
  • Has the head been milled - i dont know what that means, and i don’t think so, was told everything was brought back to stock clearances etc.
  • Have the combustion chambers been modified - again i have no clue. just was told everything was brought back to stock #'s
  • What cylinder block is being used - B17 block
  • Has the block been milled - again not sure.
  • What crank is being used - stock B17 crank that was in the engine originally
  • What is the bore of the cylinders. stock bore - 81.5 sound right?.
  • What pistons are being used - this i am not sure on. I was told JE 12.5:1 pistons but i cant seem to find anything close to that CR that JE manufactures. so i guess unless i take the oil pan off and actually look up at the underside of the pistons, i have no factual idea, correct?
8

Sounds like you need to do some serious research and learning about engines. I’d start reading as much as you can.

[QUOTE=jtkc;2312790]

  • What cylinder head is being used - B17
  • Has the head been milled - i dont know what that means, and i don’t think so, was told everything was brought back to stock clearances etc. [/quote]
    Milling is when you remove a small amount of material from the bottom of the head (the surface that mates to the block). The reason for this is to ensure that it is perfectly flat with no imperfections and thus will make a perfect seal with the head gasket/block. Generally one will always mill the head when doing a rebuild, even if it’s just a tiny tiny amount to ensure it’s perfectly flat. Milling the head will increase your compression because it reduces the size of the combustion chamber. Sometimes people will purposefully mill the head in order to gain compression. However this is generally not the best way to increase compression. It’s effective but has downsides.

[QUOTE=jtkc;2312790]

  • Have the combustion chambers been modified - again i have no clue. just was told everything was brought back to stock #'s[/quote]
    It’s unlikely that this has been done. But sometimes when headwork is performed they will weld or grind the combustion chamber. Sometimes this is to change the compression ratio, sometimes it’s simply to create a more ideal combustion chamber shape.

[QUOTE=jtkc;2312790]

  • Has the block been milled - again not sure[/quote]
    Same as milling the head.

[QUOTE=jtkc;2312790]

  • What is the bore of the cylinders. stock bore - 81.5 sound right?[/quote]
    Stock bore is 81.0mm, standard OEM oversize is 81.25mm, but common aftermarket oversize is 81.5mm.

[QUOTE=jtkc;2312790]

  • What pistons are being used - this i am not sure on. I was told JE 12.5:1 pistons but i cant seem to find anything close to that CR that JE manufactures. so i guess unless i take the oil pan off and actually look up at the underside of the pistons, i have no factual idea, correct?[/QUOTE]
    OEM pistons are labeled on the top, but I just googled a “JE Pistons” (ahem, why haven’t you done this yet?) and it looks like they are stamped on the bottom of the piston skirt with the part number. So sounds like you can just pull the oil pan and windage try to try and get a look at them.
9

[QUOTE=Colin;2312793]Sounds like you need to do some serious research and learning about engines. I’d start reading as much as you can.

Milling is when you remove a small amount of material from the bottom of the head (the surface that mates to the block). The reason for this is to ensure that it is perfectly flat with no imperfections and thus will make a perfect seal with the head gasket/block. Generally one will always mill the head when doing a rebuild, even if it’s just a tiny tiny amount to ensure it’s perfectly flat. Milling the head will increase your compression because it reduces the size of the combustion chamber. Sometimes people will purposefully mill the head in order to gain compression. However this is generally not the best way to increase compression. It’s effective but has downsides.

It’s unlikely that this has been done. But sometimes when headwork is performed they will weld or grind the combustion chamber. Sometimes this is to change the compression ratio, sometimes it’s simply to create a more ideal combustion chamber shape.

Same as milling the head.

Stock bore is 81.0mm, standard OEM oversize is 81.25mm, but common aftermarket oversize is 81.5mm.

OEM pistons are labeled on the top, but I just googled a “JE Pistons” (ahem, why haven’t you done this yet?) and it looks like they are stamped on the bottom of the piston skirt with the part number. So sounds like you can just pull the oil pan and windage try to try and get a look at them.[/QUOTE]

ive been on JE’s website. which is how i came to the conclusion i may not have JE pistons in my engine, since they dont specifically list a 12.5:1 piston for a B17. They do make a set of 12.5:1 pistons but i believe they were listed for being used with a b16 and not the b17. I have no idea how much difference there is between a b16 block and a b17 block. i know that the b17 head is basically or it is a b16 head. or something like that.
well when we replaced the oil pan, my buddy and I kinda forgot, at the time that i needed the info from the pistons, so i guess ill buy another gasket and carefully take the oil pan and windage out and go from there. As far as the milling work goes im sure it was done to it. i have no clue how much was taken off though. i guess this really sucks on my end. not knowing what i needed to know when i purchased it. i feel bad also posting this thread and not being able to provide the correct data needed. I do have the shops number that did the work with receipts. could they look it up in their files and would it be documented somewhere as to how much they removed when they milled the head and block mating surfaces?

10

I wouldn’t use that as an indicator that you don’t have JE’s, you need to check and see what’s in there. The b16a and b17a share the exact same head and exact same block - the differences are the internals, namely the crankshaft and pistons. B series pistons are basically interchangeable, so you can put b16a pistons in a b17a. However the resulting CR will be different for the two engines. For example, I had a b17a previously with P30 B16a pistons. In a b16a these pistons have 10.4:1 CR and in the b17a they yield a 10.9:1 CR. It’s very likely that they used JE pistons from another engine - the question is, were they 12.5 CR for the engine they were designed for, or were they 12.5:1 when installed in a b17a?

Check out this CR calculator to see how different pistons work in different engines: http://www.c-speedr.com/howto/compcalc/compcalc.php

11

If they told you 12:5 comp pistons I’m thinking they’re stock jdm b16a or pr3 pistons. I’ve known the pr3 pistons give b18c and b18a block a 12 comp.