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Thread: CTR PISTON COMPRESSION RATIO

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    Gods Chariot Vteckidd's Avatar
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    Default CTR PISTON COMPRESSION RATIO

    Lots of people are doing the CTR pistons in B series motors. this was a VERY well informed thread on Honda-tech.com that i think people should know. these are the CORRECT compression Ratios for using a CTR pistons in different B series engines. note the compression on a LS vtec with a GSR head.

    For Reference:
    STD=Standard Bore
    OS=a .25 OVERBORE
    P72=GSR head
    PR3=B16 Head

    PR3 head/B16 Block

    STD = 11.643438609136867
    .25 OS = 11.703231023151065

    PR3 head/B17 Block

    STD = 12.193487116069006
    .25 OS = 12.256369577319077

    PR3 head/B18C Block


    STD = 12.58636786521145
    .25 OS = 12.649248792586258

    P72 head/B18C Block

    STD = 12.924594026551906
    .25 OS = 12.989047869209281

    PR3 head/B18A/B Block

    STD = 12.825536009218106
    .25 OS = 12.88971493738735

    P72 head/B18A/B Block

    STD = 13.170743903246784
    .25 OS = 13.236528215133324

    All calculated using OEM 3 layer gasket @ .026 and the compression height provided by Omniman


    Picture of CTR piston VS P30 JDM B16 Piston
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    12.9 on a gsr motor? damn thats high, is that safe for daily driven because I was going to ctr pistons or itr.

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    12.5 is the threshhold of PUMP GAS.

    I will go into more detail of why CTR pistons are not ideal at a later time (prob tomrrow). i would go with PR3 pistons, they yield highercompression that a ITR pistons and they are cheaper.
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    Quote Originally Posted by vteckidd
    12.5 is the threshhold of PUMP GAS.

    I will go into more detail of why CTR pistons are not ideal at a later time (prob tomrrow). i would go with PR3 pistons, they yield highercompression that a ITR pistons and they are cheaper.
    which one gets a better power gain?

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    ill draw a graph tonight and post it tomrrow.

    IMO PR3 pistons will make more power than CTR pistons and ITR pistons. In an all motor car you want a even flame front with as little turbulence as possible. You dont want to split it, and that causes the motor to scavenge, and volumetric efficiency drops, making the motor less productive and efficient, power decreases. in a nutshell, ill draw graphs to explain this later tonight
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    so I should just go with pr3 pistons? thats the first time I ever had someone tell me to go with b16 pistons in my motor, everyone is always like get ITRs or CTRs.

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    As promised here is my graph. THESE ARE NOT TO SCALE, but a good enough representation.



    This graph (LEFT) depicts a PR3 piston. Notice the much flatter dome. what this does is when air is coming down the intake manifold, and is let into the combustion chamber, it has a more direct shot across the piston to the exhaust. There is less turbulence, IE air trying to push back off the dome of the piston , the air flows more freely, etc. Also, the FLAME FRONT which is the explosion that happens when the air and fuel meet in the combustion chamber is ignited by the spark plug. the "explosion" is distributed evenly across the top of the piston.

    The Next Graph(RIGHT) is a CTR piston. the higher dome DOES give you higher compression. that is true. However, look at the AIR TRAVEL on this graph vs the PR3 piston. there is MUCH more turbulence. Also notice how the Flame Front is split in two, that means less effciency.

    Volumetric Effciency is essentially how well the motor runs. Most honda motors run above 100% VE if built right. You cannot make more power without more air, and the air must flow freely. A motor will run longer and last longer and be more efficient with proper air travel and combustion effciency.
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    so my question now is, should I go ahead and switch to PR3 pistons or just rebuild with gsr pistons? keep in mind that its going in a gsr motor.

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    PR3 pistons if you are staying all motor.

    PR3 Pistons will yield around 11.6:1 in a GSR motor
    ITR pistons will yield around 11.0:1 in a GSR motor
    CTR pistons will yield around 12.9:1 in a GSR motor
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    thanks, I'm just looking for the best power gain while staying all motor in a budget, any ideas on where to get new pr3 pistons with rings?

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    Topline they are on Fulton Industrial

    or

    Honda
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    Would you recommend ctr pistons for the b16a1?

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    That's not a graph, it's an illustration! lol. Sorry, I had to do it. I'm impressed by your "graphing" skillz Mike, I didn't know you were such an artist! lmao!

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    Quote Originally Posted by TallGuy
    Would you recommend ctr pistons for the b16a1?
    I would just because I've seen a b16a with ctr's run before.

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    CTRs in a B16 arent bad. They are significantly lower compression than the other 1.8l.
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    Twan Jdm94Coupe's Avatar
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    .....yea i sounded stupid 2 years ago......
    Last edited by Jdm94Coupe; 12-02-2007 at 08:57 PM.

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    it WILL blow up.

    you cannot run CTR pistons in an LS block with a GSR head. the combustion chamber of a GSR head is too small, the piston dome on the CTR piston will hit the head. eventually itll pound the rod bearings out and rip the wrist pin out of the piston.

    get a b16 head, r get rid of those pistons. compression will be very high, look at the 1st page of this thread. its around 13:1

    P72 head/B18A/B Block

    STD = 13.170743903246784
    .25 OS = 13.236528215133324
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    Twan Jdm94Coupe's Avatar
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    yea i seen that, and stover told me it's not good to be over 12.5 or somethin like that.....well b16 head it is....it wont hurt anything to run itr cams will it?

    would a ctr head be ideal, since ctr heads are obviously meant to be used with ctr pistons? cause i wanna run either itr or ctr cams anyway..
    Last edited by Jdm94Coupe; 12-14-2005 at 03:09 PM.

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    The heads are pretty much the same. i wouldnt but a CTR head cause you can buy b16 head and buy ITR cams for MUCH cheaper.

    Even with a B16 head youll be at 12.8ish compression. still high, i suggest you get a cometic headgasket that is thicker to bring the compression down
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    Twan Jdm94Coupe's Avatar
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    ok thankz....pm me if u find a b16 head for a good price....thankz

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    Quote Originally Posted by Jdm94Coupe
    ok thankz....pm me if u find a b16 head for a good price....thankz
    think someone is selling one in car parts forum

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    I have a B16 head here, $350
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    Twan Jdm94Coupe's Avatar
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    complete? whats it missing?

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    for $450 is can come with a AEBS manifold.

    its missing a TB and fuel rail/inj
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    Twan Jdm94Coupe's Avatar
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    so it has dist? obd1?......could i use my fuel rail/inj and tb from my ls?

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    ahh
    NO dizzy, i forgot to mention that, and yes you cna use your LS stuff

    OBD2 99-00SI head
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    Twan Jdm94Coupe's Avatar
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    lol, thought so.......dist. are harder to come by then rhd del sols, lol

    so $350 is w/out the manifold?

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    yes.

    do you drive a white/silver del sol? I was going to my GFs house the other night, and i made a left on Leguin Mill, and there was a lowered del sol behind me. shot in the dark, i tohught thats what you had
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    Twan Jdm94Coupe's Avatar
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    i sold my del sol, but the guy who bought it i think he lives even further south then me(mcdonough).....if it had bronze konigs it might have been him.....i got a white dc teggy now, soon to be champ. white, and by march jdm front with ls/vtec!

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    mike i got another ?........ok i've been thinking alot about my motor plans....

    1. will my comp. be too high with a b16 head? cause i thought 12.5 was basically the highest i should go, and i think i would be at 12.8
    2. What im thinking.....
    B18 Block with CTR Pistons
    B16 Head or ITR head and sell the cams
    Skunk 2 Pro 1's
    Upgraded ValveSprings/Retainers
    CAI
    I'll prob keep my DC 4-1....
    ITR tranny....tuned w/ uber......

    what power you think i will make? over 200?

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    Twan Jdm94Coupe's Avatar
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    BTW we got my motor fixed, LoL....

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    www.jasontbarker.com speedminded's Avatar
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    Hey mike, what would the compression be with an ITR head? I guess it's still considered a PR3 but with mild porting so i'm thinking the numbers will be differant than what you have posted...I wanna pull mine and put in new rings and thinking about changing the pistons while i have it apart.

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    Use the PR3 head numbers.

    Basically, this is just a guideline, only way to be 100% accurate is to cc the motor
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    www.jasontbarker.com speedminded's Avatar
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    Quote Originally Posted by vteckidd
    Use the PR3 head numbers.

    Basically, this is just a guideline, only way to be 100% accurate is to cc the motor
    hrmm...so that would put me right at the pump gas limit. err, i think flow testing right now is a little beyond the budget...but one day!

    Have you dyno'd an ITR with CTR vs B16 pistons?

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    Quote Originally Posted by speedminded
    hrmm...so that would put me right at the pump gas limit. err, i think flow testing right now is a little beyond the budget...but one day!

    Have you dyno'd an ITR with CTR vs B16 pistons?
    Not anything i could give an adequate comparison with. I mean, I have dynoed ITR motors with CTR pistons, they usually dont make over 185-190whp.

    I have 3 cars with B16 pistons or ITR pistons making over 190whp, 1 makes over 200whp.

    but its an apples an oranges comparison, like some motors have different cams and headers compared to the others.
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    Twan Jdm94Coupe's Avatar
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    so ctr pistons in a ITR wouldnt be better then the ITR pistons...... man i was JUST bout to pm you about the exact same thing u 2 are talking about! lol... o and another thing

    how much is a ITR complete bottom end w/ 26k miles worth? $$wise

  37. #37
    www.jasontbarker.com speedminded's Avatar
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    Quote Originally Posted by Jdm94Coupe
    so ctr pistons in a ITR wouldnt be better then the ITR pistons...... man i was JUST bout to pm you about the exact same thing u 2 are talking about! lol... o and another thing

    how much is a ITR complete bottom end w/ 26k miles worth? $$wise
    No more than $1,500, I've seen them on Honda-tech for that price and that's what i got mine brand new for.

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    Twan Jdm94Coupe's Avatar
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    Ok good..... some STUPID asshole tried to tell me last night it was worth $350.... i almost killed him through my computer.... lol.... btw speedminded do u do body work???.... ima prob sell my block for bout 1200 or so

  39. #39
    www.jasontbarker.com speedminded's Avatar
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    Quote Originally Posted by Jdm94Coupe
    Ok good..... some STUPID asshole tried to tell me last night it was worth $350.... i almost killed him through my computer.... lol.... btw speedminded do u do body work???.... ima prob sell my block for bout 1200 or so
    You have an ITR shortblock?

  40. #40
    Twan Jdm94Coupe's Avatar
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    i have a ITR full swap....and a ls long block w/ ctr pistons rebuilt...and a gsr tranny....and a new job, LOL!!

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