CTR PISTON COMPRESSION RATIO

[Vteckidd]

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

[IntegraXTR]

12.9 on a gsr motor? damn thats high, is that safe for daily driven because I was going to ctr pistons or itr.

[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.

[IntegraXTR]

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?

[jenofcnd]

Sorry to post this mundane question here, but I need aid! I have to do a 1 hour Software Best Practices Training for some programmers in my company. Audience are Freshers to couple of years experience guys. Can you guys please suggest some relevant topics I can cover? I could think of the following: 1) Importance of following coding standards, indentation 2) Proper naming of files, variables, functions, classes, tables., columns, views and all other artifacts three) Layer your application - each layer must address a specific concern 4) Abstract common stuff into reusable utility classes Any help will be greatly appreciated (A positive response to this post & I promise I will contribute to the community by replying to at least 10 threads!)

[Vteckidd]

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

[IntegraXTR]

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.

[Vteckidd]

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.

[IntegraXTR]

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.

[Vteckidd]

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

[IntegraXTR]

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?

[Mangrum]

if you are trying to build a na gsr like i am wanting to in the future.. why would you not want to go with the ctr pistons if they have a higher compression? than the pr3 pistons? dont you want to gain the highest compression possible?

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

[Vteckidd]

if you are trying to build a na gsr like i am wanting to in the future.. why would you not want to go with the ctr pistons if they have a higher compression? than the pr3 pistons? dont you want to gain the highest compression possible?

no you dont want the highest compression possible. You want the highest compression with the flattest dome for an even flame front.


Optimizing combustion chamber space is often one of the most over looked aspects of an engine build. Although its a simple concept it has many rewards, including increased power, lower octane requirements, reduced fuel consumption and better overall throttle response. This is really important when your build has a compression increase as one of its modifications. Raising the compression ratio is equally important as the quality of the combustion space.



If your combustion space isn't well defined you wont see the full potential of the compression increase. Also your fuel octane requirement will be higher with a poorly defined combustion space.

The pent roof Honda 4 valve combustion chamber is one of the most efficient combustion chamber shapes, basically a triangle, with a flat piston. As the dome of the piston is increased the space becomes oddly shaped and not only takes longer to burn the air fuel mixture but also requires more ignition timing (starting the burn sooner) to do so. The reason it requires more timing is because the area becomes more like a winding passage vs an open triangle. This in turn promotes detonation and increases the octane requirement. As you can see in the diagrams below the large dome will cause the combusting air fuel mixture to hit the piston at 45 degree angles in some areas diluting and diverting the combustion energy. In the other diagram you can see the engine with the flat piston has a clearly defined area and combustion gasses will push directly on the piston downwards providing a more efficient piston push. The better defined combustion area requires less timing because of its superior burn efficiency.

Many things affect compression ratios. Here is a list of things that change compression with all other things being equal.

-Stroke length will change compression ratios, longer strokes increase compression while shorter strokes decrease compression.

-Bore size will change compression ratios. Bigger bores increase compression ratios while smaller bores decrease compression ratios.

-Head gasket thickness will also change compression ratios. Thicker head gaskets decrease the compression ratio and thinner head gaskets increase the compression ratio.

-Piston dome volume changes compression ratios. larger domes increase smaller domes decrease compression.

-Piston compression height (the distance from the center line of the wrist pin to the flat of the piston) {measured as if the piston was a flat top}. This can determine how much the piston is in the hole or out of the hole or flush with the block. the more the piston is in the hole (under the block deck) the less compression, the higher it is the more compression.

-Chamber volume changes compression ratios. The larger the volume the more it decreases the compression. The smaller the volume the more it increases the compression ratio.

-Spark plug depth also has a small effect on compression ratios. By taking off the sealing ring or washer you can add a small amount of compression to any engine.

In short anything that changes or can change the volume of the cylinder or combustion space will change the compression ratio. Even a valve job can sink the valves into the head slightly and increase chamber volume thus decreasing compression slightly.

When planning a built engine always try to increase the compression without adding to the piston dome. Here are some examples of ways to increase the compression without adding to the piston dome (keeping the flattest possible piston).

With so many areas affecting compression ratios its almost never needed to use dome volume to gain compression, although it is the easiest way. Certainly not the most efficient.

-flat faced valves can add .2-.4 on many engines
-milling the head can add upto a full point (be sure to account for piston to valve clearance changes).
-over boring can add .1+
-stroking can add quite a bit depending on how much you add to the stroke.
-decking the block to change the piston from negative deck height to flush or slightly/less negative.

When you buy pistons the advertised compression ratio is for one engine combination. For example if you buy 12:1 pistons for a 2.0 liter rsx engine and plan to put them in a 2.4 liter tsx enigne you will have a lot more than 12:1 compression.

[Vteckidd]

Topline they are on Fulton Industrial

or

Honda

[TallGuy]

Would you recommend ctr pistons for the b16a1?

[IntegraXTR]

Would you recommend ctr pistons for the b16a1?

I would just because I've seen a b16a with ctr's run before.

[99SI]

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!

[Vteckidd]

CTRs in a B16 arent bad. They are significantly lower compression than the other 1.8l.

[Jdm94Coupe]

.....yea i sounded stupid 2 years ago......

[Vteckidd]

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

[stretch]

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

not knocking you but i dont agree with you....just my .02 though

[Jdm94Coupe]

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..

[Vteckidd]

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

[Jdm94Coupe]

ok thankz....pm me if u find a b16 head for a good price....thankz

[IntegraXTR]

ok thankz....pm me if u find a b16 head for a good price....thankz

think someone is selling one in car parts forum

[Vteckidd]

I have a B16 head here, $350

[Jdm94Coupe]

complete? whats it missing?

[Vteckidd]

for $450 is can come with a AEBS manifold.

its missing a TB and fuel rail/inj

[Jdm94Coupe]

so it has dist? obd1?......could i use my fuel rail/inj and tb from my ls?

[Vteckidd]

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

OBD2 99-00SI head

[Jdm94Coupe]

lol, thought so.......dist. are harder to come by then rhd del sols, lol

so $350 is w/out the manifold?

[Vteckidd]

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

[Jdm94Coupe]

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!

[Jdm94Coupe]

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?

[Jdm94Coupe]

BTW we got my motor fixed, LoL....

[speedminded]

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.

[Vteckidd]

Use the PR3 head numbers.

Basically, this is just a guideline, only way to be 100% accurate is to cc the motor

[speedminded]

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?

[Vteckidd]

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.

[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