b18c with forges and high compression? [Archive]

MrJDMCivic

18-02-2006, 12:42 PM

hey, ive got a b18c vti-r motor - thinking its a b18c2, and i got a set of je forged pistons,
now i know that the b18c2 has a stock compression ratio of 10 and the
type r is 11.5
but these pistons are at 12
do i need to replace the valves to handle the compression, or will my stock valves be up to handling this comression ratio?

jimmeh

18-02-2006, 01:40 PM

i dont think you have to replace the valves. what makes u think that u do

tinkerbell

18-02-2006, 01:52 PM

very interesting question...

ProECU

18-02-2006, 02:13 PM

you can either use stock valves, just have them black nitrated, or use flat back aftermarket vavles to help increase your CR even further.

Most importantly, make sure the valves are installed at the correct height which will give you the correct valve to piston relief clearance.

ProECU

18-02-2006, 02:16 PM

MrJDMCivic

18-02-2006, 02:17 PM

no its cause i got told that since the aftermarket je forgies pistons rase the compression ratio to 12, the valves wouldnt hold up, this was from a guy that owned a v8 engeneering shop who works v8's but he dont really know about 4cyl, but he recons i gota change them cause the pistons will hold the higher conpression, but the stock valves wil shit them self.

ProECU

18-02-2006, 02:19 PM

have them black nitrated, or just replace them

Weq

18-02-2006, 05:33 PM

stockies will hold, just make sure the piston to valve clearance is good.

LowEk

18-02-2006, 07:03 PM

another thing...

you will need to tune so that the combustion temperatures are not excessive, you can achieve this by using an EGT along with creative spark timing!

If any of the self proclaimed tuners can explain what i'm talking about, ill give them +1RP

Now im not 100% sure on this but ill give it a try anyway.

EGT=Exhaust Gas Temp gauge - which measures your exuast gasses which give you a reading to tell you how hot you exuast temps are straight out of the manifold. used with a A/F gauge you can tune your car right and know how the plugs are working.

^^^ Am i correct sorta???

Slaz

18-02-2006, 07:14 PM

Just stick with the stock valves and as said earlier make sure the clearence's are correct and you wont have a problem.

If your going to start playing with different cams they'll still be ok but the springs and retainers might not be up for the job due to the amount of lift asked of them.

MrJDMCivic

18-02-2006, 11:26 PM

cool, so im just gona throw in these high compression pistons, and retune my ecu to match the higher compression so i dont get detanation. which should give me alot of power, any recomendations on what else i should upgrade since im rebuilding my motor with je fogies and higher compression.

Slow96GSR

19-02-2006, 01:25 AM

Sleeves and a turbo kit! Depends on how much you got to play with. How bout rods? A crankshaft? Calico coated bearings at least. Then for the valve train... port n polish, cams, cam gears, springs and retainers. You need to make sure you have good oil flow so a new pump and how bout the water pump? If you have time coat things too, do it. I run 30% cooler from the coatings and that turns in to hp. For you all down there with transit time and coating time I'd say 4 weeks to coat the head and block. Plus it's something you need if you are going F.I. or nitrous.

It all comes down to time and money. The more time you have the more you can do but you need money too. To fully build your car with a home made turbo kit, coatings, internals, externals, other parts you need I'd say 20kusd but if you have only 5kusd I'd do rotating assembly, coat the pistons, Calico bearings, cam gears, clutch, and if you can afford it more.

wynode

19-02-2006, 11:41 AM

Well when upgrading cams most of the tuner on here have suggested increasing your compression to suit.

So have you thought of upgrading your cams also?

LowEk

20-02-2006, 08:13 PM

hey was i right ProEcu on the EGT??

MrJDMCivic

20-02-2006, 11:23 PM

Well when upgrading cams most of the tuner on here have suggested increasing your compression to suit.

So have you thought of upgrading your cams also?
not really, is there any advantage to upgrading cams after rasing compression, the other thing i gotta watch out would be the fact that compression is rased, would mean less of a dish in the piston which could get closer to the valves, especially in vtec mode. which is what i dont need.

jimmeh

20-02-2006, 11:39 PM

higher comp pistons have a dome shape like this
http://blkcrx.hondata.com.au/hondata/Hondata-Photo-Web/images/DSC00623.jpg

wynode

21-02-2006, 08:01 AM

not really, is there any advantage to upgrading cams after rasing compression, the other thing i gotta watch out would be the fact that compression is rased, would mean less of a dish in the piston which could get closer to the valves, especially in vtec mode. which is what i dont need.
Do a quick search for threads on upgrading cams and see what people have said.

MrJDMCivic

21-02-2006, 11:50 PM

alright, im going to wack in the pistons, and see how i go, higher compression will cause lean,.right? , anyhow im planning on getting it dynoed before and after, so ill test with the new pistons, then ill buy a set of aftermarket cams, and retest it,. see if it will make any difference, just worried about the clearence, and the stock valves, also if i get the head port and polish, will i have to change the valves, cause i wana run type r power, if not more. with my forgies pistons cr12. and maybe some other mods.

todaek9

22-02-2006, 07:40 AM

are you using your stock cams?
You would definately get some power gain, but won't be alot. to fully maximise your PISTON, better get a set of cam gears with it and if you want, JUN stage 4 or spoon Class A cams.
Just get a Fuel press reg, fuel pump will do you fine. Clearance would not be a problem for sure but one good advice, don't oversize the cilinder head. and you don't need to change your Valves, if you got those type R Valves already.

If i were you, better find out how many VTEC those workshop done ever before deciding which one to go for.

alright, im going to wack in the pistons, and see how i go, higher compression will cause lean,.right? , anyhow im planning on getting it dynoed before and after, so ill test with the new pistons, then ill buy a set of aftermarket cams, and retest it,. see if it will make any difference, just worried about the clearence, and the stock valves, also if i get the head port and polish, will i have to change the valves, cause i wana run type r power, if not more. with my forgies pistons cr12. and maybe some other mods.

Bowzer

22-02-2006, 08:08 AM

Dude, have you got a detailed spec sheet of the Pistons? What is the Piston Dome Displacement (measured in cc)?

The combustion chamber volume of P72 head and a PR3 head is about 1.1 difference P72 being 41.6 and B16A being 42.70

The reason im giving you these figure is because piston to valve clearance is an issue when you use bigger dome pistons in a p72 head... An even more so when you use bigger lift cams

Factory P72 pistons measured to be about 2.52cc where as you take a CTR piston (PCT) its somewhere 8.63cc due to the higher dome.

With the JE piston your running hopefully the valve reliefs are sufficient for the cams your using...

If in doubt you should get who ever building your engine to clay the motor to find exactly how much clearance you have to play. That way when you do decide to use cam gears to tune the motor you also know how much room you have to play when you go to advance/retard the gears.

FYI, using CTR pistons in a B18C2 motor and P72 head the calculated CR is ~ 12.0:1 assuming std bore and 3 layer OEM gasket.
http://www.c-speedracing.com/howto/compcalc/compcalc.php

Bowzer

22-02-2006, 08:26 AM

MrJDMCivic

22-02-2006, 06:57 PM

this is the piston and the information about it, what do you think.? it turns out it was 11.5 and not 12 so i think the compression ratio is the same as the type r, the other thing is, im going to bore out my block .5 mm., and i was wondering the stock gasget and stock head should be fine, right?
http://vanortonpaper.com/pic/piston.jpg

MrJDMCivic

22-02-2006, 10:31 PM

i think the * symbol specfies that its the stock figure. example being the stroke and rod length

Slow96GSR

23-02-2006, 02:46 AM

Ya that means stock numbers. The ITR has 10.5:1 CR. As for the rod length and stroke the CR numbers are based on using that size rod with that stroke. If you change the rod the CR will change and so will the stroke. CR is also based on a stock head and head gasket. If you mill/deck the block and head the CR will change. Thicker/thinner gaskets will change the CR.

http://www.strathlan.com/TEK/images/jeb18c5specs.jpg

Bowzer

23-02-2006, 07:23 AM

So based on that table and using the Calculator yields a CR of 10.8 (3 layer OEM headgasket) and 11.16 for a 2 layer type.

Notice the Head C'Cs is for a PR3 B16A/B18C Head. The head cc for your application will be 41.6.

Also take into account it is 0.5 oversize which will increase your displacement to 1819.8cc

ProECU

23-02-2006, 07:30 AM

it will also increase his CR

MrJDMCivic

23-02-2006, 09:06 AM

dam, so i should use a two layer gasget? to incress the compression ratio. keep in mind its not a type r, its a standard b18c vtec. so with these pistons, it should be all good. where do i get a two layer gasget?

Slow96GSR

23-02-2006, 11:05 AM

it will also increase his CR

Yes, if you took a stock piston and made it bigger, but then they change the dome height and stroke and that makes the CR of 11.1:1.

I would use a high performance gasket and maybe a turbo gasket as they are stronger. So a 2 layer is fine but 3 layer is ok too.

ProECU

23-02-2006, 11:13 AM

Yes, if you took a stock piston and made it bigger, but then they change the dome height and stroke and that makes the CR of 11.1:1.

erm, I dont quite understand what you're saying.

Piston manufacturers make pistons to displacement specifications, so you can get the same cc piston in 81mm and 81.5mm and so on and so forth.

My point was, If you keep piston displacement constant, the larger bore diameter will be a net effect of increasing static compression.

Dome height alone wont effect CR.
I dont understand why you brought stroke into the equation when the dude is looking to change pistons only??

ProECU

23-02-2006, 11:16 AM

As for the rod length and stroke the CR numbers are based on using that size rod with that stroke. If you change the rod the CR will change and so will the stroke.

Also, this is not true.

Rod length does NOT have an effect on CR.

For those who are interested in how CR is calculated...
http://www.theoldone.com/articles/How_To/Comp_%20Ratio_calc.htm

MrJDMCivic

23-02-2006, 03:03 PM

so i imagine only dome height affects compression ratio, thus this having higher dome to stock?

ProECU

23-02-2006, 03:20 PM

I give up.

MrJDMCivic

23-02-2006, 09:31 PM

lol. so who does know about this.

ProECU

23-02-2006, 09:34 PM

how about you actually read and understand the info i've given you...
including that link.

The answers you are after are all there.

Slow96GSR

24-02-2006, 02:18 AM

The Calculation of an engine's compression ratio ( C.R. ) is based on the formula :
CR= (SV+CV)/CV

SV= Swept Volume for one cylinder in CC's= Bore x Bore x stroke x 12.9

CV= Clearence Volume for one cylinder in CC's= HV minus EDV plus DV plus GV

HV= Head Volume (measured in CC's)= Best if measured because head volume vaires

EDV= Effective Dome Volume (measured in CC's)= Dome volume minus valve relief and/or dish volume

DV= Deck Volume clearance (piston to deck) (measured in CC's) = Bore x Bore x Deck Height x 12.9

GV= Gasket Volume (measured in CC's)= Gasket Bore x Gasket Bore x Compression Thickness x (12.9 or enter known gasket volume)

edit: Cubic Inch Displacement measurement

Bore x Bore x stroke x .7854 x 4(cylinders)

So yes the rod affects stroke and makes a difference in CR! I think what ProEcu is thinking of is displacement.

ProECU

24-02-2006, 07:42 AM

technically, if you are formulating a general formula, the rod length will effect CR, I agree with you.

In reference to this thread, the rod length of his combination is irrelevant, as it is being held constant, which is what i've been trying to convey in a simplistic manner for all here to understand.