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Discussion Starter · #1 ·
Ok so below are my results. I have a B18b1, with crower #62403 Camshafts. My Calculated Dynamic CR using these specs came out to 8.59:1. I am guessing it is possible that I may be losing some cylinder pressure up the intake ports. If so, how can I be sure? I am planning on trying out different cam gear settings next time I hit the dyno, I am also considering the possibility of a thinner headgasket to bump the compression a little. Bottom end building is not an option right now. Any help is appreciated

Your engine summary is as follows: Bore 3.19 inches, stroke 3.50 inches, rod c-c length 5.394 inches, with a static compression ratio of 9.2 :1. Your camshaft specifications call for an inlet valve closing of 37.5 degrees ABDC (after bottom dead center).

Your chamber volume is 55.90 cc's. With this camshaft your dynamic, or effective stroke is 3.24 inches. Your dynamic compression ratio is 8.59 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 174.29 PSI.
 

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Discussion Starter · #3 ·
Stock Cranking Pressure came out to be 184.26 PSI and stock Dynamic CR came to 8.97 :1. So this kind of troubles me. I don't think I quite understand. I figured a 10.7:1 CR will give me about 211 psi of cranking pressure. Whats the significance of a 15% increase?
 

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Discussion Starter · #5 ·
Ok so basically I would need to be at a static CR of 9.6:1. What would be my best way of getting there? Thinner headgasket and possibly some milling I assume?
 

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hmm. let me try this.

With the stock cams your cranking pressure on zero ft sea level is:

9.2:1 CR and 184psi



With the 62403 your cranking pressure drops down

9.2:1 CR and 174psi



If you use the 62403 and increase the stock cranking pressure of 184psi to 15% more, you would need.


10.7:1 CR and 211.13 PSI (its about 15% over stock) OR
10.8:1 CR and 213.55 PSI ( still about 15% over stock)


Did I make my calculation right?
 

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correct.

62403's have the intake valve closing @ 37.5 ABDC , whereas 62404's have an intake closing @ 44 ABDC.


the ideal static CR's for these cams are 10.8-11.2:1 for the 62403's and 11.1-11.5 for the 62404's using the calculator and a 15-20% increase in cranking pressure "sweet spot" range at typical altitudes.

You'd have to go even higher on the static CR, if you live in say Colorado or Alberta at higher altitudes to achieve the same absolute values. If you lived in Boulder, CO at 5280-5430 ft elevation for example, 10.8 CR which would normally be in the 15% sweet spot at lower elevations, barely gets you back to stock cranking pressures with the 62403's.

at the very least, you don't want to be below stock cranking pressure which represents overcamming the package and less than ideal conditions for gains (i.e. 9.6-9.7:1 minimum).

The original dyno by Blueteg here that made 150 whp in a B18B was done with i/h/c/e , stock head (small intake ports), stock IM, stock CR (not the 9.6 CR minimum) and 62403's tuned on a piggyback with very impressive gains and torque curve shape (powerband). Imagine if you took that package to the next level and using the things you know now :buffing up the package to a more ideal combination without overcamming, opening up the intake ports, and ditching the stock Giraffe IM which is sized for a lower powerband location ?

you can achieve 10.8:1 CR in a b18b using stock honda pistons swapped in btw (i.e. PR3's). P30's get you closer to 11:1. Neither of these require your LS rods to be modified to fit the piston. You can also play around with adding a 2 layer headgasket to those pistons as well to fine tune the static CR to your liking.



I hope people see the "packaging" done in this exercise.

there is a relationship or interaction between cams and the block.

you don't just look at cams in isolation.

you don't just look at pistons in isolation.

leave that to the Lego builders.

thanks
 

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I posted this dyno graph before in here somewhere.

This motor is using 404's and p73-a0 pistons .25mm over.

Looking at the parts list, can anyone identify the "overkill" part in that list? lol




work done:
Crower 404 race cams (300/290 duration, 0.445/0.435 lift)
Crower dual titanium valve springs
Crower titanium retainers
Skunk2 Cam gears
Skunk2 intake manifold
AEM Fuel Rail
B&M adjustable FPR
Spoon Throttle body (70mm)
Custom 3" CAI (can be Converted to short ram for winter)
Balanced & blue-printed bottom end
0.25mm oversize P73-a0 pistons
Knifed, lightened and balanced crank
ACT stage1 clutch
ACT 8lb flywheel
NGK 8mm Wires
MSD distributor cap
STR Cam plug seal
Greddy Timing Belt
 

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that's in our b18b NA thread here...
I forget if that's SAE corrected hp?

no headporting to open up that intake port and the peak topped out at 177...that's a little higher than most I've seen for that head where I expect 160-170 SAE corrected.


I'm lookin for 62403's to show these guys what happens in comparison to overcamming the engine.


most people say if you're going to make a mistake, it's better to undercam than overcam since undercamming at least shifts the powerband down and the off the line performance and part throttle is much better (satisfies those butt dyno savy people
) ...whereas overcamming not only blunts the power gain due to a cylinder pressure loss but also shifts the powerband too high and reduces driveability.
 
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