Limits of intake cam timing.


Kozy

Kozy

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Does anyone know the limits of which you can safely adjust the timing of the cams on the B16B/B18C?

I'm thinking in terms of bleeding off excess compression by retarding the intake cam, but have no idea how much it can be safely adjusted by.

By my maths my engine is currently 10.88 static and 9.77 dynamic. If I were to replace the internals with ITR items it would make 11.44S/10.33D. If I used the EK9 pistons with the ITR rods and crank I get 12.89S/11.63D

Using a thicker 1mm head gasket I could drop this to 12.37/11.16, could I then bleed off the rest of the excess compression? I would need to retard the intake by 13° to drop the dynamic compression back to 10.35.

Is 13° possible/safe? Minus 10° would suffice probably.
 
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Why do you want to lower the C/R ? What octane fuel do you have available ?
 
Raised compression is a good thing, however ek9 pistons running with b18c rod / stroke ratio not such a good idea weight vs piston speed wise,,
 
Tesco 99 is all I can get on the IOW.

I want to drop it as I have no need to run that high a CR with stock cams. However, with the valvetrain already uprated, having the ability to simply alter the cam timing to up the compression it would be a quick job to drop in some silly cams at some point in the future without having to go to the hassle and expense of changing the pistons again.

Seems little point having the block apart now and paying extra for ITR pistons only to have to do it all again in future when I want to cam it, if I can instead buy a set of cam gears and simply alter the timing to suit.

My idea might be a country mile away from reality, but the theory seems sound in my head... :D
 
olly ek9 said:
Raised compression is a good thing, however ek9 pistons running with b18c rod / stroke ratio not such a good idea weight vs piston speed wise,,
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Shouldn't be to much of an issue, for the same speed the EK9 pistons put around 7% more stress on the rods than ITRs. By comparison the stock B18C puts nearer 9% extra stess on the rods compared to the stock B16B. I'll be using ARP rod bolts to compensate, should be OK?
 
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Whats wrong with running such high compression with a stock cam ? As long as your not getting any knock you have nothink to worry about. I know what your getting at with intake reversion, but you can also retard the exhaust cam to take the benefits of exhaust reversion if you are running into an knock. Your better off retarding them both togeter a bit then retarding one of them a load.

You need to clay this engine to, to work out your piston to valve clearence...
 
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Kozy said:
Shouldn't be to much of an issue, for the same speed the EK9 pistons put around 7% more stress on the rods than ITRs. By comparison the stock B18C puts nearer 9% extra stess on the rods compared to the stock B16B. I'll be using ARP rod bolts to compensate, should be OK?
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Your rpm will play a hugh role in this. Just don't get reving the crap out of it.
 
Yes, definately best off timing them both, I was only considering the intake in terms of the dynamic compression.

I have no idea if it would run very well though, say with both cams retarded 10°.

As for the compression, there's no-one here that can map Hondas that I know of, and I would not be comfortable mapping it myself with compression that high. If I can start off with a near stock DCR on a near stock base map then work up then that would be ideal though.

I'm happy to trade top end for midrange now, I would happily set the limiter at 8k, so no revving a B18C like a B16B! :nono:
 
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But arent we both getting at the same thing ? i.e. compression and knock It doesnt really matter what your C/R is along as your away from knock. I don't think you'll need to retard them both that much and i don't think it will run that bad. I think you'll be a lot worse off retarding the intake that much, those intake pulse's are going to really get the map sensor pissed off.

You maybe better off biting the bullet and getting a set of ITR piston's.
 
Why not just use P73 pistons and forget using PCT pistons. With stock cams the power difference will be minimal anyway.
 
The internals I am looking at come with PCT pistons. It would be additional expense to track down P73s, and if I want to upgrade the cams at some point in the future then they'll need swapping out again.
 
Kozy said:
The internals I am looking at come with PCT pistons. It would be additional expense to track down P73s, and if I want to upgrade the cams at some point in the future then they'll need swapping out again.
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Sell the PCT's and buy some P73's job done:))
 
i will have some used 81mm ITR pistons for sale in a couple weeks

Depends how much of a rush you are in of course
 
Couple of weeks would be fine Steven. Doesn't look like my idea is very favourable!
 
Retard intake cam to lower DCR is valid but 13º or even 10º is too much, dont forget that retarding intake valve close event will retard intake valve opening for the same duration, reducing overlap, and also move cam centerline (peak lift) for a point where piston is not anymore at it's peak speed.
 
civic4g said:
Retard intake cam to lower DCR is valid but 13º or even 10º is too much, dont forget that retarding intake valve close event will retard intake valve opening for the same duration, reducing overlap, and also move cam centerline (peak lift) for a point where piston is not anymore at it's peak speed.
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All very valid points, thanks for your input! What in your opinion would you say is the maximum you'd retard the cam?
 
Lots of aftermarket cams have the IVC event at 50º ABDC (@1mm) itr cam IVC is at 45º ABDC, so in my opinion you won't need to retard intake over 5º (crank degrees) to have a "safe" DCR
 
Get some adjustable cam pulleys and go play, find out what works best with your setup, all well and good in theory but the real world is a totally diffrent matter.
 
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