pcmhacking.net

WOW you certainly have been studying it!

Can't wait for my next car to get & dial in the best cam!

so this what your engine looks like assuming you set your cam up with the inlet on 105 degrees BTW i am using apple so I hope you can open the attachment. you have a comp ratio of about 10.5 and a dynamic comp of 7.9 to 1 which is really good thats right where I aim normally for premium fuel you can go a little higher but it starts to get hard to tune with detonation. I would imagine it had about 185 psi on a compression test?

back to a bit of cam theory
from memory I have tried to explain how I determine the most suitable compression ratio for a theoretical engine.

So another way of thinking about engines and power is to think of it as an air pump and the more air you pump through it the more power you're gonna' make. If you did have a limit to your cam size you could take a look at your valve size. remember the cam manufacturers give you a .050" spec. Lets think that we want to make that .050 event shift as much air as possible. There is probably three ways you can do this
1. installing a larger valve - this makes the door bigger = more air flow
2. installing a rocker with a higher ratio - this opens the door wider= more air flow
3. port the cylinder heads and back cut the inlet valves= more air flow

the other way is to turbo charge it - that works too but different rules for comp ratio

Sometimes you may want to install a cam in an existing setup and you don't want to machine cylinder heads and blocks etc. I always look at the existing cam and start by measuring that. If you have a degree wheel you and a dial indicator you can do that quite accurately.
the other thing I sometimes do is give the engine a compression test and if you have the compression and the cam specs you can almost guess the dynamics with a bit of practice.
If you have lousy compression you need to be careful about putting a bigger cam in it could go backwards, instead you might look at a the different cam manufacturers cam specs and look for one with the same or less duration from seat to seat but has a longer duration at .050" and more valve lift. That way you wont upset the compression but you will gain the advantages of a larger cam, as well this if you install a higher ratio rocker you can gain that little bit more as these don't hold the valves open any longer.

Anyway those are some of the things I think about when selecting cams and building engines up here in the bush.
Over the years I have kept a diary of just about every cam and comp ratio I have done and I have realised it's literally hundreds and I am still learning and thinking about stuff all the time.

BTW this is the first essay I have written since high school 25 years ago.

That is an awesome ESSAY, & totally understand as it was nearly that long ago for me too!
Only thing is I never enjoyed them back them but this 1 I could read over & over!

I totally appreciate your ideas & effort you've put into that!

I just downloaded the crane cams specs sheet & attached it here for any 1 to reference!

I'm pretty sure I few a few more questions but just want to read it a few more hundred times & make sure it's not stupid!

I still haven't tracked down my actual cam spec sheet damn it, but I never did a comp test on it so not sure if it was 185!

SO guessing if it's 10.5-1 will be 185(rough guide)
9.5 = 175(rough guide)
8.5 = 165(rough guide)

Thanks again

I pulled a 318 fireball out of a valiant today that I am building for the street, I will measure it up over the next day or week or whatever, depending on the fires up here (I service some of the four wheel drives with the slide on fire fighting units on them and there could be some repairs to do over next few days) and put the measurements up here, I know it's not a Holden but the process is the same. I did a dyno run before pulling it out so lets see how it goes.

re: boat / Mick said he was happy with it on its trial run but he said it really pulls now with the carby and distributor set up nice/ in fact he was really impressed so that's a plus

awesome work, not that I or possibly everyone here ever doubted you on the boat motor!

On the regards of the fireball, yeah be good to here how it lines up on the spread sheet, wasn't sure what you meant earlier about being on apple as all looks microsoft to me?

yeah I was using an apple computer when I put your stuff into the spreadsheet and last time I did that I had drama reading it with excel, what it is I am not that great with computers sorry.

its apple thats causing the issue

LMAO @ 202T yeah I can't say I'm very apple literate so yeah that'd be my issue too!

But from what everyone says there the best designer/programmers computer so kudos to you if you can do both!

I haven't had/wanted to jump into apple world & are quite comfortable here (LMFAO) but will have to join eventually (bloody win8) but will get there & get back to this actual thread once my head stops hurting!

Nice work!

I spent a fair bit of today looking at VCM's range of camshafts & there write up of them & various dyno tuning they'd done!

Not sure if it's going to be o.k. to post anything like it up here for copyright info, but was VCM21 camshaft they used in a 6 litre & 6.2 & the 6 litre actually ended up with a higher percentage gain & an actual higher end figure, would be interesting to compare them in the excel calculator sheet to see if 1 shows up better than the other!
I'll need to get all the figures on those motors too though!