Best Camphase to suit engine's

[VX L67 Getrag]

Is there an idiot guide to what cam's suit what fuel's & whether it's auto or manual or whether it's inline 6 or V6 or V8, just trying to figure out the best way to know how to tell people what cam lobe split's & duration's suit what?

For that fact how to know how wild an idle will be with overlap or when different phases are expected to work at what RPM?

Cheers VX L67 Getrag

[engybenjy]

I usually go off the manufactures guide but you have to be a bit careful because say you are doing a 253 the same cam that idled nice in a 308 is going to be cammy in the 253. I spent a lot of time trying to work out what compression ratios to run with different sized cams and wrote a program in excel that I use every engine I build now and it does seem to work pretty good. In my opinion getting the dynamic compression ratio right gets you the best quality idle and the best power out of your engine. I am new to tuning injected stuff but I have seen wild cams run beautifully in the 355 VN style engines a couple of times that have been tuned by someone who knows.
As a rule a wider lobe seperation will idle better than a closer lobe centre. One customer of mine had this crazy cam ground that had a shorter exhaust than inlet that went ok too.
The other thing is to set them up properly and that's not always where the manufacturers say. If in doubt I always set them up with the inlet lobe centre on 105 degrees ATDC. I dont have excel on this computer but I will try and attach a copy of my dynamic compression ratio calculator on this post if I can find it. There are some available on the internet but I do prefer mine as you don't have to reload every bit of information into t see a change (try it and you will see what I mean)
I hope I have attached the right file-take a look but only adjust values in the yellow squares or you will undo my math and also work in cm.

[VX L67 Getrag]

Man that is some good work THERE!

It's a great starting point & appreciate your input!

Where about's are you based?

[engybenjy]

In Benalla. I have a small business with a dyno and some other gear (cylinder head machining etc.) I have never been involved with a forum before but I like the way people are not critical here and enjoy the feedback and ideas people have. Keep it up

[engybenjy]

BTW if you do use the formula to help you on your rebuilds you need to bear in mind that not all pistons have the gudgeon pin in the centre (although a lot of performance stuff does) and my formula does not take that into consideration but it will get you close. the offset in piston effectively changes the rod length and my math ability was severely stretched to come up with what I did

[VX L67 Getrag]

LMAO, yeah every formula has holes if you know where to poke!

But it's a great starting point, haven't really got into rebuild yet, just want to have half an idea when starting to talk to people about it & then hopefully will turn into business & the fun stuff of putting it together, testing & tuning!

Thanks for the ideas though & yeah basic maths is my limits too!

[engybenjy]

Hi just finished a 350 for a boat. The customer complained that the engine wouldn't pull and he was keel hauling his skiers instead of pulling them out of the water quickly. The engine is a 295 hp crate motor. I dismantled it and increased the compression from 7.6 to 1 with a 224 @ .050 back to back camshaft up to 10 to 1 used the same camshaft only advanced it 10 degrees till the centreline was at 105 to get a dynamic compression ratio of about 7.5 to 1 which is a bit on the low side but gave me a cranking pressure of 175 pounds (not bad) I will be testing at the lake tomorrow with the customer.

[Holden202T]

umm .... doesn't advancing the cam give you more down low ? i'd hate to see it if it wasn't advanced then.

[engybenjy]

Here is the calculations I made before completely dismantling the engine

[darcy]

That bump in compression alone will make a massive difference in performance!

What lobe separation does the cam have?
For it to close the intake at 81*ABDC, on 105 ICL would take 312* duration, that sounds like a huge advertised duration for a 224*@050 cam.