Crazy 408 in the works....Compression Ratio question

I'm interested in what the average cylinder psi is?

A custom camshaft is definitely in order, and should help a bunch but you're still leaving a lot on the table with those pistons.

90LX - My bad, yes it is 3 - 4bolts can be done.

347Ho - Average Cyl Pressure is often misleading because it is highly dependant on the overlap of the camshaft, that's not to say that CR has absolutly nothing to do with it, but same compression ration and different camshafts can have dramatic effects on cyl pressure.


The pistons that are in there, are they full dish pistons, or do they have a quench area? This is a more important feature as you want to create eddy's in your cyl charge and burn all the fuel as quickly and efficiently as possible.

Walz

Wallzy said:

90LX - My bad, yes it is 3 - 4bolts can be done.

347Ho - Average Cyl Pressure is often misleading because it is highly dependant on the overlap of the camshaft, that's not to say that CR has absolutly nothing to do with it, but same compression ration and different camshafts can have dramatic effects on cyl pressure.

Walz

Click to expand...

BINGO!
The OP stated his CR is 8.xx:1
He also stated he will be using the camshaft designed for boost.
In my experience, you are incorrect... cylinder pressure is extremely important and is never misleading. You can dial in a camshaft using cylinder pressure, you cannot using CR.
Because of the low CR and no boost, getting the cylinder pressure right is crucial.
In my opinion, even when tuned and perfect will leave power on the table because the valve events will not be "on".

Wallzy said:

90LX - My bad, yes it is 3 - 4bolts can be done.
The pistons that are in there, are they full dish pistons, or do they have a quench area? This is a more important feature as you want to create eddy's in your cyl charge and burn all the fuel as quickly and efficiently as possible.

Walz

Click to expand...

What are you saying here?
I agree piston design is important to promote efficient "flame front", but I will say a full dish piston, when used in a well thought out combo will make power more efficiently than a piston with a squish pad.
Let me/us know what you're leading into with this?

Thanks
Dana

347HO - "In my experience, you are incorrect... cylinder pressure is extremely important and is never misleading. You can dial in a camshaft using cylinder pressure, you cannot using CR."

What i am saying is that cylinder pressure is a result of camshaft duration and overlap as well as a component of CR - there has been a lot published that goes into depth on this topic - thus i'm not sure i understand what you are saying about dialing in a camshaft with cyl pressures.

"I agree piston design is important to promote efficient "flame front", but I will say a full dish piston, when used in a well thought out combo will make power more efficiently than a piston with a squish pad."

This assumption is not correct, there has also been alot published on this topic as well. Being able to ignite the flame and make it burn fully will always give you more power. If you have a chance, check out John Heywood, he was a brilliant man and did a lot of research on these topics. Have a good one!

Walz

Wallzy said:

What i am saying is that cylinder pressure is a result of camshaft duration and overlap as well as a component of CR - there has been a lot published that goes into depth on this topic - thus i'm not sure i understand what you are saying about dialing in a camshaft with cyl pressures.
Walz

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How many camshafts have you degreed in?
how many of these same camshafts have you measured cylinder pressure?
Then, using the same setup, how many times have you moved the camshaft timing fwd or rev to increase engine output... then measured the cylinder pressures to see what's happening?
You can read books all you want, but when you start doing these things and experimenting... you'll start to really learn.

Wallzy said:

This assumption is not correct, there has also been alot published on this topic as well. Being able to ignite the flame and make it burn fully will always give you more power. If you have a chance, check out John Heywood, he was a brilliant man and did a lot of research on these topics. Have a good one!

Walz

Click to expand...

I'm not up to speed with John Heywood's research, for that I'm ignorant... however, I'm inclined to believe the applications you and he are referring to are probably not true pump gas 91 octane setups.
Not everyone will use a true custom setup, ie pistons, camshaft, crank and rods. But those who do and make outstanding hp to ci ratio in N/A form, are probably using a form of dished pistons.

347HO,

I'm not here to start an argument with you, was trying to provide insight into cause and effect. I can't count the amount of camshafts that i have degreed on chevy, dodge, or ford nor is that really important to me. I have spent my time behind a dyno, flow bench, spintron and smoketron device optimizing HP engines, so I have learned a few things over the years. I am sorry that you aren't familiar with John Heywood, that wasn't an attack at you if you infered it, it puts things into persepective answering the question of "why did that happen, oh because i did that..." As for the 91 octane and cars with high NA hp to ci ratios, those theory's from books are being practiced in today's auto industry and on average have produced much higher hp to ci ratios than have been done in the past. Well, it's time for an afternoon beer, cheers, have a good day.

Walz

Wallzy said:

347HO,

I'm not here to start an argument with you, was trying to provide insight into cause and effect. I can't count the amount of camshafts that i have degreed on chevy, dodge, or ford nor is that really important to me. I have spent my time behind a dyno, flow bench, spintron and smoketron device optimizing HP engines, so I have learned a few things over the years. I am sorry that you aren't familiar with John Heywood, that wasn't an attack at you if you infered it, it puts things into persepective answering the question of "why did that happen, oh because i did that..." As for the 91 octane and cars with high NA hp to ci ratios, those theory's from books are being practiced in today's auto industry and on average have produced much higher hp to ci ratios than have been done in the past. Well, it's time for an afternoon beer, cheers, have a good day.

Walz

Click to expand...

No attack or ill-feelings inferred nor expressed Walz, just wanted some expansion on your version and insight to the OPs post.

I admit I haven't "done it all" nor claim to... but I have tinkered a ton in this field.
I receive great tech advice and knowledge from my camshaft maker, and through the years talking with people much like yourself have taken their knowledge and applied it to the 1320'.

I never see where you listed what cc the piston is?? Typically a 22cc dish on a 408 with a 58cc head is in the 10.5:1 range. What piston are you using?? What is the cc of the dish. Usually if it is a flat top around 4cc you'll need a 72cc chamber in the head for a 10.x:1

Having a TW milled down to 58cc is no problem, you can go further the large concern is deck thickness and integrity under boost... Are your pistons made for the rotated valve? If not you may not be able to run them at all...