K well ill be getting some afr 210s probably, might be 220s but anywayz. Also gonna get a solid roller cam with these specs

Operating Range: 4500-7500 RPM
Duration Advertised: 313° Intake / 322° Exhaust
Duration @ .050'' Lift: 276° Intake / 284° Exhaust
Valve Lift w/1.5 Rockers: .660'' Intake / .630'' Exhaust
Valve Setting: .026'' Intake / .028'' Exhaust
Lobe Separation Angle: 106°

Going into a 400 sbc. Now I wanted to know whats pretty much the highest (while still leaving slight room for error) amount of compression I should run with out fear of detonatation. Needs to be 91 octane proof since thats the highest in dumb ol Cali. But ya. Quench will HOPEFULLY around .040 but might be around .060 depending on head gasket size. Um pistons will be some forged flat tops well c what in the future. But anywayz wanted to know what you guys think i should run max compression with out fear of detonation on 91 octane. THanks. Oh also just by curiousity what do you think is the lowest I should go if i some how just feel in the distant future I should want to throw a blower/turbo on it. Thanks guys appreciate it.

 

You need to keep the quench as close to .040 as possible to reduce ping I am told.

That is quite a radical cam for CA, you just racing it? Or is it a cruiser too? I would think that at least 10:1 would be OK with that cam, 91 octain, and an octain booster. I wouldn't think that cam would want much less.

Just my opinion though.

 

Just gonna be racing ya. I want to know the maximum I should run tho.

 

or COULD run safely

 

IMO it would be 10:1.

A friend of mine explained to me that 10:1 will work on pump gas as long as quench is at optimal point, which he stated was .039. He has a 10:1 406 that is a cruiser and runs on pump gas just fine. However another friend of mine built a 9.5 to one 350 without paying attention to what the quench was, we figured it was around .060, and his was a daily driver. He had problems with the motor pinging. Who knows, it was 2 different motors, and two different gas pumps, with two different drivers.

But 10:1 can be fine on 91 octain.

 

I would not go too low on compression. That cam will bleed off some cylinder pressure. With those parts you are packing, and your not concerned with cruising, only racing, I would forget the 91 octane, go with higher compression, and give that animal some REAL FUEL! IMO, that cam is not big for a 400. My 434 has a "small" solid roller, 236/242@.050, and thats with 11.2 compression, EFI, and aluminum heads. It runs on pump gas. You plan on running aluminum heads, that alone will allow you to run one point higher C/R than steel heads. If you are serious about the turbo/blower mod., then go with some 8:1 blower pistons,and cam with a wider LSA, that would be forced induction friendly. Nows the time to decide all these mods. Sounds like a great combination you want to build there. Good luck..

 

BTW, I noticed in your profile you are a marine. Hats off to you my friend!!!

 

I ran 10:1 on my vortec headed 355 with a much smaller cam and it ran fine. Im looking in the 12:1 range.

 

Right but I wanna be able to take it out maybe once a month and give my boys a run for their money so you think 12:1 is do able? The blower/turbo thing would be nice but i really dont have the cash to be doing all these things. I already have the bottle so i might as well just squeeze for now. Maybe if i get some more cash in the future ill change pistons out and get a blower. So 12:1 a go?

 

Was...got out October 15th of last year. Havent updated this profile didnt even think about it thanks for letting me know. Thanks for the support tho appreciate it.

 

I would go for 11.1 if it were my engine.

 

Ya think so huh...maybe i should play it a lil safe and do 11:1

 

Only thing that pisses me off about that is i ran 10:1 on my vortecs. These are aluminum so thats already 11:1. This cam is WAY bigger so u think 11.5:1 is workable?

 

well if your just going to use it for racing then will you be running the good stuff (race fuel)?

If so heck go 15 to 1

 

At 11.0 it should be ok with pump gas. Im doing it with mine.

 

11:1 it is

 

Now just to get my math down ... damn ... i shoulda paid more attention in HS. So anybody got a forumla for me. I did it before on the last motor but I cant remember any more lolol. So lets say the pistons are 10:1 with 64cc chambers how do i figure out what it is with 76cc chambers. Also how do i calculate deck height and head gasket thickness in. Sorry

 

example; bore 4.125
stroke 3.75
piston reliefs 3.4
deck clearance, lets say a zero deck.
gasket comp. vol. 8.8cc
chambers, 64-68cc

(bore/bore)(bore/bore)x3.1416(or pi) xstrokex16.39(converts cid to cc) =833.38

833.38+3.4+0+8.8+68/3.4+0+8.8+68=913.58/80.2=11.39:1 C/R.
yours will be a little lower, because your chambers are larger. This is an example, just fudge your figures in . Also this did not figure in an overbore. If your engine is bored , lets say 0.30, your bore would be 4.155, in my case .040 over, so 4.165. I used standard 400 bore for the example.

 

AHHHH so many numbers thanks for the formula appreciate it.

 

Thats what I would go, or 11:5:1. Still able to run on pump gas.

 

Get a dynamic compression ratio calculator, that cam is gonna need a huge static compression ratio or it will barely run, along with those AL heads. Your gonna need more then 11.5:1 atleast, more like 11.8:1.

I'd research it myself and ask some real engine builders what they would do, not believe some monkey spank of the internet if i was me.

 

Maybe we can call this site "The Real Engine Builders" site, and not TGO

 

--------------------------------------------------------------------------------

 

This is from a few days ago, I take it that the machinists input is not necessary. Until however you need the "Real Engine Builders" advice on somthing as simple as calculating C/R.

 

I machinist is much different then a race engine builder, come on!

This is a not compression ratio calculation.

Whats your problem? To much monkey spank?

 

I dont have time to argue with a moron

 

If you think he is building any everyday motor, with that cam who is really the moron.

 

Ive noticed everytime you respond to someones question, you are sometimes cocky, not only on this thread, but others as well

 

I never said it was an everyday engine!

 

I've seen cams that big streetable in a 400. Thats actually a moderate cam for that many cubes, what the hell are you smoking? This thing ain't going in a 350.-

 

True, I know many cruising the streets with solid rollers.

 

If streetable means idling at 2000 rpm and 5 mpg then yes.

 

By "real engine builders" i mean race motor building guys, not your average engine builder, but actually people that build real race motors. There are only a handful of them in the US.

Everybody on here is just guessing (monkey spank) some people say 10:1 some 11:1 some 12:1. Nobody knows that is why you need a dynamic compression ratio calculator and somebody that deals with these kind of motors everday, not just a bunch of backyard mechanics, such as myself and everyone else on here.

 

http://kb-silvolite.com/calc.php

 

Thank you...ill be sure to keep you guys posted on the build up.

 

Just curious on that calculator, the last option where it asks

Intake Closing Point (degrees)
ABDC @ 0.050 lift plus 15 degrees

do I put in the intake lift duration at .050
say im looking at a cam that puts out 260 degrees at .050 and at 15 degrees so put into that box 275?

If i did it all right the top part I chose out said it would put me to 11.017 with a 76cc head, 4cc piston, .039 head gasket, 4.180 gasket bore, 4.155 cylinder bore (.030), .025 deck height (is that standard on 400 blocks as well just curious?) and a 3.75" stroke. Now thats where i want to be at now after i did a lil reseraching. Sounds good right?

For the bottom part like i saidi put a 6" rod and put the degrees in at 275 did i do that right? Says dynamic effective compression ratio of 7.243

If this all sounds good lemme know lil help would be appreciated Thanks fellas

 

No its full duration, or the entire time the valve is off the seat.

 

your cam card has the info,check the company's websight of the cam you interested in.It'll tell you what it is than like it says just add 15 to it

Its not the full duration Meleigh is just pulling your cam

 

if your really wanting best bang for buck 12:1 on 93 oct. with octane boost

 

Wow i was wrong it is timing at .050" lift, thats what i get for not checking the site out first. I have never used any of the crappy online calculator where you +15* duration, that is not even close to being approximate. I always you the real software calculators that use full duration, or the entire time the the valves are open.

Sorry

Always follow the direction, instructions and the manufacturers sugggestions.

 

Thanks for the address forums_suck. I added it to my favorites.

 

So...I did it right?

 

with a cam that big id suggest at least 11-1 compression.big cams need more compression.U sure u cant find any higher octane gas out there, airports???

 

Its possible to find higher octane gas dont get me wrong. Just not at ur local shell. Highest is 91 so id like to keep it 91 friendly.

 

No prob its great for throwing around different combinations specially when ya start playing with the 383 and bigger engines,i noticed ive saved my self from having too much compression or too small a cam.I dont know if its as good as the software ones you buy but if your on a budget like i always am it works great

 

I like this one:
http://members.uia.net/pkelley2/DynamicCR.html


grumpyvette provides some good info
https://www.thirdgen.org/techbb2/sho...ic+compression



Others:
http://www.rehermorrison.com/techTalk/08.htm

http://www.rbracing-rsr.com/comprAdvHD.htm

http://www.wallaceracing.com/dynamic-cr.php

http://users.erols.com/srweiss/

http://www.performancetrends.com/cr12.htm

http://not2fast.wryday.com/turbo/com...pression.shtml

 

Hey guys i got my cam commin

here are teh specs

264/272 duration @.050 lift
.692/.692 Lift with 1.6RR
107LSA

Valve timeing
29btdc 55abdc
67bbdc 25atdc

Put it into one of those calculators, says my dynamic compression ratio should be at about 9.62:1 compression with a 3.75" stroke. Might go with a 3.8" stroke and then it would be 9.64 which isnt really a difference. So what do yawll think a go or a no go on 91 octane?

 

oh ya yawll i got some afr 220s and a super victor intake manifold 2

 

Whats your static out of curiosity?

 

11.26:1 with a 3.75" stroke