Buick 455 cam question

[Stich496]

the software packages are pretty amazing, couple that with someone who's done it forever and you'll get the right cam... if you want rumbly why not simply get a thumper cam?

However, with a hydraulic lifter, you never get optimum lift - good lifters give you a percent but all hydraulic lifters bleed off when they go up - thus your 2-4% optimal is probably closer to 10-15%. My thought is a solid cam, but not the rumbly stuff - a decent driver cam (the specs I sent before .500 lift, 116 LSA, 220-240 duration) which is matched to my motor - then no need for the 1000# seat pressure springs, no huge wear.... and valve events that happen when they're supposed to rather than a variance between lifts. An interesting bit about lift - anything over .500 on a street motor (455 Buick specifically, but may cross) doesn't really help since you're at the limit of the flow of the heads (doesn't matter if the valve open flows 300 cfm @ .600 when the heads only flow 260). Of course, the TA heads (IIRC) flow a bit better than the ones I'm using - so what works for me might not apply to yours. Also, I have chev rockers - so I can adjust a few thousanths.

what rpm would you need to get to to have the port at 260cfm be a limiting factor.. on a 56.875 c.i.d. cyl.?
well past the blocks useable range

[TheSilverBuick]

what rpm would you need to get to to have the port at 260cfm be a limiting factor.. on a 56.875 c.i.d. cyl.?
well past the blocks useable range

Huh? Actually right around 46* of crankshaft rotation the Buick 455 (+.038 overbore) cylinder is pulling 260cfm of air, and peaks a hair over 311 cfm at 75* of crankshaft rotation (peak piston speed), on every stroke.

[SuperBuickGuy]

Huh? Actually right around 46* of crankshaft rotation the Buick 455 (+.038 overbore) cylinder is pulling 260cfm of air, and peaks a hair over 311 cfm at 75* of crankshaft rotation (peak piston speed), on every stroke.

actual numbers
Performer RPM Buick 400, 430, 455cid 60039* 60049*

Flow Numbers as tested by Edelbrock's SuperFlo SF-1020 flow bench @ 28" H2O
#60049
Valve Lift .100" .200" .300" .400" .500" .600" .700"
Intake 68 127 190 241 274 273 -
Exhaust 58 108 150 173 183 190 -

Look at the CFM at .600 - flow actually decreases...

cut n paste n it doesn't line up

[TheSilverBuick]

Gessler and Jim Weise got the same results at .600 with the TA SE heads, where the flow actually dropped. It peaked at .550, but by then the cylinder demand surpassed the port flow ability.

[JeffMcKC]

Flowing it with the intake attached will give a different picture.

[SuperBuickGuy]

how do they know that the cylinder was at its limit? I used to work for Coca Cola, and the production manager was/is a friend - he pointed out that Coke spends millions on trying to fill a bottle most efficiently. Or to use another analogy, when you draw something out of a container with a siphon, you'll always have a air bubble at the top where the air pressure doesn't allow the cylinder to occupy that space.

[TheSilverBuick]

AHHHHH!

[TheSilverBuick]

how do they know that the cylinder was at its limit?

I'm not sure I follow you? The number I listed for the CFM demand of the piston should be simple linear physics of the volume increase of the cylinder while the piston is going down (in cubic feet) and the time based on the speed the piston is dropping.

I'm also not following the coca cola analogy, as that's a filling a container filled with air, where as a cylinder and piston is making the container bigger and not trying to displace air.

[SuperBuickGuy]

the issue is you'll never completely fill the piston's chamber (thus the suction analogy) - so not having 100% or 110% fill capacity isn't a really big issue. To A/F it is, to us - we can increase boost to force more in; but in the NA realm, I don't see how it'd make a difference. To speak in geek - the VE isn't 100%

[SuperBuickGuy]

Huh? Actually right around 46* of crankshaft rotation the Buick 455 (+.038 overbore) cylinder is pulling 260cfm of air, and peaks a hair over 311 cfm at 75* of crankshaft rotation (peak piston speed), on every stroke.

to solve for the imaginary number (yep, that's exactly how I felt in Calc, Pre-Calc and Statistics - aka lying with numbers)

presuming a VE of 80%, the 311 would be reduced to a requirement of 249 cfm....

[Bob Holmes]

The piston doesn't "pull" anything (the atmosphere "pushes"). Finite amplitude waves, reflected from the exhaust, pulls. Assuming an "atmo" engine.

VE has always been one of those debatable terms. Some would state, with good reason, that you can't fill a volume more than 100%, yet we constantly hear of well developed engines that have more than 100% VE. That's because they assume a density increase due to well engineered finite amplitude wave tuning and calculate as if the volume has increased. For example, you have "115%" of the oxygen available compared to that available at atmospheric pressure.

Simply assuming the volume available as the piston moves over simplifies. Its not that simple.

[Bob Holmes]

The piston doesn't "pull" anything (the atmosphere "pushes"). Finite amplitude waves, reflected from the exhaust, pulls. Assuming an "atmo" engine.

VE has always been one of those debatable terms. Some would state, with good reason, that you can't fill a volume more than 100%, yet we constantly hear of well developed engines that have more than 100% VE. That's because they assume a density increase due to well engineered finite amplitude wave tuning and calculate as if the volume has increased. For example, you have "115%" of the oxygen available compared to that available at atmospheric pressure.

Simply assuming the volume available as the piston moves over simplifies. Its not that simple.

That's clear as mud!

[Stich496]

The piston doesn't "pull" anything (the atmosphere "pushes"). Finite amplitude waves, reflected from the exhaust, pulls. Assuming an "atmo" engine.

.

um,, sorry when the piston is moving faster than the "atmosphere" can fill it causes vacuum that PULLS..
SO YA THE PISTON DOESN'T pull, it just is the cause that has the affect of vacuum that is the pull E

[SuperBuickGuy]

Just so we're all on the same page - I don't know what an atmo engine is (is that like an emo? but for engines)

note she uses the highly techincal term of "it sucks" rather than pull... but suck and pull are the same (as opposed to blow)

[JeffMcKC]

The piston doesn't "pull" anything (the atmosphere "pushes"). Finite amplitude waves, reflected from the exhaust, pulls. Assuming an "atmo" engine.

VE has always been one of those debatable terms. Some would state, with good reason, that you can't fill a volume more than 100%, yet we constantly hear of well developed engines that have more than 100% VE. That's because they assume a density increase due to well engineered finite amplitude wave tuning and calculate as if the volume has increased. For example, you have "115%" of the oxygen available compared to that available at atmospheric pressure.

Simply assuming the volume available as the piston moves over simplifies. Its not that simple.

Yep, this is a lot of work to get right, and seperates the men from the boys. My runners are 1/2 inch short and drives me nuts trying to think of how to fix it. Last intake I will get from Hogan...