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Cylinder Head Understanding...

 
kev8alot
I love my Chevy Chevette!
Posts: 13
Joined: 10/12
Posted: 10/06/12 09:03 PM

Hello.

I have a 1979 L48 350 195 HP engine(stock). This is what I know(or think I know) about cylinder heads. It's part of the valve train assembly ie: camshaft, rockers, valves, springs, etc. Performance wise, the heads give you the most power improvements for a NA engine. Power is achieved by porting, polishing, flow testing, and overall improving the quality of the components based on what you're doing. My questions...

1)Flow Testing, what does it accomplish ie: Rocker arm ratios, picking the right camshaft, spring strength needed, etc?
2)If I do not want to enlarge the ports to fit bigger valves is porting still worth doing?
3)In your opinion how much horsepower could I expect from just cylinder head work?
4)Maybe the hardest, what is inertia supercharging and does it work?

Check my Introduction to see pics and know a little more about my project. Thanks.
http://forums.chevyhiperformance.com/70/9265282/general-discussion/hello-chevy-community/  

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pepsi1
I mow my lawn and find Chevys
Posts: 1718
Joined: 09/11
Posted: 10/06/12 10:17 PM

kev8alot Welcome to CHP:

I thought you were going to show us some nice super-flow, flow bench...LOL...

Or a 2000 Horse Power Pro-Mod engine... Only kidding...chime in there with us okay!

Bob  

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kev8alot
I love my Chevy Chevette!
Posts: 13
Joined: 10/12
Posted: 10/06/12 11:08 PM

It's nice to be on the forum  Bob, and thank you for the welcome. Maybe once I figure out what I need to know I could show you that 2000 HP Pro Mod 350.  

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kev8alot
I love my Chevy Chevette!
Posts: 13
Joined: 10/12
Posted: 10/07/12 06:57 AM

So I may have found the answer to what inertia supercharging is. There are two important factors that I am aware of, an "aggressive" vacuum in the combustion chamber and the frequency of the "pressure waves". The first accomplishes overfilling the combustion chamber with more mixture than it normally ingest which would result in more power. The second is a little harder to understand, but I think I can explain. The intake stroke is the time when air/fuel mixture enters the combustion chamber but this only happens for a small portion of the crank rotation. For the remaining rotation ie: closed intake the built up air in the intake runners bounces back and forth until the intake stroke opens exactly when the air is coming back into the engine. What do you think?  

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waynep71222
I have an SS396 tatoo
Posts: 448
Joined: 03/12
Posted: 10/07/12 06:57 AM

on a dark night..  look up.. start counting the stars... thats about as many ways as there is to build a small block chevy..

you can build them with identical parts. and one will still make more power than the others..

there is a LOT to read over at the SAE org web site.. if you are a member...  i recall one article written that said to use T shaped intake passages on dual plane intake manifolds..  square corners for the most power.. it was full of ............   or maybe not.. perhaps it was a misleading article..

there have been a few people who have written about the shape of the cam specific to the intake flow of the ports verses cylinder volume..

there were some heads designed with less intake port volume at the tapered bowl area... to maximize the inertia effect of the inlet charge.. but since they did not flow as good people did not use them. they did make more power..  but the flow numbers were down. .   one has to look at the amount of time the intake valve is open..  its open for around 1/2 turn of the crank out of 2 turns.. so a turn and a half of the crank.. the intake is closed...  the air backs up on the back of the intake valve awaiting it to open.. with a big bowl behind it to store air..  it must have more volume and the air stops..  but with a tapered port bowl area..  there is less volume of air to get started.. so there is probably more time to get air into the cylinder..

flow testing is with a valve open...  great... but the actual flow at the valve head stops and starts.. this requires CFD programming..

it would be interesting to look at the flow through  same size intake ports and manifold runners verses various tapered intake passages...  if you get the taper just right for the operating RPM .. you are going to have quite a pressure wave building up in the port when the intake valve is closed.

one also has to look at the exhaust flow..  and the scavanging  effect of the exhaust flow.. as the exhaust valve opens at the end of the combustion stroke.. the pressure starts the flow through the slightly opened exhaust valve.. the piston moves up and speeds up toward the middle of the stroke... this really gets the exhaust flow moving.. then the piston slows down as it comes to the top of the stroke... the exhaust port is closing.. but it is usually not closed until after the intake port is opened.. this is valve overlap...  the exhaust flow enertia creates a vacuum in the combustion chamber..  this helps pull fresh air and fuel into the chamber.. and since the intake and exhaust valve are next to each other.. some intake charge escapes out the exhaust port..

if you really wanted to build a super MPG motor.. you would need to design an intake port that directed intake charge away from the exhaust valve opening.. probably what the swerl ports were attempting to do on some heads in the 80s..  this would only need to happen when the intake valve is only partially open..  during the exhaust overlap..

the issue with this.. is you need fuel to heat the current cats.. or they won't clean the exhaust flow properly..

with the late 70s motors.. you run into designs that needed to pass emissions..  you had to keep the combustion temps below 2600F to limit the formation of NOX...  they also needed to meet MPG numbers..  this was before or right at the beginning of active fuel control..   by 83/84.. they got some decent mpg numbers from very complicated feed back carbs..  i am talking 350 caprices getting 23MPG on the highway.. and 305 getting slightly more than that.. V6 models in the mid size cars could knock down numbers of 26MPG..  but they were complicated.. they also did not make massive amounts of power..  these feed back carbs at gm.. spent 7 minutes each on a computerized flow bench to get the adjustments right..

so you have to design your engine to operate at selected RPM/HP range.. is it going to be a street motor that almost never sees more than 4500 rpm.. or is it going to be a race motor that only had idle and 7500 rpm operation..  nothing between..

there are a LOT of people at LOT smarter than me.. as i don't consider myself very smart..  

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idrivejunk
I mow my lawn and find Chevys
Posts: 5119
Joined: 12/09
Posted: 10/07/12 10:07 AM

Same here, Wayne.  Wink

I'm a bodyshop guy but what the heck- engine guys forgive me and correct me if I slip, these are just my words.

Flow testing provides numbers for comparison of port flow between different heads.

An efficient (powerful) street combination of parts will provide sufficient intake air VELOCITY at idle for safe, stable operation and accurate low speed fuel metering without the potential for easy stalling. It will ALSO provide sufficient air VOLUME to support adequate cylinder filling at the maximum safe RPM level supported by the rotating / reciprocating assembly, or the valvetrain design limitations, whichever comes first. The optimal camshaft will be ground to match the limitations of the rest of the engine, to best fulfill the objectives with a compromise that best suits all-around usage.

Engines that spend most of their time in a certain RPM range can be finely engineered by trial and error to achieve best volumetric efficiency at the speed they run. That would be where to consider the NA ram effect.

Stockers are tuned for spunky throttle response working against a brick wall of gear ratio, mandated by fuel economy requirements. So they are designed to do their best work at or below about four grand, and as such, little consideration is given to hi-RPM efficiency. Who cares what it does above five grand, as long as it gets good mileage, right?

Engines that win money for their owners by running with the throttle wide open are designed with no consideration for idle quality or fuel economy. Intake air movement below 3,000 RPM becomes a who-cares issue.

Rocker arm ratios are more of a fine-tuning tool for maximizing a cam that isn't quite perfect for the engine's demands. Or- to stagger lift /duration between intake and exhaust to a greater degree than the cam grind by using two different ratios, in order to offset packaging limitations like restrictive exhaust for example.

Valvespring strength relates closely to cam choice, which is related to head flow numbers. The right (multiple) valvespring has-

-enough "closed" pressure to seal off the explosion.

-JUST BARELY enough pressure when compressed to max valve lift, to keep the valve stem tip in contact with the rocker arm tip at the maximum safe RPM supported by the moving parts, or until the RPM at which maximum intake air OR exhaust gas flow volume is reached, whichever comes first ("the redline"). Excessive pressure steals power by making the engine harder to turn, and puts more load on the entire valvetrain all the way down to the cam bearings and timing gears.

-the strength and flexibility to maintain the above without excessive fatigue.

-the size to clear everything including itself at max lift and cycle speed.

Porting is almost always worth something, but ONLY if done with prior knowledge of the particular head, and only if added (or less turbulent) flow is needed. At stock-to-medium power levels, its often more effective to just use a later head design. Manufacturing constraints leave a lot to be desired especially on older factory heads. Larger valves CAN be an improvement without porting, but as you said without the port flow to support the valve size, a larger valve just adds weight in a very bad place.  

Without other modifications, I think porting your stock heads would be worth less than ten horsepower.

Welcome to CHP, kev- lots of brains to pick here. List your head casting numbers and the suggestions might pick up!  
idrivejunk

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skyeking
I mow my lawn and find Chevys
Posts: 2738
Joined: 08/09
Posted: 10/07/12 03:50 PM

It's all depending of the flagration duration..My unwanted opinion??...Noel..  
skyeking

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pepsi1
I mow my lawn and find Chevys
Posts: 1718
Joined: 09/11
Posted: 10/07/12 08:14 PM

Icon Quotekev8alot:
It's nice to be on the forum  Bob, and thank you for the welcome. Maybe once I figure out what I need to know I could show you that 2000 HP Pro Mod 350.

We have to see if we can wake up Dave 632. He's the Pro-Mod guy.

We have to have fun with the New-Bees...

Dave 632 Ran  a Pro-Mod Beretta...

I sold my toys 2 years ago...

Skyeking has a Jag with a 350 small block.
He's our bud from the land under the Sun...Hope you don't mind me telling the New-Bee the company he is in...  Grin  Cool

If you can build us a reliable 2000 Horse Power 350 Pro-Mod engine I might come out of retirement. Maybe Dave 632 will also. As long as someone wants to pay the bills hah Dave! Grin  Cool

Bob  

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pepsi1
I mow my lawn and find Chevys
Posts: 1718
Joined: 09/11
Posted: 10/07/12 08:45 PM

Wayne, Matt..

I remember the last time I got involved with head flow. I'm staying out of this one. No Offense to any my fellow Guru's. I'm backing out gracefully...Thank you

Bob  

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kev8alot
I love my Chevy Chevette!
Posts: 13
Joined: 10/12
Posted: 10/08/12 09:08 AM

Thanks, I went and looked at my heads to try and find the casting number. It reads 462624 which from my understanding are not quite what I want. They are a crack prone head due to heating problems and thin walls. However this guy thinks they are good, http://www.bolt-on-performance.com/wp-content/uploads/LingenfelterHeads.jpg. I am going to use this engine in a street car with a rpm range of 1000-5500 and I want to get as much power as I can get staying in that range.  

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68scott385
I mow my lawn and find Chevys
Posts: 1994
Joined: 10/09
Posted: 10/08/12 09:35 AM

By the time you have your current heads cleaned, magnafluxed, pressure tested, and then have the complete valve job (grind/reface valves & seats...possible 3 angle job), probably going to need the guides replaced too, you could have bought a set of new Vortec heads that flow better anyway. You're going want to purchase a better intake manifold anyway, one for the Vortec heads won't be much more expensive than an old style intake.

Might want to do the price comparison before choosing either option.

Food for thought.  
68scott385 68scott385 68scott385

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skyeking
I mow my lawn and find Chevys
Posts: 2738
Joined: 08/09
Posted: 10/08/12 11:45 PM

Go with the Flow!!
All the best to all the people and even BOB....  
skyeking

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ethelkilledfred-#001
I mow my lawn and find Chevys
Posts: 1371
Joined: 03/10
Posted: 10/11/12 09:49 PM

Icon Quotekev8alot:
Hello.

I have a 1979 L48 350 195 HP engine(stock). This is what I know(or think I know) about cylinder heads. It's part of the valve train assembly ie: camshaft, rockers, valves, springs, etc. Performance wise, the heads give you the most power improvements for a NA engine. Power is achieved by porting, polishing, flow testing, and overall improving the quality of the components based on what you're doing. My questions...

1)Flow Testing, what does it accomplish ie: Rocker arm ratios, picking the right camshaft, spring strength needed, etc?
2)If I do not want to enlarge the ports to fit bigger valves is porting still worth doing?
3)In your opinion how much horsepower could I expect from just cylinder head work?
4)Maybe the hardest, what is inertia supercharging and does it work?

Check my Introduction to see pics and know a little more about my project. Thanks.
http://forums.chevyhiperformance.com/70/9265282/general-discussion/hello-chevy-community/


In My Opinion

1)Flow Testing, what does it accomplish ie: Rocker arm ratios, picking the right camshaft, spring strength needed, etc?

A way to compare different heads to each other

2)If I do not want to enlarge the ports to fit bigger valves is porting still worth doing?

Yes

3)In your opinion how much horsepower could I expect from just cylinder head work?

50-100hp or more depending on the head and the guy doing the porting

4)Maybe the hardest, what is inertia supercharging and does it work?

Tunnel Rams use gravity to get inertia supercharging.  
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