More Air Flow for a Model 425 on a 327 SBC

Propane, Butane, LPG, GPL, C3H8, C4H10
Marc
Posts: 73
Joined: Mon Apr 23, 2012 8:54 am

Re: More Air Flow for a Model 425 on a 327 SBC

Post by Marc »

Hey Storm,
I search for other grinds but they do not exist with larger exhaust duration compared to intake. Or then I had to custom order a camshaft...
I plan to port my exhaust port this should help flow as well.

Marc
Posts: 73
Joined: Mon Apr 23, 2012 8:54 am

Re: More Air Flow for a Model 425 on a 327 SBC

Post by Marc »

the other grind is this one but I there is a lot of lift ... a little bit more that what the rocker arm can take without modification

https://www.lunatipower.com/voodoo-hydr ... 2-268.html

storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: More Air Flow for a Model 425 on a 327 SBC

Post by storm »

Marc wrote:
Mon Jan 18, 2021 3:15 pm
Hey Storm,
I search for other grinds but they do not exist with larger exhaust duration compared to intake. Or then I had to custom order a camshaft...
I plan to port my exhaust port this should help flow as well.
I know what you mean.
If a custom grind was chosen I do the intake of this https://www.compcams.com/high-energy-ma ... block.html
with the exhaust of this https://www.compcams.com/magnum-224-224 ... block.html
and have the same lift on both intake and exhaust.
Better yet go hydraulic roller.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: More Air Flow for a Model 425 on a 327 SBC

Post by storm »

Hi Marc

Here's a video that may give you some hints with your Vortec heads https://www.youtube.com/watch?v=j8Rbpn4KRjY
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

Marc
Posts: 73
Joined: Mon Apr 23, 2012 8:54 am

Re: More Air Flow for a Model 425 on a 327 SBC

Post by Marc »

Thanks Storm.
This guy makes good videos.
On this one he explains how to pocket port the exhaust bowl.
https://www.youtube.com/watch?v=CbNnpCJSBAU&t=234s

And this seems like enough; + I can do on my own. Going to 1.6 valves requires new valves, valve seat, however mine should still be ok, I will soon have my cylinder heads out of the car and I will check for wear and see what/if I need to change some parts…

Basically I am thinking to keep my 1.5 valves…

Read this article :
https://nastyz28.com/threads/906-vortec ... lp.320597/

Thanks :-)

Marc

Marc
Posts: 73
Joined: Mon Apr 23, 2012 8:54 am

Re: More Air Flow for a Model 425 on a 327 SBC

Post by Marc »

Hi Storm

Heads are out. Parts should arrive by the next week. While waiting for the parts I decided to repaint the engine bay and engine. Took me 2 days removing all and cleaning.

Recently I am consider your comment, and I documented on internet.

I see different arguments in regards to bigger valves. Clearly there is no need for the intake side. Exhaust helps with porting. Also I read that bigger is not alway better, one said it hurt torque down low.

Some interesting topics between "" in favor of the bigger valves (my comments after *):

- "The literature with the heads claims that the valve seats are 1.625 OD. They fit 1.6" valves and flowed 200 plus so they are fine." :
* This means I can keep my valve inserts, but I will need to ask a machine shop to machine the valve seats. right?
* If this is the case what is the advantage of a bigger valve if the entry throat is the same ID?
- " Pulled the factory installed valve seats today. They 1.547 inch OD"
* For the moment without the spring tool I cannot measure anything on my head : if new insert is needed, then a bigger throat would come with bigger valves.
* I also wonder when opening for larger inserts if I would not be weakening the cylinder head as the walls will be made thinner...
- "The VORTECS don't respond well to bigger valves unless you open the bowl up, recontour the transition into the bigger seat and lower the small side radius. The best thing you can do to a Vortec is a smoothig of the guide boss in the bowl and a back cut on the intake valve to start the low lift flow a bit earlier. Adding a bigger exhaust valve does help. The bowl need some cleanup and the short side redius needs some help, so a bigger exh valve is the last piece. I did this to my '72 Vette 350 with Vortecs...and I picked up 36HP at 5300 and an average of 19 HP from 1500 to 6300. I did the back cut in a home-made jig and a 200 fine paper disc on a bench sander. I did the bowl and boss blend myself with the Summit kit for $50."
* This goes in the same direction as you dictate to go porting and install bigger valves on exhaust... However there is no clear figures about which bring what gain : porting benefit with 1.5" valves versus porting benefit with 1.6". 1.6 valves helps but is it significant?
* Most information on Vortec on the internet is about lift and porting the exhaust not specially install bigger valve... So difficult for me to document clearly and take a decision.

Getting my engine currently in pieces let me realize I should do all what is possible to get to my goal which means get the maximum HP out of it.

There is a engine builder close by, I will contact them and maybe go there with my cylinder head. Part availability and price may dictate what I can do as well.


Kind regards,

Marc

storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: More Air Flow for a Model 425 on a 327 SBC

Post by storm »

Hi Marc

I honestly don't know about the valve inserts/seats. The size differences, as far as I am aware, between the 2 valve sizes is 0.01". As long as there is enough material to seat the valve and have a visible boundary between the closed valve and the combustion chamber then I, personally, would use the original size seats. My concern, like yours, is the amount of material left in the head after the seat recess' have been machined.

The theory behind using a larger valve works like this. When everything else is equal a larger valve provides a larger opening compared to a smaller valve at the same lift. As long as the ports potential air flow (without a valve) is greater than the port can flow with a valve the larger the valve used the better for overall performance. Now there may be certain lifts that, through a combination of port design and/or valve design and/or combustion chamber design this does not work and alot of that will depend on aspects like valve shrouding.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

Marc
Posts: 73
Joined: Mon Apr 23, 2012 8:54 am

Re: More Air Flow for a Model 425 on a 327 SBC

Post by Marc »

Work progress - center plate removed - does it look Ok? Not exactly similar from both sides…
Playing with the grinding tools, I scratched the gasket surface somehow : I 'd think maybe I need now to use some silicone when using the mixer gasket…

Marc
Attachments
zoom separation plate.jpg

Marc
Posts: 73
Joined: Mon Apr 23, 2012 8:54 am

Re: More Air Flow for a Model 425 on a 327 SBC

Post by Marc »

Engine bay in progress - motor degreased first phase.
More cleaning work needed still for the chassis to be fresh for painting black.
Attachments
Engine bay.jpg

storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: More Air Flow for a Model 425 on a 327 SBC

Post by storm »

What are you wanting to achieve by doing this?
Marc wrote:
Tue Feb 02, 2021 5:27 am
Work progress - center plate removed - does it look Ok? Not exactly similar from both sides…
Playing with the grinding tools, I scratched the gasket surface somehow : I 'd think maybe I need now to use some silicone when using the mixer gasket…

Marc
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

Marc
Posts: 73
Joined: Mon Apr 23, 2012 8:54 am

Re: More Air Flow for a Model 425 on a 327 SBC

Post by Marc »

Hi Storm,
From past readings :

"I think this is a great question to ask. It's discussed on this forum every now and then, and generally people fall back on the "common wisdom" that gas works better with single planes without explaining how a single plane can get more air into a cylinder in the low and mid ranges (where you'll be using a gas engine). That's what dual planes are for.

People aren't stupid in terms of how they've perceived differences in single and dual plane manifolds on LPG though, so in the absense of the performance comparison you're looking for, it's worth asking why this would be.

The only hints I've read that could explain this relate to the mixer and its sensitivity to vacuum signal. Apparently single planes have a more consistent signal to the mixer and that makes some sense too, but what sounds more attractive to me is that the large plenum area under a mixer in a single plane allows the port ready access to the fuel/air without waiting to pull it in through the mixer. A good way to duplicate this on a dual plane may be to mill the centre wall under the mixer base plate so there is a "plenum" effect that allows one side of the dual plane to pull mixture from the other side and the mixer at the same time.
"


Also have found tuning tips from guys doing this center plate milling on gasoline operated V8.


Marc

Marc
Posts: 73
Joined: Mon Apr 23, 2012 8:54 am

Re: More Air Flow for a Model 425 on a 327 SBC

Post by Marc »

Now I feel I may have done a mistake…

Marc
Posts: 73
Joined: Mon Apr 23, 2012 8:54 am

Re: More Air Flow for a Model 425 on a 327 SBC

Post by Marc »

From older topic

This is what Jay Storer says on single plane intakes
:


Storm, I'll listen to your advice.
There is not a lot of available information for propane powered small blocks. I see 3 options :
- either I completely messed up milling the divider plate on a dual plane intake, and a std edelbrock performer RPM intake type is the way to go
- or a real single plane intake (as article suggest, open plenum mid rise single plane, like kikkegek advised as well) is the way to go for propane engines
- or finally milling the plate is OK after all...?

Of course i can still check and see how it runs… I don't really like that because of the extra work and gasket is expensive … I always prefer to act based on documentation…

Thanks!!
Attachments
Propane single plane.jpg

storm
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Location: NSW, Australia

Re: More Air Flow for a Model 425 on a 327 SBC

Post by storm »

Marc wrote:
Wed Feb 03, 2021 4:52 am
Now I feel I may have done a mistake…
Don't worry about it I asked because it always helps to keep the end goal in mind when we are doing modifications.

Let's go through some theory.
Petrol is a liquid fuel so a petrol carb will behave differently because we are always trying to keep the fuel in suspension and atomised. Petrol port EFI will behave like LPG because LPG is a gas and doesn't fall out of suspension.
HP is high RPM power, TQ is low RPM power. HP = TQ x RPM / 5252 so the higher the higher the RPM the TQ is the higher the HP will be. Low RPM TQ will give good HP but high RPM HP will not give good TQ.
With everything else being equal short runners help to make HP at the expense of TQ, long runners help to make TQ at the expense of HP.

Plenum size is important because it is like reserve capacity. A 5 litre engine with a 2.5 litre plenum only has 50% reserve capacity so it will run out of breath in half the time as a 5 litre engine with a 5 litre plenum. Take a look at modern EFI engines and see how "street" engines have plenums that roughly equal the engines internal capacity. This helps alot. The smaller the plenum the higher the potential restriction to flow.

Plenum design is also important, and this is why I asked my question. A plenum is a chamber where all cylinders have equal access to the "reserve capacity". Dual plane manifolds have 2 plenums because they have 2 levels. Taking out the dividing wall gives the lower level increased "reserved capacity" but for the higher level to use that "reserve capacity" it must suck the air out of the lower level and back up to the higher level. Airflow turning around in this way is called reversion. This won't affect a standard street engine because their volumetric efficiency will never really need the extra "reserve capacity" but a performance street engine may end up with a flow imbalance because of the increase in volumetric efficiency causing the upper level to need the extra "reserve capacity" causing a high reversion situation.

To me a much better way to increase plenum size on a carb style manifold is with carb spacers, they keep the natural torque building design of a dual plane yet create a common area with "reserve capacity" that all cylinders have equal access to without inducing reversion by having to pull the air backwards within the manifold so half the cylinders can get the extra airflow they need.

I have never tried it with LPG but on petrol port injected EFI a tunnel ram manifold is the best of all worlds with very little performance compromise at any rpm. There are people who say LPG likes tunnel rams and, remembering I have never tried it so I am working off theory in my assumption, I agree it would be the best option for a performance street engine. Single plane, common plenum, with a large "reserve capacity", and no chance of the LPG falling out of suspension like petrol does at lower rpm.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

Marc
Posts: 73
Joined: Mon Apr 23, 2012 8:54 am

Re: More Air Flow for a Model 425 on a 327 SBC

Post by Marc »

Yes I understand this theory, and the LPG behavior, therefore my cheap low cost action to mill this divider plate.
My hood is low and there is no hood area to add a spacer. I have 2 spacers available I'd like to add them but I am almost sure I cannot... Maybe with a different hood, which is not my plan.

Yesterday I got my tools and parts, I removed the valves from the head.
I have a bad PCV valve. I already noticed oil being sucked too much by this valves, and oil on the throttle blades when dismantling engine....

Not a big deal though, but good to see it and correct before having more problems.
Now shouldn't I just install breathers on valve covers?

Regards,

Marc

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