More Air Flow for a Model 425 on a 327 SBC

Propane, Butane, LPG, GPL, C3H8, C4H10
storm
Posts: 737
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
Work out your budget and go from there, What can you realistically afford?
Now ask yourself.
Do you want a nice cruiser?
Do you want a street racer?
Do you want a race car?
Each of these have a very different driving style.

With regards to the idea of fitting an Impco 600 I'd be asking what is the cost before I thought about that any further. If they can't tell you how much the they haven't done it before and you may be being used as a test mule. From memory Impco 600 mixers flow about 900cfm which is great but they are for stationary engines (e.g. large generators, pumps) and do not have an idle circuit. They run at max speed all day every day.

I, personally, am not a fan of hacking a manifold like the ones in the AMC forum link. Without airflow or CFD testing you won't know what the manifolds airflow characteristics become.

The 2nd picture in your next post is of a GRA Gas Reseach Australia) twin TB. Now I do like these and have been using them on my personal vehicles for nearly 20 years but there are 2 things you need to consider.
1. GRA parts may not be easily available outside of Australia and New Zealand. At least one member here from Canada had alot of difficulty getting what he needed and eventually gave up using the mixers.
2. They can be, extremely, temperamental when setting them up especially if the ignition system isn't at its best. I've got on of mine (single throttle body) fitted to my 3.8 litre Ecotec V6 with wasted spark. I know about 6 months before if my coils are starting to fail because the GRA mixer loses its normally excellent drivability. Because of this, now that I am getting work again, I am moving to LPG injection on my daily driver.

If you really want to go dual mixer on a Chev V8 I'd choose something like this https://www.edelbrock.com/performer-rpm ... -7525.html

1st things 1st though decide how much you are willing to spend then go from there.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

Marc
Posts: 64
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

Wisdom comes with age...
I though today about the project.
It was a sunny day here, very hot for winter time, all kids outside...

You address the right questions.
Of course, it is nice to think of all the power of a large performer engine.

Reasonnably, the car is a w-e cruiser, I will not race it, never, I have 3 daughters and my wife does't share my hobby. I am not involved in any clubs here and nobody shares this hobby to power propane V8... Here people enjoy old car in original format for a tour. In the Netherlands I know real enthousiasts (emails) but not in Belgium.
In my case, the Camaro power is only used occasionnally but sure I like to feel the power of the V8 any time , and hear it revved at high RPM :-) when I start to drive like that, I like to go and go :-)

Money ... well I should keep budget for other tasks on the car, I don't like to go in the unknown, and dual impcos as I understand will bring other unknown costly options + I already calculated 1 k$ extra only in parts around fuel delivery and intake. And the cost of this larger engine is way more + all custom fabrication and surely extra parts. + maybe some drivability issues bringing headaches...

So answering your question reasonably leads me to the 355 ci, on which I will bolt my current intake and I will port these heads before installing the engine inside the car, then we will tune it with IWEMA with the single impco 425, new coil new map control box and I will report here the results :-) They have a built mixer good for 400 Hp, it could be replace the impco if I am not satisfied. We'll see.

Questioning is always good. Here parts are not readily available. Shipping takes time and cost. So I'd better do the right choice :-)
I think I will me very happy with a good performer 355 ci :)

This projet will take months.

I decided I will concentrate my free time on other things as well, and I am soon starting to install a new electrical harness in the camaro.

Thanks for your help.


Marc

storm
Posts: 737
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
Marc wrote:
Sun Feb 21, 2021 2:38 pm
Wisdom comes with age...
Are you calling me old? :lol:
Marc wrote:
Sun Feb 21, 2021 2:38 pm
Of course, it is nice to think of all the power of a large performer engine.
Very true and when planned well the fuel consumption of a well developed, built, tuned, and driven engine can be quite good. When I owned my Trans Am (1977 Bandit with the 400-4 speed combination) I could get 22mpg out of it and it had well over 300 hp after I rebuilt and blueprinted the engine to standard specs.
Marc wrote:
Sun Feb 21, 2021 2:38 pm
Reasonnably, the car is a w-e cruiser, I will not race it, never, I have 3 daughters and my wife does't share my hobby.
I totally understand and believe you have made the right choice for you and your circumstances.

I am really looking forward to seeing your progress.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

C3H8
Posts: 1089
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

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

Post by C3H8 »

Darn, I just wrote a long winded reply on why not to use a 600 mixer and accidentally closed my browzer. Short version. 600's, as storm said are for industrial. They don't have an idle circuit. One has to be machined. They also are made to operate at lower RPM's so they have special gas valves plus what's called a power jet. These have to be matched appropriately.

Stick to your thought of a single 425 and Model E. If you want more HP then consider dual mixers. The manifold storm linked in would be ideal. You only need two Holley square bore TB's to mount dual 225 mixers (656 cfm) or dual 425's (920 CFM). Use 2 model E's. Use a single 1'2" or #8 supply line to feed both vapourizers. It should be adequate.

I once helped a drag racer with a 1400 HP Drag race engine with 4 model E's and he fed them with two 1'2 inch #8 fuel lines. He did use a 600 mixer but it was heavily modified for it to start and for the gas valves to lift fast enough to provide the fuel demand. In addition he had to machine in an idle circuit. Although idle was about 1400 RPM. His car ran sub 8 second quarters. Very touchy setup though that needed constant changes to compensate for altitude changes for every track he ran. The key point here though is it was not streetable with a 600.

C3H8
Posts: 1089
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

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

Post by C3H8 »

Also 600's are expensive. $800 to $1000 CDN. After that you would probably need different air valves and power jet combinations to get it right adding $100's of dollars.

Marc
Posts: 64
Joined: Mon Apr 23, 2012 8:54 am

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

Post by Marc »

Good to know C3H8...
Indeed I read earlier about the impco 600 being stationnary. I don't know why IWEMA told me about that...

I started with dismantling all car interior to work on the electrical harness. Also I am trying to sell my engine parts; and I am preparing my list of parts next to the BPE engine purchased.
I finally went for the 383 but I will keep 1 single mixer. This will bring me tons of torque but still drivable and no extra expense on intake stuffs... Sure I will loose top end power but I don't really care.

For the parts around the motor, I am wondering about the cooling. I have a GM 3 core 21" radiator, and on camaros.net forum they tell me this won't be enough on a AC car with a 383. I guess I believe them, but cannot say because my bypass was not working therefore I had weird temps variations.

A brass 4 core big block like is expensive. Then there are aluminum large tube 2 cores 23" radiators.
https://www.coldcaseradiators.com/produ ... e-radiator

In both case a new larger shroud is required.

Any advice?

Marc

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