454 turbo impco 425 x2 tuning help

Propane, Butane, LPG, GPL, C3H8, C4H10
cardar911
Posts: 12
Joined: Sun Jul 13, 2008 1:48 am

454 turbo impco 425 x2 tuning help

Post by cardar911 »

Hey guys

First time caller long time listener lol
May I say great forum great info hope everyone is well.

I've finally had the time to turbo my truck. Chev c10 built 454 running x2 impco 425 x2 model e converters.

The problem I believe is the balance pipes. I think they must be too long and have 90deg brass bends. Where the convertors are mounted which are abit far away putting the pick up in the carb hat makes it long.

The problem I'm having is as soon as it starts making any boost it doesn't and has a flat power curve. No back firing just nothing there. But if I hold middle to full throttle at around 4000rpm eventually builds some boost maybe 5psi
The question is can the balance pipe pick be in the turbo charge pipe with a scoop like gas research setups prefer? So my balance pipes can be short and better flowing? Or does the balance pipe need to be close to the carb?

Thanks for reading will post pics to help explain cheers

Best regards Rob

cardar911
Posts: 12
Joined: Sun Jul 13, 2008 1:48 am

Re: 454 turbo impco 425 x2 tuning help

Post by cardar911 »

Balance pipes are 800mm and 12mm Id hose

cardar911
Posts: 12
Joined: Sun Jul 13, 2008 1:48 am

Re: 454 turbo impco 425 x2 tuning help

Post by cardar911 »

Engine bay pic guys cheers. Learning how to post pics
Attachments
Picture of the setup
Picture of the setup

cardar911
Posts: 12
Joined: Sun Jul 13, 2008 1:48 am

Re: 454 turbo impco 425 x2 tuning help

Post by cardar911 »

Another pic of the setup guys thinking of putting the balance line pickup just before the y section in the piping. I want to sort all these things out before the dyno.

My tuner isn't confident with it they mainly do gas research turbo. I'm in Australia Melbourne. If I can't get it running good I have to try a gas research setup.

Thanks again guys
Attachments
IMG_20200419_084840.jpg

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

Re: 454 turbo impco 425 x2 tuning help

Post by storm »

As I mentioned in the PM I am not all that knowledgable with regards to Turbos BUT I can say you inlet track is way to small. As a comparison the L67 that I am building is 3.8 litres the Eaton M90 will be putting out at least 1 Bar of boost so the L67 would be behaving as though it is twice the size (7.6 litres). Anything less than a 4" ID intake duct is a restriction. Your engine is 7.5 litres so your intake duct should be the same size as mine just so you are not restricting the turbo that is trying to feed your engine.

Now let me ask you a question, how much HP do you think this monster (I say that is a nice way) will make? I ask this because you need to make sure you size the entire fuel system appropriately otherwise you'll have difficulty and that is even before we start considering the turbo and boost referencing the regulators. So now another question for you, would you mind telling us what components you are running starting from the tanks right through to the twin 425s you are running.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

cardar911
Posts: 12
Joined: Sun Jul 13, 2008 1:48 am

Re: 454 turbo impco 425 x2 tuning help

Post by cardar911 »

Thank you!!

Details :
Single outlet t'd to twin lines. High flow lock offs. Twin model e's twin 425s.

I'd be happy with a cruisy 10psi for now. This setup on YouTube 700rwhp done 2 times I've seen. I'd be happy with a fair bit less than that.

Car runs great very responsive till the boost starts.

Cheers for ur help

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

Re: 454 turbo impco 425 x2 tuning help

Post by storm »

cardar911 wrote:
Sat Apr 18, 2020 11:43 pm
Single outlet t'd to twin lines.
Change this to twin outlets of at least 8mm, preferably 10mm, lines right through to the regulators and this job will be so much easier.
cardar911 wrote:
Sat Apr 18, 2020 11:43 pm
High flow lock offs.
What brand and model?
cardar911 wrote:
Sat Apr 18, 2020 11:43 pm
Twin model e's twin 425s.
Good.
cardar911 wrote:
Sat Apr 18, 2020 11:43 pm
I'd be happy with a cruisy 10psi for now.
For the turbo experts on here do you have the brand and other specs of the turbo?
cardar911 wrote:
Sat Apr 18, 2020 11:43 pm
This setup on YouTube 700rwhp done 2 times I've seen. I'd be happy with a fair bit less than that.
Ah ok, so you are using youtube for inspiration. Do you have a link to the video you are referring to? 700rwhp can be approximated to 1000 crank HP.
cardar911 wrote:
Sat Apr 18, 2020 11:43 pm
Car runs great very responsive till the boost starts.
It could be fuel, lack of air, or timing.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

cardar911
Posts: 12
Joined: Sun Jul 13, 2008 1:48 am

Re: 454 turbo impco 425 x2 tuning help

Post by cardar911 »

Thanks for ur reply.

Twin outlet definitely on to do list. Will see what my tuner says if he could do it

Turbo is a gt45 t6 style china turbo. Seems to start spooling 2200rpm ish

The lock offs are electric from memory they were high flow ones

Cheers again

My inspiration for the build on YouTube

https://youtu.be/g4jZenljMNw

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

Re: 454 turbo impco 425 x2 tuning help

Post by storm »

Please don't take this the wrong way but there is very little real information for me, or anyone, to be able to give accurate and helpful advice.
cardar911 wrote:
Sun Apr 19, 2020 3:20 am
Twin outlet definitely on to do list. Will see what my tuner says if he could do it
You need a license to work on LPG systems and if your tuner isn't licensed he cannot legally touch any of your LPG system.
cardar911 wrote:
Sun Apr 19, 2020 3:20 am
Turbo is a gt45 t6 style china turbo. Seems to start spooling 2200rpm ish
This is why I like superchargers, if it is starting to spool at 2200 rpm with good gearing you are already way over the speed limit. My wagon is doing 2000RPM at 100kmh.
cardar911 wrote:
Sun Apr 19, 2020 3:20 am
The lock offs are electric from memory they were high flow ones
This is what I mean about real information. Brands and part numbers are helpful "electric high flow" means very little because 1 brands high flow is another's low performance. Please read through the thread that I have linked in my signature so you can see what I mean.
cardar911 wrote:
Sun Apr 19, 2020 3:20 am
My inspiration for the build on YouTube https://youtu.be/g4jZenljMNw
That's a Gen 3 6 litre small block that come from the factory with really good flow numbers. Yes it is a pushrod engine but the design technology in that engine was brilliant for the late 90s earlyy 00s. You are running a Mark IV (read really old style technology based on early to mid 1960s racing technology) 454 (7.5 litre). The Gen3 may be an inspiration but comparing the 2 is like comparing apples and oranges.

Re reading your PM, which I will quote relevant parts here because you haven't posted this information in this thread, you said:
"It's a 78 Chev C10 under cab mount turbo. Built 454 twin impco 425 twin impco model e. Got all the balance pipes and bits hooked up properly I believe."
Do you have a rear mount turbo? I don't understand this "fad". Why? because turbos work off pressure. The higher the heat the more pressure (think of a radiator) going into the turbo from the exhaust side, the higher the flow (speed) the more pressure (think of a hose). Put the turbo as far back as you can and you loose both flow (speed) and heat. To me it is counter-intuitive. Put the turbo at the end of a well designed header system which realistically would be no longer than 2' if you have it designed well (think of the GM 6.5 litre Turbo Diesel) and you have 4 or 8 ports flowing into the turbo keeping it turning even at low RPM. Infact I'd go as far as mimicking the design of the diesel setup.

Re reading over your posts again my thoughts are, and bear in mind I am not a turbo expert, with regards to the balance pipes I would have the pipe as large (within reason) and as short as possible. If the port on your regulator is 1/2" make sure the ID of your balance pipe is 1/2" ID. Get the regulators off the inner guard and mount them on the 425s that way the vapour hose is short and throttle response is almost instant but the balance pipes are also as short as can possibly be.

EDIT: Never having had to do this I actually didn't even know these ports were on a 425. I learn something new everyday. Holding the 425 with the fuel inlet on the left of the mixer just underneath the air filter flange there is a port labeled BAL as shown in the attached picture. That's where you plumb the balance line from the mixer to the regulator.
425-Balance.jpg
I'm used to GRA mixers more than Impco mixers. FYI GRA mixers are not warranted if the are used in a blow through configuration.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

cardar911
Posts: 12
Joined: Sun Jul 13, 2008 1:48 am

Re: 454 turbo impco 425 x2 tuning help

Post by cardar911 »

Cheers storm

Working on a different balance pipe setup atm, will see what happens. Yes it may run out of gas flow/ supply and that's for the dyno to find out exactly.

Have had Gra turbos Nissan rb's in the past they do work well just thought I'd try impco this time see how it goes for simplicity.

C3H8
Posts: 1129
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: 454 turbo impco 425 x2 tuning help

Post by C3H8 »

My knowledge of turbo's is limited, however I can see two issues with your system to check out. I would not use the balance port on the 425. It's a 1/8" NPT which means an opening of only about 1/4 inch which you then enlarged to about a 5/5" line. You should pipe those balance lines directly into the 90 degree adaptors on top of you mixers using a fitting the same size as your balance line running to the convertors.

Issue 2: The model E regs are not rated for 10 PSI of boost. The top lid will leak boost pressure and LPG out of the secondary. You will need to add a reinforcement ring to the lid. It has to be custom made. The lid is so thin it will distort and leak. Many turbo applications have custom made a reinforcement ring to prevent leakage at this pint. 10 PSI means the primary pressure will increase to 11.5 PSI on the LPG side. Although not exact the regulator is maxed out at 8 PSI, however IMPCO does not even like that. I ran pressure tests on regs many years ago and found the top gasket would start leaking at pressures as low as 6 PSI without reinforcement. We were experimenting with the E's to see if we could adapt them to a useable reg for injection.

C3H8
Posts: 1129
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: 454 turbo impco 425 x2 tuning help

Post by C3H8 »

My error! I just enlarged your photo and see you are piped into the adaptors on top of the mixer already. The system you have should work ok as a balance line. Like you mentioned I prefer not to use 90 degree fittings, however they are available in a formed pipe rather then the style you have. There not plastic but steel usually.

cardar911
Posts: 12
Joined: Sun Jul 13, 2008 1:48 am

Re: 454 turbo impco 425 x2 tuning help

Post by cardar911 »

Thanks c3h8

I'm trialing a new balance line over this week end will update.

Appreciate the info guys

cardar911
Posts: 12
Joined: Sun Jul 13, 2008 1:48 am

Re: 454 turbo impco 425 x2 tuning help

Post by cardar911 »

Hey guys made the changes to the balance pipe, has helped the problem quite a bit. Still have a big flat spot doughy Rev range. The turbo starts to spool so it seems around 2400rpm then from the there the pedal is non responsive (doughy) till say 4000rpm the turbo is acting normal get to as much boost as I hold it. No surging, real serious power

Question is how do u tune the mid range not WOT. I've seen an adjustable tap in the balance pipe before which I quickly tried not sure.

Thanks again
Rob
Attachments
IMG_20200424_102049.jpg

C3H8
Posts: 1129
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: 454 turbo impco 425 x2 tuning help

Post by C3H8 »

425 mixers only have adjustments for idle and wot. The midrange is controlled by the taper of the gas bullet based on the current airflow. Airflow increases the bullet (air/gas valve) lifts higher allowing more fuel. The midrange can be changed by replacing the air/gas valve with a leaner or richer configuration. If the mixtures are lean you can change to an AV1-1651-2 gas valve (#51 bullet). If too rich you can go to an AV1-1644-2 gas valve (#44).
I don't know what your referring to as an adjustment inside the balance pipe.

Post Reply