lpg turbo v8

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mygasser
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lpg turbo v8

#1 Post by mygasser » Wed Jan 02, 2019 11:21 pm

hi all, i'm new here and would like to ask your opinions on my ideas.
i have a 68 plymouth valiant that i'm swapping a 383 big block (jensen interceptor) into. i also have a gt45 turbo. my plan is to run the car on lpg only, no petrol at all.
i had a full size chevy blazer a few years back that had an plg conversion, one of the old type that sat over the petrol carb. the guy i bought it from had it 7 years and never put petrol in it, i had it 18 months and didn't use petrol either. from this i know that you don't 'have' to start them on petrol until they warm up as long as you don't expect to use full throttle at low revs from cold. much like a carbed engine without a choke really and i'm ok with that.
now to the main idea/question.
i'm told if you set the system up as suck through when the throttle is shut at any decent revs oil is sucked past the turbo seals so teflon seals are needed.
what if i fit either a throttle plate or a throttle body on the manifold (boost side of the turbo) and 2 impco 425 mixers (enough for the power level i'm planning, about 600hp) on the suck side of the turbo? that way i do away with the need for teflon seals in the turbo so can use it as is.
any comments on the plan?
cheers, neil.

Gilbertd
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Re: lpg turbo v8

#2 Post by Gilbertd » Wed Jan 02, 2019 11:56 pm

No, you don't have to start on petrol and any single point system will start and run from cold on LPG. Even giving it full throttle shouldn't cause a problem as long as there is sufficient coolant flow to stop the vaporiser form freezing but you wouldn't give a stone cold engine full throttle anyway until the oil is warmed and circulating fully. Why should adding LPG cause the oil to be sucked through the turbo seals? You will need a throttle butterfly anyway but whether you put it before or after the turbo isn't really relevant. Most turbo installs blow through the throttle body anyway and your mixer would need to go before the throttle body. Impco are expensive and it isn't the mixer but the vaporiser that will dictate how much gas it can supply and consequently how much power it can handle.
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mygasser
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Re: lpg turbo v8

#3 Post by mygasser » Thu Jan 03, 2019 3:55 pm

The oil issue is not lpg related but is when the throttle plate/body is on the inlet side of the turbo, i.e. suck through. If the throttle is closed at say 3000 rpm the engine still wants to 'suck' and pulls oil past the turbo seals. Like when valve guide rubbers/guides are worn, you come off the throttle while driving and oil is sucked down the inlet guides. You then get a puff of smoke when you re apply the throttle and the oil is burnt off.
So that is why I suggested the throttle plate/body on the inlet, boost side of the turbo and the mixers on the in/non boosted side if the turbo. If there is a way of increasing gas supply as boost pressure rises then that would simplify things as the mixers could bolt to the throttle plate but that's why I'm asking here as I've not scratch built a system before.
Cheers, Neil.

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Re: lpg turbo v8

#4 Post by Gilbertd » Thu Jan 03, 2019 4:15 pm

You're talking about a single point and that has been done numerous times before on turbo'd engines. Instead of having one side of the vaporiser diaphragm open to the atmosphere, it is plumbed into the intake after the turbo so the pressure is always relative to manifold pressure rather than atmospheric (something like this https://tinleytech.co.uk/shop/lpg-parts ... o-reducer/ although you'd need one capable of the output you need, would need to parallel them up or modify an R90E to reference to manifold pressure). I run a Maserati bi-Turbo (not on LPG) and that has the twin turbos arranged to blow through the throttle body so if I was to convert that using a mixer, the mixer would go between the turbos and throttle body.
'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.

LPGC
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Re: lpg turbo v8

#5 Post by LPGC » Thu Jan 03, 2019 5:44 pm

Impco stuff is a bit different to normal mixer systems, the reducer outputs gas under pressure like a sequential system reducer just at lower pressure (as opposed to a normal mixer system reducer which outputs gas at close to atmospheric pressure), the mixer unit isn't just a restriction in the air intake but has moving components.. so is more like a true gas carb that is fed gas vapour under a bit of pressure, an R90 derivative wouldn't work well with this type of gas carb.

A normal mixer system setup (usual type with dumb mixer or Impco gas carb type) allows running on gas with a cooler reducer than a sequential system at least partly because of the low reducer gas output pressure (lower the pressure needed at the output and the reducer will work at lower temps up to a point because the gas will still vaporise at low pressure). But if you have a blow through mixer setup (again usual type or Impco) the reducer always has to output gas at at least a bit higher pressure than boost pressure... so like a sequential system reducer won't work well under boost conditions until the reducer has warmed up a bit.

If you tried to use a normal mixer system reducer that isn't manifold pressure referenced (or usual type Impco mixer system reducer) it wouldn't work under boost conditions (OK the usual type Impco system reducer would probably work with just a very small amount of boost... because it outputs gas under just a bit of pressure).

Wouldn't want to start running out of gas, or for the gas tank / tank to engine bay piping / reducer setup / cold reducer not to be capable of supplying rich enough mixture for boost conditions... a backfire due to a lean mixture on a turbo'd big block could be nasty with the volume of gas present in the manifold / ducting / etc at high loads. You can get away with a lower flowing tank / piping with a suck through setup than with a blow through setup due to the fact that it is only the difference in pressure between tank pressure and point of gas exit (reducer output pressure) that makes gas flow from the tank to the exit, there's more of a pressure difference under load with suck through. But still you'd struggle to get a single tank setup to flow enough gas for much above 450bhp especially in cold conditions when tank pressure is low.

Any beefy enough mixer gear would work suck through, Impco a good bet. TinleyTech might be able to advise better on blow through big Impco gear for turbo'd engines (and I think I know what they'll say) or there are (maybe were) R90 and similar derivatives that are designed to be used on blow through mixer systems but probably not in conjunction with an Impco gas carb (mixer).
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robertXX
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Re: lpg turbo v8

#6 Post by robertXX » Fri Jan 04, 2019 8:45 am

neil , did you get my reply on rns ?

here's my astra that i refered too..


https://www.lpgforum.co.uk/viewtopic.php?f=32&t=8781

mygasser
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Re: lpg turbo v8

#7 Post by mygasser » Fri Jan 04, 2019 5:46 pm

i did thanks robert. research continues.

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