intake design for propan vapor injection

Propane, Butane, LPG, GPL, C3H8, C4H10
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intake design for propan vapor injection

Post by kikkegek » Sun Jun 10, 2018 4:01 am

hello everybody,

I have moestly been reading and following and not reeally posting, but have a question again for you guys. Cant really find it online.

My current setup is:
77 GMC C15 Suburban that is about 2400kg
has a 454 V8 Big Block connected to a 4L80E overdrive transmission controlled by a Microsquirt Transmission controller
Edelbrock Permformer cam
stock heads
stock dual exhaust
currently still has gasoline carb (Quadrajet) and IMPCO 300Mixer on top
and I had decided on my Weiand intake for my conversion, based on what I saw online.

I want to convert to propane vapour injection using this kit: ... _cyl..html

My ECU that I will be using is a MS3 and I'll be running a batch fire system, because I found little to no benefits to going full sequentiall, also looking at cost.


when you look at all the aftermarket big block injection systems they offer, they all use this kind of single plane intakes and he injectors are drilled into the runners close to the intake valves.


but when I look at more modern V8 engines, they all have the long runner design like you see in the LS engines family:


so looking at what aftermarket offers I am thinking that the Weiand intake I know have will be fine to add the propane vapour injectors and run btach fire.
But based on what I see in newer engines I am wondering if I should maybe look into an intake like the air gap style with longer runners:


So help me out guys...will my current Weiand single plane work? or are there serious problems I am going to run into because of the design?
storage/project: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.10 gears - IMPCO425 mixer
driver/project: 1977 GMC C15 Suburban - 454 big block - 4L80E- IMPCO 300A - 3.08 gears
sold: 1986 Chevrolet Suburban K20 Silverado

Posts: 648
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: intake design for propan vapor injection

Post by storm » Sun Jun 10, 2018 4:58 am

Normally choosing an aftermarket (performance) intake means you need to consider the operating range of the engine. While this is still true, EFI in general (and also LPG) give you alot of leeway.

In general theory, and real world testing (thus the types of design oem produces), indicate long runners produce more torque at lower streetable rpm ranges. Short runners and traditional single plane manifolds produce produce higher rpm horsepower. You need to remember that HP is just torque x rpm / 5250 so the more torque you produce at the desired operating rpm the more HP you'll also produce.

The thing with EFI (and also LPG) is that fuel atomisation is excellent so you don't get fuel dropping out of suspension and puddling. LPG won't drop out of suspension cause it is a gas and unless you are getting raw liquid LPG (liquid phase injection or just really freezing cold temps) it will never puddle.

Any manifold that emulates, in some way, the theory behind what oem produce for performance street engines will do the job you need (lots of torque for an extremely heavy vehicle that has the aerodynamics of a brick going down an S bend). I, personally, would go for the longest runners with the straightest shot at the valve as possible as long as the intake port isn't so big that it slows air flow at low rpm.
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Fuel flow requirements calculations viewtopic.php?f=5&t=1638

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