GM 292 Straight 6 - Yet another conversion

Red90

Well-known member
My bad, I read the bit on the first post about the Ashcroft short R380 as a requirement, didn't realize that was an option.
It is meant as a bolt in engine swap for trucks that have a 200TDI or earlier diesel in place. Any other arrangement and it will not be bolt in.
 

RDavisinVA

Well-known member
I think everyone is saying the same thing different ways.
The adapter I manufacture will bolt between the engine and any short belhousing LT77 and also the R380 Stumpy.
 

Robert

Well-known member
I think everyone is saying the same thing different ways.
The adapter I manufacture will bolt between the engine and any short belhousing LT77 and also the R380 Stumpy.

I see, somehow I was under the impression this was a 3.5 replacement


I would like to see one with this slapped on. That should break something quick. Might take a few trips to Brazil to get all the pieces



 

RDavisinVA

Well-known member
Back in one of the posts it explains:

GM inline 6 - 292, 250, 230 engines are a direct bolt in, bolt out replacement for the 3.5 V8 or a pre-300TDI 4 cylinder (2.25 diesel or petrol, 2.5 diesel or petrol, 2.5 Turbo, and 200TDI).

You must use the short belhousing LT77 or R380 stumpy. If you have a V8 vehicle, you have to use the pre-300TDI 4 cylinder floors and tunnel.

So to replace a Rover V8, you also have to change the transmission, tunnel, and floors. They all bolt in bolt out. The V8 seat base is either modified or replaced with one from a short LT77.

Have no idea what that engine is pictured, but it appears not to be a direct bolt in, bolt out option which is a major requirement for our conversions.
 

RDavisinVA

Well-known member
Its one of those wonderful mismash vehicles that GM came out with. A Brazilian Chevy Omega with a 250 I6. KISS RD with the 292 plus FI.

https://www.hemmings.com/blog/2010/02/25/chevrolet-omega-the-last-250/
Well, I stand corrected.
That would bolt in if the rear of the block casting wasn't changed from the earlier domestic engines.
Not sure it would clear the steering boxes that could reside on either side.

I have been thinking about the possibility of multi-port EFI, but with the siamese inlet ports, you'd probably only need 3 injectors.
Siamese inlet ports and multi-port EFI is nothing new as the Mini Cooper has it, but know very little about it.
 

85RED110

Well-known member
Well, I stand corrected.
That would bolt in if the rear of the block casting wasn't changed from the earlier domestic engines.
Not sure it would clear the steering boxes that could reside on either side.

I have been thinking about the possibility of multi-port EFI, but with the siamese inlet ports, you'd probably only need 3 injectors.
Siamese inlet ports and multi-port EFI is nothing new as the Mini Cooper has it, but know very little about it.
http://67-72chevytrucks.com/vboard/showthread.php?t=276823

A post from the forum thread listed above:

"For any others that are interested in hearing why MPI doesn't work on a Chevy 6, follow along. These 6 cylinders all have an intake port design called "siamese", where cyls 1&2 share a runner, as do 3&4 and 5&6. This goes right into the head, so the two intake valves are effectively side by side, drawing on the same runner. So what's the big deal? The valves are open an equal amount of time, so no problem, right? Well, no, because of the firing order which is 1-5-3-6-2-4. Obviously, any fuel injected (even at the port) can only really enter the cylinder when the valve is open. And any fuel injection system will have the injectors open up to 80% of the available time (when wide open). But, the valves are really only about 25% of the time, so the fuel just puddles on the backside of the valve. In SB chevys, this is no problem, because when the valve does eventually open, the fuel enters the cylinder, just as intended.

Okay, lets look at that firing order again (1-5-3-6-2-4). Notice how the space (and thus the time) is not equal between 1 and 2 (and also 5 and 6)? 1 fires, then 3 other cylinders fire, then 2 fires, then 1 other cylinder fires. What this means in terms of fuel is that #2 gets 2/3 of the fuel, and #1 gets 1/3 of the fuel. Not exactly an ideal mixture.

This doesn't happen with a carb, because all air contains fuel, so the cylinder breathes when it wants, and gets the same air/fuel mixture.

In my case, I was stumped by why #1 and #6 were always lean, and #2 and #5 were always rich (leading to bad stumbling at times).

Should have thought about this earlier, but then one day I discovered this link: http://www.starchak.ca/efi/siamese.htm
which explains the whole thing with far more mathematics than I want to get into here. They even propose a few solutions, but I would chalk them up as impractical.

Anyway, fed up with the MPI (and not yet knowing the explanation of why it didn't work), I switched the throttle body over to a GM TBI (real cheap and reliable, these things). Well, that cleaned the problem up right away, and had some side benefits: easier installation, less wiring ratsnest, cheaper, looks more like stock (if that matters to you).

I'm kind of thinking (but never tried) that a dual TBI on a dual 4bbl manifold would be the ultimate because it would cut down the runner length for the fuel and it would make the manifold more symmetrical for more even air/fuel distribution."

Sent from my SM-G930V using Tapatalk
 

Robert

Well-known member
TBI is terribls on I6 intake manifolds. The drastic length differences ans 90 degree turn will have fuel clinging to the walls on some runners and not others. They use a single O2 sensor and average mixture across all of them so you get what you are claiming happened to your multi port 6. Carbureted I6 does this too, but it isnt closed loop chasing a fixed AFR so you fatten it up until all the cylinders are happy which results in the inner ones richer than the outer ones. Multi port is the way to go for balanced fuel delivery on a i6 log style manifold. This is all based on experience with the AMC 6.
 

RDavisinVA

Well-known member
TBI is terribls on I6 intake manifolds. The drastic length differences ans 90 degree turn will have fuel clinging to the walls on some runners and not others. They use a single O2 sensor and average mixture across all of them so you get what you are claiming happened to your multi port 6. Carbureted I6 does this too, but it isnt closed loop chasing a fixed AFR so you fatten it up until all the cylinders are happy which results in the inner ones richer than the outer ones. Multi port is the way to go for balanced fuel delivery on a i6 log style manifold. This is all based on experience with the AMC 6.
I would think some of the same general principals would apply among the AMC 6 and GM 6.
The big difference is the AMC 6 does not have siamese inlet ports making fuel injection a lot easier.
The 3 injectors for the 292 would solve the long runner throttle body issues, but make programming more difficult.
 

Robert

Well-known member
I would think some of the same general principals would apply among the AMC 6 and GM 6.
The big difference is the AMC 6 does not have siamese inlet ports making fuel injection a lot easier.
The 3 injectors for the 292 would solve the long runner throttle body issues, but make programming more difficult.

Looks like they unsiamesed it at some point after its deportation






http://www.4x4brasil.com.br/forum/vendem-se-pecas-e-acessorios/66304-vendo-motor-gm-6cc-4-1-de-omega-parcial-r-600-00-a.html
 

rocky

Well-known member
Corvette versions of this engine generation used two inlets only serving three cylinders closest to the carb.
 

Robert

Well-known member
Impressive amount of work, but is that good for more than 1/4 mile? I'm guessing the cooling passages aren't functioning
 
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