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GM - Chevy 250 Engine Conversion

178949 Views 785 Replies 86 Participants Last post by  hanzo111
Starting a separate thread on the 230 & 250 inline 6-cylinder engine conversions.
This engine conversion will bolt in and out of a 90/119/130 without vehicle modifications, like the 292 making it an easy, inexpensive weekend conversion.
Since the 230 and 250 blocks are 2" shorter than the 292, and the ancillary mounts are different, this thread should eliminate any confusion with the 292.

Why convert?
The performance and ease of conversion are remarkable and well-suited to a Defender-style vehicle.
After driving small diesel for over 15 years and having to deal with high maintenance and poor performance coupled with reliability issues it was time for something better.
We built conversions for the Diahatsu 2.8 TD, the Iveco 2.8 and 3.1 TDI, and the OM617, and drove Land Rovers with 200 and 300 TDI engines.
These mechanical diesel are generally loud and smoky while the GM inline 6 is smooth and so quiet, you often don't hear it idling or driving.

The Chevy 250 was used in cars, trucks, and vans, and had many industrial uses being manufactured from 1962 to 1990.
A good used GM inline 6-cylinder engine typically sells for under $500 and is usually less than $250.
The cam is driven by metal timing gears eliminating the need to change a timing belt or timing chain.
The GM High Energy Ignition (HEI) systems are extremely reliable and were used on military vehicles without issue when submerged.
Parts are inexpensive with over-the-counter support from any local parts store.

There were several different versions of the 250 engine with different cylinder heads.
Some of the heads had a separate bolt-on manifold, while other versions had the inlet manifold integrated into the head casting.
Both versions will fit into a 90/110/130 using our conversion kit.

If you want Electronic Fuel Injection (EFI), the Holley Sniper is a good choice.
We will be working out the details for the Sniper as we did for the 292 conversions.

The other deciding factor was the accessibility to the engine and all the components.
Everything is within easy reach making for much shorter work intervals.
I timed changing a starter with hand tools which took 12 minutes.

With HEI and EFI, the only maintenance is changing the oil along with the rare wires, plugs, cap, rotor, and air filter renewals.

We will be offering kits as soon as they are manufactured.
As of the date of this post, we are waiting on the engine adapter castings to be machined, which hopefully won't take much longer.
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Trial fit.
We picked up a running non-smoking Chevy 250 for $125 that the previous owner had removed from a Chevy Nova.
The engine is complete with the power steering pump and alternator.
This particular 110 is RHD.
The factory ancillary mounts clear the inner fender and frame, making a RHD conversion extremely simple.
We will be fabricating the prototype motor mounts over the weekend.


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Even more simple than the 292 conversion...This is SOOOOOOOO cool! Can't wait to get the kit!
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Just looked up the specs. "It developed 155 horsepower and 235 ft.-lbs. of torque." EFI should further improve that.

Very close to the 3.5 RV8. Ideal for a LR, but I wonder how the LT77s will handle it, even late ones.
Just looked up the specs. "It developed 155 horsepower and 235 ft.-lbs. of torque." EFI should further improve that. Very close to the 3.5 RV8. Ideal for a LR
The key is at what RPM the power band comes in and with the Chevy pickup cam the 250 power band for max torque is at 1,600 RPM and the truck version is about 245 ft. lbs. of torque.
The other thing is the gearing.
The 3.5 uses the 1.4 Transfer case, while we recommend a 1.22 for the Chevy 250.

I wonder how the LT77s will handle it, even late ones.
You can tear up an LT77 with the stock engine if you try.
We used the heavy duty R380 Stumpy with the 292, so we'll have to see how the LT77 holds up to someone who is impressed with the quick performance.
Certainly the early suffix LT77 will be challenged by the Chevy inline 6.
Motor mounts prototyped and ready for the production metal fabrication shop.
Looks like the engine was meant to be under the hood of a Defender.
Engine fits nicely without any modifications.
With a RHD 4 cylinder frame, the stock Chevy 250 alternator and power steering fit just like they were made for this application.
We are working on the AC compressor bracket and the LHD alternator mount, but so far very promising.
The prototype running engines cost $125 and $50 respectively and both run fine and with GM HEI ignition and the Holley Sniper EFI are virtually maintenance free.
We are installing the GM/Chevy 250 in a 2 door RHD 110 with AC, so stay tuned as this conversion is simple and very very inexpensive.


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250 excitement

Hard to hold back the excitement as this project gets closer to fruition. The ability to have a conversation and have then decent acceleration is going is going to be the bomb. Can't wait!!!
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Strangely, I think I want this one instead of the 292.
I think the 250 with its shorter stroke would be a smoother running engine and probably a bit lighter.
I'm very intrigued with Robert the Davis' latest effort and I think the 292 might be a bit more motor than I personally would need.

As Robert is fond of pointing out you have to work within the limits of whats downstream in the running gear for ultimate longevity.
Torque has a wonderful way of breaking stuff.

I've had Chevy trucks with the smaller engine and its a sweet running motor.
People have different opinions on the 292 vs 250 vs 230, but JW is right the 292 puts out more torque than the 250 or 230.
With the Holley Sniper and HEI, the 292 is extremely smooth and has more than enough power to do anything you need it to do.
Under normal driving conditions, you cannot even hear the engine.
I have almost engaged the starter when the engine is running, it's that quiet.

Dropped the prototype mounts off to be manufactured today around lunch-time.
Will have a 110 this fall or winter with a 250 under the hood.
Feel confident that the 250 engine can easily pull a 1.22 transfer case.
And the best part of these motors for you guys who want more power - they share a lot of common parts with the old Chevrolet V-8 - pistons, valves,rockers, rods and some other parts if I remember correctly - and anything else you need for better performance is available from Clifford Performance.

Their motto is 6=8 - we built up one hell of a Ford 300-6 back in the 1970's using their stuff - that's how we found out about the whole breaking stuff possibilities of a big torquey six cylinder. Like I said this is putting some very bad thoughts in my head....
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There are a number of vendors that supply parts to boost performance if one wants to go in that direction.
The nice thing about the GM/Chevy six cylinder engines is the stock power output is more than sufficient and the petal response is instant.
No more pushing the accelerator to the floor and waiting 2 or more seconds for a turbo to finally spool up as you listen to a diesel clunking along.
With the inline 6 you get a very quick response as the 110 jumps forward.
Inspired by Robert’s Chevy/GM inline 6-292 conversion thread, I recently took on and just completed an engine conversion in my 1992 RHD Exmod Defender 90. All I can say is that the conversion is AWESOME! My 90 is now enjoyable to drive, can pull into traffic without fear of getting rear ended and doesn’t have the smell and knock of a diesel, which for me, was wicked desirable (I know diehards like the diesels). It is actually quite fast now and pulls great in all gears (hills I use to have to drop down to 2/3 gear are nothing in 4th). I still have some local reliability runs to make before I take any long trips, but I’m feeling optimistic.

I replaced my pitiful 12J (2.5NA) with a Chevy inline 6 (250/4.1L) from a 1968 Chevy Camaro. Although there are cheaper options, I chose to rebuild the engine locally, which did cost a bit more than some online options, but I wanted that local connection and ability to talk to the rebuilder face to face. This option did take a long time and did screw up my summer deadline, but it eventually came together and I’m hoping to enjoy at least 2 months of New England weather before putting her away for the winter.

Some details...

-I ended up getting a Scotty’s Adapter from Robert because his bell housing adapters weren’t ready yet and I was trying to get it on the road before summer, however I do plan to swap it out once his become available because I like his design better. They are the same depth, so it is an easy swap. Engine and transmission fit bell housing adapter with ease.

-I ended up having the motor mounts fabricated locally by a local hot rod shop, as I again was hoping to get it in the road for the summer and Robert’s RHD 250 mounts weren’t ready yet. Because of this I paid much more than I suspect his will cost, but it was the decision I made to try to get on the road faster. The mounts use the original chassis mount locations and original rubber pucks, so no changes needed and they just bolt in. The engine aligns with the mounts like it was meant to be there.

-My stock bonnet clears the top engine bits no problem.

-My engine had a 1 barrel Rochester Monojet carburetor, so I just rebuilt that and plan to use that for now. I would like to get the Holly Sniper EFI eventually, but need to figure out a new intake manifold too, so I’m going to wait. The 1brrl Monojet seems to work fine so far.

-Although I didn’t have to, I ended up switching my LT77 with a R380 stumpy from Ashcroft, but I still have the 1.4 LT230 and it seems fine even though it isn’t the 1.22.

-I decided to buy a new fuel tank and run a new fuel line rather than cleaning out and reusing the 27 year old tank. It was cheap enough, so I figured it was a good choice.

-I decided to buy and use the Revotec V8 electric fan kit and install it on my 2.5NA radiator, which was only a year old. The electric fans work great and eliminate the manual fan, which was around 3.5” away from radiator (with a 2” extension). The fans keep the engine running at 180 degrees no problem. the top radiator hose is from a BMW 318i. The fans weren’t designed for this radiator, but fit great and use the stock mounting pins and lower brackets.

- I have no crowding in any areas the engine at all, so the alternator and starter both have plenty of room. I currently have manual steering, which I don’t mind at all, so I don’t have a need for a power steering pump bracket. That said I will likely get a bracket from Robert in case I ever add it back (had PAS on it originally, but it never worked, so got a manual box to simplify).

-I purchased an inexpensive starter and alternator from DB Electrical for under $120 for both.

-I added an Electrical VDO oil pressure gauge and sender along with an Electrical VDO water temp gauge with sender. Both seem to work great...runs at or below 180. I did have to get a small 1/8” npt extension (1.5” from Lowe’s) to extend the oil pressure sender due to the thickness of the side covers and the block shape.

-I purchased nice cast valve and side covers from These are thick, but very nice. The fins on the side cover had to be dremeled a bit for the distributor cap to fit.

-I am currently using my original exhaust with a hodgepodge downpipe, but plan to either get a new downpipe made this week or an entirely new exhaust at a local muffler shop. Current exhaust is fine if I get a new downpipe, but I would like to add a little rumble to it.

-The install can definitely be done in a weekend with a kit. Mine took longer since I pieced it together myself, but the install and removal is easy and with a kit would take out the guess work. I didn’t have any experience taking an engine out before this year and now I can remove and replace it within 1 day no problem.

-I used a throttle cable from a LHD 300tdi, which is pretty cheap and made my own bracket that mounts off the exhaust manifold.

Here are some pics...

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Wow That is a sweet engine. Very nice!
Just wow! Very nice engine swap - you guys are being a bad influence.
I really like the valve cover and side covers.

What is the length of the Chevy six from the back of the block to the front of the crank pulley?
That fits so nicely!

Only odd looking bit is simply the heater hose runs. Those will be much easier in lhd conversions.
That fits so nicely!

Only odd looking bit is simply the heater hose runs. Those will be much easier in lhd conversions.

I agree on the heater hoses, I’m going to try to redo them this winter.

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