HT 383 install

[77 K20]

I bought a GM crate motor and it was delivered last Friday for my '77 K20. So far I've removed my old engine and am now running into a few issues. GM stated that the HT383 was for '76 and older GM vehicles and would work with very little modifications. I'm posting what differences I find for future use and hopefully someone knows some answers on this forum.

First issue I found was the mechanical fuel pump they recommend just has 1 inlet and 1 outlet. Stock pump has 3 connections on it. Sounds like I'm supposed to just cap off the return line back to the tanks. The fuel pump they recommend is internally regulated to 6-8 psi, so I don't need an additional fuel regulator.

Today I found that the coolant sensor from my old 400 will not move over to the new 383. The hole in the block is smaller. My plan was to just order a new coolant sensor for a newer style GM truck. I've heard rumors that the newer style coolant sensors have a different resistance and my gauge will not work correctly? Anyone confirm/deny this?

I'll need to find a different adapter for my mechanical oil pressure gauge. The new block has a hole in it for one, but it is a different (smaller) size.

Went to move over my transmission TV cable... will not fit. Vortec intake manifold is flat, old style is at an angle. Thought about trying to modify or bend the bracket around so it will not hit the valve cover, but it was brought up by a friend of mine that I need to make sure the cable is still mounted in the same spot in relation to the carb. How is everyone else slapping iron vortec heads on their trucks?? I've never seen anyone mention a TV cable bracket in any threads. Anyone have any input on this? (I have a TH350)

Not quite an issue, but something I didn't know about. Vortec engines need an external coolant bypass from the water pump to the intake manifold.... but no fittings are provided. The hole in the water pump is about twice the size as the hole in the intake manifold. Need to find fittings and put in a short piece of heater hose (I guess).

I'm sure there will be more little suprises, but I've been trying to take pictures and will post them when I have time. I've been working on the truck during the day when I should be sleeping, then going to my job and work all night (I work a night shift).


Now for some good things- the HT383 crate engine comes with AC delco spark plugs installed, and came with a oil filter in a box (not installed). Wasn't expecting that. Also the flex plate that comes with the 383 has the same number of teeth my 400 has, so I should be able to move my starter over.

 

[77 K20]

In my coolant temp sensor issue so far I have found that the HT383 uses a 1986 and later 350 engine block. I looked up a coolant sensor for them- and they have a different electrical connector on it. It is a 2 pin weather pac style connector (same sensor is used 1986-2010). Some have modified the truck's wiring to be able to hook up to it, but the temperature then reads a bit high.

Others say if you have a machine shop there is enough metal to turn the original one down and then tap it to fit in the small hole in the head. (I don't have a machine shop).

Others have taken the vortec head to a machine shop and had them enlarge and tap the hole to accept the original temp sensor.

Lastly it seems most just use an empty hole in the intake manifold for the original sensor. It will read cooler up there.

Basically- no good answer.

 

[foamypirate]

Hmmm, my 87' TBI 305 has a single wire connector on the coolant temp sensor in the head for the gauge. May be something to look at, it may be the smaller size that you need, but I can't say for sure. Just make sure when you look, its the sensor the gauge, not the ECM.

 

[robert8096]

If the coolant sensor hole has NPT threads and you have enough room just go to the hardware store and find an adapter. Something like this:

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[77 K20]

If the coolant sensor hole has NPT threads and you have enough room just go to the hardware store and find an adapter. Something like this:

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I tried something like that but the "probe" part of the sensor is so big it doesn't fit into the adapter. Some I've read then did some machining to open it up a bit to make it fit, but then all the metal heats up with the exhaust manifold and you get much higher temp readings.

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[77 K20]

Hmmm, my 87' TBI 305 has a single wire connector on the coolant temp sensor in the head for the gauge. May be something to look at, it may be the smaller size that you need, but I can't say for sure. Just make sure when you look, its the sensor the gauge, not the ECM.

That is strange- I've done a search on Summit Racing, O'reilly auto, and NAPA auto and all I see your yours is the one with the weather pac connector.

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[77 K20]

 

[foamypirate]

That is strange- I've done a search on Summit Racing, O'reilly auto, and NAPA auto and all I see your yours is the one with the weather pac connector.

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If you look at RockAuto for an 87' R10 with a 5.0L TBI, they show both the weatherpak and single terminal sensors. Might be able to cross reference the part number to something O'reilly's carries to see if it will work without the hassle of shipping.

 

[77 K20]

I've spent the last few hours reading more about temp sensors. I'm getting irritated things are not as simple as they should be.

I looked up that sensor and did finally find one with a single terminal connection (blade style). However as far as I can tell the coolant sensors in 1979 changed resistance. The one you are using (TU66) at 100*F is around 1500 ohms. At 220*F it is 150 ohms.

My stock one at 100*F is 600 ohms, and at 220*F 83 ohms.

So then I could take out my temp gauge and install a newer one from the 80's, or start playing with resistors in parallel to try and dial it in.

 

[robert8096]

Ahh I see. If you go the resistor route use a variable resistor to dial it in to your liking.

 

[77 K20]

Spent a good part of the day moving the accessories and whatnot over to the new engine. Called a guy who does a lot of engine work and he said I need to buy an aftermarket TV cable bracket that bolts under the stock q-jet carb.

And as far as the coolant sensor thing- I removed the 1/2" NPT fitting on my intake manifold and could NOT screw in my stock coolant temp sensor. The way they machined the intake manifold there isn't room for the probe part to protrude inside the manifold. Looks like I'll just try to buy an aftermarket gauge locally. I didn't want to do that- but it will be more accurate than the factory gauge. Since I don't have AC I'm thinking of mounting the gauge in the little cubby hole the dash has on the upper right. A 2-1/16" gauge will fit nicely there I think.

My last possible surprise I found today is the GM high flow fuel pump. That thing is so big the case of it hits my motor mount. It is way bigger than the stock pump. The lower 1/2 of it you can clock it around so that the inlet and outlets can point a different direction (they are 180* out from each other). I was hoping to bolt it on with the engine out, but since there is clearance issues looks like I'll fiddle with it when the engine is installed. That "should" happen tomorrow.

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[77 K20]

Ahh I see. If you go the resistor route use a variable resistor to dial it in to your liking.

Turns out when talking to my dad tonight (who owns a '79 K15) that ever since he had Edelbrock vortec style heads put on his truck last year his temp gauge hasn't really worked. Put 2 and 2 together... he has the same issue with the coolant sensor. The shop must have put in a mid 80's one where the resistance is too high. And since his truck looks like it is off the showroom floor he will never even consider aftermarket gauges.

Do you have any details on how to add a resistor? I somewhat remember something about you can add one to the back of the temp gauge? Or there is one there from the factory?

Think I might experiment on mine and once I figure it out then go fix his.

 

[robert8096]

I would add it inside the cab in the sending wire between the gauge and the coolant sensor. Have you tried using multiple adapters to use the correct sensor. Like a short piece of brass pipe that the sensor fits into and then convert that with an adapter to fit the hole in the block?

 

[77 K20]

Thought about multiple adapters, but read where others have done that and you end up measuring the exhaust manifold temp instead (all that metal heat soaks).

Today I lifted the new engine out of the crate and looked into the fuel pump. It hits the motor mount. The motor mount has a built in nut in a bracket on it... so used a cutoff wheel and chopped the built in nut off of the mount. Still hit part of the clamshell-- so ground that down a bit also. Not enough to weaken it, but enough for just a bit of clearance. Then had to clock the fittings on it around to get away from the motor mount also. Dropped the engine into the truck and bolted it down thru the motor mounts. On the side with the fuel pump the bolt head is near the fuel pump. The other way won't work. The mounts are new, so should last a while. IF/when I redo them I'll need to remove the fuel pump first. No big deal.

Don't know why on my computer the pictures are "right side up" and when I download them onto GMSB they get rotated?

I also ordered an Edelbrock TV cable/throttle cable adaption plate that is made for flat vortec intake manifolds, and some VDO gauges. Figured they are more accurate than the stock gauge- might as well.

 

[77 K20]

Also made a little progress on the coolant bypass hose that vortecs need. So far I just have the brass fittings in from the water pump to the intake manifold. Also ordered a 5/8" silicone elbow to connect them.