Zed Head

Here are a couple of threads on the topic just to fill it out. One talks about head gaskets for sure. https://forums.hybridz.org/topic/59029-head-cooling-on-cylinder-5-solutions/#comments https://forums.hybridz.org/topic/98875-90mm-gasket-coolant-holes/

There was a whole big conversation on Hybridz years ago about head gaskets and holes. The end impression that I got was that not all of the holes were meant to be open. You'd probably have to see factory original gaskets to know for sure what the engineers intended. The head design in general has uneven cooling as I understand things. Cylinders 5 and 6 on the turbo engines are the ones that detonate most often. People took extensive measures to try to improve the cooling, drilling in to the passages and adding a manifold to control coolant flow. The funny thing was, as I recall, that the guys that got it evened out would just get detonation on all 6 cylinders at the same time.

Engineering type nerd talk but I took a GDT course long ago and Fidanza's concept makes me nervous. Stacked error (wrong term, can't remember, probably stacked tolerances). Are you supposed to have that plate skimmed before usage or just bolt it up and go? Make sure that you understand well how it's supposed to be used. Even if Fidanza is confident it wouldn't hurt to have it checked.

Piston availability has varied over the years. Here's an old post about alternatives. Takes some extra work. https://www.zcar.com/threads/honda-xl500-pistons.45301/ Datsun Spirit has possibilities too. Expensive of course. https://www.datsunspirit.com/shop And Rebello might have something. Haven't seen much written about what's happening there, but if he's still building engines he needs pistons. http://www.rebelloracing.com/nissan1.htm

Are you losing spark or injection? The resistor is part of the 280Z tachometer circuit. Here are the instructions for the Crane modules. People often have problems when they use aftermarket ignition on the 280Z EFI systems. Not sure why. I have had odd problems with loss of injection if the ECU doesn't like the tach connection. https://static.summitracing.com/global/images/instructions/xr700 instructions.pdf

Edit - It might be just a partial conversion. Just realized that you did not read the CL ad. If you read it you'll find - "Nice V8 scarab conversion with engine still intact." https://datsunforum.com/the-scarab-legend-the-original-hybrid-datsun-z/ "As time has passed, the number of legitimate Scarab conversions have become cloudy – Some claim less than 200 “factory” Scarabs were ever produced, while others put that number upwards of 270. Adding to the confusion, many “customer cars” were converted by Scarab – and even more were converted on a DIY basis by owners in other states, as over a thousand conversion kits were sold during the life of the company with an approximate price tag of $1200. Some customers opted for all of the upgrades, some just wanted the V8 swap..."

The engine seems to be in the Scarab position. Jammed against the firewall.

Some sources call it the Auxiliary Air Regulator. AAR. If you look closely at where it attaches you should see a plate underneath it with heating cooling lines attached.

That would be because the coolant plate underneath the AAR has heated up. That means that the valve is not binding. All signs point to no electrical power through the AAR heating coil. Unlikely that a vacuum leak would disappear when the engine warms up. Just trying to be helpful.

This video just popped up. Interesting results.

The math is correct. That's about all that can be gleaned from your post. You'll want to match the pistons to the heads, not the block, to get the desired CR. The L28 was used for small and large combustion chamber heads, the pistons were changed to achieve the desired CR.

His problem is with the AAR, not the thermotime switch. The AAR has power as long as the fuel pump has power.

You can also stick a Noid light in the connector and start the engine. The light should stay on when the engine is running.

It's on the same circuit as the fuel pump. Looks like it grounds through pin 34. You can test the whole circuit at the ECU connector. The FSM instructions describe how to use the Start circuit to actuate the fuel pump relay to provide voltage. But you could also just disconnect the AAR and test for voltage at the AAR connector with the engine running. The AAR should get power when the fuel pump does and the fuel pump only gets power when the engine is running.

This is a sign that there is no electrical power at (edit - actually should say "passing through". The ground side must be there also to complete the circuit) the AAR plug.

There should be no skipping or jumping ever. You broke something. Probably not worth fixing, even if it's possible. Find a new diff. Consider an R200 conversion, Nissan started using them to take the torque of the L28 engines. p.s. please post pictures of the destroyed gears or shafts after you open it up.

Pretty easy to siphon from the Z cars. On your 75 you can see right down in to the tank through the filler neck. Use an Oklahoma credit card. Should easily get the level down to where you can at least try to replace the sender without dropping the tank. Looks cramped under there though. Good luck.

Unbolting the fuel rail would remove the heat path that Jeff G described. Insulation won't help that. Conduction, convection, radiation.

Did you do these three things at the same time? Maybe there's a problem with the transmission, not the rims or tires. Or maybe something got bent when the car was lifted to put the wheels on. If you used the rebuilt transmission with the old wheels and didn't have the problem then you can narrow it down to what happened when the wheels were put on. Since it worked well before it is most likely a problem that was created when the recent work was done. Don't get distracted by other things. Look at the work that was just done.

So, considering your last post about deadheading the metal rail, it seems that the big difference might be the rubber hose versus metal lines. Maybe the key is fuel temperature before it gets to the bowls. The cooler the better. We've talked about fuel differences in the various EFI heat soak threads. Fuel quality varies across the country. Might explain the AL versus MI difference. Could be a winter blend thing also. Jeff G were you running aviation or race fuel, or pump fuel?

That is pretty severe "vapor lock" if it happens just sitting at idle. Is this on a car without a fan shroud? Sitting out in the hot sun with the hood closed? The carbs need air flowing past them to cool, the coolant flow is for the engine. A quick test might be an electric fan under the hood pointing at the carbs. See what happens. Jeff G, is your deadhead mod using the mechanical pump or an electric pump? Your solution creates more pressure in the supply lines. I wonder if VaCat33 has the proper orifice in his return line. Or if a smaller one would help. A quick test might be to clamp the return line to create a deadhead system. If it helps then your solution should do the same. Things to "try" that might shed some "light".

Yes, they're both up under the dash behind the glove box. Easy to see. The vacuum cark has a vacuum hose connected to it. If I remember right if you lose vacuum to the vacuum tank it stops working, no heat. So your problem might be under the hood. I had a problem with the hose splitting, and got used to fixing it when I suddenly didn't have heat.

Could be the vacuum cokc. It controls coolant flow through the core.