This problem has persisted through three water pumps so that is not the problem. It has good flow out of the head to the radiator. I use only NGK BP5EY V-Groove plugs and have since they first came on the market in the late 70s/early 80s so their heat range is not the problem. My timing is on 0 TDC right now so that is not the problem. The new High Compression head still pings when the motor is hot just like the old head did. I am using a lot of octane boost but it still isn't stopping the detonation when I give it much throttle, just like before.

Now, one person has said that they used the same carb and they had a similar overheating problem, just not as severe. The Holly/Weber has to go.

I am going to go with a fuel injection from a Sentra instead of another carb. It just makes more sense. Later I can add another throttle body to it. I do not want to use the port injection. Why? It only has one small port opening and very much restricts the amount of air that is available to the intake system. I want more air. More air means more HP. More HP means more fun. That is the reason that people use twin carbs, it lets in more air to breathe. The FI will regulate the amount of fuel in to the air much more good than a carb can. Right?

Mareo

I've run the Holley/Weber(holley5200/weber DFEV pinto carb) for a long time. I had a B210 radiator and a 185deg thermostat. I didnt have over heating problems. It would get hot if i drove fast ( at about 4500 rpms and up in 5th) on a hot day (90+deg) for a long time.
What I mean by 'it would get hot' is the water temp would go up to about 215deg and the oil temp would get to 200. I figured if I was driving 85-95mph for 3-4hrs straight (SF to LA via Hwy 5) that those temps are 'normal' .
I have SU's now and i does the samething. Now i watch the EGT gauge and make sure it doesnt get over 1300deg or the coating on the headers will get messed up. (i just thought of a new topic)
Have you tried to richen up the carb? Just to see what happens. Find some old jets from a Ford/holley/weber and drill them out.

Hey mario, have you checked for a restriction in the exhaust system? Sometimes even a slight restriction will cause a car to overheat on the freeway(high rpm). I ran over a speed bump too fast one time and it partially crimped the pipe in front of the muffler. Sounds like you've covered every other base, so I thought I would throw that in. Good luck.

roughneck

I also ran Holley/Weber carbs for about two years - with zero overheating problems.

That reminds me. The heat riser, if stuck partially closed will cause overheating. Or do all A-series have one?

Mareo, we know that you are experienced with all sorts of vehicles and obviously would have checked the easy stuff. That doesn't mean we shouldn't mention them -- many people will read these posts and the suggestions might eventually benefit somebody who runs into a similar problem.

this is long, but please bear with it, it will make sense.
Mareo this is not personal, so lighten up a little will ya? you are frustrated with a problem you can't figure out, so you asked those who are here for help, but it seems that you don't like the answers you are getting, WHY?
first off you are using the wrong plugs, please get a second opinion to confirm this, Nissan specified BP5ES for the A series with point ignition, BPR5ES-II for electronic ignition. BP5EY is for toyota's and honda's NOT NISSAN, again I beg you to have someone else confirn this.
despite how it might appear, I DO NOT claim to know everything, no one does, we all make mistakes, me, you, everyone.
stop and think about a few things, then go back to the basics. a restrictor plate works great for a race car, but isn't very practical for the street, why? very simple a thermostat is there to regulate engine heat, as in keeping warm water in the motor until it reaches normal operating tempurature, after the motor warms up, it also controlls the flow of coolant TO PREVENT OVERHEATING. if the coolant does not spend enough time in the radiator to allow it to exchange heat and cool off, IT WILL CAUSE AN OVERHEATING PROBLEM., go buy yourself a 160 degree thermostat and a new gasket and put them into the car and run it, maybe it will help, maybe it won't, but it can't hurt to try, at least you will know for sure that this is not the problem. with as big as radiator as you say you have you should never have a cooling problem.
you say you tried water pumps, radiators, flushes, etc., etc. and didn't get results. the only other thing besides the carb you haven't changed is that restrictor plate, or so you said, could that be the problem?
again, NOTHING PERSONAL, we are all here to help each other, not get into pissing contests. I've doing this for the better part of 30 years, and have seen a bunch of things cause problems like you are experiancing, problem is that I don't know you, your background or you car so I do need to cover all the seemingly stupid possabilities just to make sure. I could be way off in the ozone on this, but please think about it.
in re-reading your last post, I have a few questions, what motor (as in A12, A14)?
what compression ratio are the pistons? (stock dished, flat tops, domed) which cylinder head (casting number H10, H23, H62, H72, etc.) has it been bored?, with or without a heater (yes this could make a difference) what cam? is it possable that the cam timing is a tooth off? (see this all the time on belt driven motors) I ask that one because you say the timing is set at TDC and you still get ping, could be that the cam is advanced 1 tooth and causing the problem. I have ran A12's at 25 degrees advance flat out hard on pump gas and never had a pinging problem.
it sounds as if you have covered most of the obvious stuff, might be that you are going to have to start taking things apart and verifying that the mechanicals are where they need to be. if that isn't it and the motor has been bored, could be that the cylinder walls are too thin, this would have been caused by core shift in the block casting.
good luck.

Mareo, has your head been shaved, I know you said its new, but if you shave it to far it will cause overheating. you mentioned it pings on acceration, too much compression or to lean, also cam timing can effect temps. if you think it is too lean try this, run the engine at 2500 to 3000 rpms slightly cover top of carb with your hand if rpms increase your too lean.
BOb

rgrinder thanks for taking the time to post a great deal of info for Mareo's prob. He's right Mareo, there aint much left to cover so I'm guessing you're gonna have to go back over some teritory already covered. I'm picking a heat exchange problem.

Quote:
Lean a/f mixture should cool the cylinder heads a little, not make the water temperature go up. But pinging alone can cause the piston to burn, then the gasket can get scorched, start leaking water and then an engine will massively overheat.

That's probably not the problem with your car Mareo, if it's not losing coolant on most trips where it gets warmer and warmer. If the coolant is leaking out somewhere ...

Bob makes a good point, detonation is bad if it continues for more than just a brief period. The newer engines run just on the edge of detonation (using the knock sensor) to get the best mileage and power (advanced timing). But you shouldn't hear it, the knock sensor is like a microphone and can hear it when it's just starting. Then the black box reduces the timing within a few thousandths of a second.

Heat will affect pinging (replacing a 180 or 195 degree thermostat with a 160 one will often stop pinging). Compression will do it most dramatically (regular gas likes 8.5-9.0 generally speaking). Timing will cause it.

Anything that causes hot spots in the combustion chamber can potentially cause or contribute to detonation:

- hot intake air
- stuck heat riser in exhaust manifold
- stuck heated-air flap in air cleaner
- Spark plugs with too high heat range
- overly warm engine
- deposits in the engine
- lean burn
- initial timing
- timing advance (vacuum)
- centrifical timing (weights in distributor)
- low octane fuel
- high compression

Lean a/f mixture shouldn't heat up the water temp. However, it'll cause burning later in the cycle and burn through the exhaust port, sometimes creating hot valves and piston tops. Deposits in the engine (carbon, etc) can get hot enough to detonate the fuel before the spark goes, causing the "ping" sound. Sometimes it can burn the valve or valve seat or piston top. If bad enough the hammering can break the piston.

Quote:
Not always. Some EFI systems (speed-density) are designed strictly for one particular engine with specific exhaust system and other parts. They can regulate the a/f ratio only within a relatively narrow range. Most of it is pre-programmed. I would think if you put that system in a bigger or smaller engine it wound't run well, maybe someone has experience with that. The automaker will put different computers (or chip) in for each model. The oxygen sensor is used to fine-tune the end result, but O2 sensor doesn't work when the engine is cold or at wide open throttle.

EFI systems using MAF (mass airflow) sensor generally can work well with engine modifications, like if you put a different camshaft in. MAF directly measures the airflow coming in, and so the computer can figure out what the a/f should be (not pre-programmed). Again the oxygen sensor fine tunes it. I think these system have a speed-density map also in case a sensor stops working they still run.

So yeah, I've never driven a carbureted car that ran as smooth as a good EFI system. But if a sensor goes out, EFI can run poorly. I once drove 1000 miles with a bad TPS. It made the throttle jerky and put a big black smudge on the back of the car above the tailpipe. But it started perfectly and never stalled. And the beauty is the engine diagnostic told me which part to replace -- no expensive tools needed.

before you yell at me,could it be cavitation of the water pump at speed,this isn't usually a problem,but were the 3 pumps different brands. used to be a problem with racing cleveland v8s,& you seem to have looked at just about everything else.i always thought a lean mixture would cause overheating however.hope you find the cause real soon,so you can enjoy driving it again.best wishes,don't let it get to ya.