383 240Z is dog slow....confused?

[TheNeedForZ]

I have some concerns about the 240Z I bought. The engine is said to be a 383, the rest of the engine is unknown to me. I sent the car out to have the carb choke set up properly along with other problems to be fixed(battery and air filter)

 

When the car came back I test drove the car a bit. It was my first time actually driving the car. And it was quite disappointing, I wonder what had gone wrong. The car felt like my daily driver VW Jetta(115hp, 2900lb). Gunning the gas pedal more didn't help much, the engine gets louder, the car goes a bit faster but it is still like the Jetta(and I dare say it's slower then the VW) The only thing that makes me glad is that one neighbour kid seem to like the look of the car.

 

This is what I know about the car :

 

1971 240Z

 

Engine : said to be 383 Chevy

 

Carb : Q-Jet with choke just fixed

 

Air filter : Idiots at the shop "Installed" a wrong size air filter (and they insist it's the correct size). The air can flow into carburetor without going thru the filter, so the carb is breathing freely at time of test drive. I now installed K&N filter that allows breathing thru the top, but I haven't test drove it since the K&N is in.

 

Trans : said to be TH350

 

Diff : said to be from a 85 300ZX

 

When I drove the car I put the gear in "D", Do I have to put it in 1,2,3 or is Chevy automatic trans different or something? Just want to ask in case it is something very simple which I do not know.

 

Weather on that day is sunny and dry. I was driving the car around the block, not on the big roads because the car does not have insurance. As a result I can't get the car up to a speed where it shift to another gear.

 

What could have gone wrong? Where do I start my troubleshooting?

 

Thanks

The Creeping Fastback

[chucky]

are you positive its a 383, I took the 383 out of my friends chevelle after he wraped it around a tree. when the motor was in his chevy it was a rocket. in a lighter z this things gonna scream! if its a 383 you'll know. a local speed shop should be able to help you, good luck

[Mrtemp]

Hmm, maybe some of the more technical guys can help you out, as im still learning as well. My car has the "boat anchor" chevy 305 (5.0l) and she feels NOTHING like my daily driver which is a 115 hp, 2003 Mini Cooper. The zed 'feels' like a rocket up to 3000 rpm then drops off. I've dyno'd my car at 161 rwhp @ 5000 rpm, and 238 ft-lbs @ 3000 rpm, explaining why the car feels slower after 3000 rpm.

 

Anyways, my point is, with a 383, your car should be a tire-roasting monster!

 

Which shop did you take your car too? Sounds like they arent all that great. I'd reccomend ATEB in burnaby. I went there for some basic tuneup stuff, and they're friendly knowledgeable people. The shop owner Jon bought me lunch the first time i met him! It's somewhat of a small shop, but they do big business.

[Guest Magnum Rockwilder]

take off full throttle from a stop and count the shifts. make sure the car is using all 3 gears.

[Guest zfan]

I have a 383 in my 240Z and you will know for sure. I can barely control the car with street tires from a launch, It goes all over the road. With drag radials it pulls so hard and my 383 is not a very radical build. Low to mid 11's in the 1/4. Some guys around here have much faster rides.

 

Get the numbers off the block and make sure the block is a 350 block to begin with. What rpm's is it shifting at when you punch it from a dead stop. If it shifts out early it will really kill the power, especially if it has a cam that brings the power in late.

 

Good luck and keep us posted.

 

Mike

[Guest WHITEBOY]

The tranny might have a manual valvebody. A lot of performance guys use them. Put the shifter all the way in first, and run it through the gears as magnum rockwell stated, only do manually. If this is the problem, the car will fly now.

 

Does the motor idle good and rev smoothly in neutral? If so, the engine probabaly isn't the problem.

[Corzette]

Another word of advice. Check your plug wires, distributor cap and rotor and Plugs. If they are fouled or your cap is bad or your wires are fried or your wires are not completely attached etc, then you will have issues with power. You might check your fuel pump and filter as well.

 

Terry

[Guest SC457A]

also do not forget to check your timing. that can play huge factors in power output.

[Jolane]

Maybe your transmission is slipping due to low fluid level or band adjustment. I would definitely check the fluid level in the tranny to start.

Joshua

[Pop N Wood]

For that matter if the plug wires are on the wrong plugs the engine will be down on power.

 

Make sure the carb throttle blades are opening fully, especially the secondaries. Pull the air cleaner, look in the carb and have someone floor the gas pedal (engine off of course). Are all 4 blades fully open?

 

Is the engine otherwise running smoothly? No rough idle, excessive vibration, loud clanking noises, smoke? No oil in the radiator or antifreeze in the oil? Is the parking brake stuck? Can you easily push the car when out of gear? No slipping, i.e. do the engine revs follow the speedometer correctly? Oil level good?

 

Might be worth taking the car to a diagnositic station and have an experience mechanic give it the once over.

[Drax240z]

Not sure where you are in BC, but if you are on the island you can bring it by my shop in Vic and we'll sort it out for you. http://www.zensport.ca

[Guest tony78_280z]

Welcome to the hobby car. Wanna know why it is called a hobby car? It becomes a hobby just keeping it running. Build it yourself, or bought it, you better learn about it.

 

Your problem can be a whole lot of things to try and diagnose. Particularly if you don't know where to start, because you never drove it before. Not enough fuel, too much fuel, air chocked, catalytic clogged, weak spark, engine not built to specs and not holding compression properly, distributor not advancing correctly, Vacuum leak, etc. I'm sure I can sit here and come up with many more.

 

I allways lean towards the carb being the fault, (cause it allways is with mine.) Do you have mechanical or secondary back barrels? Are they opening properly and at the right time? tryin to run off of just two it will run ok, just sluggish.

 

As helpful as this site is, you are gonna need to aquire technical manuals for different components in your car (ie. you got a Q-jet carb, get a Q-jet manual) and learn as much as you can. Most have helpful troubleshooting sections.

 

Good luck

[Sumo]

also do not forget to check your timing. that can play huge factors in power output.

What SC457A said, i had a car worked on once and had the same symptoms. It revved all day but went no where. We checked the tranny, fluid, shifter, throttle cable adjustment and it turned out to be just the timing was retarded due to a loose locknut.

[cameron]

maybe took a lobs off the cam, I've done that and it gose from a v8 to a v6 really quick!

[DavyZ]

What SC457A said, i had a car worked on once and had the same symptoms. It revved all day but went no where. We checked the tranny, fluid, shifter, throttle cable adjustment and it turned out to be just the timing was retarded due to a loose locknut.

 

Ditto!!!

 

maybe took a lobs off the cam, I've done that and it gose from a v8 to a v6 really quick!

 

Ditto again!!

 

All this advice is VERY applicable to your problems--I'd go through each one of these and MAKE SURE each gets a definitive answer before going to the next one. Timing is the first one I'd address if the car is slow.

 

Also, check or replace your fuel filter(s). They can do the exact thing you describe.

 

Davy

[baddriver]

How I would approach the problem:

 

1. Compression test - actual compression is unknown, so check for differences from cylinder-to-cylinder. Post the numbers if you're unsure.

2. Check timing.

3. check fuel filters/pumps, etc.

4. check for clogged exhaust

5. Check tranny fluid for 'burnt' smell.

6. Make sure drivetrain turns freely in neutral - parking brake sticking????

[Psykovertible]

and dont foget to make sure its shifting. if its not or it manual valve body you will be trying to drive in just 3rd which will will suck and burn the trans up

[Guest davido]

sounds like my dads old 1981 el camino, 305 auto and was slow as a dog.

[Michael]

If the engine is idling smoothly, yet lacks power at EVERY rpm, chances are that it's not the carb.

 

Some years ago I test-drove a Norskog (similar to Scarab) 240Z conversion - it was a 327 or maybe a 350, with some sort of 5-speed (probably a T5). That thing was incredibly sluggish at every speed. I mean, it was slower than my Corolla; it felt like it had maybe 40 hp. Some engines are just dead tired. Maybe the rings are shot, the cylinder walls scored and the (like already mentioned above) the cam lobes are worn off.

 

My 280Z has a 454, originally from a 1978 Suburban. For whatever reason, it wiped maybe half of the cam lobes. Some were so bad that the lobes were worn clear down to the base circle! The engine sounded horrible, backfired all the time, and eventually sent flames through the carb. It ran on maybe 5 cylinders, and of those, maybe 2 were seeing correct valve opening and closing events. And this was in an engine that was originally rated at a whopping 215 hp. Nevertheless, if I mashed the throttle off the line, the torque was enough to swing the back end out.

 

Morals of the story:

 

1. A large displacement engine in a light car can be in unbelievably bad condition and still produce enough power to deliver impressive acceleration.

 

2. An engine can sound like it's OK, idle like it's OK, have exhaust like it's OK, and still have such devastating problems that power is miserably low.

[awd92gsx]

I've often thought about that Michael,

 

I've little to no V8 experience and wonder if I would know if my setup is working properly or not.

 

Maybe I should have it dyno'd just so my butt-o-meter doesn't tell me otherwise.