Thread: 83 Z-28 w/ 406 roller hasn't the power it should, please comment?

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Hi everyone! I'm new to the forum. Hope I'm on the right website for my needs.

I'll make this as a short as possible!

I traded a dirtbike for an 83 Z-28. The owner purchased a 1970's model 400 ci motor. He had the machine shop bore the motor over .030", which I have heard makes the motor a 406. Please correct me if I'm wrong.

According to him, the motor has 500 miles since rebuild. He said it has powerpack heads, hedman headers, roller rocker, big cam, edelbrock performer 750 carb w/ intake, holley fuel pressure regulator, hei distributor, pro street pulleys, etc.

When I go to accelerate, the car kind of chokes out if too much gas is given, and it simply does NOT have the power you would expect from a motor of that caliber. I haven't really torn on the car hard or anything, have put a few hundred miles on the motor. Like I say, I haven't gotten into it really hard at all, but it will hardly even burn tires in 1st gear without just losing power and launching. The motor seems VERY, VERY underpowered compared to other 400's I've ridden in that had far less done to them.

Someone told me that it shouldn't be that way at all, and that a calibration of the distributor, carb, and checking fuel flow could all help me immensely. Does this forum have any suggestions? I greatly appreciate it.

gear ratio??? carb jets/metering rods?? timing? curve?

have you checked the plugs????

Do you know the compression ratio???or what pistons were used???Cam specs???and exhaust specs--

I replaced the plugs. The gear ratio is likely stock for an 83 Camaro, definitely highway. If i remember right the 750 performer carb comes stock jetted for fuel efficiency. The timing and curve I am unaware of, as well as the compression ratio. He said that special pistons were not used in the rebuild. He was misleading about the cam, and just said "big cam". The exhaust is longtube hedman headers, hooked to dual exhaus that if I remember right goes into one muffler, and back out the back as dual again. And to be honest, I have no idea what metering rods even are.

I think my next step is probably to call the machine shop he claimed to have the work done at, and see just what they have to say. Being as it is a small town, and this guy owns a business and does regular business with them, hopefully I can get a little bit of info, but if they ONLY machined the block, it's likely they wont know.

Edit - I was typing as you posted. Hopefully my approach is not too elementary - no offense intended. Like Jerry says, there's a ton of details that would help understand your problems, but before you get too deep hit the basics. It sounds like your carb is not properly adjusted, or maybe it needs to be rebuilt to get the accelerator pump giving you a full shot in transition acceleration. Pull your plugs and see how they look, which will give you some clues to your problem - here's a chart with pictures of what you should see:reading_spark_plugs.jpg
If you cannot read it here's a link:
reading spark plugs - Google Search Also take your air cleaner off, look down into the carb throat (engine off) and open the throttle once - you should see two strong streams of fuel from the nozzles into the venturi.
Like Jerry says, rear gear ratio will also tell you a lot about what performance to expect. You might find a tag on the rear differential, or you can jack up a back wheel, spin it one revolution and count the turns on the driveshaft (or rotate ten times for more accuracy). Post up what you find, and people will have ideas about where your problem lies.

Originally Posted by rspears

Edit - I was typing as you posted. Hopefully my approach is not too elementary - no offense intended. Like Jerry says, there's a ton of details that would help understand your problems, but before you get too deep hit the basics. It sounds like your carb is not properly adjusted, or maybe it needs to be rebuilt to get the accelerator pump giving you a full shot in transition acceleration. Pull your plugs and see how they look, which will give you some clues to your problem - here's a chart with pictures of what you should see:Attachment 49948
If you cannot read it here's a link:
reading spark plugs - Google Search Also take your air cleaner off, look down into the carb throat (engine off) and open the throttle once - you should see two strong streams of fuel from the nozzles into the venturi.
Like Jerry says, rear gear ratio will also tell you a lot about what performance to expect. You might find a tag on the rear differential, or you can jack up a back wheel, spin it one revolution and count the turns on the driveshaft (or rotate ten times for more accuracy). Post up what you find, and people will have ideas about where your problem lies.

No, man, thanks! No offense taken! I was glad you sent me that spark plug photograph, I printed it and am taking it home to compare it to my old plugs. The ratio I may be able to find.

Also, I want to learn this method you speak of rotating one revolution and count turns on the driveshaft. Looking forward to getting home to wrench on this gutless thing. I want it to scream like the 406's I see when I search 406 sbc on youtube. I should definitely have a motor that will do more It sounds good though. Thanks for all the comments! Sounds like I traded my bike for the red headed step child of camaros Hopefully the motor or some aspect of this car ends up being worth the money and trouble in fun and excitement. Hope I don't just have an old farm truck motor on my hands at best LOL.

Welcome to CHR!

Good deal or bad deal may depend on what type of dirt bike you traded away!!

Here's a few more suggestions:

Get us the numbers from the block and the heads. The casting number is typically on the rear (drivers side) and the engine number is stamped on a pad on the front of the engine on the passenger side.

Head numbers are typically in the middle of the head, but you need to remove the valve covers to get to it (you'll be doing this anyway - trust me)..

Look at this link for a real clear picture of where to find these numbers. GM Engine Casting Number Locations

The term "Power Pack" has been used for a lot of different heads - we really need the numbers to tell you what these heads started life as - I say that because depending on the head, they may have been machined during their life time up to and including different valves.

It's pretty tough to tell what you've got for cam (the "big cam" scares me a bit because it is almost always wrong and a typical rookie engine building mistake!) and pistons without major opening of the engine so let's work with the obvious stuff first. As has been mentioned, check the plugs and try and get the rear end ratio, get us some numbers and we'll combine a gazillion years of hot rod know how to help you get things sorted out!

Regards,
Glenn