What to do with this original numbers matching engine...

I thought I'd ask for advice about my 71 Road Runner.

This is a show car I've had for almost 30 years and it's in very nice original factory condition. Aside from a repaint in the 1980's, new upholstery, and wear & tear and maintenance, it's all original. I've only put on about 6,000 miles since I bought it.

The problem is that when I bought the car it had 100,000 miles and the engine wasn't winning any 1/4 mile races. It starts and runs reliably, but the power just isn't there.

How can I refresh the engine while keeping the originality of the car? Can a rebuild keep everything original, including the bore?

Thanks.

I don't see why not. An engine rebuild does not change the originality of the car.

Not going out on much of a limb to say no, the bore will likely not be original when you are done.

An untouched 1971 engine at 100k miles it's almost guaranteed to be wore out.

When I had my numbers matching engine rebuilt I only had it bored +.010, just enough to clean the bores. Then I had custom pistons made for an extra $30 each instead of going the standard +.030 overbore.

To really do it right, and correct any issues found, it'd be best to allow for fresh machine work, pistons and so on.

That said, you may be able to get by with a hone/re-ring and valve job if it is not worn too horribly bad. But, by then, it's torn completely down and that's the golden opportunity to really get it right.

Regular stock Service manual specs are almost crazy for a performance application, allowing a whole lot...like .010 bore taper before boring was supposedly deemed necessary. That said, you can make one run reasonably well again with a hone and a fresh set of rings if the bore wear is less than that.

If you go that route it's more like an overhaul than even a rebuild...polish the crank, hone it, rings, valve job, gaskets, and that's it.

But what will you do if anything is worn past spec, which almost guaranteed it will be? Like the cam. Or what will you do if a crank journal is scored, machine it or find another one? At some point if the quality of the build vs. originality conflict with each other, it'd really be better to err towards quality.

Personally? I'd stash the original numbers engine (or just the bare block) get another similar engine to build (you didn't mention what it is?) assuming it's a 383 you can get another one, or a 400 which looks the same externally, and build it for fun with a stroker kit, etc. and have a bunch more power/fun.

Shouldn't cost a ton more than rebuilding a stock engine with what's available off the shelf today. This way you can have fun beating on it and not worry about damaging the cars numbers matching status.

.02

I agree

There are folks who prize originality - including worn-out ignition parts & hoses - over good running condition; but if you want to actually drive & enjoy the car, a stock-spec rebuild isn't going to detract from the car's market (or enjoyment) value.
I'd hold the boring & crank work to the minimum, but all of that + the valve job will depend on the wear you find when you open the thing up & inspect it.
Worst-case scenario, keeping the external appearance stock is really the only concern as far as market value.

Nobody asked the first question:

How are you using the car?

Maybe he doesn't need a stroker 400 and doesn't run the car hard.

Yep. If you're not pushing the car hard why separate it's pieces.?
Many never find themselves back together again.
Owner then has the * in his thoughts and conversations about the car; "it IS numbers matching but that motor is tucked away in my shop" blah blah blah.

Keep it together unless you run it hard.

With a repaint and new interior, a rebuild wouldn't matter. But one big to remember, nobody is going to ask to see in the bores. But one thing could be done, put sleeves in it then the original pistons could be reused. Just a thought

This post has been a little confusing to me. If the goal is everything must be original as built, then you can't do a rebuild. If the goals is OEM original, folks are really only going to see exterior parts and matching numbers block and exterior components are the most important. Certainly having a good reputable Mopar guy do the work. Internally, if not really worn, original valves maybe salvage, heads cleaned up, seats corrected, who cares if the springs are new.

Minimal work to the engine if possible. Frankly, you can still find good original pistons and rods if necessary.

Engine builder I help is freshening up for performance a 73 440. Basically only needed a cylinder honing, though it probably did not have 100K on the motor. Resized the rods, added a forged crank instead of cast, better valve springs and moved to early 440 stock high compression pistons and a mild cam. You can even get bearing and seal to rebuild the water pump. But I bet it is not original anyway at 100K and 47 years. Do you want to trust the oil pump or do you go with new, but use your old housing and just swap ring and impeller... Nothing wrong with a OEM rebuild with new rotating parts. Obviously if a survivor car or going for a gold standard, all NOS parts would be used, but cost goes through roof.

Frankly no one will know what was done internally unless you show them documentation and pictures.

If this is going to be a cruiser and you don't change the way you use it, I would find a good engine machine shop near you and at least rebuild the long block, send the carb to Scott Smith at Harms (i am assuming you still have the original carb?) and then once the motor is home, have fun putting it all back together detailing it, reinstall..

Happy deciding and tinkering...

Had 100k on it when you got it, but you do not know if it was ever apart, right? If it was me, I would remove it, take it apart for inspection etc. If all orig, it is WAY overdue for valve stem seals and other wear items, timing chain etc. Cool thing is date of mfg is usually on rod and main bearings, gives you an idea if ever rebuilt and all. If the bores are close enough to re-use, maybe just re-ring and replace freeze plugs, cam bearings and whatever else looks bad. The problem with stem seals is the way they love to become brittle, crack apart and find their way to oil pick up screen. And that would cause you expensive grief when out motoring around one day. Hopefully the timing chain is steel based cam gear that won't fall apart and also jam up pick up screen like the older ones.

Two things come to my mind.
One. Check the engine condition to get an idea of what specifically may be worn. That also will give an idea of whether condition relates to seeming lack of power.
Spark Plugs.
Compression check dry and wet
Leakdown test.
Vacuum at idle

Two. Winning or losing races has a lot to do with whom your lined up with. But I'll take it that the top end seems disappointing. Go over the tune. On a factory stock setup, the factory specs are a great baseline. See that everything is in top condition. Make sure it has the factory timing curve. Then start experimenting at the strip. Might want a little more timing. Maybe a change in jetting. One step at a time. Use the mph and check the plugs each time a change is made.

For your use id look at a simple hone, rings, bearing, vj, cam, ect..... I think alot of us forget our youth and working hard just to keep a car going.

A very budget rebuild with a good cam can go 40-60k miles of good driving, I used to do it often, even with alot more taper in the bore then the book said was cool.

I used to do it to many 440s including my 440-6 runner and with a mild cam it ran stronger after the re ring, ect then it ever did and I beat it hard for nearly 60k before selling it.

Dont be spinning it past 5500 and a simple job goes a long way and runs like new.

Thanks for all the good replies.

To answer the questions:

It's a 383. I've never raced this and I don't drive it hard at all. It's a nice clean cruiser, something to take to shows.

Really, because I don't drive it much nor race it, is why it's lasted so long in its current condition. It's just that when I most recently took it out for a drive I kept asking myself "what if it had better pickup, what if I tightened up the steering, etc". I've never even taken off the heads the whole time I've had the car.

Shouldn't need to.
As far as what you're asking. Better, quicker throttle response, could just be a matter of some tuning. Tuning can take two forms, and in this instance both forms apply.
The first is tuning to factory. Mostly making sure its got the carb and timing to factory specs along with the matching emissions equipment.
The second form more applies to hot rodding, but can be done with a stock baseline as well. That is tuning (adjusting) for best performance.
It might just take some adjustment of the timing, and maybe some minor tuning of the carb, to change how it feels.

My suggestion is to establish current baseline. Check the initial timing and advance. See if there is any anti-smog equipment that might cause a delay either because it is or is not hooked up. Check manifold vacuum for indicaitons of problems. That would be the starting point. Then a compression check and leakdown if you want a better picture of the engine condition.

Tech guide shows '71 383 likely came with a timing retard solenoid
http://www.imperialclub.org/Repair/Lit/Master/287/Page11.htm
and possibly a solenoid controlled vacuum advance valve.
http://www.imperialclub.org/Repair/Lit/Master/287/Page12.htm

If either of those is stuck in 'retard', then the timing will be late and the throttle will feel sluggish.

You'll have to check your car to see if it has either or both, and if so whether they are working correctly, or at least not retarding the timing.
Those are the only emissions items I see in the guide that could effect throttle response. But they are big ones.

What is the rear gear ratio? Even if the engine was new/rebuilt it may not ever feel frisky off the line like you think it ought to if you have highway friendly gearing.

If the engine compression numbers are good and it's not using any oil you may not gain a lot rebuilding it back to stock specs. If it's apart and you change the camshaft, mild head porting work, etc. then you can expect more power.

Man, 6,000 miles divided by 30 years equals about 200 miles per year...
Anyway, it sounds like you just want it to run as good as it looks, and right now it doesn't quite cut it. As was already said, 100,000 miles is quite a bit for a car of that vintage. Does it show any of the usual signs of being worn out, like blowing white smoke out the tail pipe??? If so, I'd rebuild it to stock specs, AND do what's spelled out below. If it doesn't show signs of being worn out, you might just want to spend some time fine tuning it like checking the rotor phasing, maybe degree the cam, and figure out if re-jetting the carb might pep it up a little. Just my thoughts...

Why not to stroke the stock engine from 383 to 426 ? it won't harm the block, original crank can be storaged, is just about upgrade the rotation assembly ( crank and pistons ), and just if whished, one step up camshaft to enjoy the power sensation without loose the driver comfort on street

just my .02 :P

AN if not...

Why not simply rebuild the engine with KB pistons?. They are higher than stock ones so will raise the compresssion a bit. Keep the Magnum camshaft or replace it for something just a bit hotter and done! its time to do it as any other job after all these years. It hasn't to be something to worry or a headache.

You don't want to keep the original bore. It's a lot of work/time/money to remove/replace an engine. If you're going to go through all of that you want to do a rebuild. Fresh everything. The bad part is when you get the engine out, the engine compartment is going to look pretty bad. When these cars were 5 years old there was rust under the battery tray, etc. You're going to start thinking, well if I'm ever going to paint the engine compartment, now's the time to do it. So my advice is before you get started on this project think it over good. Either do it right or continue to drive/enjoy it as you have for the last 30 years.

i have an engine deal worked out for my charger that will come together the first of the year.
i'm with you, rick. i know the engine compartment on my car already looks bad, and to top it off, i covered it with the texaco equivalent of z-bart ! i'm NOT looking forward to cleaning that mess up !

to the OP, if you decide to re-do your engine, at that time, do what you will want to do to the engine compartment [cleaning, restoration, whatever], or just leave everything together as has been mentioned.

Rebuild it properly and run it. Nobody will care that it's been bored out and it will not decrease the value. Stash the original engine and build a different one.... Stupid IMO. Original engine will never make it back into the car if you do that.

So, originality is the most important thing to you. Is this because you like the idea that everything is original in the car AS you drive it around and enjoy it? Or is it that you feel it protects its value by having every original part, in an as close to original condition as possible? If your feeling stems from protecting its originality, pull the motor and either pickle it or disassemble and store it. Buy another 383 and put it in the car to whatever performance you want. Why continue to add wear and tear to the original block. If you like the idea that its totally original AS you drive it you will have to make some compromises. Even if you can get by with a dingle ball hone and a rering/bearing refresh. The bores are just going to continue to wear so at some point it will need to be bored. My car is NOT a highly desireable car. It will never be a high dollar car. With this in mind I decided to store the original 340. Having the original motor IN the car never matter to me, so why not save the wear and tear.

Maybe try to do it using some logic:
Do a compression test to see how the ring and valve seal is.
Check the timing chain to see if it's stretched.
How is the oil pressure?
Is is smoking on startup, compression braking or acceleration?
Does it use oil and how much?
After you have this information we can make informed advice.
Just because the engine has 100,000 miles does not mean it requires rebuilding but it might.

A couple of us are on the same page anyway..

I agree - diagonose the actual condition of the motor. Maybe all it needs is a valve job and a timing chain to bring it back to better performance.

FWIW, cylinder bore wear is not linear. It compounds over miles. For example, if it wore the bore out 100 microns its first 40k miles, it wore the next 100 microns over the next 30k, then the next 20k, etc. So even if the bore is still in spec now, and you hone and re-ring it, you are at the tail end of its potentially useful life and you likely won't get another 100k out of it.

It sounds like you use it as a very causal cruiser. I'd certainly agree with some of the earlier suggestions to go through a good analysis of condition, if its decent then a very thorough tuning procedure to see if that net an increase you are happy with. If it does not and a rebuild is absolutely needed, then based on what you find inside, go with a minimal .010 or .020 overbore to leave as much material as possible.