Advice needed on 383 motor

[69SKCharger]

I came across a '70 383 HP motor for sale at a good price. It's a low mile rebuild. 30 over with a cam, offenhouser intake, Holley carb, etc. The part that I'm concerned about is that the owner says it has 12.5:1 TRW Pistons. I want to run pump gas, so it's that going to be a problem? After purchasing, would I need to swap the Pistons to lower the compression ratio?

The owner built the motor back in the 70's then put it in proper storage in '83. He said it was great in the day, but fuel was different...

 

[Kern Dog]

Most engines that have sat that long should be disassembled and inspected. GREAT time to swap in a better set of pistons, something that comes close to but not above ZERO deck!

 

[69SKCharger]

Yeah, I'd go through it thoroughly anyway, so could change them if needed. It would be better if I didn't have to change them though...

 

[1 Wild R/T]

First off I agree with Greg, it should be torn down anyway... Second 12.5-1 C/R pistons but probably with a 78 cc chamber & zero decked... So the true number with a set of 1970 906 cylinder heads with 88-90 cc chambers & a true deck height leaving the pistons .020 in the hole means a true C/R of maybe 11-1... So pull it down & check those domes, most old TRW's had solid domes with minimal relieving on the back side... So if the dome of the piston is .160 which is common & you mill the dome down .040 leaving you a nice safe .120 thick dome & a C/R down around 10-1.... Without measuring this is all assumptions & we all know how that can go.... But you might just get lucky....

 

[Lefty71]

Those are gonna be pop-ups for sure. You may be able to shave the tops, and you may be able to get the compression down with a different cam, and maybe with thicker head gasket (or spacer ) set-up too. But you'll likely lose your quench in the process and the whole motor won't be what it once was. You won't know for sure until you pull the heads and start measuring everything, it may just be Ok. Or you may be starting over with some flat-tops, aluminum heads and set-it up to suit your new purpose for the engine $$.

 

[wyrmrider]

and some of the TRW domes could be completely removed to flat
however they are still heavy
440 rods and light pistons make it rev much better
and a 440 crank, 440 rods and custom pistons will really wake it up
someone used to stock those pistons but I forget who
I have a custom quench dome piston for that combo on a rod (the 9th piston for r&D) which we did for a matching number superbird 4 speed car
could post a picture after the middle of the month if anyone is interested
and yes back in the day you could get just about any combo special ordered if you clicked the right boxes (showcar, racecar)

 

[Challenger340]

I came across a '70 383 HP motor for sale at a good price. It's a low mile rebuild. 30 over with a cam, offenhouser intake, Holley carb, etc. The part that I'm concerned about is that the owner says it has 12.5:1 TRW Pistons. I want to run pump gas, so it's that going to be a problem? After purchasing, would I need to swap the Pistons to lower the compression ratio?

The owner built the motor back in the 70's then put it in proper storage in '83. He said it was great in the day, but fuel was different...

Personally, unless he's GIVING it away I'd run the other direction.
#1) Blocks are all the same so the "hp" means absolutely nothing once the Engine is rebuilt.
#2) If it's been in storage since '83 ? No way you should even consider firing it without a teardown, inspection and re-assembly as a minimum, and unlikely to be all fine ?
#3) If the guy is claiming 12.5:1 TRW Pistons ? WHO built it, WHERE is the paperwork, WHAT did "proper" storage consist of ? WHEN and how often was someone priming it, and then giving it half a turn to UN-compress V/Springs over the decades ?

Just say'ing...
IMO, unless he's GIVING it away ? It's a PARTS core highly likely to cost you more to resurrect it ? than starting afresh on a new build on even a 440 at 60 cubic inchs MORE for the same money = NO replacement for displacement.

 

[66Satellite47]

Agree with need to see what the motor really is. Challenger340 makes really good points. Storage is a relative term. If price is right, OK. PLAN on a complete teardown & lots of mods. In terms of "true CR" everything needs to be measured (deck, dome/dish, actual chamber volume). If it's a '70's 906 head, even with a real 12.5 TRW that's milled flat(can be done, seen it several times) the CR will be too much for today's gas, even with fairly stock chambers & low timing. The TRW's are very heavy compared to many other pistons. They still will get the job done. Honestly evaluate what your real use will be. A lite piston stroker will make more power & maybe more fun, depending on what you are shooting for. Those TRW's do the job, but at excessive RPM(much over 6000), they kill crankshafts, I know. Decide what your application is & how much reliability you need.

 

[Xp29h]

I also agree on the teardown! The 383 that came in my charger was a “new” rebuild but was a royal pain in the butt! It was not right from the day I got it. I ended up throwing all kinds of money at it trying to fix the issues. As it turned out the pistons were installed too tight and rings had zero clearance / gaps. The cr was 7:1! No wonder it was a pig without lipstick! Tear it down and do it right! I know money is always an issue. Was for me, but if I had taken it out and apart I would have saved a ton even with the costs of new pistons and better machine work to fit correctly!

The one thing I’ve found in this hobby with ole Mopar is if you try to cut corners, save a buck here and there, it just comes back to haunt you!

Good luck!

 

[BSB67]

Personally, unless he's GIVING it away I'd run the other direction.
#1) Blocks are all the same so the "hp" means absolutely nothing once the Engine is rebuilt.
#2) If it's been in storage since '83 ? No way you should even consider firing it without a teardown, inspection and re-assembly as a minimum, and unlikely to be all fine ?
#3) If the guy is claiming 12.5:1 TRW Pistons ? WHO built it, WHERE is the paperwork, WHAT did "proper" storage consist of ? WHEN and how often was someone priming it, and then giving it half a turn to UN-compress V/Springs over the decades ?

Just say'ing...
IMO, unless he's GIVING it away ? It's a PARTS core highly likely to cost you more to resurrect it ? than starting afresh on a new build on even a 440 at 60 cubic inchs MORE for the same money = NO replacement for displacement.

I'm pretty much with Bob on this. Every time someone starts with: ".....its a really good deal....." its usually not.

First, what is the price? If you are not going to verify any claims about the motor, assume it is nothing more than a core and only pay a core price for it. Alternatively, you should do at least a partial tear down and verify a few things. If you pull a head you can verify two key items: 1) what pistons, 2) cylinder wear. If you cannot use the pistons that are in it as is, or the cylinders are too worn, the motor is nothing but a core. If you have to fix either of those two things, you're all-in for a total rebuild. And personally, if you're into a total rebuild, why do a 383?

The dome on a 383 12.5:1 is about a 0.5" tall. Like some said, it will not be 12.5:1 in reality. But it won't be pump gas friendly either. If you pull the pistons and mill the dome, the entire engine assembly will need re-balanced, and if you replace the pistons you're very very likely into a full rebuild. I'm not sure if you can run a tall dome 383 piston with maybe an Edelbrock 88 cc head and a fat head gasket and big cam to get away with pump gas.

And, also presume that the heads are near valueless.

 

[BeepBeepRR]

Maybe this will help.. A guy down the road told me he had a rebuilt 383 in his garage and I swapped him work for the engine. I finally got the engine but it was a disaster. Stored? Yes Stored correctly? Negative this thing was a habitrail for all the little creatures that lived in his garage. The entire cooling system was full of uncooked rice it literally took me 2 hours to get it all out of the block. I tore it down to the bare block used air and washed the complete block and cleaned every hole in the block. Its now ready to be put back together but what a waste of time if they would have just stored it the correct way. Pulled the valley pan to discover a huge mouse nest with one dead mouse still in it. Here is the result of a year or 3 of rat piss.

 

[69Bee]

Lifters will need to be disassembled and cleaned, or replaced. The oil will have gelled, and the lifters will be stuck. Valve springs will NEED to be replaced, and bearings should be replaced too. Contaminants in the oil will attack the bearings and turn them black. Check all surfaces for damage or rust. However you deal with the piston issue, do NOT forget to rebalance the motor.

 

[wyrmrider]

Motor may have not been balanced when the TRW slugs installed

 

[66Satellite47]

Motor may have not been balanced when the TRW slugs installed

That is a scary thought. But don't recall weight diff between stock & 12.5 TRW's. But I'd never build a performance motor that didn't have quality race balance job. Never know what someone else did though.

 

[69SKCharger]

Thanks for all the advice, that's exactly what I was looking for. Based on this, I'm calling the motor a core at best, and given that, it's not really a good deal at all.

What would be the going rate for a core these days?

 

[Kern Dog]

For a standard 2 or 4 barrel engine, I often go about a dollar per inch or less. 383 = $350. A 440 6 pack mill is another animal though.

 

[wyrmrider]

383 for core = free unless it is a real Hi po with the manifolds-
which are worth more than the block
and if you need them or are into swap or e-bay
most today would build a 400
or a 440 if it easily fits your chassis meaning B or E or C not A
The last several true 383's I built were all matching number deals- a couple with 440 cranks and rods
so if someone needed that year of block they might pay up
otherwise mostly all the same
pistons are not as common for 383 as 400 for example- in fact I know of no quench eliminating pistons for 383 with open chamber heads today
so to make one- or a 400 - run good (non "race only" on today's gas) you need 915 or aftermarket heads
still better than a 350 chevy

 

[69SKCharger]

Good point. Probably far easier and cheaper to go with a 440 versus another 383 if considering a full rebuild.

 

[Curiousyellow71]

This isn't really any new info for you but the image is right out of my 1989 TRW book and a 1996 Federal module book ... most 906 head we have measured have been 90cc making it about 11:1 but I would guess 10.75 :1 or less since factory machining vary A LOT. You would have to measure the piston deck height. The 12.4 rating is for a closed chamber head. On any used engine spin it over for tight spots...take a valve cover off look for rust. The seller should be concerned what he is selling..or you need to buy from some one who cares. And as far as rodents..2 years ago I had a critter chew a hole through a intake hose on a 8.3 Cummins diesel and filled the engine up with soybeans 2 the point the engine locked up. I didn't have 2 overall it but had to do the valves and take it completely apart. Mouse pee is super corrosive. Lol. The mice moved 5 gallons of soybeans into the engine in 1 month. I was shocked when it wouldn't start

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[66Satellite47]

IMHO, 383 like you describe is worth more than a core, but expect a lot $$ to make it "right". A 440 will make more power & torque, but it's the same deal, anything that's a "core" costs. To be really sure what you got you need to check everything, or as much as you can. My 1st drag car was a '65 Coronet 426 Street Wedge drag car with the time slips & broken drive train parts to prove it's worth. I still had the motor rebuilt by a trusted race guy, 5 tenths faster. For a street application, worth the cost....? BTW the performance from strokers is amazing. With parts availability today, big motors are fairly reasonable. Cranks, rods, heads lots of choices for both 440 blocks & 400's. Enjoy