Rebuilding Original Engine 383-s Fastback

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rklein383

rklein383

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Went down to the machine shop today to talk about my build. The shop has already installed three sleeves to repair the jacked up cylinders that another machine shop did along time ago.

Looks like flat top KB pistons giving a CR of 10 to 1. Probably go with a Comp Cam 268.

Since I only had the block, I have to round up a bunch of parts to get it together. I went to my local junkyard and they have quite a few old B bodies with big blocks in various tear down progress. I should be able to get most of the fasteners, brackets, etc there.

Getting excited about putting together the engine.

I sold my 440+6 I had in the car, so I am committed now.

Looking for a reasonable priced 301 intake (68-69).
Rod
 
Auto or 4 speed? Any pics of car.
 
I'm not sure what all's been done to that 383, but KB flat tops won't get you anywhere near 10:1. That'snot a big deal, but it will be closer to 9.2:1 depending on the head gaskets and chamber size - but that XE268 is a great cam with it. I've used that a couple times in 383s and never been disappointed.
 
I have not finalized the piston choice yet, but the KBs is what my machinist has had good results with. Will be using stock 906 heads. My 440 has flat top TRWs and 452 heads. Based on my measurements, it is at 9.3-1 compression.

Didn't stock 69 383's have flat tops and around 10-1 compression with 906 heads?
 
nope, mine aren't flat tops. 10.25:1 originals, and I can send you pictures of them if that will help. I love hearing about another 69' 383 four speed car, as I am finishing one up as well.
 
Don't need any pics. I will give my machinist a call to make sure the CR ends up where I want it to be.
Thanks,
rod
 
With that cam and iron heads it would be best to keep the compression at 9.5:1 or less. Any higher and you could have detonation issues.
 
The KBs are a good piston. 10:1 with factory heads will be a handful to tune - I'd alter your requirement for that. Have the block blueprinted, run the steel shim gasket, and use the chamber size to set the compression around 9.5:1. That more than likely will require milling beyond a basic clean up which will mean you probably will need custom pushrods and milling the intake flange on the heads As I said - there are no shelf number pistons that will give more than 10:1 using factory heads on a 383. Custom pistons would but you start having issues with detonation and that huge chamber so the camshaft has to be larger.
 
Well,
I don't want to deck the block such that I need to machine the intake or have special length push rods...
 
rklein383 said:
Well,
I don't want to deck the block such that I need to machine the intake or have special length push rods...
Click to expand...

If it's the original engine, you probably don't want to deck the block and lose the numbers on the right front pad.
 
Spent a couple hours this afternoon and I have the 440+6 ready to pull. Tomorrow, I will push the car out of the garage so I can pull it.

A little cleaning of the engine compartment and the original engine will be ready to be put in.
 
He's right about the 10:1 compression ratio. You'll hafta run Octane Booster or it will ping. Even worse in the Summer. Dropping down the timing wont work. Detonation is really bad news for a performance motor.
You need the 9:1 compression for street survivability.
Your engine Guy shoulda told u about this.
 
Wow, you don't have to yell at me.

Don't worry, I have not even ordered any parts yet. I am in discussion with my machinist on how to go with the build.

By the way, you can get away with a little more compression ratio at higher altitudes. I am at 4000 feet here.
 
If you're not going to deck the block or heads, you have no reason to worry. There's no piston that will get you anywhere near 10:1 without blueprinting and milling. The problem is not the pistons. It's the block and heads.
In terms of numbers - if you use a shop with modern equipment the numbers are not at risk. I've done several without touching the ID pad. You just have to have the right machinery and/or a guy that knows he has to keep them.
 
rklein383 said:
Wow, you don't have to yell at me.

Don't worry, I have not even ordered any parts yet. I am in discussion with my machinist on how to go with the build.

By the way, you can get away with a little more compression ratio at higher altitudes. I am at 4000 feet here.
Click to expand...

True about the altitude, I didn't catch that before I posted. I am at 750 ft. here so it is a big issue for me if I don't plan a build right.
 
rklein383 said:
Don't need any pics. I will give my machinist a call to make sure the CR ends up where I want it to be.
Thanks,
rod
Click to expand...
It sounds like you have a good handle on it, I'm sure your machinist will guide you to the desired result. I wanted to share a recent experience with a 68' 383 HP with the 10:1, and decided to follow the advice of a couple other roadrunner guys in phoenix, where it is really hot. I discarded the original Mopar cam and went to a comp cam. I wanted bone stock, .455 lift, and apparently the center line is different, and a few other changes in the specs as well. (I 'm not an expert in that area).Then I tightened up on the dist advance springs just a hair, and that engine will not ping with 91 octane Octane even when it is 90 degrees out. Once in a while I will add some 106 from the local station and mix, and that engine just runs even better. I did the same thing to my 69' 340 with the 10:5.1, and other than being a little less perky, it doesn't ping either. When I had the stock Mopar replacement cam, I couldn't keep either engine from rattling. it was Very irritating to say the least. This is just my experience, and I don't race, and I stick to the original specs on all my engines. Good luck with it, I am Interested in hearing how it comes out!
 
Ok, I spoke with my machinist this morning. I verified he is only machining the deck enough to clean it up, will leave the factory markings alone. No mods to the intake or special length push rods necessary.

CR will be between 9 and 9.5 to 1 with the KB pistons as several seasoned moparites have stated before.

Sticking to the Comp Cams 268 stick.

Should be a nice combo.
Rod
 
rklein383 said:
Don't need any pics. I will give my machinist a call to make sure the CR ends up where I want it to be.
Thanks,
rod
Click to expand...
I want to apologize Rklien383 for the previous entry, as I was brain dead at the time . I bought this gorgeous Cuda, and it came with the original 383 HP engine.. Parts were in the trunk, and in boxes. The seller (my friend for 30 years)said everything was stock original stuff. I delivered everything to my friend at the machine shop, and thought nothing of it. After this post I began to question the wisdom of my post. So, I visited my friend that owned the shop, as I did periodically.
I asked about what his observations were, and the stock condition of the engine. He laughed, and said: I was happy for once to see you want to build a great 383 engine. I asked what that meant, and he said the Engine is perfect, standard bore, and where did you get those Forged 11:5. 1 pistons for it? 108 will work perfectly, if you can afford it. So. my apologies to the previous post for my lack of Knowledge regarding the piston height of a stock 10:.1 383 HP engine. I asked my good friend about the pistons, and his statement was: Is that where they went? I was looking for them! oh well,,,,,HA HA HA



The next question is to those brighter than me, Should I purchase 9:5.1 pistons, or make a bad 383 that needs hi octane?
 
if that +/- half point in compression bothers you. You can, down the road, use the thin .026 head gaskets or find some 915 heads to get it back. I'd run the 9:5 pistons and enjoy it being able to drive it anywhere.
 
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