Need some engine advice

[mopar Joe 65]

I have a 68 383 iam rebuilding it had low miles on it so i only had to bore it .020 over, i put a set of kb flat top hyper pistons with valve reliefs. I didn't realize this motor come stock with a positive deck height and now its about .025 I did a compression ratio calculation and it come out to 8.31 to 1. Is this going to be a dog now ? I plan on putting an edelbrock performer manifold on it and eddy cam and lifters. It has 323 gears and a 727 automatic in it, i had the heads rebuilt and i am using hp exhaust manifolds. Without changing the crank or pistons what can i do to help it out ? Any advice would be welcome.

 

[furious70]

Did it have the factory flat tops or dished pistons? While I've not torn apart any HP 383's that were still as built, I've seen reports from others that they weren't actually positive deck/true 10:1. Would be good to know what yours was before you tore it down to give a relative assessment of how it might behave rebuilt.
What CC are your heads? Which gasket are you planning on using? My experience is that actual measured 8.5:1 engines aren't terrible with a small cam and dual plane.

 

[commando1]

and it come out to 8.31 to 1. Is this going to be a dog now ?

NO. 8.31 is ideal for a mild 383 street machine.
You can use Regular grade gasoline to it's fullest efficiency or go to Premium if you want to push forward the advance a tad more.

 

[mopar Joe 65]

This motor only had 60,000 miles on it the pistons are stock flat top with valve reliefs. The heads are 906 heads and i think they are 88 cc .i bought a set of engine gaskets and the head gaskets are felpro, i put my mike on them and they look like there about .042 thick ? I had the heads rebuilt or i would just buy the eddy top end kit with the aluminum heads.

 

[furious70]

I would put a .020 steel gasket on it to help a bit

 

[Davea Lux]

I would agree with Commando if your intent is to build a mild engine that will run on today's crap gas without pre-ignition issues, the ratio 8.31 will be ok. Use an embossed metal head gasket so you don't drop the compression ratio any further, Fel-Pro makes both the sandwich type and the embossed metal type gaskets.

The after market aluminum heads can be bought with a smaller chamber size which will boost the compression ratio. It depends on what you are trying to achieve. If you want a balls out performance street engine, the aluminum heads will give a significant boost in performance, but only with premium fuel. Rather than spending a small fortune on the aluminum heads you could also consider going to stock height pistons as this will cost a lot less that a set of aftermarket heads. If this is going to be a daily driver, go with what you have. If you are not happy the performance, you can upgrade to the expensive aluminum heads later.

Dave

 

[mopar Joe 65]

You guys make a good point when considering fuel , mostly i want to cruise around with it and go to car shows and it would be nice if i could smoke the tires now and then. I need to decide on a cam for it but i want to use the stock rockers so i don't have to spend my spare time adjusting rockers. Also do i need a stall converter ?

 

[commando1]

Also do i need a ...new... stall converter ?

If you match the cam to your 8.3 CR, no.

By the way, you can smoke the tires even with a stock 383, so no need to go all nutzo over being cool pulling out of Dairy Queen.

 

[Davea Lux]

You guys make a good point when considering fuel , mostly i want to cruise around with it and go to car shows and it would be nice if i could smoke the tires now and then. I need to decide on a cam for it but i want to use the stock rockers so i don't have to spend my spare time adjusting rockers. Also do i need a stall converter ?

You probably do not need a stall convertor on a mild street machine. Look at the range specs for potential camshafts. If the cam shows a range of 2500 to 6000 rpms, you need a stall convertor. If the cam shows a range of 1000 to 5000 rpms you do not need one. The main purpose of the high stall convertors is to keep the engine from dying at low rpms and to engage when the engine gets into a usable torque range. At the 8.3 compression ratio, you probably should use something close to a stock magnum cam.

Dave

 

[LeBaron1973]

Also remember these cars are large and heavy and will never perform like a sports car no matter how much money is spent on whatever modifications someone chooses to make.

We wish you happy motoring when she's back on the road.

 

[theadmiral]

Also remember these cars are large and heavy and will never perform like a sports car no matter how much money is spent on whatever modifications someone chooses to make.

Tell that to @The Horvaths . :-D

 

[furious70]

Tell that to @The Horvaths . :-D

That's not a large car , my Charger is bigger and heavier.

 

[Trace 300 Hurst]

I would put a .020 steel gasket on it to help a bit

And I would spray those steel gaskets with Copper Coat to prevent water and oil passage leaks: https://www.permatex.com/products/g...rmatex-copper-spray-a-gasket-hi-temp-sealant/

K&W Gasket Compound, 12 oz., Copper, Aerosol - 5EVZ4|401612 - Grainger

Two thin, even coats, please!

 

[LeBaron1973]

That's not a large car , my Charger is bigger and heavier.

Lol, I was considering it like those who buy a 5500 pound car and want to know how to make it faster.

I wish him well with his car.

 

[PontiacJim]

You can take advantage of the lower compression by selecting a cam which builds higher cylinder compression or "Dynamic Compression."

Built a Pontiac 400 with 8.2 compression with a Competition Cams having a 110 LSA that builds "Dynamic Compression" on a Pontiac engine. Ran on good old ethanol/regular 87 and pulled like a freight train. I would email/contact Hughes Engines and see if their "Whiplash" cams might work for you. They can most likely suggest a cam that would be best for your application. Don't guess on it as this is one of the most critical pieces in selecting which can make or break your engine with regards to HP/TQ results. Hughes Engines

 

[Trace 300 Hurst]

You can take advantage of the lower compression by selecting a cam which builds higher cylinder compression or "Dynamic Compression."

True. That thing about "higher cylinder pressure"? It makes this funny thing called TOOOOORQUE.

 

[moper]

No 383 was what it was supposed to be. The blocks are all cut taller than the blueprint height at the factory. So none were "10:1" when an actual engine was taken apart and the parts measured.
That being said - no big deal with the lower static ratio. The 2bbl engines were that low anyway.
On a side note - using the KB hypereutectic pistons - you or your machinist did follow the KB guidelines for the top ring gaps - correct? Don't just say "sure". You need to know for a fact the guidelines were followed or you should take the thing apart and re-gap the rings to those specs.

 

[mopar Joe 65]

Yes i did file the ring gap correctly. Also i was wondering do you spray the copper coat on both sides of the gasket or the block and head ? I did order a .020 steel gasket.

 

[Trace 300 Hurst]

Yes i did file the ring gap correctly. Also i was wondering do you spray the copper coat on both sides of the gasket or the block and head ? I did order a .020 steel gasket.

Both sides. Thin coats, twice, about 10 minutes (flash time) apart. And it's some really sticky stuff, so beware.

 

[MoparJim]

If you match the cam to your 8.3 CR, no.

By the way, you can smoke the tires even with a stock 383, so no need to go all nutzo over being cool pulling out of Dairy Queen.

commando1 is absolutely right about a stock 383 being able to easily smoke the tires. I learned to drive in my parents' 67 Fury III with a 383 4bbl and 727. I don't know what rear end was, but it was a Sure Grip and had the towing package. As a young driver I had to be very careful not to get too crazy with the loud pedal as it would easily smoke the tires. And that was bone stock with lots of miles on it. As I think about it, our '72 Fury III with a 360 4bbl and 727 would smoke the tires at will, too, but I confess dear old dad had replaced the factory intake manifold with an Edlebrock street manifold, installed a set of Hooker headers, and upgraded to an electronic ignition on the '72 so it wasn't stock.