Need some advice for my 383 top end

[MuscleCar91]

Hey guys,
I posted awhile back about picking up my 383, well now I'm trying to decide what parts to start buying for it... That's where you guys with all your experience come in . It's a 68' 383 906 heads, originally 2bbl IIRC. I have talked to a couple people who have given me similar advice and now I want yours. I want to go fast. Here's what I am thinking: Performer RPM, Headers, a cam like this http://www.lunatipower.com/Product.aspx?id=1579&gid=287 , maybe a little juice, 2500-3000 stall... That's about all I've thought about, anything you guys would do/have done differently? I'm also interested in other builds with time slips or possible dyno numbers that may temp me.

Thanks a lot guys!
~Nick

 

[dobie]

My 383 is also an original 2bbl 383 out of a '68 Newport. I have a set of Jet-Hot coated headers, XE-274 .488/.491 cam, 906 heads which were milled and gasket matched, Holley 650DP, and a Mopar Performance intake. The car is a 4 speed with 3.91 gears. So far, Ive been happy. Of course, you can always do more. At the time, it was all I could afford, and so far it's been a great set up. It's definitely not the fastest, but it's been 100% reliable and fun.

I do have another 383 and 440 block sitting in my garage though which Im sure someday I'll build from the bottom up.

 

[4spd69RR]

What gearing in the rear do you have 3:23's? If so you might also think about changing to 3:55, 3:73, 3:90. However, your gasmiles will go away and the runner will burp everytime you drive by a gas station. It is the price to pay for speed though.

 

[mcmopar]

That is not a bad cam but there are better. Comp and Hughes have some excellent offerings. Check them out.
http://www.Compcams.com and http://www.hughesengines.com
Also, what pistons/compression ratio are you shooting for?

 

[MuscleCar91]

Thanks guys,
I have not torn into the engine, it was supposedly rebuilt (looks like it) but who knows. I have no idea what pistons or the CR. I will pull the heads off one of these days.. I will also check out those sites. What kinda cam would make good TQ?

At the moment I believe I have 2:73? gears. I plan on buying a 8.75 rear, I bought one last year with 4:56 center but that may be to much? As far as gas mileage goes it can't get much worst.

 

[4spd69RR]

Agree on the 4:56 gears I have the same in mine at the moment. I am also looking at changing mine out.

 

[moparchris]

A good idea is to decide what hp or e.t. goal to shoot for. 906s will be good to 450 hp with the right combo of cam, compression, headers, intake, and carb. What are looking for?

 

[MuscleCar91]

A good idea is to decide what hp or e.t. goal to shoot for. 906s will be good to 450 hp with the right combo of cam, compression, headers, intake, and carb. What are looking for?

Well... I would like to see high 11's low 12's with slicks and suspension work, whether I need a little nos or all motor I'll be happy. Most of my driving is on the street. Depending how much money is left in the budget I will be getting aluminum heads, that will allow for more CR on pump gas, correct?

 

[moparchris]

A good idea is to decide what hp or e.t. goal to shoot for. 906s will be good to 450 hp with the right combo of cam, compression, headers, intake, and carb. What are looking for?

:stuckup: :stuckup:
Well... I would like to see high 11's low 12's with slicks and suspension work, whether I need a little nos or all motor I'll be happy. Most of my driving is on the street. Depending how much money is left in the budget I will be getting aluminum heads, that will allow for more CR on pump gas, correct?

I would put together a fresh bottom end with good stock parts and some flat top KB pistons and set them at zero deck. Then buy the 440 source stealth heads or if you want to save money a REAL competition valve job with bigger valves in a 906 will do good. Then buy a medium sized solid flat tappet somewhere the mid .500 lift range and 245-250 degree at .050 range. A Performer RPM with a 750 Holley Dp. Run a MSD distributor and a digital 6 ignition. 1 7/8 headers and a good 2 1/2 exhaust. 10 inch converter 3.91s and good drag radials. Good for low 12s in a full dress 68 Road Runner.

 

[MuscleCar91]

A good idea is to decide what hp or e.t. goal to shoot for. 906s will be good to 450 hp with the right combo of cam, compression, headers, intake, and carb. What are looking for?

:stuckup: :stuckup:
Well... I would like to see high 11's low 12's with slicks and suspension work, whether I need a little nos or all motor I'll be happy. Most of my driving is on the street. Depending how much money is left in the budget I will be getting aluminum heads, that will allow for more CR on pump gas, correct?

I would put together a fresh bottom end with good stock parts and some flat top KB pistons and set them at zero deck. Then buy the 440 source stealth heads or if you want to save money a REAL competition valve job with bigger valves in a 906 will do good. Then buy a medium sized solid flat tappet somewhere the mid .500 lift range and 245-250 degree at .050 range. A Performer RPM with a 750 Holley Dp. Run a MSD distributor and a digital 6 ignition. 1 7/8 headers and a good 2 1/2 exhaust. 10 inch converter 3.91s and good drag radials. Good for low 12s in a full dress 68 Road Runner.

Thanks, sounds good. I was wanting a cam with a big lift like that but was told that a 383 didn't have the cubes to take advantage of it unless the CR was over 10:1.

 

[moparchris]

As JJRJR found, that getting big compression from a 383 can be a challenge. If going with the aluminum heads you may want a small dome on the piston instead of a flat top. Compression is funny, some think its tied to hp but in reality its a means to an end. Without decent compression the motor wont tolerate a big cam carb intake or headers. So try to shoot for at least 9 to 1 with a cast iron head and 10 to 1 for an aluminum.

 

[mcmopar]

Compression = cylinder pressure. A big cam will bleed cylinder pressure and render the engine sluggish if too much cylinder pressure is bled off. Chris is steering you right. If going with aluminum heads you'll need 1 point more cr than if going with cast iron heads. One of the previous owners of my car installed domed TRW forged L2293 11:1 pistons in my engine and put closed chamber 1967 915 iron heads on it! Later owners could not figure out why it pinged so badly - even on "good" 93 octane gas. Well, it was pushing 11.5-12:1 compression, that's why! When I took the car apart to freshen up the interior and engine bay I tore the engine down to the shortblock and found the domed slugs. Not being able to afford to swap pistons, and having found evidence of a balance job on the reciprocating assembly, I decided to keep the domed pistons and go to a set of open chamber 452 iron heads with 2.14"/1.81" valves and a serious porting job. We estimate a CR between 10.5 and 11:1 with this setup. Weirdly, with a bit of tuning in the timing, I can run 87 octane gas in it without too much of a problem for everyday cruising. My setup would be easily capable of running a set of aluminum heads but my finances won't allow it at the moment. If you can find a set of the TRW pistons they would get you where you need to be in terms of compression. Just be sure to polish the domes and round off any sharp edges in order to reduce the likelihood of detonation. A spray on anti-heat treatment would also help out.

 

[JJRJR]

As Moparchris has mentioned, I learned the hard way. I just finished going through what you are doing now with a 69 383. I'll tell you what I did, and then the good and bad of my mistakes.

Motor bored .030 over, fully balanced rotating assembly, Eagle rods, PRW stainless 1.6 ratio rockers, all new bearings, etc. Went with Keith Black flat tops with a 5 cc valve relief. Comp Cams XE-275HL, (kit includes the double springs, timing chain, lifters, etc.) Eddy Performer RPM dual plane intake, Eddy Performer RPM aluminum heads (Be sure to get the 84 CC, not the 88). I had the heads hand ported. Holley 750 Double Pumper, TTI Headers (1 7/8). MSD distributor/blaster and 6AL box.

OK, so I tell my engine builder very clearly up front that I want 10:1 CR. To make a VERY long story short, he said he got 9.8:1. I took to dyno and got 392HP/407TQ @ 5,500. Needless to say, I was disappointed. Found out that the CR was really about 8.6:1. Builder tears engine apart again, angle mills the heads .050 (also the intake manifold needed milling). Had to order a custom set of head gaskets from Cometic (.030 thickness) and the builder had to square deck the block, leaving the pistons between .004 and .008 in the holes. He measured the combustion chambers and we got the 84CC heads down to 76CC.

After ALL of that, I'll be at about 9.8:1 CR. She goes to the dyno again this week so we'll see. I'll be running 3.91's.

SO, what does all that mean? When I first started on this board back in September, the advice that I only half-heartedly followed was to KNOW what you want BEFORE you buy the first part. Know what builds will get what results, etc. My builder dropped the ball many times, but I'm nearing the end. I highly recommend getting a big block mopar book that shows various builds and various results. There are plenty of them out there and it's worth every nickel.

I hope that helps. Getting 10:1 isn't as easy as it seems and there are dozens of factors that play into the end result.

Best,

John

 

[MuscleCar91]

Thanks guys,
Well me and my dad pulled off one of the heads today to check it out turns out it was fully rebuilt and brand new inside. looks to have been bored and honed 30 over, I am wondering if anyone knows who makes a piston that would only have 030 and an arrow pointing to a grove on the edge on top? Btw they are flat top so I'm guessing no more than 9:1?
I was also trying to id my cam but having a hard time reading the numbers on it.. probably wont know til it's out...
I also got my valve body all back together after doing my shift kit all that's left is the springs in the trans.

JJRJR, your build sounds very similar to what I was thinking about. I have read your thread before and I too am disappointed thats all she made... I do appreciate your help, I'll have to follow your thread and see how it does at the dyno.

 

[MuscleCar91]

Well guys today we took everything off the front and pulled the cam out turns out it is, http://www.summitracing.com/parts/CCA-21-222-4/ . We also flipped it over and found out the pistons are KB .030 over flat tops http://www.summitracing.com/parts/UEM-1271-030/ . So what do you guys think? Where should I go from here?

Also I wanted to ask you guys two questions, 1. The heads are 906 and I was wondering about shaving/milling them some? Would it be a good idea or not? and 2. I was wanting to put on an engine plate and I was wondering the easiest thing to do is shave the thickness of the plate off the water pump? Does that effect any thing on the water pump?

Thanks again,
~Nick