Team Chevelle banner
1 - 11 of 11 Posts

·
Premium Member
Joined
·
68 Posts
Discussion Starter · #1 · (Edited)
So I purchased the car with a 383 in it with about 1000 miles on the motor.

I had an oil leak on the back after changing the oil pan while it was in the car and decided to pull the motor and fix it while I was changing out to a higher stall torque converter. And I was getting oil out of the right side exhaust with a good even compression on all cylinders. So I wanted to investigate a bit.

I had partial records of the engine build but missing some of the details. So I started to tear down to a short block to measure everything.

Everything else looked good except for about 1/2” of muck and rust in the bottom of the block and the cooling passages.

I popped the plugs and have been washing out the cooling passages.

I had oil on the top of some intake valves and I could see oil weeping down the stem on the exhaust valves as well. Heads had seals but not guides replace when the motor was rebuilt by the previous owner per the work order.

Scat cast 383 crank
Stock style rods
Kb silv-o-lite cast pistons 5cc dish
Piston in the hole .020
Thumpr cam 12-600-4 Hyd Flat
Stock 76cc heads
Performer intake
Edelbrock 4160 carb
2200-2800 stall converter.

I’ve been eyeballing the Brodix IK200 heads and some 1.6 rockers. With a 64cc that is going to put me right around 10.6:1 CR with a .040 Head gasket. I could bump up to a .045 or .050 head gasket but don’t want to go that thick. Alternative is 70cc heads but that drops the Cr to 9.75:1.

With 93 gas and thumper cam is 10.6:1 pushing it on the CR?

The car is just a street cruiser but I want to make sure I size everything right and not make the wife mad about the cost.
 

·
Registered
Joined
·
712 Posts
So I purchased the car with a 383 in it with about 1000 miles on the motor.

I had an oil leak on the back after changing the oil pan while it was in the car and decided to pull the motor and fix it while I was changing out to a higher stall torque converter. And I was getting oil out of the right side exhaust with a good even compression on all cylinders. So I wanted to investigate a bit.

I had partial records of the engine build but missing some of the details. So I started to tear down to a short block to measure everything.

Everything else looked good except for about 1/2” of muck and rust in the bottom of the block and the cooling passages.

I popped the plugs and have been washing out the cooling passages.

I had oil on the top of some intake valves and I could see oil weeping down the stem on the exhaust valves as well. Heads had seals but not guides replace when the motor was rebuilt by the previous owner per the work order.

Scat cast 383 crank
Stock style rods
Kb silv-o-lite cast pistons 5cc dish
Piston in the hole .020
Thumpr cam 12-600-4 Hyd Flat
Stock 76cc heads
Performer intake
Edelbrock 4160 carb
2200-2800 stall converter.

I’ve been eyeballing the Brodix IK200 heads and some 1.6 rockers. With a 64cc that is going to put me right around 10.6:1 CR with a .040 Head gasket. I could bump up to a .045 or .050 head gasket but don’t want to go that thick. Alternative is 70cc heads but that drops the Cr to 9.75:1.

With 93 gas and thumper cam is 10.6:1 pushing it on the CR?

The car is just a street cruiser but I want to make sure I size everything right and not make the wife mad about the cost.
What I can tell you is that with ETech 200 cc aluminum heads, a 406 will run on 93 octane all day long at 10.85:1 with the Comp Cams 292H (244°/244° , 0.507"/0.507").
 

·
Premium Member
Joined
·
11,705 Posts
  • Like
Reactions: 71malibuu

·
Premium Member
Joined
·
17,775 Posts
BJL, that DCR stuff incorporates the cam timing to get a comparative dynamic compression given the static + intake valve events. Dont over think this, but the DCR will give you a better idea of "pump gas friendly." I;m not sure the Thumpr cams have alot of bleed down, just excessive exhaust duration for the sound.

BUT DONT SWAP CAMS NOW< Dang, you may not find one!
 

·
Premium Member
Joined
·
68 Posts
Discussion Starter · #5 ·
Thanks,

In my younger years I just focused on the plain ol regular cr ratio without even considering the cam

I haven’t had time to sit down and to the extra calculations yet for the dcr.

Yeah, parts availability is terrible right now. I have at lease found the brodix heads in stock and they are made in the USA. I see the afr enforcer and the other overseas stuff and even if it cost a few bucks more I’d rather buy the Brodix.
 

·
Registered
Joined
·
565 Posts
hi
383
RpM air gap
190--200 cc heads minimum
pump gas max 10.75 for most street cams below 240 duration
1 3/4 header primary ,a quality set that does not foul the ports

Tire size ???
rear gear ???
Overall ratio [both above ] will tell u how much of a cam u can run for a cruiser and influence cam/compression .
IE if your car runs with low gears u can run slightly more cam/ compression compared to tall gearing
 

·
Registered
Joined
·
3,874 Posts
hi
383
RpM air gap
190--200 cc heads minimum
pump gas max 10.75 for most street cams below 240 duration
1 3/4 header primary ,a quality set that does not foul the ports

Tire size ???
rear gear ???
Overall ratio [both above ] will tell u how much of a cam u can run for a cruiser and influence cam/compression .
IE if your car runs with low gears u can run slightly more cam/ compression compared to tall gearing
This and converter also will make a diff.
 

·
Premium Member
Joined
·
11,705 Posts
I would be concern with this stuff below.

"Everything else looked good except for about 1/2” of muck and rust in the bottom of the block and the cooling passages."

Get all that mess out.

Take the pan off and clean all that out and replace the gasket. Check your bearings while doing that.

I would not mess with anything else. Don't touch the pistons or cylinder walls. Leave all that alone.

Those thumper cams are garbage. You can leave it or find a better one.

You could take the heads to a machine shop and get the guides checked, but 1000 miles, I would just leave them alone.

If you swap the cam, you will have to maybe change springs, so then you might want to go to the machine shop for the guides and springs, but you can see where the bill is going to escalate.

You could buy tools to do that at home.

Once you get the pan on and back on the stand, I would pour diesel down into the engine and rotate it over to clean out the block. However, don't do that if you swap a flat tappet in there as you will be washing all the break in lube off. You could use diesel first without the cam in there. Then you could install the flat tappet cam with lube. If you went to a roller, no issues or worries about lube.

You can see all that can create a mess and stick you with a bill. Think about all that.
 

·
Banned
Joined
·
2,671 Posts
Id say lose the thumper but as already mentioned you may be hard pressed to find another cam .
If you do want to swap cams be sure you can get one .

I bought these 2 for my 385 sbc
Still have em brand new.
Started with the Lunati voodoo
Then decided to change to the clay Smith
Then ultimately ended up with a howards solid roller.
I was gonna part with the lunati and the clay Smith but not now lol
I hang on too em . I've got more blocks hangin around.
And actually I started out with another lunati flat tapet that I sold to my buddy along with the heads and intake i was running on my chevelle prior .
The cam was the lunati
101 207 02 .
Along with skip white nkb heads and an airbgap intake.
my buddy put those heads and intake and cam on a tired dish piston 350 . They dynoed the motor and it made. 372 hp @ 5200 and
390 torque @ 3300 . Nice nice street deal there. Put that to the pavement and tear some shit up lol

these are the 2 i still have



 

·
Premium Member
Joined
·
68 Posts
Discussion Starter · #10 ·
I miss typed. The gunk was only in the water passages. The oil came out clean with no metal.
 

·
Premium Member
Joined
·
11,705 Posts
I miss typed. The gunk was only in the water passages. The oil came out clean with no metal.
I miss typed. The gunk was only in the water passages. The oil came out clean with no metal.
Ok. I would make sure water is not restricted in flow though.

To comment on the camshaft. Quality is your only concern in getting a new one if you decide to do that. Brand does not make a difference for what your doing. If you go with a roller, you will have a little more piece of mind. Just pay attention to the timing events or you will have a dog.
 
1 - 11 of 11 Posts
Top