383 help!!!! our motor combo needs suggestions

[694life]

Ok we will test all the cylinders and report back. Is there a some math to get you the comp ratio off of that?

[XH29N0G]

I had thought the math would be simple, and made the mistake of assuming it would be atmospheric pressure multiplied by the compression ratio. It turns out that it depends on a lot of things (when the valves close in the compression cycle, and also properties of air related to heating and cooling during compression).   

There may be someone who can work it out, but as far as I know it is not something you can just plunk into an excel sheet and solve for.

[Supercharged Riot]

Ive been thinking about a new cam setup myself
I also have a 383
I havent picked a setup yet tho

[firefighter3931]

The domed pistons I put in my 383 were rated at 12.0:1 IIRC (it was 1978).  I bought these because you could not buy the factory correct compression height forged TRW/Speed Pro (i.e. NHRA approved) piston for the 68/69 383.   You know, the one that would be 0.020" proud when blueprinted. The dome on the piston I bought were almost .500 tall.  I had them milled down to about .180 and figured them to be about 11:1.  With a 906 head and the old "Hemi Grind" cam, it blows 210 psi still today.

I remember the Fireball cams....I went with the Racer Brown SSH-25

Russ, sounds like the same set of pistons....couldn't have been that many options back then.

Good to hear yours is still up and running. Mine is long gone....spun some bearings acting stupid and trashed the motor !  Replaced it with a 440 and never looked back. I'm thinking the SSH25 was a better choice than the ole Fireball 

Ok we will test all the cylinders and report back. Is there a some math to get you the comp ratio off of that?

No real way to determine actual static compression off a cranking test....too many variables (cam lsa/overlap/intake closing etc....)

The only reliable way is to pull a head, CC a chamber and measure piston to deck....then calculate 


Ron

[cdr]

lots of good suggestions so far,but this thing is not makin much hp,my 1st question is this open headers,if not what kind of exhaust,i have seen .7 pick up because of crappy exhaust

[694life]

The car has true dual 3" mandrel bent with an H pipe and flowmaster series 40's. As far as the heads go they are gonna be swapped pretty soon then we will know what we have.

[Cooter]

Remember that the Mopar 383 has very little crank in it. Smaller than the stroke in a SBC in fact. You will have to have your ducks in a row in order to make some serious power with a 383.

[cdr]

had flow masters 40s on this car changed to magnaflo,picked up 4 tenths  from 11.3 to 10.93

[c00nhunterjoe]

And it begins.......   

What was you mph on the 11.3. And the 10.9 run? If just mufflers were changed and nothing else, 4 tenths on a 10 second car is nearly 60 hp.

I swear, I'm just about at the point to dump the money out on a set of ultraflos and dyno my car before and after and do a track run before and after. So tired of the unrealistic claims made against flowmasters.

[firefighter3931]

had flow masters 40s on this car changed to magnaflo,picked up 4 tenths  from 11.3 to 10.93

That i can believe  

Years ago a member here had a 493 street/strip build and was running consistent 11.70's and was looking for more. I suggested uncapping it and bingo he went 11.04 !  

The exhaust was 4 ft of straight 3in pipe going into a set of Flowmasters dumping at the axle. Pretty much the most unrestrictive exhaust pipe layout possible....no bends, no curves. Yep them FlowBastards rob power. If you're index racing and want to slow the car down just install a set  

Not every combo will suffer from poor muffler flow but if you're making enough steam they will hurt  

The car has true dual 3" mandrel bent with an H pipe and flowmaster series 40's. As far as the heads go they are gonna be swapped pretty soon then we will know what we have.

It probably wouldn't hurt to inspect the heads and while you have it apart get some measurements.  

Depending on what you find, the cam recommendation might change  


Ron

[cdr]

And it begins.......   

What was you mph on the 11.3. And the 10.9 run? If just mufflers were changed and nothing else, 4 tenths on a 10 second car is nearly 60 hp.

I swear, I'm just about at the point to dump the money out on a set of ultraflos and dyno my car before and after and do a track run before and after. So tired of the unrealistic claims made against flowmasters.

118.4 to 121.2       why the sarcasm to me I AM TRYING TO HELP SOMEONE,SO YOU ARE SAYING I AM LYING,i 

[c00nhunterjoe]

Didn't mean to offend you. That was not the intent so sorry if I did. There are tons of things that can affect the times of your passes on any given day. Air temp and humidity alone can change a car more then 6 tenths. I'm not sayingyour car didn't improve from a muffler swap, I guarntee that a straight thru mufler will put down more power then a flowmaster, but the claims of hundred hp increases I have a hard time swallowing unless you have a 2inch muffler behind a 500 inch motor and then swap.

So again, I'm sorry if I offended you, I just get frustrated when the "flowmasters are total garbage" posts start, 

[cdr]

Didn't mean to offend you. That was not the intent so sorry if I did. There are tons of things that can affect the times of your passes on any given day. Air temp and humidity alone can change a car more then 6 tenths. I'm not sayingyour car didn't improve from a muffler swap, I guarntee that a straight thru mufler will put down more power then a flowmaster, but the claims of hundred hp increases I have a hard time swallowing unless you have a 2inch muffler behind a 500 inch motor and then swap.

So again, I'm sorry if I offended you, I just get frustrated when the "flowmasters are total garbage" posts start, 

its all good mr c00hunterjoe,we have been running this car since it was new,& have had lots of motor,gears,exh,carb,intake ,you name it if they make it for a poncho we have probably tried it,& i promise it was muffins only that we changed,& we have a very good base line for how the car runs in all kinds of weather,at least you dident accuse us of running a bigblock chevy in this car like everybody else has & does,whats real cool is running 10.96 thru the muffs & tail pipes & open the hood & its got a quadra jet carb on it. thanx charlie keel

[cdr]

to the OP,it dont cost anything to uncap the car

[c00nhunterjoe]

You now have me extremely interested in your car! Pm me with some more details so we don't clutter up this thread.  

Also, I agree, uncap and run it, if nothing else it will sound awesome. Be sure to take a video!

[c00nhunterjoe]

For what its worth I just went out and pulled a plug on my car. Dry cylinders(been sitting for over a week). Throttle closed compression was 165, throttle open was about 188. My block is not decked, nor are my heads milled. The only headwork done was new guides and seats. I'm .030 over with trw flat tops, no releifs, unknown pn as I got them used and it was 12 years ago. My cam is 248@.050 with 292 adv, .510 lift.  The head gasket I used was whatever felpro advance auto carried on the shelf as stock replacement. Don't know the thickness.(edit: appears stock replacement felpros are .040)

Have you rechecked your compression numbers?

[694life]

Sorry guys Ive been on vacation so we havnt got anywhere on the car. Going back on vaca tomorrow be back to it next week. As for now we have the cam we want just gotta pull the trigger on it after we confirm the OPEN throttle cranking compression.

[Budnicks]

.509 MUST BE installed at 104-105*, NO LATER.
Dunno if you have enough Piston to Valve to advance it ? If you.... can that will pick up the pressure a bit for some more Torque and get the .509 coming on a bit earlier.
Also,
2.02" 60 Ft ??
Anything "lost", or conversely "Gained" in 60 ft time, can pretty much be doubled off the E.T.
example;
go to an honest 3800-4000 stall and you should see 1.7's 60 ft, thats 3/10 faster than the 2.02, so the E.T. should drop around 6/10th to 12.70's right there...
and,
with the advanced Cam I'll guess another 3 mph for around 12.50's @ 105mph.

NOT your low 12's but closer.......and still cheapest way to 12 sec street car.

great advice 

[694life]

we finally got to pulling the car apart last night after getting the voodoo 303 cam and timing chain and some few other goodies. Hopefully it will be back together and getting break in tonight. Thanks again for all the help guys!!!

[c00nhunterjoe]

Did you ever redo the compression test

[694life]

No he decided to do the cam swap after he developed a mean timing cover oil leak. We are gonna do a comp test  again in next time we work on it. gonna do it  with the throttle closed to see how it compares to the 509 test we did and open so we can bring that number to this forum for discussion. After first drive timing is set to 28 deg total and the car drives real nice and responsive with very little throttle. He said it feels like we replaced the converter with a tighter one. Hoping to get a dyno session going soon then hopefully to the track to crack open its first ever 12 second pass. Any ideas how much power this thing should be making?

[694life]

whoops sorry timing is at 38 deg not 28 deg

[c00nhunterjoe]

Have you re-jetted the carb since the swap? Probably going to retune that monster carb.  While the 303 cam will greatly improve low end power over the mp509, I don't think a mild 383 with 28 inch tires stalling at 3k is going to launch hard enough to give you the times you want.

[SRT-440]

The Comp XS274S is a great cam for a 383...and with a 4000+ stall mine runs great....of course I have a tad more compression to work with. 

[694life]

We called Nickerson performance who did the carb and they took the cam specs and said its gonna need a few jet changes. We are going to go to a new ignition box and lock the distributer out at 40 deg and let Nickerson tune it on there dyno. As for the tire size they are M/T ET street radials 275/60/15 we are not against going to 4:30 gears. Think she's got a 12.50 in her?