Help diagnosing 500ci problem?

[oldschool]

Hey everybody, I'm new to the site hoping to find some advice.

I have three 500ci Mopars, that are identical.

Specs on all three motors:
13.5:1 compression
Indy Dual plane
1000 cfm 4150 carb
Indy R1 roller cam .649" 272/276 @.50
1.6 rockers
Indy cnc'd 295sr heads
tti stepped headers
MSD pro billet distributor w/6AL box
full 3" exhaust through mufflers
timing is around 35-36 total degrees

Two of them come in at 573rwhp, and one of them is at 480rwhp. I've been trying for a while to find the lost hp in the third motor. I have tried advancing and retarding the cam, I bought the heads new, and have had them off and had spring pressure checked by a shop. AFR is right at 12.5-12.6:1 on all three motors.

The one in question seems to run very well, with no misfires, but it does have a slight sputtering sound in a steady throttle cruise that the other cars do not have.

On the dyno, this one didn't sound anywhere near as strong as the other ones, and would not make HP past ~5300, and it sounded labored, while the other ones sounded strong.

Thanks for the help, and glad to be on board.

[Musicman]

I know this is a stupid question, but have you tried any of the dummy checks yet like swapping carburetors, compression checks etc...
At least you have 3 identical motors to play with for comparison... That should speed things up a bit.

[firefighter3931]

I would run a compression test to see what's going on and perhaps compare the cranking numbers to one of your other engines to see if things are the same. Afterwards run a leakdown test and see if the rings are still in good shape.

What were your clearances like on this build : main/rod as well as piston to wall ? It sounds like something inside the block (rotating assembly) is holding it back and you need to find it.


Ron

[mally69]

 

[Streetwize]

Check you fuel system first, looks like maybe a fuel related restriction...found a few demons that way so don't be suprised if it's something simple. trash in the float bowl/pvcr, even the needle/seat can make it lay down....seen lots of tank/sending unit corrosion related fuel feed problems too.

Check your ignition system, could have a bad or defective coil...reluctor gap can cause power issues at high RPM too, especially with high compression...usually not major but check it nonetheless.

Di you build all three? are you 100% certain all the specs are the same?

Next take it and your best car to a chassi dyno and over lay the tq/hp curves, if youcan't diagnose post them and lets have a look.

Are all three intake manifolds equal..there is a lot (and I mean A LOT) of casting variances in the 440-2, I went through and Max wedged mine per this article...actually went one step beyond on the lower plenum.

http://www.moparmusclemagazine.com/techarticles/mopp_0505_440_project_engine_build_2/install_photos.html

This is IMO the Best intake you can run on a street driven stroker motor..needs a little work but it's worth it!!
combo sounds pretty close to my 517.

[firefighter3931]

A couple of thoughts ;

(1) what were the A/F ratios when you had it on the chassis dyno ? As Wize said it could be a fuel delivery problem causing it to fall over on it's face

(2) Do you have any engine dyno numbers to compare it too ? There could be some parasitic losses through the drivetrain but you won't know that unless there are crank hp/tq numbers to compare.



Ron

[oldschool]

everybody,thanks for the replys.

the air/fuel was 12.5 to 12.7.it stayed steady thru the dyno pulls.
i will post my dyno sheets,later today.
the motor combos are the same.
the short block was assembled by the same guy at the machine shop,that did all my motors.
the specs. are the same.
im going to do a leak down test and,will post.

[oldschool]

Click on each link to see my dyno sheets.

http://img88.imageshack.us/my.php?image=dynosheet1dr8.jpg
Here is the dyno sheet of 1 of my cars that runs correctly. The pink shaded run is my first run - before tuning. The yellow shaded run is after tuning.



http://img84.imageshack.us/my.php?image=dynosheet2vr1.jpg
This dyno sheet is from the car with the undiagnosed problem. As you can see from the sheet it does not run much past 5200 rpms. There are 2 runs on this sheet, but the original run was very close so I didn't pick up much. If you notice on the base line (pink) on the first dyno sheet and the dyno sheet #2 that they are almost identical. I am at a loss as to the where the other 92 hp is. I did check the cam shaft intake center line - it was on the money. I checked tdc - on the money. I also checked the cam lift - on the money. I am going to a warm leak down test and will post results. Also going to change carb to see if that helps.

Check out that torque curve on the first dyno sheet - top yellow line! not bad for a street car.

[firefighter3931]

Brian, the second engine seems to be laying over early. Are both motors running the same carb ? What carb is on both of these ? 

If the leakdown tests come back good a carb swap from the strong engine to the weaker one would be the logical course of action. 

Very nice numbers on the first engine  What type of fuel are you using ?


Ron

[Rob R]

The very first thing that comes to mind is VALVE SPRINGS..
that old indy roller needs a stiff spring...

[oldschool]

the heads are brand new.i use k-motion 950's with titainium retainers. that should be enough spring,as i also run the exact combo on two other motors.
i thought the same thing with the springs,so i pulled the heads back off and had the preasures checked.also checked the valve job too.both were good.
im doing a leak down test tomorrow and will post the results.


i use sunoco 110 race fuel in all of my motors,as VP isnt avalable near me.

[Challenger340]

Curious how the leak test goes.

[cjs69mope]

  i have a 493 rb motor that a put together my self with indy sr heads and mopar m1 single plane intake with a demon 850 carb , i am sure with no dowt that my motor will pull to 6 grand on pump 93 octane gas . i am runnin avery fast distibutor curve all in by 2000 rpm with 25 deg inital seting , have not had it on dyno but i can tell you it will run , i know it sounds stuipid but did you try differant timming curves ?