Engine will not rev past 3000rpm

[superflytnt]

Hello fellow wrenchers,

Beforehand I would like to apologize for this long thread;) I have a peculiar issue with the 413cui I am currently running in my 68 Plymouth Satellite. For some reason the engine will become harder to rev up past the 2500rpm and will hardly go past 3000rpm. Here are the specs for the drivetrain:

- Chrysler 413 truck engine (thick wall 426 casting), 71 casting, standard bore, 10:1 cast pistons, new rings, balanced rotating assembly including balancer and 11 inch flywheel, 300mls since rebuild.
- Open chamber 452 heads, standard valve size
- Edelbrock 600cfm on Holley Street Dominator, 7547 size rods, 0.100" jets (one step up from standard 0.098").
- TRW TP203 hydraulic camshaft 280°/298° duration, .443"/.465" lift (in/ex)
- Standard waterpump, standard dual field alternator
- HP exhaust manifolds dumping into 2,5" dia. exhaust
- Electronic ignition w/ new regulator and orange box ECU, 16° initial advance.
- 26" standard radiator.
- A-833 manual transmission with new Centerforce dual friction clutch
- 8 3/4 rear with 3.55 gears and 31" dia. tires.

With the new MP distributor I bought in the first place I could barely reach 2200rpm at WOT. I noticed that the new Mopar distributor would not give more than 5 degrees mechanical on top of the initial advance, even after adjusting advance weights to full advance (Mallory type advance). Also, vacuum canister was inoperable.

Then I changed out the distributor for a rebuilt 'older' type with the 'radial' slots for the advance weights. Mechanical advance on this unit was 16 degrees and the vacuum canister works (non-adjustable). Now I can drive 2800 rpm at part throttle (about 70mph), but the engine has a very hard time accelerating any faster than this up to 3000 and then it stays there. Overtaking another vehicle is going painstakingly slow...

I checked the ingition cables; 5 had about 20000ohms resistance. I changed out these 5 with new cables from an incomplete set and that helped some, but the acceleration rate of the engine still decreases after 2500rpm. From idle up to 2500rpm it runs fine. It is like the distributor just stops advancing or is actually retarding the timing or it may be fuel related...

I am now thinking towards a fuel related problem (carb too small, fuel pump pushrod worn, clogged fuel filter), but without having a distributor from a known good running engine I cannot rule out an ignition problem. It is hard to start after, say, a stop at a gas station, but that may be due to the aluminium intake and carb soaking up heat from the engine (I have a 0.5" phenolic spacer installed underneath carb). I changed out the standard jets in the carb for the 0.100" jets, but I have not run the engine yet.

What are your thoughts on this?

Thanks in advance.

[fugly]

Unless I missed it, you did not say anything about new valve springs- first though, is to check maximum timing (should be around 34 at 3000-3500 or earlier). If that is low, it could cause this. I doubt it is fuel if it idles and performs to 2500-next thing is your valve springs and rocker adjustment- if they are stock springs , you may be floating the valves-also, many times if you are using stock valvetrain, after decking and cleaning the heads, your pushrods become too long and will not let the hydraulic lifters work properly.

[superflytnt]

Damon,

Thanks for your reply. About the valvetrain; I am using stock length pushrods, stock valvesprings and stock rockers. I will first check out the distributor timing.

[fugly]

If you keep the stock valvetrain and that is the issue, you can shim the rocker shaft up off the stands some to take preload out

[superflytnt]

Damon,

Thanks again for the help. I should be getting a 64 Dodge 440 wagon with a good RB electronic ignition setup in it within a couple of days, so I can try out that distributor and see if it has any effect. The distributor I have now does not seem to have an adjustable vacuum advance unit on it (or I don't have the correct tools to do so). I do have an adjustable vacuum advance unit I can swap with the current one, though.

Could there be something external to the distributor that may cause it to retard? Or mechanical and vacuum advance are counteracting each other at some point? However, notonly under part throttle, but also at WOT the engine does not seem to want to move beyond the 3000rpm and I should have little to no vacuum at WOT.

I haven't tried running the engine without vacuum advance hooked up or on manifold vacuum (it's on ported now). I plugged the distributor into manifold vacuum with the car running in the garage and it did give some snappier throttle action and engine returned to idle much faster than using the ported vacuum.

I did try a different ECU, but it had no effect (if I'm correct, the distributor sends a signal to the ECU, which in turn triggers the coil to send a spark to the distributor)

Some more info, which I forgot to put into my first post. The engine pulls a steady 10" of vacuum, idles @750 rpm. Also, here in Holland the octane ratings of gasoline offered are 95 (about USD 8,00/ga) and 98 (about USD 9,00/ga). I usually run 98, but availability of 95 octane is a lot better. I haven't tried to tune the engine to see if it pings with 95, but I first want to sort out this phantom rpm limiter.

[fugly]

I am referring to advance with the vacuum disconnected- if you are setting it with vacuum it will be waaayyy off. You need to get idle and 2500-3000 rpm readings and see what they are- if it does not change with rpm, your centifugal advance is froze up and it will not rev like that.....if you are setting advance with vacuum, it will be low...

[superflytnt]

Damon,

I have set up the advance with vacuum disconnected. The first distributor I set up (new from MP, but 'new' isn't what is used to be) only gave 5° mechanical advance, regardless of how the weights were adjusted. With that distributor, and the vacuum advance hooked up, I was not getting beyond 2200rpm at WOT. And the vacuum pod was inoperable as I did not see the timing mark advance further when I hooked up the line and went from WOT to part throttle. The distributor I have now gives 16° mechanical advance @ 2600rpm. Initial advance for both distributors is 16°. The vacuum pod also gives additional advance @ part throttle. I will do some more tinkering over the weekend.

[superflytnt]

I checked the timing today again. With the dial back timing light and vacuum advance disconnected I get 18° mechanical advance @ 2600rpm. However, at 1600rpm I already have 16° of mechanical advance coming in. So, it looks like the springs (or just the light spring) in the mechanical advance unit are a bit too light. I'm OK with the amount of mechanical advance, but it comes in too early.

Vacuum gauge reading on manifold vacuum port in carb is 10" @ idle and in the ported vacuum port it is about 7.5"(?) @ idle. I do hear a hissing sound when I expose the ported vacuum port and I had this on both the carbs I tried. I was under the assumption that the ported vacuum port would have 0" @ idle.

I also noticed on the vacuum gauge, which I plugged into the ported vacuum on the carb, that when I apply the throttle gradually from idle to 1500rpm that the vacuum increases from 10 to 13~14 (which I did not expect) and then drops off to zero. Is the ported vacuum set up to provide this additional vacuum?

[fugly]

You should have 32-36 degrees at 2600-3200 depending on the combo- at any rate , 32-36 should be the number without the vacuum- the vac canister has little to do with acceleration as vac drops during this process- you may want to read the ignition paper on our homepage. The ported vacuum showing a reading at idle means your carb is not adjusted properly as the primaries are open too far, thus exposing the transfer circuit and the vac port. Once everything else is right , you will need to retune as this will cause a major bog.You are correct in assuming the ported vac should be zero at idle

[superflytnt]

Well, I found the problem. It looks like I was having my eyes closed when I installed the cam, because it was installed 26° advanced...

[fugly]

good deal

[teddyd]

We have a 318 poly with bent push rods. There is no apparent cause. Cam and lifters seem ok. The engine ran with one cal. missing. When we checked compression with no spark and plugs out, 4 more lifters were bent into severe s shapes. We have not opened to see timing chain, and have not yet pulled a head, but does anyone know of this with the poly engines?