Stroker Motor wont Rev pass 5200Rpm

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AirForceRacer

AirForceRacer

Mopar or No Car
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Indio, CA
I have a 402ci stroker motor based on the factory 318ci LA motor. I know this is not a very common stroker but we're Mopar people and were different.

The motor has custom Ross forged Pistons, Forged connecting rods, and a Forged 4-inch stroker crank. The heads are mildly ported 360 heads with Harland Sharp 1.5 roller rockers. I believe the push rods are factory length. I am not sure what cam is in the motor maybe off the shelf Mopar Purple Cam. The MSD box is set to 7k reline and the car also has Fitech Fuel injection which is also set to 7k reline..

The car has a custom turbo set up and set for 9-10lbs of boost. When I take the car out for some spirited driving Ive notice the motor will not rev pass 5200-5300rpm in either 1-2-3 gear. I first maybe it was the spark plugs blowing out under boost but I have changed plus and gapped them tighter and and still having the issue.

Any and all advice will be appreciated.

Jared
 
No idea what camshaft is? Yeah that's the key piece here.

What is the idle vacuum at 750 rpm and say 16* of idle timing. Is the idle really smooth or is it a choppy cammed up idle.

I bet it has a small cam in it and runs out of steam early that is exacerbated by the larger CI stroker.

Just a WAG based on limited information.

Ha you actual live pretty close to me...
 
9-10 pounds of boost requires a pretty good ignition system. And plugs gapped down a little. Hopefully you’ve got both of those two things. My second thought is I hope it’s not detonating at 52-5300 because that will stop it from making power and accelerating and also destroy it. Last thought is it’s floating the valves. You should figure out what camshaft is in it and make sure the springs are adequate. Pull a plug and send us a pic. Close up and clear.
 
There’s a lot of missing info and some really good blind guess that have merit.
 
Another thing that can cause a symptom very similar to this is the mag pick up wires on the MSD box to the distributor being switched.
 
I agree with Cracked. I would think camshaft and valve springs would be the limiting factor in red line RPM.

Why did you choose to build a boosted forged stroker motor around an unknown camshaft or at least one that wasn't right for that build? I would think a lot of thought would have gone into camshaft selection for a motor like that?
 
Did this combo ever run strong? There are lot issues like the other guys have written. The EFI is also new? If so you need a lot of time and knowledge just for the basic map. Your cam is a N/A grind, i recommend one from a expert for Turbos including matching springs.
 
"Mystery Cam", "Custom Turbo Setup", undefined "Mildly Ported 360 Heads" with no flow#s. Honestly, that may be all She's got Cap'n. The turbo'd 340 We worked out in My Buddy's AAR never got much past 5,600-5,700rpm, with up to 21psi. The heads & the wastegate dump are gonna show You just how far they fall short right quick, and the cam could be all wrong, but ????????
 
For reference, the T/A heads were done with the boost in mind, & the fact that the solid cam was netting .475" lift. They flowed [email protected]", & excellent all the way up-to, We used a set of DC/MP Dual springs & Mancini valves.
We need waaay more details, like exhaust setup etc. etc....
 
Killer6 said:
For reference, the T/A heads were done with the boost in mind, & the fact that the solid cam was netting .475" lift. They flowed [email protected]", & excellent all the way up-to, We used a set of DC/MP Dual springs & Mancini valves.
We need waaay more details, like exhaust setup etc. etc....
Click to expand...
and this is just the mechanical part...
 
As above, detonation can be a rumble or growl, not the traditional "tingling ping" people are famliar with. We were using timing control and water/meth injection when We got over 10psi, which worked great until it didn't one night at Quaker City.
 
Is your ignition boost reference, ie does it retard under boost? You could be running up against this. If you have a retard controller (MSD) you can retard ignition 1 degree per PSI and see if there is any effect. you could also dial back your timing a tad and see if affects top end only, it will disturb bottom end but will give you an idea on what the motor likes up top under boost. Stroker on boost and running that high in RPMs is a combo that will require some careful management as those 3 usually don't work together easily. Whats your compression?
 
The Motor won't spin pass 5k when in park either. With everything you guys have pointed out makes me lean toward the springs. This is an old build. I'm going to pull a spring and have it checked. Most likely replace them but not sure what I'll be upgrading them to.

Thanks for all the input I'll keep you guys updated.
 
While you're in there dicking with the springs put a dial indicator on the intake and exhaust and figure out what the max lift is. That'll give folks at least a general rough idea what cam we're working with.
 
did you change/ worked on something since the last good run?
Put the timing light on and rev to 5k+, still ignition? Do you see fuel in the throttle body above 5k.
Take a data log, look for strange events, bad widebandsensor killed your tune?
Can you load up a backup file to your EFI?
 
AirForceRacer said:
The Motor won't spin pass 5k when in park either. With everything you guys have pointed out makes me lean toward the springs. This is an old build. I'm going to pull a spring and have it checked. Most likely replace them but not sure what I'll be upgrading them to.

Thanks for all the input I'll keep you guys up
Click to expand...
Do you still live in Indio CA? If so, I would start by drving to IMM and asking them what they think.
 
I would start with checking the rev limiters. If the MSD unit is a dual limiter (launch and run), what is the launch limit set at? If it is set around 5200, that would be very suspicious. You could try changing the launch limit setting and see what happens.

Or, either the FiTech or MSD units might have been accidentally set to 6 cylinders, because 5250 is exactly 6/8 of 7,000? You could start by verifying both the FiTech and MSD "cylinders" selections are set at "8". If they are, I would start with the MSD box and reset the rev limiter to 6,000 and see if the engine is still limited at 5200-5300. Then if the engine is still limited ato 5200-5300, reset that limiter back to 7,000, and set the FiTech unit to 6,000 and see what happens. Even if both the FiTech and MSD units were set correctly to "8" there could be an internal circuit problem that set it to "6".

Next, I would look for a fuel problem.

I don't know whether a cam/spring problem would cause a sudden and repeatable rpm limit. I would think it would be more gradual. IMM coould answer that question for you.
 
Definitely try to see what your exhaust pressure is at max intake boost, even after you fix this issue. I increased my spring seat pressures by the IN and Ex pressures times the areas of the IN and EX valve diameters.. If you are buying springs anyway, might as well maintain the proper seat pressure for the cam, at boost. Area of a 2" IN valve is 3.14 x 10 lbs boost is 31.4 pounds of additional seat pressure to meet seat specification of cam.. Finding your cam specs is going to be interesting.
I'm not saying this is your problem as I, along with others, need more info.. Use any changes you make to establish a known baseline and enjoy!
 
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