Retarded timing acting like a rev limiter

vwchuck · Post by **vwchuck** » Tue Aug 20, 2013 2:12 pm

Has anyone ever encountered a turbocharged engine that would not rev past a certain RPM due to the timing being too retarded? Engine seems to hit a wall at 7000RPM. Timing is set to 21 degrees at around 15 psi boost. The engine is 139 ci four cylinder. The same engine with the same cam but naturally aspirated runs aroun 30 degrees timing and revs to 8000RPM no problem. Any input would be appreciated.

ImportAction · Post by **ImportAction** » Tue Aug 20, 2013 3:55 pm

What makes you think it is the ignition timing that is causing the problem? Most of the time that adv would not be a problem.
What is the cam, what is the turbo, what fuel are you running, and carb or inj?

Post by **In-Tech** » Tue Aug 20, 2013 8:34 pm

Yes, I have seen that. The closer you are to tdc, the higher the cylinder pressure, as you know, so it's takes more energy to jump the gap. Easy test is to close up the gap and see if you have any gains in rpm. If so, re-think your ignition system.

Dodge Freak · Post by **Dodge Freak** » Tue Aug 20, 2013 10:19 pm

In-Tech wrote:Yes, I have seen that. The closer you are to tdc, the higher the cylinder pressure, as you know, so it's takes more energy to jump the gap. Easy test is to close up the gap and see if you have any in rpm. If so, re-think your ignition system.

Sounds cool to me, racers don't spend $$$ for those MSD spark boxes just because they look pretty, lol MSD makes 7,8 and 10 boxes for a good reason, they are needed sometimes.

ImportAction · Post by **ImportAction** » Wed Aug 21, 2013 4:17 am

In-Tech wrote:Yes, I have seen that. The closer you are to tdc, the higher the cylinder pressure, as you know, so it's takes more energy to jump the gap. Easy test is to close up the gap and see if you have any gains in rpm. If so, re-think your ignition system.

So that would be caused by a bad ignition rather than retarded timing. Even easier test for the same thing, does it rev out if you don't have your foot up it?

SWR · Post by **SWR** » Wed Aug 21, 2013 5:04 am

vwchuck wrote:Has anyone ever encountered a turbocharged engine that would not rev past a certain RPM due to the timing being too retarded? Engine seems to hit a wall at 7000RPM. Timing is set to 21 degrees at around 15 psi boost. The engine is 139 ci four cylinder. The same engine with the same cam but naturally aspirated runs aroun 30 degrees timing and revs to 8000RPM no problem. Any input would be appreciated.

If it's THAT retarded - and not just a weak spark - that's very unlikely. Drop the ignition to that degree and you'll be into antilag and melted valves-mode real quick. And it doesn't stop pulling rpms either...

vwchuck · Post by **vwchuck** » Wed Aug 21, 2013 8:08 am

I guess I didn't explain my question well. The engine does not miss at 7000RPM but the acceleration rate slows down considerably. At the track in third I had my foot to the floor and it would not pull past 7000RPM. It also seems to do it on the street. Kind of like I am hitting a big resistance at the 7000RPM point. It is very strange.
The engine is running on pump gas, cam is 268@.050 with .575 lift at the valve, GT-35R turbo and 138 cubic inches. The car does run a single 3 inch spiral core muffler and it runs an aircleaner on the turbo.
My thoughts were something weird going on with the timing vs pump gas, the air filter is restricting flow or the muffler is causing back pressure.

Cubic_Cleveland · Post by **Cubic_Cleveland** » Wed Aug 21, 2013 8:15 am

I would also check the valve springs. This is my go to (or hyd lifters) if a motor lays over sooner than expected and the basic fuel/air/spark has been checked.

vwchuck · Post by **vwchuck** » Wed Aug 21, 2013 8:21 am

Yes I forgot to add that.That was my first idea but I did measure them and they should work up to around 8500.The seat pressure was around 175psi when I put them on.I was going to attack the easy stuff first and if that didn't work then it was valve springs.

Tuner · Post by **Tuner** » Wed Aug 21, 2013 2:30 pm

Too much plug gap?

vwchuck · Post by **vwchuck** » Wed Aug 21, 2013 2:43 pm

As I stated the engine is not missing at 7000RPM it just kind of noses over. Wouldn't the plug either fire or not fire if the gap is wrong?

Tuner · Post by **Tuner** » Wed Aug 21, 2013 3:34 pm

You would think so, but depending on what kind of ignition it is, a too-wide gap can just make an engine get soggy at high speed. The RPM will plateau depending on the load. It can misfire without popping and banging, just loose power because it only misfires randomly.

What is the gap you are using?

What is the plug heat range?

It is possible a too-hot plug will cause preignition which causes the combustion to advance too far before TDC and the pressure holds the engine back instead of pushing it forward. Engine damage occurs quickly if that is the case and it is left at WOT in that condition for more than a second or two.

Dodge Freak · Post by **Dodge Freak** » Wed Aug 21, 2013 3:36 pm

vwchuck wrote:As I stated the engine is not missing at 7000RPM it just kind of noses over. Wouldn't the plug either fire or not fire if the gap is wrong?

Might not fire as often, how many times a second does it fire at 7,000....I'm bad sometimes in math but isn't it a few times ? Lets see, at 4,000 rpm the plugs each fire 1,000 times in a minute...right ? If so, at 7,000 thats like 1,750 times each min--what if the plugs just fired 1,200 times

What I do know for sure is my Mopar 340 liked the 7 msd box more then the 6 box and its just has 10 to 1 compression and was "a waste of money" from MSD tech. Yet my cold starts for sure are much smoother-stronger and once warmed up, engine feels a tad more powerful...maybe the carbs were not tuned perfect, whatever.

Yeah, don't run projected plugs with pump gas and colder is better then too hot.

Tuner · Post by **Tuner** » Wed Aug 21, 2013 3:45 pm

Dodge Freak, did you change the coil at the same time you started using the 7 box?

ImportAction · Post by **ImportAction** » Wed Aug 21, 2013 3:55 pm

Valve springs are still possible. Remember you are loosing 40 lb of spring pressure to gas pressure against the valve. Could try tightening the lash up for a run and see if you get a few more rpm. That's a lot of cam for a turbo. How many rpm are you wanting to run?
If it's ignition it should be load sensitive. Does it rev out if you don't have your foot up it. Or try winding 5 lb of boost out of it and see if it makes a difference. There would usually be a point where it runs fine, then 1 lb more boost it turns to poo at the top. However in my experience this would normally be noticeable miss-fire.

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Retarded timing acting like a rev limiter

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