at 4500 rpm my engine sputters and i don't know if it is an rpm limiter or weak valve springs as the car was in storage for 15 years (but started several times a year).
so my 1st question is how do i determine if i have a limiter
my 2nd question is if i change valve springs to just a tad better than stock springs as the cam is still stock should the old lifters work ok or could a lifter be breaking down and if so how do i know its the lifter and not the spring
my 3rd question is assuming it is the spring would slightly stiffer springs make mpg go down as now the engine has to work a little harder
thanks guys...hope this made sense to you

 

i think the limiters are real high on tpi cars, because one day i was racing a car from a stop light and i accidently put the car in neutral and stomped the gas pedal the car reved up to like 7000rpm and nothing happened it was strong all the way up, i am not really an engine guy so u have to wait untill the real experts answer ur quesition.

Sounds like to me it might be a injector problem/fuel problem..
Also i would maybe check the air intake maybe something is clogged up..

 

I would try replacing the gas in the car, see if that helps.

 

i have used 93 octane with octane booster, checked the intake path and cleaned the K&N filters, checked timing and verified problem exists with/without the MSD hooked up so it has to be either a limiter or in the valve train ad i have run about 2 gallons of intake/combustion cleaner thru the system to clean the valves/injectors etc

 

4-SP,

First, if you are running around at 4,500 RPM and/or touching off the rev limiter or VSS speed limiter periodically, fuel milage can't possibly be your prime concern, just a factor.

Stiffer springs should have very little real-world effect on fuel mileage. Your therory does have some basis, but you need to consider the entire cycle of the valve train and the number of cylinders. As the crankshaft and timing set work a little harder to get the lifter to rise against one stiffer spring, another stiffer spring on a different valve is also working harder to push the lifter down the closing ramp of that lobe, effectively helping the cam to rotate forward. The forces tend to negate each other, to a point.

There are peaks where the engine may turn a little harder to operate the valve past the top of the lobe, but the greatest change in total load will be due to the overall increased friction caused by more pressure of the all the lifters against the lobes. You can easily reduce that by at least ten percent on a flat tappet cam and lifters by changing to synthetic engine lubricant instead of running the old mineral oil. You camshaft will love you for it, not to mention the rings and bearings.

 

thanks VADER, i see your point about the springs, and i do run synthetic oil. how can i determine if i do have a limiter for sure, is there a module somewhere i can verify by? very seldom do i go to the 4500rpm extreme...only at the strip so that is why i am concerned about daily commuting mpg
thanks again