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How much RPM is a stock PI bottom end good for?

2K views 50 replies 15 participants last post by  JoeyICU 
#1 ·
before the toothpicks give way?

normally aspirated of course.
 
#5 ·
Palmguy said:
You would need to have some major airflow mods (heads, cams, intake, headers) to be able to take advantage of those relatively high RPMs. On a stockish motor there doesn't seem to be any reason to go that high.
Guy on mod depot made solid gains to 6500 rpm on a dyno with VT stage 1 cams.

Stock pi heads/intake/manifolds
 
#6 ·
Kentwood said:


Guy on mod depot made solid gains to 6500 rpm on a dyno with VT stage 1 cams.

Stock pi heads/intake/manifolds

Wow...got a link for that? I don't feel like searching through the forums. That's cool...:)
 
#7 ·
I can't find the thread, it was along time ago

but here is his graph




SCT Tune before and after


Stock PI longblock/heads/intake - Comp cap springs


He had a 75mm accufab TB and plenum.


He may have had some shorty headers but I'm 99% sure it was stock manifolds.


He did have an aftermarket exhaust and h pipe.




Still impressive though......the pi intake flows alot better than people give it credit for.
 
#8 ·
I would say that 6300-6500 is a safe range for a maximum. There are people revving higher, but I don't think I would chance it unless I was ready for another buildup.

Russ
 
#9 ·
I don't remember exactly what year it was that Ford started putting the same rods in the Cobra motors as in the 2V. I do know that all the 4Vs in 02 on up used the 2V rods. With exception of the 03/04 Cobra that is. Whether is was done on the 4Vs back to 99 I don't know.
 
#10 ·
id think you could set a shift point at 6100-6200, even if its not worth reving there and go with that, puting some work on your heads and intake (pi intake) would definitly make it worthwhile to rev up there

but from the word of mouth of afew very renowned 4.6 guys, stock npi bottom end, 6300 to 6400 is about the point you have to worry
 
#11 ·
JoeyICU said:
id think you could set a shift point at 6100-6200, even if its not worth reving there and go with that, puting some work on your heads and intake (pi intake) would definitly make it worthwhile to rev up there

but from the word of mouth of afew very renowned 4.6 guys, stock npi bottom end, 6300 to 6400 is about the point you have to worry
as you can see by that dyno graph, with some vt cams that engine is still pulling to 6100 with stock heads and pi intake
 
#12 ·
with pi cams id think it would still get power that high, the npi intake is really the biggest hold back, that and the stock cams, but yeah, dont wanna kick a dead horse, im gonna try to see what i can get from the engine i have as it sits because im poor and pressed for time, college is nice and sucks at the same time
 
#13 ·
JoeyICU said:
with pi cams id think it would still get power that high
Nope...somewhere around 4700 for the peak with unported NPI heads, PI intake, and PI cams.
 
#14 ·


Anyone remember that graph...NPI heads, PI intake, PI cams, a '02 GT MAF and a tune by KD. No need to shift at 6500 or anywhere close to it with PI cams. I would have to plug in numbers to tell exactly where to shift but it isn't anywhere near there. Probably something around 5400.
 
#15 ·
with my sct tune with 02 gt maf and stock npi cams and npi intake the car run outs of power after 5100 rpm. the tune is set to shift at 6000 rpm. will change out to pi intake (maybe pi cams also) once i find the right gasket.
 
#17 ·
guitar maestro said:
casper, are both your 1-2 and 2-3 shift points set at 6000?

96bird, based on that dyno graph, the 1-2 should be at around ~6000 and the 2-3 around ~5550 in order to keep the pre-shift HP equal to the post-shift HP
Like I said I could have plugged in the numbers....
 
#18 ·
You guys should read the tech articles on MD for Max Acceleration

MD

One of the things you guys aren't thinking about is how long it takes for the trans to actually complete the shift. The EEC commands the shift at a certain point. Then the time it takes the trans to complete that shift is a totally different point.

This also depends on your transmission. The earlier AODEs and 4R70Ws like in the 94/95 MN12s take a little longer to shift than the newer trans. A stock trans will shift slower than one with a Jmod. And a completely built Jerry spec trans will shift even quicker.

Now the SCT programming and depending on the programmer will speed up the time it takes for the shift to complete also.

So for instance you have a stock trans and shifting from 1 - 2 at WOT from the command point to the completed shift could take up to a full second. In that time at full throttle your rpms continue to climb at a very fast rate. So if a commanded shift at 5200 takes place it could be at 5800 or higher before the shift is completed. So setting your shift at 6100 like someone mentioned would end you up with a failed shift since it would hit the rev limiter.

Take for instance Casper's shifts, his 1 - 2 is set for 5700 but it isn't completed until close to 6000. Also remember your stock tachs are worthless when up that high so don't count on them to be accurate.

Then you also have to take into consideration of what your rear gears are. Say you have a set of 3.73s or 4.10s. In that same amount of time it takes the trans to complete said shift your rpms are climbing even faster due to the gear multiplication. So now instead of only 300 - 400 rpms from the command to complete it could be as high as 1000 or more.

And finally, you want your shifts to happen so that when the shift is completed and you are in the next higher gear that it is in the engines power band. So if this means you have to wait until what seems like the car is nosing over or losing power to shift then that's what you have to do. Since the vehicle is still accelerating and will accelerate quicker keeping the next gear in it's power band. Read the articles I link and they will explain it.
 
#19 ·
im pretty sure when people refer to seting the shift points at a certain rpm, the general idea is that when we say shift points, it means the end result, where it actaully shifts at, not the rpm the eec actaully commands the shift

j-mod will drop a shift about 150-200 rpms, it speeds it up that quickly!

go j-mod
 
#20 ·
Lonnie said:
I don't remember exactly what year it was that Ford started putting the same rods in the Cobra motors as in the 2V. I do know that all the 4Vs in 02 on up used the 2V rods. With exception of the 03/04 Cobra that is. Whether is was done on the 4Vs back to 99 I don't know.
They started to do that crap in '99 or '00..from '93-'98 the rods in the 4V were of a better quality-I've had both here to look at,and they're visibly different.
JL
 
#22 ·
Take for instance Casper's shifts, his 1 - 2 is set for 5700 but it isn't completed until close to 6000. Also remember your stock tachs are worthless when up that high so don't count on them to be accurate.
once the shift is complete i have to hold my neck or it will break because of the sudden surge. almost feel like jump forwards 2 steps. I LIKE IT!!!:D
 
#23 ·
As far as the strength of the rods, I am pretty sure that the stock fuel cut off on a the older 4v was 6800 RPM, and if they are the same as ours and Ford feels comfortable enough to put a warranty on those engines, I would say that you can get away with 6500 RPM, eventhough the chances of failure increase. I don't think this is a smart thing to do though for a couple of less obvious reasons:

First, just because the engine has some sort of cam, PI manifold, valve springs, and the stock shortblock is good to 6500 RPM doesn't mean your converter will cope with the added speed, especially with the 12" stocker. Cavitation is not your friend.

Second, if you have an improved converter, you need to upgrade the tranny as well. There is a spring for the one way clutch (somebody correct me if I'm wrong on what the spring does), that when pushed past 6000 RPM, has a greater tendency to fail. Do you really want to push your luck, or just wait a little bit until you can put something in that you know won't leave you stranded? Personally, that means a good shortblock and a solid tranny so you don't have anything to worry about, and not worrying is worth waiting. Why push your luck when you can just put some solid rods and a good tranny combo in and not worry?

By the way, Lonnie, good post on the shift timing.

Pete
 
#24 ·
BIG PETE said:
As far as the strength of the rods, I am pretty sure that the stock fuel cut off on a the older 4v was 6800 RPM, and if they are the same as ours and Ford feels comfortable enough to put a warranty on those engines, I would say that you can get away with 6500 RPM, eventhough the chances of failure increase. I don't think this is a smart thing to do though for a couple of less obvious reasons:

First, just because the engine has some sort of cam, PI manifold, valve springs, and the stock shortblock is good to 6500 RPM doesn't mean your converter will cope with the added speed, especially with the 12" stocker. Cavitation is not your friend.

Second, if you have an improved converter, you need to upgrade the tranny as well. There is a spring for the one way clutch (somebody correct me if I'm wrong on what the spring does), that when pushed past 6000 RPM, has a greater tendency to fail. Do you really want to push your luck, or just wait a little bit until you can put something in that you know won't leave you stranded? Personally, that means a good shortblock and a solid tranny so you don't have anything to worry about, and not worrying is worth waiting. Why push your luck when you can just put some solid rods and a good tranny combo in and not worry?

By the way, Lonnie, good post on the shift timing.

Pete

Who said anything about running stock heads/cams/intake/tranny ;)
 
#25 ·
BIG PETE said:
As far as the strength of the rods, I am pretty sure that the stock fuel cut off on a the older 4v was 6800 RPM, and if they are the same as ours and Ford feels comfortable enough to put a warranty on those engines, I would say that you can get away with 6500 RPM, eventhough the chances of failure increase. I don't think this is a smart thing to do though for a couple of less obvious reasons:

First, just because the engine has some sort of cam, PI manifold, valve springs, and the stock shortblock is good to 6500 RPM doesn't mean your converter will cope with the added speed, especially with the 12" stocker. Cavitation is not your friend.

Second, if you have an improved converter, you need to upgrade the tranny as well. There is a spring for the one way clutch (somebody correct me if I'm wrong on what the spring does), that when pushed past 6000 RPM, has a greater tendency to fail. Do you really want to push your luck, or just wait a little bit until you can put something in that you know won't leave you stranded? Personally, that means a good shortblock and a solid tranny so you don't have anything to worry about, and not worrying is worth waiting. Why push your luck when you can just put some solid rods and a good tranny combo in and not worry?

By the way, Lonnie, good post on the shift timing.

Pete
yeah a stock 12 inchers will start squeeling at 5500rpms, you can hear the thing whine like the little girl it is, poo on ford for that converter that should go in trucks and never a car...
 
#26 ·
Yeah you sure can hear it. first time i heard that after playing with my shift points. i about freaked out. Ive read that article on modular that lonnie reffered to, thats how i determined my shift points. makes a difference at the track, still need to do some more tweaking at the track on those shift points to make sure i have exhausted every tweak i can.
 
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