Can't seem to give my 4.1 enough air...

[Eric Stage I]

My 4.1 (.040" over) Stage I engine has GN1 heads, Erson 214/214 cam flat tappet, V2 intercooler, and 84# injectors. I've tried 3 different turbo's over the past 1 1/2 years. A PT51, TE62, and PT70-1 (old style 68mm).
PT51, power done at 5000-5100rpm, 1/4 mph 115, no more power after 22psi.
TE62, power done at 5200-5300rpm, 1/4 mph 117, no more power after 24psi.
PT70, power done at 5500-5600prm, 1/4 mph 123, no more power after 26psi.

I think I should make power to maybe 6000rpm. The PT70 got me closer, but not quite.

Do the 4.1's and larger require that much more turbo than a 3.8? Or is something else wrong in my combo?

Let me know if more info is needed.

Thanks,
Eric

 

[RealFastV6]

Whats your stroke/totalCI ?

 

[Eric Stage I]

Total CI is 257". Stock stroke 3.4". Bore is 4.007".

 

[Jeff Harrington]

Hey Eric, what kind of seat pressure on your valve springs? I run the same cam, M&A heads, PTE front mount with a PT-70 and had a 72 on at one time, 273 ci. Have to shift 5600 for best ET. Thought it would be good for more RPM also. Mine was set for 110# on the seat.

 

[Eric Stage I]

My springs are 100# seat pressure. Maybe thats all the rpm I can expect from that cam?

 

[RealFastV6]

I would definately go bigger on the cam, but I'm not sure thats the reason you're only trapping 123 at 26psi on a T70. Do you have 373 gears in the car or a 26" tire?

 

[Eric Stage I]

Yes, I'm using 26" tires, stock gears. My rpm thru the traps is 5600-5700ish. I just seems like it should keep pulling to at least 5800, but it seems to die off around 5500ish. But I agree, taller tires are in my future.
My winter project list: get taller tires, get bigger cam (maybe 220-224 @ .050" flat tappet?).

Eric

 

[RealFastV6]

Originally posted by Eric Stage I
Yes, I'm using 26" tires, stock gears. My rpm thru the traps is 5600-5700ish. I just seems like it should keep pulling to at least 5800, but it seems to die off around 5500ish. But I agree, taller tires are in my future.
My winter project list: get taller tires, get bigger cam (maybe 220-224 @ .050" flat tappet?).

Ah ok, makes sense now why the trap speed is so low.

I bet 28" tires alone would get you into the 130s. The car probably stops pulling at like 900ft.

Someone with a little more experience may be able to recomend a good cam. 214 is definately a little on the small side for a motor of that displacement. 224 would be a good start but I'd go even bigger, as big as ~230 with a flat tappet hyd. I would want the motor to pull to at least 6500 if its got a forged crank.

 

[Jeff Harrington]

Try using overdrive. I have 373 with 28inch tire and I use overdrive.

 

[quickt]

I am having that same problem with a 274 stage 2 with M&A heads. This car also had the 214 cam. The car was out of power at 5400 with the 214. Best ET was 10.76@122 Changed the cam to a 220/216 roller and the MPH shot up to 129 with a cam change. The car now ETs 10.40@129 at 25 psi boost all day long. But now the car stops pulling at 6100. The gears are 3.89s with 29" tall tires. If you turn the boost up the car goes faster in the 1/8 but not much change if any in the 1/4. I am thinking we need more cam or less gear. The part that is odd is that same cam in my 234 motor will pull strong to 6500 and my car ran 10.32@130. This car kick some tail in the 1/8 6.43@108.

 

[JCotton]

Lonnie,

Put a BGC intake on it!!!!

 

[Eric Stage I]

Seems like it has something to do with the CFM requirement at X rpm. The 3.8 requires less, so the 214 cam is fine for it. I guess the big inch motors just require airflow capability if you intend to rev it, although mines not quite as big as yours (did I just say that? ).

 

[RealFastV6]

It would make sense that if you're going to build a stroker motor, then you'd want to take advantage of the mid-high torque by using a larger cam and less gear. 3.89 is a retarded amount of gear for a motor thats going to run out of breath so quickly, and has a small cam to boot.

What happens with the long stroke, is the piston is moving up/down so much faster (has to travel more distance in the same amount of time) then a short stroke, that you have to give it much more cam to reach a reasonable cylinder fill, just like if you were reving it to 10k instead of 6. The piston speed and cam durration are what go hand in hand, weather it be stroke or RPM.

 

[quickt]

When Chris bought the car it had the 214 and the 3.89 already in place. I wanted to put a 236 roller in the car from the start. Unfortunatly the way the heads were set up this was the largest cam we could use without removing the heads to have them cut for springs. With the gains we had from the camshaft change alone (4 solid tenths and 7 mph) and even larger gains in the 1/8 makes us wonder with the proper gear for this cam how fast this car can go with the PT-70 turbo 220/216 cam and 3.50 gears. He is installing the gears this week and off to the track Sat.

 

[Eric Stage I]

Thanks for the info. Lonnie, keep us updated on what happens. This may give me some direction on where I need to go.

Thanks,
Eric