No gain with LTs on a blown 2v -suggestions?

[TonyG]

Just thought I'd share this information, and see if others had similar experiences.

With a Vortech V1 S-Trim, and a 3.05" Reichard Pulley, I was reaching 10-12 psi at ~6200 rpms. This was with the stock manifolds and Bassani X-pipe with cats. Power level was ~ 440 rw-ish.

I put in BBK longtubes and a BBK catted X-pipe. Now my peak boost dropped down to about 8-9 psi. I really didn't expect the stock manifolds to be that restrictive. Because of this better flow of air, I had to upgrade my fuel pumps (Cobra -> Focus) and get retuned. From this, it would appear that I'm in for a nice bump in rwhp.

Now the confusing thing is that it appears that I didn't gain anything. I'm very sure of this -I have over 150 passes on the dragstrip, and keep careful records. Since the longtube install, I have raced in nice cool air as well as hot humid air. My ET/MPH in each weather condition are pretty much unchanged from what they were with the stock manifolds. The range of MPH from cold air to hot air is unchanged.

OK, one way to look at it is that I'm making the same power with less boost.
So should I pulley down my blower to get back to 10-12 psi in order to see gains? Opinions?

 

[Superhereaux]

So should I pulley down my blower to get back to 10-12 psi in order to see gains? Opinions?

i would

keep us posted

 

[CobraRed_96_GT]

yeah, the LT's just made less resriction - which brings down boost sometimes which isnt bad - but this mean thats you can bump it up still now to 12psi again since it wont be putting your car in much more danger - but seeing better number with the same psi.

 

[lover]

Up the boost.....

 

[gnat]

just forget it and give me your LTs

 

[jstreet0204]

You are more than likely making more power whether you realize it or not. If nothing else has changed, adding the longtubes allowed more air flow into the engine. This extra airflow decreased your boost pressure. The decrease in pressure means a cooler intake charge while still flowing the same cfm. All of that means more power.

 

[smallstang393]

you did gain power becasue now your at same power with less boost if you up boost back to orginal boost then you'll see what you gained

 

[TonyG]

you did gain power becasue now your at same power with less boost if you up boost back to orginal boost then you'll see what you gained

Less boost because less restriction and more airflow. More airflow should give more power, but it doesn't. That's the mystery I'm trying to understand.

 

[the98stang]

Did you dyno the car? How do you know for a fact you LOST power?

 

[TonyG]

Did you dyno the car? How do you know for a fact you LOST power?

Yes it was dynoed. But the "before dyno" was from 3 years ago -the last time Kauffmans tuned it. Since then, the only change was a gear swap (3.73-> 4.10s).

The "after dyno" was immediately after the longtube install. After tuning to the same A/F and timing, it showed about 15 rwhp/15 rwtq loss throughout the midrange. Above 5500 rpms or so, the two curves ("before" and "after") look the same.

I didn't really trust the dyno numbers, so I took it out to the dragstrip for the "real" test. I made one trip in 50 degree air back in April, and another in 90 degree air last Saturday. In each case, the ET/mphs were virtually identical as they were with the stock manifolds in similar weather conditions.

 

[thomas91169]

Less boost because less restriction and more airflow. More airflow should give more power, but it doesn't. That's the mystery I'm trying to understand.

PSI is a measure of a restriction. you lost boost and kept the same or equavilent power level because the motor is now moving air more efficiently than it did before.

like others have said, pump up the boost back to where you had it before and see what happens.

 

[TonyG]

Yeah I'm gonna do that, but I'll be shaking my head the whole time confused over this boost vs airflow thing.

 

[thomas91169]

you dont have cams do you? if you do, are they blower grind or n/a or nitrous grind?

you could also be experiencing the loss of boost because IF you have cams and NOT blower grind (IE na/nitrous grind) you are losing power because the LT's are increasing the scavenging effect, thus all more boost is escaping during the overlap and thusly hurting your performance. If you have blower grinds the overlap is less.

 

[TonyG]

you dont have cams do you? if you do, are they blower grind or n/a or nitrous grind?

you could also be experiencing the loss of boost because IF you have cams and NOT blower grind (IE na/nitrous grind) you are losing power because the LT's are increasing the scavenging effect, thus all more boost is escaping during the overlap and thusly hurting your performance. If you have blower grinds the overlap is less.

I have stock cams. Interesting thought nonetheless.