Not making good power

[wakeboarder193]

1996 Cobra, forged motor at 8.5:1 compression, stock heads and cams, full exhaust, procharger D1SC with 3 core intercooler, 3.40" pulley making 13lbs of boost.

Car is leaning out past 6k, and the boost seems to fall off after about 5800. After the first run, the car was making in the neighborhood of 470rwhp/410rwtq.

Ideas? The car should be making way more than that on 13lbs with a D1 Procharger...

 

[wakeboarder193]

also, in tank walbro 255 with a pro-flo in-line pusher pump. should be able to make enough fuel.

 

[2002mustanggt]

Do you have good valve springs ?? I don't know if this matters but I lost power past 5500 rpm cause of exhaust valve floated, now I have 120lb comp cam valve springs. If you still have stock valve springs then it might be floating .

 

[Erich]

Your boost should not be falling off. Do you think you are getting some belt slip? I am running the same pulley and see 20 psi at 7000 rpm.
Erich

 

[01yellercobra]

FWIW, the guy I bought my D1 from was making 14psi with a 3.4" blower and stock lower crank pulley on his 01. I know his compression was lower then stock, not sure what it was though. But he had stock heads and cams. Made about 530rwhp with a conservative tune.

If the boost is falling off I'd look into belt slip or a leaking BPV.

 

[9cobrastang7]

compression ratio is way low. This is why you're making less hp than stock compression, but that does not explain why the boost drops off. How many miles are on the kit?

 

[wakeboarder193]

kit only has about 7k miles on it. Also I don't expect much belt slip as I had them convert everything to a G.I. Joe 8 Rib kit before tuning. That's where i made the mistake of ordering the 3.4 instead of 3.2 blower pulley.

SLO984Now - I was expecting 530 ish as well. The tuner just did a 98 cobra stock motor with a 10lb P1SC and it made 470, so why shouldn't my 13lb D1SC make more. On the previous 3.2" pulley the car only made a best of 509/461, and again was falling off after 6k ish.

 

[Chris98vobra]

Is this the small 3 core IC that they sell? It is common for that to be a cork if it is. I had a very similar one that was custom and it blocked me at about 13lbs also. Boost would flat line. You might try bypassing the core with a pipe see what happens to the boost levels. In my case I removed my core and used alky injection only for a few years.

 

[meaty mac]

I would be more concerned with the lean condition right now. You have the pump for it, but what size are your squirters?

 

[THAITED]

I would be more concerned with the lean condition right now. You have the pump for it, but what size are your squirters?

Agreed also what's MAF you are using?

 

[Myzticsnake]

with a 3.4 pulley i made 17psi at 6500 rpm with the stock filter. ~530 rwhp but 470 like yours at ~57-5800 rpm. Torque was in the 430-440 neighborhood.

Im using 60lb injectors with dual inline walbros, fwiw.

 

[kyoshosp2]

Wow that compression is for 25lbs boost. the intercooler is your boost problem I delt with that core a few times. get a better cooler . also make sure the meter is not pegging and you have 60# squirters atleast. Also a 9:1 block would have been better for you and still safe on pump gas. Remember these 4valves and cintri's like compression.

 

[2V99GT]

can't tell you what you're problem is, but that compression i don't like.

 

[Chris98vobra]

Your compression is not the problem. That will cost you a little rwhp but it has nothing to do with the extent of your problem. 03+ Cobras run the same compression, I know many others who also have that in their rebuilt engines, and I run it too. I have seen some good power made with your boost levels with your blower and with your compression. I make over 600rwhp with 8.5:1 and 18lbs of boost.

 

[97desertCobra]

OP what are you running for your fuel system in full detail? I'm more concerned with the lean condition. Don't forget that forged shortblocks can blow up too.

The intercooler may be a cork but also what by pass valve are you using? The stock Procharger BPV is really only good to 10# or so. After that is doesn't flow enough cfm to keep up. Its possible that its bleeding off boost at the upper rpms restricting you to 13#. Just a thought.

 

[Chris98vobra]

Its possible that its bleeding off boost at the upper rpms restricting you to 13#. Just a thought.

Excellent thought. You might be exactly correct.

 

[04SilverSerpent]

Out of curiosity, how would the boost be bleeding off? I thought what with a centrif setup that the boost would slowly ramp up as the RPM's went up? I'm not very familiar with centrif setups, but I thought that you would still need a wastegate to bleed off boost like you do with a turbo?

 

[Chris98vobra]

Out of curiosity, how would the boost be bleeding off? I thought what with a centrif setup that the boost would slowly ramp up as the RPM's went up?

Correct. But there is a bypass value that opens up when under vacuum to bleed off the boost. Sometimes these are either too small for the level of boost or defective so boost will leak even when you don't want it too and that will result in lost lbs. Often people increase their boost levels and keep the stock bypass valve, which isn't up for the task.

 

[wakeboarder193]

update: car got back on the dyno today, and pumped out 498rwhp in 110 degree heat, but is still leaning out after 6k.

Car is now running a 3.20" pulley on a G.I. Joe 8rib setup (no slip). Fuel was all swapped out, 255 in tank, plus an in-line pusher pump brand new. Also, custom MAF housing was made to fit the SCT BA-3000 and MAFia. Meter isn't pegging.

I didn't build the engine so the low compression is something we're just gonna have to work with.

We seem to have plenty of air, but the fuel isn't delivering. MAF isn't pegging so that's not the issue either. Our next thought is the fuel rails. Should the car be flopping at 500rwhp because of fuel rails? Also, the previous owner told me we had 60lb injectors, but I'm having the tuner pull them to verify. Otherwise we're stumped. I have no idea at all why its running out of fuel. Any other ideas guys?

 

[slvr35th]

Your compression is not the problem. That will cost you a little rwhp but it has nothing to do with the extent of your problem. 03+ Cobras run the same compression, I know many others who also have that in their rebuilt engines, and I run it too. I have seen some good power made with your boost levels with your blower and with your compression. I make over 600rwhp with 8.5:1 and 18lbs of boost.

is that with a d1sc?