Blown 427 Losing Boost
Thread Starter
Racer
Joined: Oct 2005
Posts: 367
Likes: 3
From: maple grove and North Port fl mn and now florida
Blown 427 Losing Boost
First I want to help all you CF folks as you have helped me greatly in the past.
I have a forged LS7 427 L92 heads L76 intake 90mm TB ported and polished, 80 lb injectors with a D1SC with a 3.70 pulley running around 15 lb boost. I have 2 high flow fuel pumps, one that is boost referenced. Cam is a 238/254 at 114 lsa with around .600 intake and exhaust. My original kit was an A&A from 5 years ago and it has been great. Andy makes excellent kits. Upgraded to the 8 rib with a 10% overdrive and a larger BOV, but not the really large one that is available. ARH 1 7/8 tube headers and 3" exhaust to B&B Bullets. At around 5100 rpm my boost drops from 15 to 10 lbs and hp drops off. Fuel pressure is still high, 63 psi plus and spark was retarding from 17 to 12-14 degrees but we have stopped that, so no retarding now.
Took the air filter off to see if that would make a difference and still the same result.
We dont think the belt is slipping but are going to put another one on and see what happens. Made almost 700 rwhp.
Any ideas as to why the loss in boost
I have a forged LS7 427 L92 heads L76 intake 90mm TB ported and polished, 80 lb injectors with a D1SC with a 3.70 pulley running around 15 lb boost. I have 2 high flow fuel pumps, one that is boost referenced. Cam is a 238/254 at 114 lsa with around .600 intake and exhaust. My original kit was an A&A from 5 years ago and it has been great. Andy makes excellent kits. Upgraded to the 8 rib with a 10% overdrive and a larger BOV, but not the really large one that is available. ARH 1 7/8 tube headers and 3" exhaust to B&B Bullets. At around 5100 rpm my boost drops from 15 to 10 lbs and hp drops off. Fuel pressure is still high, 63 psi plus and spark was retarding from 17 to 12-14 degrees but we have stopped that, so no retarding now.
Took the air filter off to see if that would make a difference and still the same result.
We dont think the belt is slipping but are going to put another one on and see what happens. Made almost 700 rwhp.
Any ideas as to why the loss in boost
Team Owner
Joined: May 2006
Posts: 21,473
Likes: 356
From: Palmdale, Ca----- 2009 Cyber Gray 4LT A6 F55 452 RWHP 422 RWTQ- RIP 1998 C5 734 RWHP & 585 RWTQ-----
To me it sounds exactly like Belt Slippage! 
Watch your Voltage gauge as you pull the Dyno and see if it drops, if it does then your belt is slipping. Usually belt slip occurs at the Crank so look for some Belt dust or evidence of slippage in that area or any pulley for that fact - just to be safe
You are using a Single serpentine Belt - correct? * Rib can slip too, especially with the TQ you no doubt are making!
keep us updated
Thanks,Matt
Watch your Voltage gauge as you pull the Dyno and see if it drops, if it does then your belt is slipping. Usually belt slip occurs at the Crank so look for some Belt dust or evidence of slippage in that area or any pulley for that fact - just to be safe
You are using a Single serpentine Belt - correct? * Rib can slip too, especially with the TQ you no doubt are making!
keep us updated
Thanks,Matt
Thread Starter
Racer
Joined: Oct 2005
Posts: 367
Likes: 3
From: maple grove and North Port fl mn and now florida
Thanks for your thoughts. Very minimal belt dust but will replace the belt first.
It is one of Andys older kits that has 1/2 " Stainless steel clamps and they seem to be holding but will spray with hair spray, any specific brand?
I will check the MAF as I am still using it.
I will ckeck for a voltage drop next time on the dyno.
I checked that there was not a restriction at the air filter so it came off and still the same result.
No loss of fuel pressure and not leaning out at WOT.
Narrowed down to belt slippage, BOV overpowered or leak downstream of the blower, or Intercooler can't flow the air at high boost.
Making lots of power but much more is there.
Any other ideas will be appreciated and will keep you posted, cheers
It is one of Andys older kits that has 1/2 " Stainless steel clamps and they seem to be holding but will spray with hair spray, any specific brand?
I will check the MAF as I am still using it.
I will ckeck for a voltage drop next time on the dyno.
I checked that there was not a restriction at the air filter so it came off and still the same result.
No loss of fuel pressure and not leaning out at WOT.
Narrowed down to belt slippage, BOV overpowered or leak downstream of the blower, or Intercooler can't flow the air at high boost.
Making lots of power but much more is there.
Any other ideas will be appreciated and will keep you posted, cheers
Race Director
Joined: Apr 2009
Posts: 10,581
Likes: 252
From: SE TEX
Similar to what mine is doing. At around 4750 rpms I drop from 8psi to almost no boost. D1SC with 3.9" pulley, stock crank, 6 rib and a 402. I am pretty sure mine is belt slip being 6 ribbed with only 8 lbs. Yours however..... What rpms is that spinning the blower to? 5100 motor RPMs plus 10% overdrive with a 3.7 blower pulley? I have read where D1s have trouble really boosting big cubes and was told that 14psi may be my limit. Again just what I have read and was told, but you seem to have had no problem pumping 15lbs into the 427. If you are at 15 at only 5100 rpms, what the heck is your goal? 
Just throwing out ideas, I know exactly how frustrating this can be, believe me.....
Just throwing out ideas, I know exactly how frustrating this can be, believe me.....
Thread Starter
Racer
Joined: Oct 2005
Posts: 367
Likes: 3
From: maple grove and North Port fl mn and now florida
I wanted to go to a bigger blower anyway and so now have the F1C installed and it is still losing boost at 15 lb at 5100-5200 rpm and it drops to 10 lb. Should not be a problem of over spinning the blower now, but same symptoms.
Arun if it is belt slippage on the crank what do you recommend to correct the slippage?
thanks rick
Arun if it is belt slippage on the crank what do you recommend to correct the slippage?
thanks rick
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Team Owner
Joined: May 2006
Posts: 21,473
Likes: 356
From: Palmdale, Ca----- 2009 Cyber Gray 4LT A6 F55 452 RWHP 422 RWTQ- RIP 1998 C5 734 RWHP & 585 RWTQ-----
I wanted to go to a bigger blower anyway and so now have the F1C installed and it is still losing boost at 15 lb at 5100-5200 rpm and it drops to 10 lb. Should not be a problem of over spinning the blower now, but same symptoms.
Arun if it is belt slippage on the crank what do you recommend to correct the slippage?
thanks rick
Arun if it is belt slippage on the crank what do you recommend to correct the slippage?
thanks rick
I'm gonna help out. It's quiet an easy and simple soloution-------
FLIP-DRIVE! This will eliminate Belt Slip and especially with the Blower and power you are putting out
I have one on mine and it is certainly the best invention for Centri's
I know ARUN will speak up too, but I could not resist - You can see a write-up I did on the Flip-Drive Install w/Pics by searching it!
Thanks,Matt
Thread Starter
Racer
Joined: Oct 2005
Posts: 367
Likes: 3
From: maple grove and North Port fl mn and now florida
Thanks Gentlemen, I was already thinking the same thing. Now which manufacturer do you recommend and can I install it without to many more mods.
I have seen several advertised and some get great reviews and others are questionable.
Cheers Rick
I have seen several advertised and some get great reviews and others are questionable.
Cheers Rick
Race Director
Joined: May 2005
Posts: 15,960
Likes: 21
From: West Norriton PA
St. Jude Donor '08
RICK<
I'm gonna help out. It's quiet an easy and simple soloution-------
FLIP-DRIVE! This will eliminate Belt Slip and especially with the Blower and power you are putting out
I have one on mine and it is certainly the best invention for Centri's
I know ARUN will speak up too, but I could not resist - You can see a write-up I did on the Flip-Drive Install w/Pics by searching it!
Thanks,Matt
I'm gonna help out. It's quiet an easy and simple soloution-------
FLIP-DRIVE! This will eliminate Belt Slip and especially with the Blower and power you are putting out
I have one on mine and it is certainly the best invention for Centri's
I know ARUN will speak up too, but I could not resist - You can see a write-up I did on the Flip-Drive Install w/Pics by searching it!
Thanks,Matt
Hey Matt,
are you running a six or eight rib set-up ?
I saw the second version Flip drive this weekend and bought one at the show. Decided to go with the centrifigal over the turbos.
Thread Starter
Racer
Joined: Oct 2005
Posts: 367
Likes: 3
From: maple grove and North Port fl mn and now florida
Thanks for all your help. I went with a 3.90 pulley and replaced the 8 rib belt. PROBLEM solved. Making 18-19 lb boost and just unbelievable power. Taking it to the dyno for the final tune on Tuesday and will let you know how we do. Really excited... You folks are the Best, cheers Rick
Racer
Joined: Apr 2004
Posts: 282
Likes: 0
From: Cumming GA
That's the nice thing about going to the F1, you can run a larger pulley
and not have to max it out like with the D1. I did the same thing.(Actually I went from the P1SC to the D1SC to the F1C.) Now let's talk about getting it to hook-up!
and not have to max it out like with the D1. I did the same thing.(Actually I went from the P1SC to the D1SC to the F1C.) Now let's talk about getting it to hook-up!
Thread Starter
Racer
Joined: Oct 2005
Posts: 367
Likes: 3
From: maple grove and North Port fl mn and now florida
Still getting belt slip at 5400 rpm in 4th gear which does not show up on street use but on the dyno it does. Looks like I will have to go to another belt setup like the flip drive. I dont know much about these systems and have the older version of the A and A brackets. Will the flip drive work with this setup and can I stay with my 8 rib on the blower side of this system? What system do you recommend?
Thanks again, Rick
