YSI boost question
Thread Starter
Racer
Joined: Feb 2012
Posts: 418
Likes: 7
From: Sugar Grove IL
St. Jude Donor '12, '15
YSI boost question
So I had my car on the rollers today and all went well except that the boost would only go to 17psi at 5800 rpm and held steady there up to 7000 rpms. This a billet impellor YSI on a 427 cu in motor with mast heads, custom cam, holley high rise intake and American Racing ZO6 racing headers...... it has a 10% over driven crank pulley and a 2.75 s/c pulley. I'm thinking I have a boost leak somewhere but I've not yet looked over everything. I do have a dual nozzle alky kit on there which isn't being used and was wondering if maybe at that boost level boost is leaking past the nozzles, they are just in one of the silicone couplers and pretty wobbly. I also have an unrestricted 4" intake tube with an air filter on the end so I don't know if that is maybe restrictive. Just looking for opinions and maybe it anyone else has had a similar situation. Thanks for any help.
Drifting
Joined: Aug 2008
Posts: 1,399
Likes: 30
It could be belt-slip but I'd dyno and tune the car with a bellmouth on the centri unit to see what it makes. Most air filters choke these setups.
Thread Starter
Racer
Joined: Feb 2012
Posts: 418
Likes: 7
From: Sugar Grove IL
St. Jude Donor '12, '15
I was going to look into getting a bellmouth for it. I removed the meth nozzles and put a new coupler on, I can't see any evidence of belt slip....no belt dust anywhere but that doesn't mean it isn't slipping. I will check the belt and try to tighten it as well. I just found it strange that for 1200 rpm the boost didn't increase at all so there has to be either a restriction or a leak or possibly belt slip.
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Drifting
Joined: Feb 2010
Posts: 1,310
Likes: 99
From: Arlington Texas
What kind of power are you making? You have a big engine and big heads. You might not see more than 17 psi. Isnt KPA how the computer measures air? What does the kpa do?
Last edited by silver408z; Jun 1, 2018 at 09:11 PM.
Team Owner
Joined: Nov 2007
Posts: 24,035
Likes: 2,342
From: Gilbert AZ
Big overlap cam?
I see 23-24psi on my Ysi setup. I find the people who throw donkey dick big lopey cams so they sound cool have this exact issue. Put a blower limited setup on, then bleed off a good amount of boost right out the exhaust with 20+ degrees of overlap. On a 427 with big heads, you are just doing a disservice pushing your limited amount of incoming air right into the exhaust.
I see 23-24psi on my Ysi setup. I find the people who throw donkey dick big lopey cams so they sound cool have this exact issue. Put a blower limited setup on, then bleed off a good amount of boost right out the exhaust with 20+ degrees of overlap. On a 427 with big heads, you are just doing a disservice pushing your limited amount of incoming air right into the exhaust.
Drifting
Joined: Feb 2005
Posts: 1,869
Likes: 61
From: montreal quebec
I made 21 22psi with a 408 decent size cam and heads that flowed 345cfm 8inch crank and 2.75 pulley....and a bellmouth vs a filter and a cast impeller ...I would think 17psi sounds about right at 5700 but would expect it to climb moving towards 7000 or whatever your shift point is..... I’d be looking for signs of belt slip
Last edited by c5mtl; Jun 2, 2018 at 01:52 PM.
Team Owner
Joined: Nov 2007
Posts: 24,035
Likes: 2,342
From: Gilbert AZ
Agreed it is probably slip, as it shouldn't level out unless something is just off on the setup. At this level, even having a few month old belt, or a 1/4" adjustment is the difference between 17psi and 20+.
Thread Starter
Racer
Joined: Feb 2012
Posts: 418
Likes: 7
From: Sugar Grove IL
St. Jude Donor '12, '15
I will check on the cam specs tomorrow, I had Pat G spec it out for this set up so I would think it would be ok. The mast heads are LS7 285's with titanium valves. The whole set up is brand spankin new, this was the first time one the dyno. I know the belt is going to stretch a bit so I will check that tomorrow as well, no evidence of slipping that I can find but that doesn't mean it isn't. 1100 rwhp@6200/940trq@5200
Pro
Joined: Oct 2013
Posts: 520
Likes: 31
From: Austin, TX
I'm only pulling 9.6 PSI on my build and put down 900rwhp, the heads had a lot of work done by Greg Good here locally so I'm pretty happy with the efficiency. That's with the stock throttle body and the filter on it.
Melting Slicks
Joined: Jun 2006
Posts: 2,497
Likes: 261
From: Miami Florida
I will check on the cam specs tomorrow, I had Pat G spec it out for this set up so I would think it would be ok. The mast heads are LS7 285's with titanium valves. The whole set up is brand spankin new, this was the first time one the dyno. I know the belt is going to stretch a bit so I will check that tomorrow as well, no evidence of slipping that I can find but that doesn't mean it isn't. 1100 rwhp@6200/940trq@5200
How many lbs of boost?
At that power level lots is been asked of the belt so you will have to tighten it up more than you would think, again add some VHT it helps quite a bit.
You will not see trace of rubber dust if belt slips unless there's a jammed idle pulley.
Racer
Joined: Jun 2016
Posts: 336
Likes: 15
From: outside new orleans Louisiana
exactly as stated above. you can see belt slip in boost graph. your making 1100hp on e85 i assume. Cant ask for much more power than that out a ysi.
Last edited by gameover4; Jun 5, 2018 at 12:00 PM.