Grog

Does anyone out there have a Whipplecharger on their Formula with unmodified Silent Thunder exhaust?

My '99 271 Fastech 502 MPI is currently at AZ S&M getting a Whipplecharger installed. They had it out for lake test/ECU reprogram yesterday. According to Jim, the boost pressure spiked to 14lbs when he gave it full throttle (5# kit). Everything was fine at partial throttle.

He said that a possibility is that the Silent Thunder exhaust system is too restrictive and causing back pressure. Does this sound right???

Work done along with the install:
Reworked heads
aftermarket head gaskets
ARP bolts
roller rockers
IMCO exhaust

Any insight is greatly appreciated.

Breathe Later

Sounds like the bypass isn't operating properly. It's mounted on the side of the supercharger and it needs to be open to atmospheric pressure. Even at partial throttle, 5 # of boost sounds high. I don't see my boost gauge move much until I really apply the throttle and there's alot of load on the engine. The bypass closes when both sides of the diaphram are at equal pressure-atmospheric, and you get full boost (6-7psi). Make sure the diaphram on the bypass isn't jammed.

mosport1

iTrader: (1)

Grog, I know this is off subject, but did the Whipple's intake bellmouth interfere with your engine cover/sunpad actuator? If so, what was done to solve the clearance problem?

CayFomula

I have a much older 272SR1 Formula with Whipples. I found that when I removed the Silent Thunder platform my boost dropped 2# and I picked up 7mph on top end (from 83 to 90 mph).

I didn't have nearly as drastic a problem with my boost as you described though. When I changed heads and cam I should have seen a 4# drop and only seen about a 1 1/2# drop with the Silent Thunder platform.

Ian T.

Grog

I'll question AZS&M on the bypass when I pick up the boat today. That theory sounds more logical than a Silent Thunder exhaust restriction.

According to Jim at AZS&M, the problem was solved by an adjustment to the valve train (push rod adjustment???). I don't understand this explanation.

mosport1 -
I'll get back to you as soon as I see what was done.

Thanks for the feedback.

mosport1

iTrader: (1)

Grog, thanks for your consideration. I'm now collecting parts to accomplish the same thing on a 95 271SR1 Indy. Just trying to figure out all of the complications I might face before I get started. Now that you have a template, this probably won't be the last time I pick your brain. Can't wait to hear how the finished product works out.

Grog

mosport1 -

There were no clearance issues with hatch hardware and the whipple, although as I watched the hatch close, I could tell that there wasn't a whole lot of clearance between the two.

The trial run was less than perfect. It ran great.....for about 5 minutes, at which point my new IMCO exhaust riser on the starboard side melted and finally blew a hole in the 4" exhaust hose to my transom. The port side was getting ready to go too. Turns out there is an alignment problem between the exhaust and the transom that put just enough kink in the hose to make the inside tube of the exhaust contact the hose.

From that point on, something wasn't right. The HP just wasn't there anymore. I'm still trying to understand how a hole in the exhaust hose could cause a huge loss in power. Taking it back to AZ Speed & Marine tomorrow to look things over.

FWK

If you have a hole in the exhaust I assume youare also pumping water ot of the hose. The engine will not run well on steam.

Grog

FWK -

That was one of my theories also. I thought that maybe my engine was trying to breath and burn steam and spent exhaust gasses instead of oxygen. Another symptom was that my EGTs never got above 900F which would make sense also. No oxygen = nothing to burn = low cylinder temps.

WHADDAYATHINK?