Can anyone explain this? I have a 355 LT1, GT42 76mm, with a 14lb spring in the wastegate. On 2 seperate ocassions the car has spiked to more than 30psi. The lastest time I caught it on a data log registered at 288kpa. I have a walbro 255 fuel pump and 75# holley injectors, other than that the fuel system is stock. A/F never went above 10.81 and I didn't register any knock. This is all on 93 octane. Usually the car will stay below 16psi and pull hard. These odd times the boost has spkied the car doesn't feel like its boosted at all, very sluggish. I have not duplicated this since because I am afraid of doing damage. I don't really think these readings are what the combustion chamber is seeing because there would be pieces of my motor on the freeway. The car is not pushing water and everything under the hood looks fine. Any ideas?

 

Faulty signal from the MAP sensor. If it did truly spike that high you might feel it, but definitely something would change in the datalogging fuel and timing wise (some serious knock).

 

What was the highest kpa you actually saw? 250 is 2.5 bar and something like 23ish psi, so 288 is along the lines of 26-28? No calc here, but that sounds a bit more possible.

Still, even an extra 10 psi would probably be enough to overpower your ignition system (unless you built for that much) so I would guess (if the spike is real) you are blowing the pspark out and losing power. Check the simple stuff, wastegate opening, is the spring really what you thing it is, reference line to the gate?

 

250 kPa (2.5 bar) is 36psi. 288 kPa is about 42psi. 14.7 psi is 1 atm or 1 bar (100 kPa).

 

that is true but what learned to remember since this post is that you must account for 14.7psi of constant atmosphere pressure. This has calmed my nereves a bit knowing that it was less than 30psi, but I still need to know what causes the spike.

I have the Delteq coil kit with NGK TR6s gapped at 32 (if I remember right) so I don't think I am blowing out the spark.

I just replaced the wastegate line last weekend and will be out for a test drive tonight to see if it made a difference

 

100kpa is 0 boost, its atmospheric....
that may be 14.7, but we have to pick a reference. He may have seen 36psi above absolute VAC, but thats nots 36psi of boost

 

A decent setup, but I don't know if it will hold up to 25+ psi.... you are talking about a similar setup to the stock ls1 cars, and I don't think they are making it that high without an ignition box or something

I'm not an expert, I'm running a Ford ignition