Boost at WOT

fturner

Registered User
When I did the HG's last spring I port matched the intake side of the heads making them all the same size and opened them up enough to have the "entrance" into the heads larger than the end of the passageway before the bowl, so creating a "funnel" down to the valves which promote acceleration of the air mass into the cylinder (in theory of course ;) ).

On the exhaust side all I did was smooth it up a bit, and took the ridge off the exit side of the valve sleeve (its the darnest thing I've ever seen with that ridge right around there) and thats it... no gasket matching the head to manifold or anything. The exhaust manifolds I opened up at the exit getting rid of the ridge there and got it opened to almost 2".

Nothing done to the cumbustion chamber except cleaning and smoothing.

Here's what I've notice all summer........ the car blasts away like a bat outta hell like its never done before, and she'll even light up the tires on drive pavement doing 30mph and flooring it..... there's no mods like od pullies etc, and the exhaust is stock except no resonator, and the air silencer is removed.

When I plant the right foot from a stand still (barely chirps the tires new Michelin Hydro Edges), the boost gauge hits 8psi right away, then climbs up with RPM's hitting 11 psi as the rpm's go through 5000. The car seems to lag a little when its below 1800 RPM's but really starts pulling at 2100 and just keeps on pulling harder and harder blasting through 5000.

Now don't get me wrong as I'm not complaining the way its running, but only hitting 8 psi then climbs as the RPM's go up... is that normal? I don't think I have vacuum/boost leaks as I've done the tests on this site for such and everything passed beautifully.

Before the HG's went, I'd floor it, and it would nail 11 psi right off the bat, and stay there till about 4500 RPM's then start dropping off a little. Now I do know when things are opened up boost will drop, and you can OD the blower.... but THAT much????

Anyways, I'm thinking of getting a 5% Jackshaft pully but I'm hesitant..... it just seems a little wierd the way its behaving right now... and my wife would kill me if I killed the car :eek: .

Frit
 
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Mine is doing something kinda similar after I put the double IC and raised top on the car and putting little hose clamps on all of the vaccum lines and plugging the crosstalk tube. BTW, I already had the 10% pulley and decent exhaust.

It seems like I've had some noticeable seat of the pants improvement, but the odd thing was the the first few times I got in the car it was a little faster, prolly mental.... However the first few times I nailed it, the boost guage climbed to what I would assume was around 12-13 lbs and whined real good.

The next day it seems like it only gets to 11 pounds :confused:

Now it does jump up to 10lbs pretty darn quick, but it takes a few RPMs to get the full 11ish.

Now I'm using fresh Tbird88s IC gaskets, and have checked for vac leaks with ether, so I know I don't have a large leak, but I guess I may need to pressure test the system to see if there is a leak somewhere else.

Now this also happend after I installed the 10% pulley awhile back. Boost was really high, like 12-13the first couple of times I nailed it, then it kinda dropped back to about 11-12 lbs.

Now I assumed that with my exhaust, raised top, and double IC that I would have loost a pound or so, but its acutally pretty close to what it was...

So I am kinda anxious to get back u8nder there and check for some more leaks, and maybe see if I can tighten any IC nuts down at all....

Has anyone else seen an immediate increase in boost, followed by a slight reduction? Is there a particular spot that might be checked for leaks???

I guess a compressor and some kinda of adapter to the TB would be required to find such a small leak...
 
Frit, that is noramal, my Cat did the same with my early model blower and various OD pullies . . . go to a set PSI (8 or 9 when stock) and climb a bit, the longer I reved it. I would see a peak of 2-3 PSI higher than what it would climb too off the start by redline in 3rd.

Dave
 
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