yellow73bb

I am currently running a 1227747 on my 73 corvette, and am getting the tuning better and better, but am having problems with my Holley throttle body -- the butterflies start to stick open a little bit after it warms. Sometimes, it won't drop below 2000 RPM, never does it go below 1200. I have taken it apart twice, smoothed the bores, lined up the cable and spring perfectly, etc. It works as smooth as silk when cold, but starts to stick after it warms up.

I have decided to replace the Holley TB with a TB from a 454 engine. I have been using a Holley 4 barrell 900 cfm unit with four 85 lb/hr injectors and will be putting on the stock GM unit with (I think) two 80 lb/hr injectors. Other than changing the BPW and the AE vs TPS and AE vs MAP, is there anything else I am going to need to change.

Hopefully, the chevy injectors will be a little more reliable too, as I have already had to replace all four of the injectors once and some twice in my Holley TB in the last few thousand miles.

Any suggestions will be greatly appreciated.

Thanks

va454ss

iTrader: (1)

Just out of curiosity, what are your engine specs?

Grumpy

Get a few quality jewlers files.
Then use a magic marker on the edges of the butterflies.
Back off the throttle adjustments.
Operate the throttle a few times.
Slowly file down the high spots as they apprear.
Repeat as necessary.

yellow73bb

I think that one of the problems is that when the shafts move right to left, they stick worse. I lined up the throttle cable and the spring on the primary so that it works fine now, but now the secondaries stick. I opened them a little more using the setscrew, and lowered the primary to get the right IAC, and they work a little better most of the time, but I have pretty much gotten frustrated with them. The only thing I wonder about is if the Stock GM TB and injectors will support the horsepower of my engine -- probably somewhere around 400 or so.

I may give it one more try to get them to stop sticking, but short of putting the TB in an oven and heating it up, I'm not sure how to tell if it is working or not since it works fine till it heats up.

Grumpy

Maybe a phenolic spacer?.

yellow73bb

I've thought of putting nylon, teflon, or phenolic spacers on each side to keep the plates centered in the bores, I might try that.
Is there that much advantage to keeping the Holley?

Here's the engine specs:

10.5:1 compression, hypereutectic pistons, .060 over. Oversize 2.19,1.88 valves. Mild port and polish job done to heads, heads and intake manifold port matched. Original intake manifold and exhaust manifold, but exhaust is ceramic coated. No EGR. The cam is a Crane Powermax H-272-2 hydraulic, with 272/284 I/E advertised duration, .515/.510 lift, installed at .004. Lobe separation angle is 10 degrees. It says the recommended operation is 2000 to 5000, with valve float at 6500. Today I had it briefly up to 6000.

Low C1500

My thoughts on GM big block injectors (80# or 90#) are that there great , but there hard too find, and there expensive.

After melting one 80# injector, I went back to my 350 injectors (55#) and raised the fuel pressure to a little over 30psi (with a walbro 255 pump) now they flow right around 100#.

They've lasted longer than the used 80# injectors I had. And if they ever crap out, 350 injectors are cheap to replace.

I think the 454 tb will be ok for ya, just open the bores up as much as possible, and polish the bores.

yellow73bb

How do you get 100 lb/hr with just over 30 psi on 55 lb/hr injectors? Seems like it would take nearly 40 psi.

I am glad to hear that these injectors will work reliably at higher pressures. If my 80 lb/hr don't feed my engine well enoug, I'll crank up the pressure.

Low C1500

Alot of people say the GM 350 injectors are more like 61# @11psi.

Crank that to 30 psi and thats 100#.

To prove this take holleys 85# injector thats used in there 670 cfm 350 replacement tbi. They rate there injector @ 22psi. Now put those numbers into a flow calculator with a new fuel pressure of 11psi. It comes out to 61#. Thats how the holley tbi is able to run fine on a stock 350. Eqaully flowing injectors.

But theres no real way to tell unless you flow tested them.

I'm acutally going to take the fuel pressure down to 25 psi, as right now I can make my engine go really rich (bogging) at 6000rpm, so I don't need the injector flow that I currently have.

YOur big block is probably gonna need 100# of injector or so.