Tuning Holley 500 for rebuilt gpu 220

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Hjbjzj
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Tuning Holley 500 for rebuilt gpu 220

Post by Hjbjzj » Mon Aug 08, 2016 5:45 pm

Hey everyone,

So I ended rebuilding my gpu 220. It needed 4 new jugs.
Relaced valve seats on all 6 cylinders. Put in the o470 pop up pistons. Dual plug/mag. Fresh rod bearings. All new seals for the top end.

Original motor was all stock with a holley 500.

What tuning am I going to need to do to make the holley work with the rebuilt motor.

Thanks and regards
Justin

jeepinocala1111
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Re: Tuning Holley 500 for rebuilt gpu 220

Post by jeepinocala1111 » Mon Aug 08, 2016 8:56 pm

Hjbjzj wrote:Hey everyone,

So I ended rebuilding my gpu 220. It needed 4 new jugs.
Relaced valve seats on all 6 cylinders. Put in the o470 pop up pistons. Dual plug/mag. Fresh rod bearings. All new seals for the top end.

Original motor was all stock with a holley 500.

What tuning am I going to need to do to make the holley work with the rebuilt motor.

Thanks and regards
Justin
Curious did you have your piston tops cut?
Holley 500 will work fine 52 jet and a 6.5 power valve.

Hjbjzj
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Re: Tuning Holley 500 for rebuilt gpu 220

Post by Hjbjzj » Mon Aug 08, 2016 9:11 pm

Hmmm not sure. Don Davis was ordering all my parts for me and assembling the jugs for me.

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Deano
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Re: Tuning Holley 500 for rebuilt gpu 220

Post by Deano » Mon Aug 08, 2016 9:24 pm

jeepinocala1111 wrote: . . . Holley 500 will work fine 52 jet and a 6.5 power valve.
That looks like a typo to me. I'd expect more like 74ish, which is a typical start point for a 472 Caddy.
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Re: Tuning Holley 500 for rebuilt gpu 220

Post by jeepinocala1111 » Mon Aug 08, 2016 9:45 pm

Deano wrote:
jeepinocala1111 wrote: . . . Holley 500 will work fine 52 jet and a 6.5 power valve.
That looks like a typo to me. I'd expect more like 74ish, which is a typical start point for a 472 Caddy.
Yes you are correct 74 jet 6.5 power valve.

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John Fenner
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Re: Tuning Holley 500 for rebuilt gpu 220

Post by John Fenner » Tue Aug 09, 2016 9:02 am

74# jets and a power valve block off plug is my choice, be sure the float balance spring is installed, I like to preload them a bit more than stock, 100LL has less specific gravity than car gas, will tend to flood without the spring installed
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Re: Tuning Holley 500 for rebuilt gpu 220

Post by dshaw94 » Tue Aug 09, 2016 10:31 am

John Fenner wrote:74# jets and a power valve block off plug is my choice, be sure the float balance spring is installed, I like to preload them a bit more than stock, 100LL has less specific gravity than car gas, will tend to flood without the spring installed
Why wouldn't you want to run a power enrichment circuit?
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Re: Tuning Holley 500 for rebuilt gpu 220

Post by John Fenner » Tue Aug 09, 2016 12:22 pm

Really don't need it on an aircraft engine, have tried with and without, didn't make a noticeable difference, plus just another part to fail down the road or trail for that matter.
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glades cat
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Re: Tuning Holley 500 for rebuilt gpu 220

Post by glades cat » Tue Aug 09, 2016 12:53 pm

John Fenner wrote:Really don't need it on an aircraft engine, have tried with and without, didn't make a noticeable difference, plus just another part to fail down the road or trail for that matter.
X2….the thing I would add when not using the power valve on a Holley is to increase the jet size a couple of numbers. This is to make up for the lack of extra fuel the power valve supplies at a given engine load/vacuum. Holley's power valve fuel delivery system is like having a second set of jets, which opens when the manifold vacuum reaches the power valve number. It increases the jet size by about 8-10. Think of the power valve as an "auxiliary fuel switch". It's either open or it's closed...there is no in between. The higher the number on the power valve, the sooner it opens. By changing the power valve number, you chose at what vacuum/engine load you want the extra fuel. That is one reason Holleys can be fuel misers until the power valve opens. The power valve can you a safety margin at wide open throttle if your jetting is a little small.
Tune wisely grasshopper. :D
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Re: Tuning Holley 500 for rebuilt gpu 220

Post by dshaw94 » Tue Aug 09, 2016 2:10 pm

I don't see where an aircraft engine has any less of a requirement for an enrichment circuit than any other engine. Furthermore if it fails, you simply have power enrichment circuit delivering fuel all the time, which as i understand it is always safe. To jet a carburetor rich enough that it doesn't need an enrichment circuit is a very wasteful way to run. The economizer in an aircraft carb serves baiscally the same purpose, and that's an aircraft specific carb.
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Re: Tuning Holley 500 for rebuilt gpu 220

Post by rjonesboy » Tue Aug 09, 2016 8:44 pm

With the domed pistons, I would err on the rich side. 76 or 78 (no power valve) with 100LL only. Been there, done that, and learned the hard way.

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Re: Tuning Holley 500 for rebuilt gpu 220

Post by John Fenner » Tue Aug 09, 2016 10:49 pm

dshaw94 wrote:I don't see where an aircraft engine has any less of a requirement for an enrichment circuit than any other engine. Furthermore if it fails, you simply have power enrichment circuit delivering fuel all the time, which as i understand it is always safe. To jet a carburetor rich enough that it doesn't need an enrichment circuit is a very wasteful way to run. The economizer in an aircraft carb serves baiscally the same purpose, and that's an aircraft specific carb.
Have been running same setup on the 1995 , 220/470 conversion on the avatar in my page, it has a 500 Holley, annular discharge boosters I took and installed from an 85 HO Mustang carb, it actually has #73 jets due to the hard pull and atomization, but the stock size fuel fittings kill it.
When the original tune was done, #78 jets, .080 needle and seat for alcohol and wroughted out fuel fittings. I'd rather fit injection.
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Re: Tuning Holley 500 for rebuilt gpu 220

Post by John Fenner » Tue Aug 09, 2016 10:53 pm

rjonesboy wrote:With the domed pistons, I would err on the rich side. 76 or 78 (no power valve) with 100LL only. Been there, done that, and learned the hard way.
I've found leaner on tune with higher compression, due to fact the 100ll was not being quenched.
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Re: Tuning Holley 500 for rebuilt gpu 220

Post by lotacarnage1 » Wed Aug 10, 2016 7:38 am

don't forget about the accelerator pump cam profile. may have to try a couple different ones till you get it right.no hesitation when stomp of throttle. that's pretty important.
smeller's the feller

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Re: Tuning Holley 500 for rebuilt gpu 220

Post by rjonesboy » Wed Aug 10, 2016 7:15 pm

I was thinking more about CHTs with the domed pistons. Other than a cooling shroud, more fuel is about the only way to cool these things. Of course the weight of boat, depth of water, and a lot of other things can affect this. No disrespect intended to you, John F, I know you know your stuff

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Re: Tuning Holley 500 for rebuilt gpu 220

Post by John Fenner » Wed Aug 10, 2016 9:46 pm

Lauderdale speedometer has a cheap dual sweep CHT gauge if you want, I tune em by WOT runs and plug checks, as air fuel gauges get coked by lead and get lazy by the O2 sensors. I only have an oil pressure gauge on my boat, lights brighten when it charges, to heck with other worrisomes.
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Re: Tuning Holley 500 for rebuilt gpu 220

Post by Hjbjzj » Thu Aug 11, 2016 11:45 pm

I think ima need an education on this. But, yes the boat will be running av gas 100LL. If anyone is near the clewiston area. And when the boat is fully back together. Maybe someone show me what to do?

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