750 DP to Holley HP Update - Chevelle Tech
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post #1 of 15 (permalink) Old May 29th, 19, 3:45 PM Thread Starter
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750 DP to Holley HP Update

Swapped out main body to get rid of choke tower. Holley sends 76-82 jets, 31 squirter and 4.5 PV w/kit.

I swapped out to supplied jets, kept my 6.5 PV and kept my 40 squirters.

Made a 60.45 mile hwy trip with 4.3 gallons. 100*, engine temp pushing 180*, a little warm.

Plugs are black sooty. Going back to original 69-78’s as engine was dynoed with.

Made a test run. Now engine temp (w/leaner jetting cooled back to 175)

I’ve heard rich jetting will heat engine, never believed it. I do now !

Butt dyno does not record any increased HP w/new Holley HP main body, but IMO, worth the $125 to clean up under the hood and retro S/S look

What the butt dyno really liked is the Holley $35 progressive linkage delete. Instant HP 💪

383, M 21, 4:11 in 3500 # Chevy.
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post #2 of 15 (permalink) Old May 30th, 19, 9:54 AM
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Harry
 
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Re: 750 DP to Holley HP Update

Quote:
Originally Posted by Reelysalty View Post
Swapped out main body to get rid of choke tower. Holley sends 76-82 jets, 31 squirter and 4.5 PV w/kit.

I swapped out to supplied jets, kept my 6.5 PV and kept my 40 squirters.

Made a 60.45 mile hwy trip with 4.3 gallons. 100*, engine temp pushing 180*, a little warm.

Plugs are black sooty. Going back to original 69-78ís as engine was dynoed with.

Made a test run. Now engine temp (w/leaner jetting cooled back to 175)

Iíve heard rich jetting will heat engine, never believed it. I do now !

Butt dyno does not record any increased HP w/new Holley HP main body, but IMO, worth the $125 to clean up under the hood and retro S/S look

What the butt dyno really liked is the Holley $35 progressive linkage delete. Instant HP 💪

383, M 21, 4:11 in 3500 # Chevy.
Nice looking setup !
I did this same swap of my DP body for an HP body to get air bleeds and choke horn delete. I have a wideband in my '70 SS396. The larger IFR (.033) in the Quick Fuel red DP upgrade metering blocks was perfect. It solved my tip-in stumble. For air bleeds, I started going big, then, ended loving the small -- HSAB - 25 to 31; LSAB - 68 to 72. This improves gas mileage. (Right now, I am debating between 27 and 31 for the LSAB, and settled on 68 for the LSAB). 68 LSAB will not lean out the IFR and give me plenty of transition gas for overdrive on the fwy - idle is at a perfect 14.2 for my cam, with approx 1 turn of the idle mixture screws. I also ended up with a larger PVR (larger than the stock .059 - I drilled the next size up), high flow power valve, and 9.5 rating even though I have a 292H Cam (high duration). This large PVR and quick opening PV allowed me to go to 72 on the front jets. Rear jets are around 83, 84. The smaller HSABs (25 to 31) will make everything richer on the top end and leaner in the mid-range, so, you need a good, quick opening PVR to avoid going lean in the mid-range. I also ended up with the blue cam on hole 2 for the front and the black cam (hole 1) for the rear. 31 nozzle with extensions in the front and 35 nozzle in the rear with extensions.

Note: This is my second HP body (AL) upgrade. I have one of the original zinc ones (2012?) with added quick fuel DP metering blocks and chrome bowls upgrade kit. This made my screws too short and after many, many, jet, IFR, emulsion changes, I ended up pulling out the threads on 2 screw holes in the zinc. So, now I have the 2-3/4" screws that I ground down to the perfect size for this new aluminum setup.

Harry
1970 Chevelle SS396 (408), Fathom Blue,
Original Block & Forged Crank, KB Pistons, Edelbrock 6045 Heads,Comp Cam 292H, March Serpentine, RPM AirGap,750HP,100hp Nitrous
A/F Wideband,Tremec TKO 600, 12 bolt,
30 spline Moser Axles, Richmond 3:73's, Hotchkis control arms, swaybars, springs, Wilwood 12" rotors D/S, 4 piston calipers

Last edited by hjdca; May 30th, 19 at 10:15 AM.
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post #3 of 15 (permalink) Old May 30th, 19, 11:18 AM Thread Starter
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Some good info! I don’t have a wide band and am afraid to disturb air bleeds as I hear I can lean out mixture too easy.

I’ve also heard changes to idle air bleeds can help w/gassy idle. I kinda like the smell first thing in the morning 😁, but it’s really the smell of a poorly tuned carb.

Do you have an opinion on idle air bleeds & rich idle relationship? (cam idles at 1000)
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post #4 of 15 (permalink) Old May 30th, 19, 12:02 PM
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Harry
 
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Re: 750 DP to Holley HP Update

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Originally Posted by Reelysalty View Post
Some good info! I donít have a wide band and am afraid to disturb air bleeds as I hear I can lean out mixture too easy.

Iíve also heard changes to idle air bleeds can help w/gassy idle. I kinda like the smell first thing in the morning 😁, but itís really the smell of a poorly tuned carb.

Do you have an opinion on idle air bleeds & rich idle relationship? (cam idles at 1000)
Yes, I have lots of opinions.... Larger LSAB will give you a leaner idle and let you adjust the idle screws farther out, but, and this is a big but, it will also lean out your transition from idle and could give you a lean stumble. If that happens you have to increase the IFR in your metering block to fix it. I like the .033 IFR, so, going over 72 on your LSAB may lean out your transition too much. I found that optimizing the IFR and LSAB so that idle is approx. 14.2 with my big cam with approx. 1 turn out on the idle adjustment screws gives me the best transition with no lean stumble and a nice clean idle. That was approx. 68 LSAB and 27-31 HSAB. With a big cam and 14.2 at idle - 800 rpm (stick), you will get no stink, no smell.

Harry
1970 Chevelle SS396 (408), Fathom Blue,
Original Block & Forged Crank, KB Pistons, Edelbrock 6045 Heads,Comp Cam 292H, March Serpentine, RPM AirGap,750HP,100hp Nitrous
A/F Wideband,Tremec TKO 600, 12 bolt,
30 spline Moser Axles, Richmond 3:73's, Hotchkis control arms, swaybars, springs, Wilwood 12" rotors D/S, 4 piston calipers
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post #5 of 15 (permalink) Old May 30th, 19, 12:29 PM Thread Starter
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Thanks 👍
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post #6 of 15 (permalink) Old May 30th, 19, 12:59 PM
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Harry
 
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Re: 750 DP to Holley HP Update

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Originally Posted by Reelysalty View Post
Thanks 👍
No worries. The biggest problem I had with the DP both before and after the body upgrade to the HP was a lean stumble off idle unless I kept the idle very rich, too rich. I could not fix it with the stock DP metering blocks and the new HP body with air bleeds. When I went to the Quick Fuel red DP upgrade metering blocks, they came with a bigger and adjustable IFR (.033). Much bigger than the stock DP metering blocks IFR size. This is the main thing that allowed me to have an idle at 14+ and gave no stumble off idle. I highly recommend the QFT-34-105QFT quick fuel metering blocks upgrade kit for the DP if you have an off idle stumble when adjusting to a reasonable AFR at idle. It looks like you already have blue billet metering blocks with adjustable IFR, so, you are in good shape and ready to tune that thing perfectly. Your blue Billet base plate is also cool looking. I still have the original DP cast base plate.

Harry
1970 Chevelle SS396 (408), Fathom Blue,
Original Block & Forged Crank, KB Pistons, Edelbrock 6045 Heads,Comp Cam 292H, March Serpentine, RPM AirGap,750HP,100hp Nitrous
A/F Wideband,Tremec TKO 600, 12 bolt,
30 spline Moser Axles, Richmond 3:73's, Hotchkis control arms, swaybars, springs, Wilwood 12" rotors D/S, 4 piston calipers
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post #7 of 15 (permalink) Old May 30th, 19, 8:08 PM Thread Starter
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Thanks again
IMO you’re a credit to this forum !
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post #8 of 15 (permalink) Old May 31st, 19, 11:37 AM
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Harry
 
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Re: 750 DP to Holley HP Update

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Originally Posted by Reelysalty View Post
Thanks again
IMO youíre a credit to this forum !
Thanks ! BTW, for the Aluminum 750 HP body, I am still using the old DP zinc baseplate. This base plate fit OK with the 750 HP Zinc body, but, for the new Aluminum HP body body (same part), I had to grind down the vacuum port housing on the back of the base plate to get the quick fuel distribution blocks and chrome DP bowls to fit correctly. No big deal, but, it kind of messed me up for a while. Note: the bleeds that came on the new Aluminum 750 HP body were just about perfect for me -- 31 HSAB and 68 LSAB. The jets that came with it were 76, 82, which I did not use.

Harry
1970 Chevelle SS396 (408), Fathom Blue,
Original Block & Forged Crank, KB Pistons, Edelbrock 6045 Heads,Comp Cam 292H, March Serpentine, RPM AirGap,750HP,100hp Nitrous
A/F Wideband,Tremec TKO 600, 12 bolt,
30 spline Moser Axles, Richmond 3:73's, Hotchkis control arms, swaybars, springs, Wilwood 12" rotors D/S, 4 piston calipers
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post #9 of 15 (permalink) Old Jun 1st, 19, 9:30 AM Thread Starter
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Am I correct this screw replaces the set screw accessed from bottom of carb to adjust secondary butterflies ?
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post #10 of 15 (permalink) Old Jun 1st, 19, 12:07 PM
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Harry
 
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Re: 750 DP to Holley HP Update

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Originally Posted by Reelysalty View Post
👍

Am I correct this screw replaces the set screw accessed from bottom of carb to adjust secondary butterflies ?
No, this is to let unmetered air into the engine for a high duration cam shaft to allow a higher and leaner idle. Unless you have the ultra XP throttle plate this feature probably does not work. If this is a Quick Fuel base plate then, the hole in the middle of the base plate to let air in is probably not there.

I have a 112-116 throttle plate with a 134-300SA body HP body. This works well, but, does not have that feature. I want to put an ultra XP body on it (134-313) to get that feature, but, I do not think it will work.

Harry
1970 Chevelle SS396 (408), Fathom Blue,
Original Block & Forged Crank, KB Pistons, Edelbrock 6045 Heads,Comp Cam 292H, March Serpentine, RPM AirGap,750HP,100hp Nitrous
A/F Wideband,Tremec TKO 600, 12 bolt,
30 spline Moser Axles, Richmond 3:73's, Hotchkis control arms, swaybars, springs, Wilwood 12" rotors D/S, 4 piston calipers
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post #11 of 15 (permalink) Old Jun 1st, 19, 5:34 PM Thread Starter
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My base is a 750 Ultra, no HP

I have 68 LSAB, would 70 or 73 be a good place to start to reduce rich idle ?

Any experience w/this ?

http://highvelocityheads.com/ss4150-...-series-carbs/

Thanks Again !
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post #12 of 15 (permalink) Old Jun 3rd, 19, 9:48 AM
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Harry
 
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Re: 750 DP to Holley HP Update

Quote:
Originally Posted by Reelysalty View Post
My base is a 750 Ultra, no HP

I have 68 LSAB, would 70 or 73 be a good place to start to reduce rich idle ?

Any experience w/this ?

SS4150-2AL - 2" tall Aluminum Super Sucker Carb Spacer for 4150 series carbs - High Velocity Heads

Thanks Again !
yes, you could go to a 73 LSAB and turn down your mixture screws to get leaner. Also, you can close your secondary and primary throttles more and use the air bypass you showed us in the middle of the carb. You can also reduce the IFR in your metering block. This meters fuel, so, a little smaller restrictor bleed for the IFR will make a big difference in your transition fuel. I like those carb spacers you sent a link about. I have a half inch nitrous plate and 1/2 inch of heat spacers which I might change out to that 1/2 inch velocity plate you showed me. Pretty cool looking. Thanks.

Harry
1970 Chevelle SS396 (408), Fathom Blue,
Original Block & Forged Crank, KB Pistons, Edelbrock 6045 Heads,Comp Cam 292H, March Serpentine, RPM AirGap,750HP,100hp Nitrous
A/F Wideband,Tremec TKO 600, 12 bolt,
30 spline Moser Axles, Richmond 3:73's, Hotchkis control arms, swaybars, springs, Wilwood 12" rotors D/S, 4 piston calipers
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post #13 of 15 (permalink) Old Jun 3rd, 19, 10:32 AM Thread Starter
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“I have a 112-116 throttle plate with a 134-300SA body HP body. This works well, but, does not have that feature. I want to put an ultra XP body on it (134-313) to get that feature, but, I do not think it will work.”

Your right. Call to Holley confirms 134-300 is XP part and does not have idle air adjustment under air cleaner hole. Only HP has this and HP main body is not available as a separate part.
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post #14 of 15 (permalink) Old Jun 3rd, 19, 11:54 AM
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Gary
 
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Re: 750 DP to Holley HP Update

that idle bypass screw allows you to set the throttle opening to get the amount the transfer slot is exposed correct and still be able to set your idle speed without drilling holes in the throttle plates
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post #15 of 15 (permalink) Old Jun 3rd, 19, 1:12 PM Thread Starter
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I want to lean idle
to cut down on gas
smell @ idle, and
to avoid washing
cylinders w/gas @
idle
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