Quick Fuel SS750AN Tuning

General engine tech -- Drag Racing to Circle Track

Moderator: Team

eric8
Member
Member
Posts: 75
Joined: Sat Mar 20, 2021 7:10 pm
Location: SC

Re: Quick Fuel SS750AN Tuning

Post by eric8 »

Hey guys just checking back in. Like I said, I've ordered the new six sizes smaller jets but I just thought of something that (may) be relevant with the backstory of all this. When I first got the engine installed and fired it up with the Delphi mechanical fuel pump, said pump was putting out 12 psi. 😳 Ran it for a few minutes and saw it wasn't going down, so I immediately swiched out to a Carter "muscle car" fuel pump which put out a steady 6 psi. Could running the carb briefly with this pressure have blown out something internally causing these full throttle rich mixtures? Just thinking out loud.
F-BIRD'88
Guru
Guru
Posts: 9802
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: Quick Fuel SS750AN Tuning

Post by F-BIRD'88 »

Power valve could be leaking or loose.
Metering block gasket crossleaks.
User avatar
FC-Pilot
HotPass
HotPass
Posts: 913
Joined: Tue Mar 17, 2009 2:23 pm
Location: Springtown, TX
Contact:

Re: Quick Fuel SS750AN Tuning

Post by FC-Pilot »

eric8 wrote: Mon Apr 26, 2021 3:49 pm Hey guys just checking back in. Like I said, I've ordered the new six sizes smaller jets but I just thought of something that (may) be relevant with the backstory of all this. When I first got the engine installed and fired it up with the Delphi mechanical fuel pump, said pump was putting out 12 psi. 😳 Ran it for a few minutes and saw it wasn't going down, so I immediately swiched out to a Carter "muscle car" fuel pump which put out a steady 6 psi. Could running the carb briefly with this pressure have blown out something internally causing these full throttle rich mixtures? Just thinking out loud.
No. If anything it would have overpowered the needle and seats and just have flooded over through the boosters and at worst the fuel vents. (The only time I have seen it co e out the vents is when the needle and seat was stuck open).

As a side note, are you looking for peak power or good power with good drivability? I ask as we dyno tested a 358 a few years ago with a 750 annular booster holley style carb. The boosters had been machined to flow more air, and showed it had flow close to a down leg booster. We spent days dialing in the carbs e-bleeds, main air bleeds and jets. We then dropped on a decent 750 dyno carb from the shop and bested the annular by 30 hp. We were devastated. We put a main body on with the down leg boosters and got it making two more HP than the dyno carb. We learned that annulars in a 750 holley would be best suited for something maybe in the 300 cubic inch range when looking for peak power. Now the whole reason we started down the annular path was because a previous engine with an annular booster 750 had great manners, we just had never dyno tested it and never tested it against anything else. Anyway, I am not telling you your stuff is junk, just that it has its limits. If you want to tune it to be a fun street car it may be just perfect for what you want. Good luck and keep learning.

Paul
"It's a fine line between clever and stupid." David St. Hubbins
eric8
Member
Member
Posts: 75
Joined: Sat Mar 20, 2021 7:10 pm
Location: SC

Re: Quick Fuel SS750AN Tuning

Post by eric8 »

Interesting info. Carbs apparently can do funny things as I'm learning. I actually chose this carb for the good street manners. So far the throttle response is great except for the pig rich wide open throttle.
User avatar
FC-Pilot
HotPass
HotPass
Posts: 913
Joined: Tue Mar 17, 2009 2:23 pm
Location: Springtown, TX
Contact:

Re: Quick Fuel SS750AN Tuning

Post by FC-Pilot »

I am glad you like it. As I said, we used another due to the characteristics of the first one. For that it was great! Keep it up and you will find it’s sweet spot.

Paul
"It's a fine line between clever and stupid." David St. Hubbins
1980RS
Guru
Guru
Posts: 1636
Joined: Thu Oct 13, 2016 10:03 am
Location:

Re: Quick Fuel SS750AN Tuning

Post by 1980RS »

eric8 wrote: Mon Apr 26, 2021 4:47 pm Interesting info. Carbs apparently can do funny things as I'm learning. I actually chose this carb for the good street manners. So far the throttle response is great except for the pig rich wide open throttle.
I was going to post that spec sheet for you but as I looked at it the part number looked strange. Here it's for a 600 cfm and that does not make me very happy and I do not want you to put the wrong jets and bleeds in. Sorry.
eric8
Member
Member
Posts: 75
Joined: Sat Mar 20, 2021 7:10 pm
Location: SC

Re: Quick Fuel SS750AN Tuning

Post by eric8 »

steve cowan wrote: Sat Apr 24, 2021 7:14 pm Do the plugs show rich??
Kinda surprised it that rich with that main jetting size.
Afr can lead you astray,been talked about alot lately
I pulled two different plugs today just for the hell of it. Don't know much about reading them, but as you can see the insulator is VERY light colored. Light tan in a few spots, but more ivory white than anything. But the outer ring surrounding the insulator is sooty black. This was pulled after idling for a few minutes, but just prior I had done another full throttle run showing 10:1 at wot.

20210427_185824.jpg
20210427_184718.jpg
You do not have the required permissions to view the files attached to this post.
Tuner
Guru
Guru
Posts: 3184
Joined: Sun Apr 01, 2007 5:26 am
Location:

Re: Quick Fuel SS750AN Tuning

Post by Tuner »

What is plug heat range?
eric8
Member
Member
Posts: 75
Joined: Sat Mar 20, 2021 7:10 pm
Location: SC

Re: Quick Fuel SS750AN Tuning

Post by eric8 »

Tuner wrote: Tue Apr 27, 2021 7:28 pm What is plug heat range?
These are Autolite 3923 heat range 3. Spec'd by the builder, but I always wondered about this, because AFR says to use 3924's in their heads with "normally aspirated, pump gas engines with a compression ratio between 9:1 and 11:1." This is a 9.5:1 sbc.
Tuner
Guru
Guru
Posts: 3184
Joined: Sun Apr 01, 2007 5:26 am
Location:

Re: Quick Fuel SS750AN Tuning

Post by Tuner »

eric8 wrote: Tue Apr 27, 2021 7:43 pm
Tuner wrote: Tue Apr 27, 2021 7:28 pm What is plug heat range?
These are Autolite 3923 heat range 3. Spec'd by the builder, but I always wondered about this, because AFR says to use 3924's in their heads with "normally aspirated, pump gas engines with a compression ratio between 9:1 and 11:1." This is a 9.5:1 sbc.
Autolite says that is equivalent to NGK 6, which I think would be too cold for street use, however OK for towing or continuous high speed. Your 10/1 WOT is rich enough to wash the plug clean and also put a lot of gasoline in the oil. If the plug were hotter you might see some color if it could cook the carbon. Unleaded fuel does not make much color like you would expect leaded fuel. The color is the lead oxides. MMT octane booster makes the orange or red brick color. I don't think you have driven those plugs far enough to color them. The soot tells the story.
F-BIRD'88
Guru
Guru
Posts: 9802
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: Quick Fuel SS750AN Tuning

Post by F-BIRD'88 »

You read the colour of the porcelin way up deep with a light.
The carbon black outer ring is from idling. its normal.
eric8
Member
Member
Posts: 75
Joined: Sat Mar 20, 2021 7:10 pm
Location: SC

Re: Quick Fuel SS750AN Tuning

Post by eric8 »

Ok thanks for the insight guys. Jets came in from Summit today so gonna try to throw in the 6 sizes smaller ones tomorrow. Don't wanna be putting gas in the oil.
steve cowan
Guru
Guru
Posts: 2253
Joined: Wed Jul 27, 2011 5:22 am
Location: brisbane AUSTRALIA

Re: Quick Fuel SS750AN Tuning

Post by steve cowan »

eric8 wrote: Tue Apr 27, 2021 9:19 pm Ok thanks for the insight guys. Jets came in from Summit today so gonna try to throw in the 6 sizes smaller ones tomorrow. Don't wanna be putting gas in the oil.
Once you have fuel curve working where you like it i think that engine can and will take more total timing,you have vac advance there as well,I understand the engine builder gave you a number but that's all it is.
One of my 383 combos I am running at the moment is 11.3:1 compression, pumps 220 on the gauge,cast iron darts heads,32-33 deg timing
I use NGK 6 at the track and a 5 cruising the street runs pretty good for what it is,and runs pump gas,going to test next weekend with a pumpgas/103 race gas blend .
steve c
"Pretty don't make power"
eric8
Member
Member
Posts: 75
Joined: Sat Mar 20, 2021 7:10 pm
Location: SC

Re: Quick Fuel SS750AN Tuning

Post by eric8 »

Okay, I got the 64/72 jetting in and it helped some. Helped a lot on the primary side and has it pretty much perfect. Cruise on flat ground at 60 mph fluctuates between 14.8 to 15.2:1. Mash into it staying only on the primaries, afr comes down to a nice 12.5:1. But throttle into it more and bring the secondaries on, its back to 10.5:1 afr. It still has gotten better though, because as the rpms rise and approach redline with secondaries open, AFR gradually rises to 11.5:1 which is better. The secondaries just seem to be pulling way too much fuel. Especially if you bring them on in the lower rpms like 3,000 or so.
Tuner
Guru
Guru
Posts: 3184
Joined: Sun Apr 01, 2007 5:26 am
Location:

Re: Quick Fuel SS750AN Tuning

Post by Tuner »

Seems a trifle odd, doesn't it. This is a bit like snake handling without knowing the details of emulsion bleed and main bleed sizes, but I would go down another 4 sizes in the secondary.
Post Reply