Pontiac 400 carb setup - Pontiac GTO Forum
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post #1 of 9 (permalink) Old 04-07-2018, 01:00 PM Thread Starter
 
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Pontiac 400 carb setup

Have a buddy with a 77 TA with a 400 motor. Edelbrock Performer top end with the Performer 87cc heads (215cc, 2.11intake valves), performer cam, and performer intake. Stock cubes but forged pistons and rods.

It has the really shitty spread bore 4175 series 650 Holley. The thing is garage.

I've got a 750 holly DP on my chevelle that's not being used at the moment. With a little massaging we got it to fit the factory shaker hood and are using a spread bore to square bore adapter plate.

Question is if I jet that 750 DP down will it be OK with his setup? His car is a bit of a dog at the moment and his 4175 has no tuning ability besides jets and idle air mixture. I figure we can dial in my 750 a lot better than his and jet it down to not bog when the mechanical secondaries open.

So main question, will the 750 double pumper too much? Any tuning recommendations based off what you see with his setup?

Thanks for any info.

Extra notes:
2800 stall, TH-350 with a shift kit, 3:42 rear gears, vacuum advance HEI distributor, MSD 6AL box, Long Tube headers, Pypes Exhaust

2006 GTO M6

Motor - Stock with Vararam
Bunch of suspension
Bunch of brakes
Stock tune

365/368 std
12.81 @ 110.6 2.03 60'
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post #2 of 9 (permalink) Old 04-07-2018, 06:20 PM
 
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Why not just go with a Q-jet and be done with it? Fits like factory. Doesn't require an adapter plate. Correct height for the shaker scoop. And, no rigging of the factory linkages.
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post #3 of 9 (permalink) Old 04-07-2018, 09:59 PM Thread Starter
 
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We're putting a 461 stroker in it in a couple months and just want it to run better until then. The new motor is getting a Fast XFI fuel injected setup so no need to spend money on a q jet

2006 GTO M6

Motor - Stock with Vararam
Bunch of suspension
Bunch of brakes
Stock tune

365/368 std
12.81 @ 110.6 2.03 60'
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post #4 of 9 (permalink) Old 04-07-2018, 10:41 PM
 
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Probably won't get it to run too strong with 87cc alum heads on a 400. They'd be great on a 455 or similar 400 block stroker. It is said that you need about 1 number higher CR when using alum heads. So, you'd need about 10:1 or more CR for a strong street 400, when using alum heads. IMO

I ran a Holley 750 vac on a 455 bracket car I bought, because it was on the car when I bought it, and ran just fine. And since it's just a temp fix, slap the DP on it & see what happens. My guess is that it will dump gas too quick, but I'm not a Holley guy, so my advice isn't worth much about Holley tuning.
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post #5 of 9 (permalink) Old 04-11-2018, 03:08 PM Thread Starter
 
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What spark plugs do you guys recommend for the above combo?

2006 GTO M6

Motor - Stock with Vararam
Bunch of suspension
Bunch of brakes
Stock tune

365/368 std
12.81 @ 110.6 2.03 60'
GTO44 is online now  
post #6 of 9 (permalink) Old 04-11-2018, 07:52 PM
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750 cfm is probably borderline too small for the 400 with good heads, it'll be way too small for the 461 build - but since you said you're going EFI at that time you probably don't care. Which pistons will you be running in the 461?

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post #7 of 9 (permalink) Old 04-14-2018, 03:57 AM Thread Starter
 
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For the new motor its either going to be Butler/Ross or SRP. We're looking at the Butler 461 bottom end package. Ive also been talking to the engine builder at the machine shop i use and he prefers the srp pistons. Depending on price we may just have him price out the same package individually but with the the components he usually uses.

Also, carb ended up working pretty good. Need to change the main nozzle and main jets but its running like a champ. The top end really woke up and It pulls hard now pretty much to 6k. Before it fell on its face around 4k. Feels like a whole new car. Also put an electric crank case evacuation setup on it and its working great. He kept blowing oil out of the rear main. Been thru 3 rear mains. Installed the electric vacuum pump setup to the valve cover and absolutely no leaking rear main now even under hard driving. Its amazing.

2006 GTO M6

Motor - Stock with Vararam
Bunch of suspension
Bunch of brakes
Stock tune

365/368 std
12.81 @ 110.6 2.03 60'
GTO44 is online now  
post #8 of 9 (permalink) Old 04-15-2018, 05:34 PM
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I'm in the process of putting my 461 back together right now, and using Ross from Butler this time. They're gorgeous. Even though I'm running long 6.800 rods, the pin boss doesn't encroach on the oil rails at all (unlike my previous KB Icons). They supplied very detailed balance and machining data for each piston also. Full floating pins, double spirolocks (each piston uses 2 on each side of the pin).... really nice pieces.

Butler has a volume deal with Ross, so what you've getting are actually custom pistons made specifically for your engine at an 'off the shelf' price. Very hard to beat.

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post #9 of 9 (permalink) Old 04-17-2018, 10:21 AM Thread Starter
 
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Sounds bad ass bear! We are definitely leaning toward the Butler Package with the Ross pistons.

Just got the motor back together. Like I mentioned earlier we put an electric crank case evac setup on it and it's working great. No more leak from the rear main, especially under power. You can see the -10AN lines ran in the pics below. Also added a griffen 4 core radiator with a flex-a-lite dual fan setup. The dual fans pull 4,600 cfm, they are the nicest ones I've used... Even comes with a little controller to wire in temp probe, a/c activation, manual off/on, and ignition.

Also with the Holley 750dp... Ended up going 6 sizes up on the primary to a 72, and 4 sizes bigger on the secondaries to an 80. No more off idle or tip in bog.

Cleaned up the engine bay as well. His wiring was all over the place so I replaced the old stuff with new wiring and loom. Here's some beauty shots from sunday. And yes the A/C is running in these pics and works perfect on a hot Florida day!















2006 GTO M6

Motor - Stock with Vararam
Bunch of suspension
Bunch of brakes
Stock tune

365/368 std
12.81 @ 110.6 2.03 60'
GTO44 is online now  
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