1979 400 ci Engine Questions
Old Pro Solo Guy
Joined: Dec 2017
Posts: 8,095
Likes: 4,449
From: Marlton NJ
In this case Google AI seems to have good answers, since they refer to a very respected source "Cliff's High Performance""
Cliff literally wrote the best book on QJets.
Just Google: "I.D. a 800cfm Quadrajet"
Cliff literally wrote the best book on QJets.
Just Google: "I.D. a 800cfm Quadrajet"
Drifting
Joined: Jun 2025
Posts: 1,731
Likes: 600
Relying on AI is another gamble. Even Musk is frightened by it.
AI is essentially an aggregator of data from multiple sources it reviews from internet.
AI doesn't know which source is valid or invalid.
No doubt Mr. Ruggles is a respected and reliable source. AI didn't teach me that; Ruggles book helped teach me that.
Review history
Recall former members durangoboy & headsup ? Each routinely spouted one piece of BS after another. In the aggregate, they accounted for a fair volume; albeit containing lotsa BS.
Sadly, because of their sheer volume, too many folk believed it too. Compare & Contrast w/ AI.
AI is essentially an aggregator of data from multiple sources it reviews from internet.
AI doesn't know which source is valid or invalid.
No doubt Mr. Ruggles is a respected and reliable source. AI didn't teach me that; Ruggles book helped teach me that.
Review history
Recall former members durangoboy & headsup ? Each routinely spouted one piece of BS after another. In the aggregate, they accounted for a fair volume; albeit containing lotsa BS.
Sadly, because of their sheer volume, too many folk believed it too. Compare & Contrast w/ AI.
Race Director
Joined: Mar 2017
Posts: 11,953
Likes: 4,510
From: Virginia
7045223 is from a 1975 Corvette, manual transmission (doesn't say displacement)
17059229 is from a 1979 Chevy truck, 400 ci, automatic transmission
These are from the Q-Jet white papers that @lars keeps up to date. You should email him for the latest copies if you intend to rebuild one of these carbs. Ask for his timing and HEI papers as well. Good luck!
17059229 is from a 1979 Chevy truck, 400 ci, automatic transmission
These are from the Q-Jet white papers that @lars keeps up to date. You should email him for the latest copies if you intend to rebuild one of these carbs. Ask for his timing and HEI papers as well. Good luck!
Thread Starter
Advanced
Joined: Dec 2025
Posts: 79
Likes: 114
From: BC
A bit of an update on this thread. I cleaned up the 400 engine I pulled from the RV. Painted it. Added some goodies including:
New Edelbrock Performer intake manifold
Hedman Headers
MSD distributor assembly plugs and wires
New fuel pump and water pump with new belts
New power steering hoses
Edelbrock chrome cover air filer housing with K&N air filter
New timing chain and gears set
New aluminum radiator
New rad hoses
Removed oil cooler adaptor on engine oil filter assemby
Replaced alternator with the one I pulled from the RV
Cleaned up and repaired some engine bay wiring
Repaired cracked bellhousing mount bolt at rear of engine block
I had disassembled the Quadrajet. Cleaned it extensively in my ultrasonic cleaner. Reassembled and installed it. When I fired up the engine, it was puking gas. I pulled the Q-jet back off and set it aside. I bought a new Edelbrock AVS2 carb. The Edelbrock carb so far has been flawless. Fired right up. Idles well and seems to run great.
I am currently testing and tuning with open headers. I have an appointment in 9 days for 3 1/2" true dual exhaust. Then I'm fully road ready. True road testing may uncover further required tuning. We'll see. Ithe 400 pull and swap has been a very rewarding, fun project. So far so good.
New Edelbrock Performer intake manifold
Hedman Headers
MSD distributor assembly plugs and wires
New fuel pump and water pump with new belts
New power steering hoses
Edelbrock chrome cover air filer housing with K&N air filter
New timing chain and gears set
New aluminum radiator
New rad hoses
Removed oil cooler adaptor on engine oil filter assemby
Replaced alternator with the one I pulled from the RV
Cleaned up and repaired some engine bay wiring
Repaired cracked bellhousing mount bolt at rear of engine block
I had disassembled the Quadrajet. Cleaned it extensively in my ultrasonic cleaner. Reassembled and installed it. When I fired up the engine, it was puking gas. I pulled the Q-jet back off and set it aside. I bought a new Edelbrock AVS2 carb. The Edelbrock carb so far has been flawless. Fired right up. Idles well and seems to run great.
I am currently testing and tuning with open headers. I have an appointment in 9 days for 3 1/2" true dual exhaust. Then I'm fully road ready. True road testing may uncover further required tuning. We'll see. Ithe 400 pull and swap has been a very rewarding, fun project. So far so good.
Last edited by C3Cruiser; Jun 6, 2026 at 10:38 AM.
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Thread Starter
Advanced
Joined: Dec 2025
Posts: 79
Likes: 114
From: BC
I have limited experience building performance engines. Research tells me the 400 pistons sit down in the hole a bit. 64cc chamber aluminum heads should net about 9.5 or so to 1 compression ratio with the stock pistons. Ideally I’d like to run pump gas, that set-up seems right for me. I’m thinking I’ll leave the bottom end alone. Its a street cruiser. It’ll never see the strip.
Last edited by C3Cruiser; Jun 6, 2026 at 04:53 PM.
Drifting
Joined: Jun 2025
Posts: 1,731
Likes: 600
NO AI here, hands-on:
400 pistons are cast eutectic (Not hyper, Not forged) & are exceptionally heavy with a Very Narrow quench band and which has a Very Pronounced outer bevel. Both of those wreck and prevent any attempt at a meaningful quench.
Also, they have a deep dish And 4 valve reliefs. Fully-enclosed round slipper skirt. 400 sbc is unique in that is uses much shorter (5.565") rods than most others' 5.7". 400 cylinder liners are notably Thinner than other sbc.
Suggest abandon both shorter OE 400 rods and 400-style replacement pistons. Don't bore any further than necessary to get the piston ya need.
Use modern-design pistons having thin, metric ringpaks. Suggest choose 6" long aftermarket rods with pistons' compression height to match; there are lotsa choices of either.
It'll pay dividends to have a very good working relationship with local automotive machine shop. Smart parts choices can save ya money. Longer rods offer Many more piston choices. It's always cheaper to drill away unnecessary mass that it is to add it !
Have owned several 400-block based combos and built several more.
** When at True TDC, True genuine OE GM 400 piston's crowns will sit about 0.025" below an OE Uncut 400 deck. Much as a 350 does.
400 pistons are cast eutectic (Not hyper, Not forged) & are exceptionally heavy with a Very Narrow quench band and which has a Very Pronounced outer bevel. Both of those wreck and prevent any attempt at a meaningful quench.
Also, they have a deep dish And 4 valve reliefs. Fully-enclosed round slipper skirt. 400 sbc is unique in that is uses much shorter (5.565") rods than most others' 5.7". 400 cylinder liners are notably Thinner than other sbc.
Suggest abandon both shorter OE 400 rods and 400-style replacement pistons. Don't bore any further than necessary to get the piston ya need.
Use modern-design pistons having thin, metric ringpaks. Suggest choose 6" long aftermarket rods with pistons' compression height to match; there are lotsa choices of either.
It'll pay dividends to have a very good working relationship with local automotive machine shop. Smart parts choices can save ya money. Longer rods offer Many more piston choices. It's always cheaper to drill away unnecessary mass that it is to add it !
Have owned several 400-block based combos and built several more.
** When at True TDC, True genuine OE GM 400 piston's crowns will sit about 0.025" below an OE Uncut 400 deck. Much as a 350 does.
Last edited by Rebelyell; Yesterday at 05:41 PM.
Le Mans Master
Joined: May 2007
Posts: 5,031
Likes: 1,121
From: North tonawanda NY
Don't know if your car is manual or auto. The 400 flywheel probably won't fit inside your bellhousing. 400 will also use a different starter. Make sure you get the correct flywheel. If 400 auto then the 400 flywheel will probably work but if manual you will probably need a special flywheel. JP
Last edited by augiedoggy; Today at 09:23 AM.
Le Mans Master
Joined: May 2007
Posts: 5,031
Likes: 1,121
From: North tonawanda NY
I have limited experience building performance engines. Research tells me the 400 pistons sit down in the hole a bit. 64cc chamber aluminum heads should net about 9.5 or so to 1 compression ratio with the stock pistons. Ideally I’d like to run pump gas, that set-up seems right for me. I’m thinking I’ll leave the bottom end alone. Its a street cruiser. It’ll never see the strip.
Drifting
Joined: Jun 2025
Posts: 1,731
Likes: 600
no shim gaskets for sbc 400 block
Similiar to my goals spirited street driving... I ended up finding a rebuilt 406 a family friend had built for his square body but never installed... it had undersized edelbrock 190 heads on it and a vortec style intake along with dished KB hyper pistons which I removed. I went with replacement KB hyper pistons with a smaller dish that nets me about 9.8:1 compression if I remember right. My engine is decked but I couldnt find any steel shim gaskets for a 400 so I settled for .039 gaskets. I installed a summit stage 3 1223 ls firing order roller cam and heads I ported to likely around 215/ 64cc along with a port air gap intake.. Everything from my 355 bolted up fine and I also put a 2004r transmission (I know I will likely blow this up and ill be looking for a beefier build). Idrove the car about the side streets for the first time yesterday and man you should have seen the smile on my face! I also went with Aces TBI injection.
Many other top brand pistons available in FORGINGS made of either 2618 or 4032 forging alloys. For most street/street-strip use, 4032 forgings are ideal material. W/ chambers about 64cc, probably will want a Reverse-Dome aka D-Dish Crown, and, of course, modern thin, metric ringpaks. No AI here.