402 Big Block 4 Barrel dual Ex - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jfw867 · 09-25-2005, 04:41 PM

How come I can`t get more power out of my stock 1972, 402, dual exhaust,4 barrel, no cat converter, big block. My new Tundra will out run it easy. The motor and tranny were rebuilt 3000 miles ago and the truck runs great. Just not the power I remember and about 10 mpg using premium. Thanks, Joe Watson

Dual quad · 09-25-2005, 05:40 PM

Assuming the motor is bone stock, a cheap place to start would be to ensure that the ignition curve is allowing you to make max. power. A good satarting point is 12-16 degrees base, limit vac. advance to 10 degrees, & mech. advance should be about 20 degrees, all timing in by 3000 rpm. Also, electronic ignition will provide a big improvement over points (if you still have them).

Next an aluminum dual plane intake manifold, a VS square bore carb, headers, and maybe a cam. These mods would wake the old girl up big time.

Goose · 09-26-2005, 03:48 AM

How does the Tundra out run it? Top end? Or thru the gears? I don't know anything about a Tundra, but I'll bet the gearing is significantly different. The Tundra probably has taller rearend gears - 3.70's lets say and better matched to the trans gearing. Poor ol' 402 with 3.07's and a 350 turbo just can't get it movin' as fast. If you went to taller gears, shift kit, and modified stall converter then may have a better chance. 10 mpg is pretty standard in these ol' trucks and it won't get better with these suggested mods. I dropped a 396 Chevelle motor in mine once. Had lots of power but just couldn't take advantage of most of because of the gear ratios. Didn't have any problems towing stuff up hill tho.

jfw867 · 09-26-2005, 12:47 PM

The Tundra just seems to be able to run circles around the Chevy. I have not got a top end speed on either. I do know the Tundra is much lighter. The chevy sounds like it is running out from under you it just does not preform as I remember. Sometimes we just remember what we want to. I did install electronic ignition and it did help some. The chevy is a preminum gasoholic. Just seems with that much fuel I could have some more power. It was also rebuilt with a mild cam. Thanks, Joe

**StingRay** · 09-26-2005, 01:06 PM

Are your secondaries opening up on the carb. My choke wasn't coming all of the way off a while back and the secondary lock out was keeping the secondaries out. It was pretty lame till I made a few adjustments. A good running big block shouldn't feel slow. My 350 with a 373 rear end will probably give a Tundra a good run though I don't know whether I'd win a race.

Bill72BB · 09-26-2005, 01:52 PM

I have the same combo , but a 2000 Tundra . The new Tundra has 285 HP our BB were rated at 210 HP if my memory serves me right .

*FUNMUDDER* · 09-26-2005, 03:36 PM

Seems like a low hp rating for a big-block. Didn't 72 350's have around 255hp or so?????

GMC Jim · 09-27-2005, 07:00 AM

Per GM 1971 Service Manual; the 402 was rated at 300 hp @ 4800 rpm

70c10 · 09-27-2005, 07:15 AM

I would also look at the timing and carb.

Derrickbwg · 09-27-2005, 08:29 AM

The Tundra is a 7.5-8 sec 0-60 truck. That's pretty darn respectable. Some midsize Japanese family sedans are doing it in 5.5 seconds now. My Honda s2000 makes 240hp normally aspirated out of 2.0 liters(no torque), that's 120 hp/liter. Displacement is going down and HP is up.

Bill72BB · 09-27-2005, 11:24 AM

Quote:

Originally Posted by FUNMUDDER

Seems like a low hp rating for a big-block. Didn't 72 350's have around 255hp or so?????

Just double checked , Both the 72 restoration guide and the Sales brochure show 210 HP .

1969 C/K CST · 09-27-2005, 11:32 AM

Quote:

Originally Posted by 70c10

I would also look at the timing and carb.

I agree. Sounds like your not getting all you $$$ out of the gas your using. What kind of carb?

**PICKMUP** · 09-27-2005, 12:12 PM

That motor is 8.5:1 compression, unless you changed it, and premium doesn't help it. Premium actually burns slower and needs higher compression.
210 HP is computed same as the Tundra. 71 & older used different system and the same motor is rated 300 HP, explaining the higher earlier numbers.
Weight makes a big difference...about .010 sec per 100 lbs in the 1/4 mile.
Too much cam can kill a heavy vehicle, if it makes less torque/low end power.
The qjet carb was rated at 750 cfm and small primaries for better mileage, but they are spendy new and sometimes fussy old. If you replaced the carb with a smaller 4bore, it may be holding that BB back.

**StingRay** · 09-27-2005, 01:32 PM

Something to consider on anything Japanese is that they use JIS (Japanese Industrial Standard) horsepower ratings which are about 15% higher than SAE net numbers for the equal HP.

William72c20 · 12-12-2012, 11:42 PM

I have a 402 with a quadrajet fuel ex. Turbo 400 4.10 gears . Haven't seem a new truck yet that could beat it . Especially the new silverado a they have no guts . I'm getting 7 mpg but that's just my setup . Mess with the timing some I set mine at 12 advance with no dis vaccum . Seemed to help alot especially with off the line acceleration
Posted via Mobile Device

Longhorn 70 · 12-12-2012, 11:44 PM

weight? Throw a thousand pounds in the back of the tundra....

**WIDESIDE72** · 12-13-2012, 01:54 AM

I have a rebuilt 70 BBC 400 that is going into a 71 Swb step along with a 700r4, 3.73 open (for now) rear axle. I am swapping the stock low rise intake for an edebrock performer 2.0 and cast iron manifolds for hedman full length headers. Stock cam is also coming out for an "rv" torque grind from Comp. All of the old parts will be kept. I plan to run the stock qjet as well after a rebuild.

Correct me if I'm wrong but doesn't my 70 have higher compression (stock) than a 72?
Posted via Mobile Device

**68350** · 12-13-2012, 03:58 AM

What gear ratio do you have? What carb are you running?

*bk2life* · 12-13-2012, 04:06 AM

seems everyone is recommending the same thing. get your truck to the dyno and get your carb/ignition spot on..

SS Tim · 12-13-2012, 05:02 AM

You do realize this is a seven year old thread and it has been that long since the OP posted anything?

**68350** · 12-13-2012, 05:09 AM

Nope didnt see that until now, lol

Longhorn 70 · 12-13-2012, 10:20 AM

Quote:

Originally Posted by SS Tim

You do realize this is a seven year old thread and it has been that long since the OP posted anything?

lesson learned: Look at dates.... hahahahaha

William72c20 · 12-13-2012, 08:43 PM

Dates ...

Compression may not be much different from year to year ?
Deck milling and head port blend and head mill .
Compression and better flow to go with all the other goods
Posted via Mobile Device

09-25-2005, 04:41 PM	#1
jfw867 Registered User Join Date: Sep 2005 Location: florida Posts: 13	402 Big Block 4 Barrel dual Ex How come I can`t get more power out of my stock 1972, 402, dual exhaust,4 barrel, no cat converter, big block. My new Tundra will out run it easy. The motor and tranny were rebuilt 3000 miles ago and the truck runs great. Just not the power I remember and about 10 mpg using premium. Thanks, Joe Watson

09-26-2005, 03:48 AM	#3
Goose Goose Join Date: Jun 2000 Location: Austin Posts: 142	How does the Tundra out run it? Top end? Or thru the gears? I don't know anything about a Tundra, but I'll bet the gearing is significantly different. The Tundra probably has taller rearend gears - 3.70's lets say and better matched to the trans gearing. Poor ol' 402 with 3.07's and a 350 turbo just can't get it movin' as fast. If you went to taller gears, shift kit, and modified stall converter then may have a better chance. 10 mpg is pretty standard in these ol' trucks and it won't get better with these suggested mods. I dropped a 396 Chevelle motor in mine once. Had lots of power but just couldn't take advantage of most of because of the gear ratios. Didn't have any problems towing stuff up hill tho. __________________ '72 GMC short-step 350/350

09-26-2005, 01:06 PM	#5
StingRay Senior Member Join Date: Mar 2000 Location: Saskatoon,SK,Canada Posts: 2,476	Are your secondaries opening up on the carb. My choke wasn't coming all of the way off a while back and the secondary lock out was keeping the secondaries out. It was pretty lame till I made a few adjustments. A good running big block shouldn't feel slow. My 350 with a 373 rear end will probably give a Tundra a good run though I don't know whether I'd win a race. __________________ Saskatoon, Saskatchewan Canada

09-26-2005, 01:52 PM	#6
Bill72BB Thats the Hillbilly way Join Date: Jul 2001 Location: Torrance,Ca Posts: 5,979	I have the same combo , but a 2000 Tundra . The new Tundra has 285 HP our BB were rated at 210 HP if my memory serves me right . __________________ BILL Torrance Calif 90504 Member DUF Club Member Old Farts Club 72 3/4ton Custom Camper BB402/400 trans Dynomax Cerama-coat headers , Hei distributor ,Edelbrock 1411 air,ps,pb,leafsprings ,98 chevy 60/40 seat,S10 shoulder belts tilt,3.54 Dana 60 rear. 16" Eagle wheels with LT265/75 16 tires,Gaylord Lid,H4 headlights with 100W relay conversion. " If I knew I was going to live this long I would have taken better care of myself " Marriage changes passion...suddenly you're in bed with a relative. A GUY'S PRAYER.... Lord, I pray for a nympho with huge boobs who owns a liquor store and likes to fish and hunt and has a Harley .Amen , Last edited by Bill72BB; 09-26-2005 at 01:58 PM.

09-26-2005, 03:36 PM	#7
FUNMUDDER Account Suspended Join Date: Jun 2005 Location: Maine Posts: 427	Seems like a low hp rating for a big-block. Didn't 72 350's have around 255hp or so????? Last edited by FUNMUDDER; 09-26-2005 at 03:37 PM. Reason: typo

09-25-2005, 05:40 PM	#2
Dual quad Smell that burnin' rubber Join Date: Sep 2000 Location: Ontario Posts: 171	Assuming the motor is bone stock, a cheap place to start would be to ensure that the ignition curve is allowing you to make max. power. A good satarting point is 12-16 degrees base, limit vac. advance to 10 degrees, & mech. advance should be about 20 degrees, all timing in by 3000 rpm. Also, electronic ignition will provide a big improvement over points (if you still have them). Next an aluminum dual plane intake manifold, a VS square bore carb, headers, and maybe a cam. These mods would wake the old girl up big time.

09-26-2005, 12:47 PM	#4
jfw867 Registered User Join Date: Sep 2005 Location: florida Posts: 13	The Tundra just seems to be able to run circles around the Chevy. I have not got a top end speed on either. I do know the Tundra is much lighter. The chevy sounds like it is running out from under you it just does not preform as I remember. Sometimes we just remember what we want to. I did install electronic ignition and it did help some. The chevy is a preminum gasoholic. Just seems with that much fuel I could have some more power. It was also rebuilt with a mild cam. Thanks, Joe

09-27-2005, 07:00 AM	#8
GMC Jim Senior Member Join Date: Dec 2002 Location: Portland, Oregon Posts: 901	Per GM 1971 Service Manual; the 402 was rated at 300 hp @ 4800 rpm __________________ '71 GMC;fleetside;PB/PS/AC/CC/402 Eng./Custom Paint/110,000act miles/3 fuel tanks(52gal).

09-27-2005, 07:15 AM	#9
70c10 67-72 Addict! Join Date: Feb 2002 Location: The TAX State! Posts: 7,856	I would also look at the timing and carb. __________________ Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads

09-27-2005, 08:29 AM	#10
Derrickbwg Registered User Join Date: Sep 2005 Location: Lexington KY Posts: 64	The Tundra is a 7.5-8 sec 0-60 truck. That's pretty darn respectable. Some midsize Japanese family sedans are doing it in 5.5 seconds now. My Honda s2000 makes 240hp normally aspirated out of 2.0 liters(no torque), that's 120 hp/liter. Displacement is going down and HP is up. __________________ 1971 Chevy swb Chevy trucks and import cars

09-27-2005, 12:12 PM	#13
PICKMUP "Trucks with Class" Join Date: Jul 2000 Location: OLYMPIA, WA, USA Posts: 8,158	That motor is 8.5:1 compression, unless you changed it, and premium doesn't help it. Premium actually burns slower and needs higher compression. 210 HP is computed same as the Tundra. 71 & older used different system and the same motor is rated 300 HP, explaining the higher earlier numbers. Weight makes a big difference...about .010 sec per 100 lbs in the 1/4 mile. Too much cam can kill a heavy vehicle, if it makes less torque/low end power. The qjet carb was rated at 750 cfm and small primaries for better mileage, but they are spendy new and sometimes fussy old. If you replaced the carb with a smaller 4bore, it may be holding that BB back.

09-27-2005, 01:32 PM	#14
StingRay Senior Member Join Date: Mar 2000 Location: Saskatoon,SK,Canada Posts: 2,476	Something to consider on anything Japanese is that they use JIS (Japanese Industrial Standard) horsepower ratings which are about 15% higher than SAE net numbers for the equal HP. __________________ Saskatoon, Saskatchewan Canada

12-12-2012, 11:42 PM	#15
William72c20 Registered User Join Date: Nov 2012 Location: Odessa Tx Posts: 25	Re: 402 Big Block 4 Barrel dual Ex I have a 402 with a quadrajet fuel ex. Turbo 400 4.10 gears . Haven't seem a new truck yet that could beat it . Especially the new silverado a they have no guts . I'm getting 7 mpg but that's just my setup . Mess with the timing some I set mine at 12 advance with no dis vaccum . Seemed to help alot especially with off the line acceleration Posted via Mobile Device __________________ 1972 C20 402cid

12-12-2012, 11:44 PM	#16
Longhorn 70 Registered User Join Date: Dec 2012 Location: Chandler AZ Posts: 1,149	Re: 402 Big Block 4 Barrel dual Ex weight? Throw a thousand pounds in the back of the tundra.... __________________ 1970 Longhorn, Front Disc, 350/4 bolt, 882 heads, HEI, Edelbrock, 700R4, HO-52/4.11. 1996 Corvette, Collector Roadster, LT4, 396, 450RWHP, 6sp, 4.11/Dana44/posi 5 point roll bar And let us not grow weary of doing good, for in due season we will reap, if we do not give up. Gal 6:9

12-13-2012, 01:54 AM	#17
WIDESIDE72 Senior Member Join Date: Aug 2008 Location: Cedar Park, Texas Posts: 7,500	Re: 402 Big Block 4 Barrel dual Ex I have a rebuilt 70 BBC 400 that is going into a 71 Swb step along with a 700r4, 3.73 open (for now) rear axle. I am swapping the stock low rise intake for an edebrock performer 2.0 and cast iron manifolds for hedman full length headers. Stock cam is also coming out for an "rv" torque grind from Comp. All of the old parts will be kept. I plan to run the stock qjet as well after a rebuild. Correct me if I'm wrong but doesn't my 70 have higher compression (stock) than a 72? Posted via Mobile Device



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12-13-2012, 03:58 AM	#18
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: 402 Big Block 4 Barrel dual Ex What gear ratio do you have? What carb are you running? __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

12-13-2012, 04:06 AM	#19
bk2life Account Suspended Join Date: Oct 2012 Location: phx, az Posts: 868	Re: 402 Big Block 4 Barrel dual Ex seems everyone is recommending the same thing. get your truck to the dyno and get your carb/ignition spot on..

12-13-2012, 05:02 AM	#20
SS Tim Registered User Join Date: Aug 2010 Location: Edwards, CA Posts: 7,503	Re: 402 Big Block 4 Barrel dual Ex You do realize this is a seven year old thread and it has been that long since the OP posted anything? __________________ Thanks, Tim * VIN/Model Decoders * Power Team Charts (engine/transmission/gear ratio) * Post Your Pickup SPID Blazer SPID Suburban/Panel SPID * RTFM ... Read The Factory Manuals... download 'em here Highlanders Do you have a 1972 Plaid Pickup? Plaid Blazer ** Plaid Suburban

12-13-2012, 05:09 AM	#21
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: 402 Big Block 4 Barrel dual Ex Nope didnt see that until now, lol __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

12-13-2012, 08:43 PM	#23
William72c20 Registered User Join Date: Nov 2012 Location: Odessa Tx Posts: 25	Re: 402 Big Block 4 Barrel dual Ex Dates ... Compression may not be much different from year to year ? Deck milling and head port blend and head mill . Compression and better flow to go with all the other goods Posted via Mobile Device __________________ 1972 C20 402cid

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