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Username Post: 1980 CHEVY 400 ENGINE SPECS        (Topic#348358)
77 Sierra 
Forum Newbie
Posts: 6
77 Sierra
Age: 55
Loc: Coutts,Alberta,Canada
Reg: 02-23-16
11-23-17 11:49 AM - Post#2715479    

I`m planning an engine swap for my 77 C1O this spring,want to replace 2bbl 305 {runs great with 59000 original miles,but gutless} with a 400 out of my 1980 chevy G30 21 ft class c motorhome.Does anyone know where I can find specs such as compression ratio,valve sizes,etc?Iplan to run a edelbrock 1406 600 carb,headers,but cant afford to do any much more than maybe a cam swap and intake.The 400 has about 55000 miles,runs good,good power,could push that old camper at 70 mph when I dared drive it that fast{scary handling}.The truck has a TH350 and 3.08 gears,just want to make a good daily driver,not a dragster.Any ideas or opinions?



 
raycow 
Honored Member
Posts: 27355
raycow
Loc: San Francisco, CA
Reg: 11-26-02
11-23-17 11:58 AM - Post#2715480    
    In response to 77 Sierra

You might want to check if a stock TH350 can handle a 400 engine, because I don't know if GM ever offered that combination. Of course you could always have your TH350 built for the purpose by a competent shop.

If your 400 is bolted to a TH400 now, you might consider swapping the trans with the engine to save the cost of having the TH350 built. The downside of the TH400 swap is that you will need to modify the driveshaft and relocate the trans crossmember.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
1983G20Van 
Super Senior Member
Posts: 3687

Loc: Bedford, Texas, USA
Reg: 11-13-02
11-24-17 08:43 AM - Post#2715562    
    In response to raycow

  • raycow Said:
You might want to check if a stock TH350 can handle a 400 engine, because I don't know if GM ever offered that combination. Of course you could always have your TH350 built for the purpose by a competent shop.

If your 400 is bolted to a TH400 now, you might consider swapping the trans with the engine to save the cost of having the TH350 built. The downside of the TH400 swap is that you will need to modify the driveshaft and relocate the trans crossmember.

Ray



GM DID offer the 400/TH350 in ALOT of G10 and G20 Vans and chances are it may already be bolted to a TH350. Not like a stock 400 makes much power anyway. In stock form it only makes something like 180 HP and 300 TQ. The 882 heads and tiny 929 factory cam are HORRIBLE when combined with the massive dish in the factory piston. No compression, no flow, and the valves barely bump open from the tiny cam.

If you do open it up to put a cam into it, make sure it is something mild like a 204/214 @ .050 RV cam such as the MTC-1. Otherwise you will drop any resemblance of cylinder pressure at lower rpms and kill the low-end torque.

1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


Edited by 1983G20Van on 11-24-17 08:53 AM. Reason for edit: No reason given.

 
Keith Seymore 
Silver Supporting Member
Posts: 677
Keith Seymore
Loc: Southeast Michigan
Reg: 09-17-08
11-24-17 02:26 PM - Post#2715587    
    In response to 77 Sierra

Generic info packet from the GM Heritage Center archive, showing engine availability for 1980 G30 vans; the 400 cu in engine was RPO LE4:

https://www.gmheritagecenter.com/docs/gm-heritage-...

Engine details for engine LE4, from the 1980 pickup information (page 84):

https://www.gmheritagecenter.com/docs/gm-heritage-...

K

Chevelle Intro: http://www.popularhotrodding.com/features/1005phr_...
My Pontiacs: http://forums.maxperformanceinc.com/forums/showthr...
Pickup: http://67-72chevytrucks.com/vboard/showthread.php?...


 
gchemist 
Senior Chevytalk Moderator
Posts: 24274
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
11-26-17 06:02 AM - Post#2715757    
    In response to Keith Seymore

Welcome to the site. The 400 SB will be a nice pusher. The 350TH will handle it. Instead of an intake, which you need anyway, consider adding a better torque converter. A better torque converter will add a poor mans overdrive. A 700R4 trans costs a lot more than a torque converter. I drive my truck around town in D. The torque converter locks in saving fuel. If speeds go above 45 MPH, then I can shift up to OD. I don't drive it OD within city limits. The 3.08 gears are not ideal. RPMs drop to ~1200-1500. Though the ZZ4 has power to push the truck at such low RPMs, higher RPMs are better. It's fun though smashing the throttle from such low RPMs. The trans kicks down hard and speed goes up fast. If done right, it will kick down to 2nd then really get going and shift back to OD as it accelerates.

If you keep the 400 intake for now, a spread bore to square bore adapter can be used. Later, you can add a nicer dual plane intake with a spread bore setup.

'95 Jimmy SLT (Bought @131,814)
'83 Silverardo XST - ZZ4 powered
'96 GMC Jimmy LS Ret. @236651 miles


 
77 Sierra 
Forum Newbie
Posts: 6
77 Sierra
Age: 55
Loc: Coutts,Alberta,Canada
Reg: 02-23-16
12-01-17 12:03 PM - Post#2716552    
    In response to 1983G20Van

Hi guys, thanks for the info!I have a couple of other questions being as I am just in the planning stages of this project.Would it be worth while to use my 305 heads on the 400?I understand that I would have to get steam holes drilled in them,but maybe I would get more compression.Also does anyone know anything about the old Edelbrock C3BX intakes?My neighbor has one he`s wanting to get rid of.



 
elcamino 
Dedicated Member
Posts: 5330
elcamino
Loc: Lake Superior-Michigan US...
Reg: 03-30-00
12-03-17 02:44 PM - Post#2716758    
    In response to 77 Sierra

The 400 has external counterweight on both ends ... both damper and flexplate/flywheel are counterbalanced so don't swap 350 parts or the motor will self-destruct.

Mike
2017 GMC Sierra Denali Ultimate 6.2L(420hp)/8-sp
2016 Polaris RZR 900 EPS


 
77 Sierra 
Forum Newbie
Posts: 6
77 Sierra
Age: 55
Loc: Coutts,Alberta,Canada
Reg: 02-23-16
12-15-17 08:28 PM - Post#2718078    
    In response to elcamino

thanks,but I knew that,my question was would it be worthwhile to use 305 heads which I already have on the 400.Iknow I would have to get the steam holes drilled.Has anyone out there ever done this?



 
Stinky 
Senior Member
Posts: 1590

Loc: Whitewater, CO
Reg: 05-25-01
12-16-17 11:17 AM - Post#2718141    
    In response to 77 Sierra

I hate to sell a good running engine...which is what the 305 is.

I'd sell it and use the money to buy parts.

AND, I think that their chamber volume is low or otherwise non-compatable w/your 400. That was your question wasn't it. You got lots of good advice, but nobody told you if your motor would run good w/those heads or not.

I'd keep your heads....maybe mill them a bit to bump the compresson & change the cam.



 
Keith Seymore 
Silver Supporting Member
Posts: 677
Keith Seymore
Loc: Southeast Michigan
Reg: 09-17-08
12-17-17 06:03 PM - Post#2718301    
    In response to Stinky

  • Stinky Said:


AND, I think that their chamber volume is low or otherwise non-compatable w/your 400. That was your question wasn't it. You got lots of good advice, but nobody told you if your motor would run good w/those heads or not.



I believe this is true. The edges of the chamber of the cylinder head will stick out in the larger block bore, allowing hot spots and making your build more prone to detonation.

I'd spend money on some good cylinder heads before anything else.

K


Chevelle Intro: http://www.popularhotrodding.com/features/1005phr_...
My Pontiacs: http://forums.maxperformanceinc.com/forums/showthr...
Pickup: http://67-72chevytrucks.com/vboard/showthread.php?...


 
77 Sierra 
Forum Newbie
Posts: 6
77 Sierra
Age: 55
Loc: Coutts,Alberta,Canada
Reg: 02-23-16
12-23-17 12:17 PM - Post#2718857    
    In response to Keith Seymore

OK Good to know,I never thought of that,I was only thinking of combustion chamber volume,my bad.



 
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