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1970 GTO / 400 / 4 speed
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Discussion Starter · #1 · (Edited)
My 1970 is a few weeks out from having it's driveline completely updated. Going in is a fresh 428, a rebuilt M20, Yukon LS and 3.55s. I'm doing a CVF serpentine conversion on the 428 along with DUI HEI, DUI 1 wire alternator, Eddy carb, FlowKooler pump, Carter fuel pump, etc. So the 400 that's in the car will be coming out complete from oil pan to air cleaner. She still runs strong although the Quadra Jet and points both need some TLC (or replacement.) I didn't bother after buying the car a couple months back since I knew it would all be updated in short order... The motor has an Edelbrock Performer intake and a mild cam (don't know the specs... just going by the idle). It's not consuming oil or smoking and has 40psi of pressure at idle / 60 under load. Runs cool at 160 (new Griffen rad is helping with this.) The motor also has 6X heads into stock manifolds.

Anyways, the shop I bought the rebuilt trans from is taking my M20 back as a core and giving me decent money for it. Now I'm trying to figure what to ask for the motor? I know it's an unknown so we don't know the condition of the internals... But I'm just trying to figure what it's worth if I pop it on CL or FBM? I'm not looking to squeeze every last penny out of it. I just don't want to scrap or leave behind a decent 400. I haven't looked at the date code or casting number but it's a WT block. Any thoughts or advice on value? Thanks in advance guys...
 

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1970 GTO / 400 / 4 speed
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147 Posts
Discussion Starter · #3 ·
Thanks @Duff I have just that video on my phone from this morning. I think I'll take a second while driving too to give a bigger picture. I'm wondering if I should buy a cheap Harbor Freight engine stand so it doesn't look like I just tossed it onto the floor? I'm going to bring it home on a tire in the bed of the truck but that won't look great to a potential buyer when they come to see it in the garage.
 

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1970 GTO / 400 / 4 speed
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Discussion Starter · #5 ·
LOL, sure thing... 🤣🍻

Hey, where exactly are the date stamp and casting # near the distributor? Is it really hard to see with the motor in the car? I'd like to finish my research on what exactly this 400 is...
 

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My 1970 is a few weeks out from having it's driveline completely updated. Going in is a fresh 428, a rebuilt M20, Yukon LS and 3.55s. I'm doing a CVF serpentine conversion on the 428 along with DUI HEI, DUI 1 wire alternator, Eddy carb, FlowKooler pump, Carter fuel pump, etc. So the 400 that's in the car will be coming out complete from oil pan to air cleaner. She still runs strong although the Quadra Jet and points both need some TLC (or replacement.) I didn't bother after buying the car a couple months back since I knew it would all be updated in short order... The motor has an Edelbrock Performer intake and a mild cam (don't know the specs... just going by the idle). It's not consuming oil or smoking and has 40psi of pressure at idle / 60 under load. Runs cool at 160 (new Griffen rad is helping with this.) The motor also has 6X heads into stock manifolds.

Anyways, the shop I bought the rebuilt trans from is taking my M20 back as a core and giving me decent money for it. Now I'm trying to figure what to ask for the motor? I know it's an unknown so we don't know the condition of the internals... But I'm just trying to figure what it's worth if I pop it on CL or FBM? I'm not looking to squeeze every last penny out of it. I just don't want to scrap or leave behind a decent 400. I haven't looked at the date code or casting number but it's a WT block. Any thoughts or advice on value? Thanks in advance guys...
Is an M20 going to up to the task of that motor? Is it getting beefed up?
 

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1970 GTO / 400 / 4 speed
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147 Posts
Discussion Starter · #9 ·
I believe the M20 will be fine. I think lots of times folks get hung up on ratings. Same happened with my TH350 I had behind a 400 small block in my 69 Camaro back 30 years ago. I had that motor really built and threw a 140 shot of nitrous on top of that. Ran 11's and I beat the snot out of it every weekend on the street. The only thing I ever broke in the driveline was a rebuilt 8.2 GM posi after almost 4 years of this abuse. Now, that's anecdotal evidence and I may grenade this M20. However, after returning the old one to the guy who built the replacement, I'm only out $850. So, if that $850 turns out to be money spent poorly, I'll get on AutoGear's waiting list for a wide ratio M22 and pony up the $2300 they want... I guess time will tell... 🍻
 

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I believe the M20 will be fine. I think lots of times folks get hung up on ratings. Same happened with my TH350 I had behind a 400 small block in my 69 Camaro back 30 years ago. I had that motor really built and threw a 140 shot of nitrous on top of that. Ran 11's and I beat the snot out of it every weekend on the street. The only thing I ever broke in the driveline was a rebuilt 8.2 GM posi after almost 4 years of this abuse. Now, that's anecdotal evidence and I may grenade this M20. However, after returning the old one to the guy who built the replacement, I'm only out $850. So, if that $850 turns out to be money spent poorly, I'll get on AutoGear's waiting list for a wide ratio M22 and pony up the $2300 they want... I guess time will tell... 🍻
I asked Darrin from Nitemare about how long a stock built Muncie (M20) would survive behind the 461 I have in my car now. His take was that it would be fine for a street application. Same with the factory 10 bolt. I've put ~1200 miles since the engine went in the car and the rear and transmission both seem fine. That being said, things could change if I decided to throw some super sticky tires on the back and bring it to the track.
 

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1970 GTO / 400 / 4 speed
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Discussion Starter · #12 ·
I was thinking that about showing it in the car too @Jared . I just didn't want to do it too soon as I'm still a few weeks out from my swap. I would be happy to show it to you though...

On the M20 and 10 bolt, I agree completely. Mine is not an over the top built motor and I'm not dumping the clutch with drag radials on. When I talked to Mike at Ram clutch, he said that so many guys go strictly by HP ratings and estimates. He said, while that might be safe, it's often completely unnecessary and guys end up with a leg shaker of a clutch because they over bought. He said long before something breaks or the clutch slips, the tires will break loose.
 

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I believe the M20 will be fine. I think lots of times folks get hung up on ratings. Same happened with my TH350 I had behind a 400 small block in my 69 Camaro back 30 years ago. I had that motor really built and threw a 140 shot of nitrous on top of that. Ran 11's and I beat the snot out of it every weekend on the street. The only thing I ever broke in the driveline was a rebuilt 8.2 GM posi after almost 4 years of this abuse. Now, that's anecdotal evidence and I may grenade this M20. However, after returning the old one to the guy who built the replacement, I'm only out $850. So, if that $850 turns out to be money spent poorly, I'll get on AutoGear's waiting list for a wide ratio M22 and pony up the $2300 they want... I guess time will tell... 🍻
Gotcha, and if you don't have big sticky tires and traction it should be ok, you're probably not racing it every weekend either, but if it goes put in the Tremec TKX (y)
 

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1970 GTO / 400 / 4 speed
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Discussion Starter · #14 ·
Oh, so many ways to spend my money...LOL. Now to get the 400 sold and try to recoup what I've already spent. I'm up to the point where I have about the same into the car as all my current upgrades and mods...
 

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1970 GTO / 400 / 4 speed
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Discussion Starter · #15 ·
Oh, hey, no one replied to date and casting numbers. Easy to see when still in the car? I took a preliminary look and came up empty but for all I know, I'm looking in the wrong spot....
 

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Oh, so many ways to spend my money...LOL. Now to get the 400 sold and try to recoup what I've already spent. I'm up to the point where I have about the same into the car as all my current upgrades and mods...
Welcome to the club, you're now an official member, but when you get the high signs going down the road or you mash the go pedal it will all be worth it :D
 

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1970 GTO / 400 / 4 speed
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Discussion Starter · #17 ·
It's amazing, I get thumbs up etc. at least once every time I'm out... And often lots more than once...
 

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I was thinking that about showing it in the car too @Jared . I just didn't want to do it too soon as I'm still a few weeks out from my swap. I would be happy to show it to you though...

On the M20 and 10 bolt, I agree completely. Mine is not an over the top built motor and I'm not dumping the clutch with drag radials on. When I talked to Mike at Ram clutch, he said that so many guys go strictly by HP ratings and estimates. He said, while that might be safe, it's often completely unnecessary and guys end up with a leg shaker of a clutch because they over bought. He said long before something breaks or the clutch slips, the tires will break loose.
Keep me posted if you don't find someone before it's ready to come out. I'd be looking at this as a potential backup for the future so I'm kind of a bottom feeder on this one. That being said, for the right price I'd help you pull it.
 

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One way to tell is the large number cast near the distributer. Some year blocks had the year cast in fairly large numbers on the drivers side under the distributer. The numbers are large and face the back of the block. Engine in mine now is from a 1971 and has a large 71 and the one that came out was from 1974, large 74 cast in the same spot. I'm not an expert and am not not sure if this carries to the older engines. Either way, if it's there, you should be able to see it.

Here are a couple more resources to narrow down what you have.


 
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