400 w/ 7.4:1 SCR

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mopowers

mopowers

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As some of you know, I've been slowly building a big block 66 Dart. The car will eventually have a hot 470ci in it. But to get it back on the road, I've got a 400 that a buddy gave me that I'll be using temporarily - while I build the 470. After popping the heads off and taking some measurements, I've found that this turd 400 has a whopping 7.4:1 compression ratio w/ the 906 heads, .039" thick gasket, and stock height .030" over pistons .120" in the hole.

Without going crazy and completely rebuilding this 400 with new pistons, can you recommend any worthwhile low-buck improvements that would boost performance a smidge.

Since this engine is just a temporary deal, I'm inclined to just lap the valves, install a new timing chain, bolt on the heads, and call it good. Is a low buck cam upgrade worthwhile? Maybe advance the hell out of it?
 
If it was me I wouldn't sweat it. I'd drop it in run and drive it. Even if it is a turd it would be much funner to drive a big block dart than to not drive a big block dart! Funner, more fun, more funnest? I don't know im just saying it would be fun to drive it rather than it setting without an engine! Lol
 
mopowers said:
As some of you know, I've been slowly building a big block 66 Dart. The car will eventually have a hot 470ci in it. But to get it back on the road, I've got a 400 that a buddy gave me that I'll be using temporarily - while I build the 470. After popping the heads off and taking some measurements, I've found that this turd 400 has a whopping 7.4:1 compression ratio w/ the 906 heads, .039" thick gasket, and stock height .030" over pistons .120" in the hole.

Without going crazy and completely rebuilding this 400 with new pistons, can you recommend any worthwhile low-buck improvements that would boost performance a smidge.

Since this engine is just a temporary deal, I'm inclined to just lap the valves, install a new timing chain, bolt on the heads, and call it good. Is a low buck cam upgrade worthwhile? Maybe advance the hell out of it?
Click to expand...

That's almost a nut and bolt copy of mine. My pistons are down "only" .115 on the hole. LOL I put the old Melling 444/466 214/224 on a 112 in it. Advanced 6*. DP4B intake and will have a 780 vacuum secondary Holley soon as I get it built. It has an 800 DP on it now, but that's a tick big. C body HP manifolds. Summit plastic windage tray/oil pan gasket combo. HV oil pump. Moly rings and new bearings. Dirt CHEAP dirt road build but a lot of fun so far. Probably start fitting it sometime this year.
 
Drop it in and drive it. So what if it's a "turd". If it wasn't, you'd have no reason to build the 470. Plus, it could be a blessing in disguise- it'll give you the chance to get the bugs worked out of your setup before putting big power to it- and you'll have plenty of those. Every build does.
 
Trust me when I say, It will NOT be a turd in an early a body.
 
mopowers said:
As some of you know, I've been slowly building a big block 66 Dart. The car will eventually have a hot 470ci in it. But to get it back on the road, I've got a 400 that a buddy gave me that I'll be using temporarily - while I build the 470. After popping the heads off and taking some measurements, I've found that this turd 400 has a whopping 7.4:1 compression ratio w/ the 906 heads, .039" thick gasket, and stock height .030" over pistons .120" in the hole.

Without going crazy and completely rebuilding this 400 with new pistons, can you recommend any worthwhile low-buck improvements that would boost performance a smidge.

Since this engine is just a temporary deal, I'm inclined to just lap the valves, install a new timing chain, bolt on the heads, and call it good. Is a low buck cam upgrade worthwhile? Maybe advance the hell out of it?
Click to expand...

what are you going to use for exhaust?
 
Stuff a pair of these on, and gain .2 or 3! MrG. 1135G
100_3234-jpg.jpg
 
Thanks for all the input guys!

RustyRatRod said:
That's almost a nut and bolt copy of mine. My pistons are down "only" .115 on the hole. LOL I put the old Melling 444/466 214/224 on a 112 in it. Advanced 6*. DP4B intake and will have a 780 vacuum secondary Holley soon as I get it built. It has an 800 DP on it now, but that's a tick big. C body HP manifolds. Summit plastic windage tray/oil pan gasket combo. HV oil pump. Moly rings and new bearings. Dirt CHEAP dirt road build but a lot of fun so far. Probably start fitting it sometime this year.
Click to expand...

Yeah, I've been following your 400 build for sure. Thanks for documenting it in such great detail! I'm still on the fence on whether to toss in a mild cam or not. What valve springs are you running? My 400 does have a factory 4 bbl intake and I've got a Proform 650 DP and Holley 80457 (600 VS) I can use. I figure since its opened up, I might as well toss in a timing chain.

First things first, I'll degree the cam that's in it now just to confirm what it's got and go from there. The current cam looks to be in great shape, and it's a relatively low mile rebuild so there's small chance it's not stock.

upload_2021-1-10_9-54-57.png


upload_2021-1-10_9-55-22.png

RustyRatRod said:
what are you going to use for exhaust?
Click to expand...
When I build the 470 for it, I'll be building a set of long tubes and 3" exhaust.

For now with the stock 400, I'm just going to build a set of log-style manifolds - quick and easy style. I'm running an engine plate and mid plate, so factory manifolds aren't an option unfortunately, due to clearance issues. I've already got some header and collector flanges, 1-3/4" tubing, 2-1/4" tubing and a couple cheapie flowmaster knockoffs.

Jadaharabi said:
Check this out.
Dyno a 7.5:1 400? Sure, why not?
Click to expand...

Thanks! I followed that thread when he made that thread and completely forgot about it.

Max1196 said:
Stuff a pair of these on, and gain .2 or 3! MrG. 1135G
View attachment 1715667295
Click to expand...

Thanks! I've never used those before. Do you spray them with copper sealant, or install them dry?
 
mopowers said:
Thanks for all the input guys!



Yeah, I've been following your 400 build for sure. Thanks for documenting it in such great detail! I'm still on the fence on whether to toss in a mild cam or not. What valve springs are you running? My 400 does have a factory 4 bbl intake and I've got a Proform 650 DP and Holley 80457 (600 VS) I can use. I figure since its opened up, I might as well toss in a timing chain.

First things first, I'll degree the cam that's in it now just to confirm what it's got and go from there. The current cam looks to be in great shape, and it's a relatively low mile rebuild so there's small chance it's not stock.

View attachment 1715667455

View attachment 1715667456

When I build the 470 for it, I'll be building a set of long tubes and 3" exhaust.

For now with the stock 400, I'm just going to build a set of log-style manifolds - quick and easy style. I'm running an engine plate and mid plate, so factory manifolds aren't an option unfortunately, due to clearance issues. I've already got some header and collector flanges, 1-3/4" tubing, 2-1/4" tubing and a couple cheapie flowmaster knockoffs.



Thanks! I followed that thread when he made that thread and completely forgot about it.



Thanks! I've never used those before. Do you spray them with copper sealant, or install them dry?
Click to expand...
So u have a forged steel crank in there or just the dampner? Kim
 
Well, I went out and measured the camshaft. Overall, the specs look very close to a stock replacement, so that's probably what it is. Any difference is probably due to my measurements. Here are my results:

Intake: .285" lobe lift (.428" theoretic valve lift), 206* duration @ .050", 290* duration @ .003", 108* ICL
Exhaust .285" lobe lift (.428" theoretic valve lift), 210* duration @ .050", 300* duration @ .003", 117* ECL

Obviously, the ramps are incredibly slow - almost cringeworthy.

I popped the timing cover off and the chain, though it's a stock link type replacement, is in great shape with very little slop. You could definitely tell it is a low mile rebuild for sure.

upload_2021-1-10_13-10-2.png


At this point, I'm pondering 3 options:
1. Button it up as-is (with thin shim-style head gaskets).
2. New timing chain and advance this cam at 102-ish.
3. New timing chain, new cam/lifters (maybe valve springs?).

What option would you guys choose??? I'm leaning toward option 1 or 2 since it's just a temporary engine to get the car back on the road.

oldkimmer said:
So u have a forged steel crank in there or just the dampner? Kim
Click to expand...
That's a good question. I didn't even think of that. I have the pan off, so I'll have to go out and look. I didn't even realized 400's came with forged cranks.
 
mopowers said:
Well, I went out and measured the camshaft. Overall, the specs look very close to a stock replacement, so that's probably what it is. Any difference is probably due to my measurements. Here are my results:

Intake: .285" lobe lift (.428" theoretic valve lift), 206* duration @ .050", 290* duration @ .003", 108* ICL
Exhaust .285" lobe lift (.428" theoretic valve lift), 210* duration @ .050", 300* duration @ .003", 117* ECL

Obviously, the ramps are incredibly slow - almost cringeworthy.

I popped the timing cover off and the chain, though it's a stock link type replacement, is in great shape with very little slop. You could definitely tell it is a low mile rebuild for sure.

View attachment 1715667595

At this point, I'm pondering 3 options:
1. Button it up as-is (with thin shim-style head gaskets).
2. New timing chain and advance this cam at 102-ish.
3. New timing chain, new cam/lifters (maybe valve springs?).

What option would you guys choose??? I'm leaning toward option 1 or 2 since it's just a temporary engine to get the car back on the road.


That's a good question. I didn't even think of that. I have the pan off, so I'll have to go out and look. I didn't even realized 400's came with forged cranks.
Click to expand...
Option #1.
Why sink any additional money into a solid engine that you'll be replacing anyway? Use your money to build the 470 while you run the 400 and get the quirks ironed out.
 
mopowers said:
Hey Rob - When you installed those gaskets, did you use any copper spray on them, or just install them dry? Thanks sir!
Click to expand...

I always use Copper Coat on steel gaskets. I don't care if they are already coated or not. It's good insurance.
 
BELIEVE ME..it WONT be a turd in an A-body..I went to the junkyard and pulled a 440 out of a 1975 new yorker..stock 7.5:1 engine. Rebuilt it stone stock, just new rings and bearings and dropped it in my 1972 dart and let me tell you, it was scary! The torque of a big block in a dart is fun and scary at the same time! Yes, its a 440 but the 400 wont be a heck of a lot different in a dart! The one fun yet scary thing was when i was cruising down a curvy road at 45 MPH and stepping on the gas, it would break sideways! It didnt take long to literally desintagrate the original to the dart 7 1/4 dana . When i took the rear cover off, bits and pieces just crumbled out, like broken glass.. I since pulled the 440 out and upped the compression and installed a much bigger cam and its a little better on top end now but like i said, even bone stock it was scary and fun at the same time! You will see!!
 
Sounds like the 206/209 cam which they list as the factory 440 365 HP cam. I'd run it the way it is.
 
I didn't mention it but the car has a 4.10 Dana 60 w/ powerlock and 30" tall tires.

RustyRatRod said:
Forged crank. Nice! Hell, I'd put me some kinda little cam in it. lol
Click to expand...

What would you recommend cam-wise? Something with shorter ramps and a tad more lift would be nice. I'm just not convinced it's worth the expense since it's a temp motor. Plus breaking in a new FT cam does not appeal to me. If I had another hotrod to drop it in, I'd throw some $$$ at it for sure, but after a year or so (if that), it'll be tossed to the side.

qkcuda said:
Sounds like the 206/209 cam which they list as the factory 440 365 HP cam. I'd run it the way it is.
Click to expand...

Could be. Any idea where I can find the complete specs of that cam?
 
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