Difference between Dart 347 and stock block 408 - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 17 Old 02-28-2016, 10:13 PM Thread Starter
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Difference between Dart 347 and stock block 408

Dad's Maverick....(not mine)

Been running a Dart block 347 (4.030 bore and 3.400" stroke) for a couple years and it's been doing good. Methanol injected, 13:1, solid roller (268-274 @ .050", .688 lift on both), out of the box victor Jr heads, victor JR 302 intake, Powerglide w/5500 converter, 5.13 rear gear, backhalf ladder bar car 32x14 slicks, weighs 2703 with my brother in it-he is around 310 lbs. Always dialed in the 6.35-6.40 range depending on weather.

Last weekend they went to the track, car ran a few 6.36's in a row. Next pass, it died and would not restart. Broke cam dowel and bent some valves. I had a 408 built at home but no camshaft. Same exact out-of-the box victor Jr heads on it. The 408 is also 13:1 (actual 12.93), victor jr 351w intake. We pull the cam from the 347 and put it into the 408, with a new dowel pin and a new bolt just to get the car back to the track. No major changes to the trans or anything else for that matter, just the engine. Even the little 1 5/8" Ford VAN headers got re-used. They were on a 302 that was in a junkyard van; got them for $5 when I was helping the original car owner build the car (before my dad bought it).

It went 2 6.01's in a row yesterday, with too much timing. I had him pull it back to 32° from 36, which should pick it up a few hundredths and probably 2 or 3 mph. So what's that? Nearly 4 tenths improvement? Oh, did notice that the stall speed is up to around 5800 based on the LM-1's log, from 5600-ish with the 347. Torque will do that. Don't have any timeslip because the printers were screwed up; and I didn't think to get any pics of the nice wheels-up launches.

Just thought you guys might be interested in the real-world difference.

I wonder how much ET gain there is with some decent headers, if any.

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post #2 of 17 Old 02-29-2016, 12:17 PM
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Tough to beat cubic inches....
I'd also think the converter was tight for the 347 and now either ideal or even a bit loose for the 408.

Interesting comparison though!

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Bests:1.35 60' / 6.21 /9.76 and 138.8 mph.
Thanks MCRP, UCC, FTI, Sepanek, Braswell, Racecraft, and Team Z
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post #3 of 17 Old 02-29-2016, 09:40 PM Thread Starter
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Tough to beat cubic inches....
I'd also think the converter was tight for the 347 and now either ideal or even a bit loose for the 408.

Interesting comparison though!

Now that I think about it, you're probably right on the converter. Dad's car. I assume it's an off-the-shelf Jeg's special 8". Probably a tenth or thereabouts in the converter alone, but as I told them, if it's consistent and repeatable, run it until it breaks, and then address it.....

the 408 is an oddball, that hardly anyone builds, had to make it fit in a C9 (shorter deck) block-and still allow for deck squaring.

'92GT, 427" and '93 "LXVO" coupe
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post #4 of 17 Old 03-02-2016, 11:35 AM
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Not bad at all for a 408 choked up on intake an exhaust both.


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post #5 of 17 Old 03-04-2016, 01:03 AM
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Not only from power perspective now, but the 408 must also be lighter due to being stock block?

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post #6 of 17 Old 03-04-2016, 06:26 AM
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Stock for stock I kno a Windsor block is atleast 50# more. I can carry 302 block no problem but a Windsor is borderline my limits of carrying lol


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post #7 of 17 Old 03-04-2016, 11:46 AM
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Stock for stock I kno a Windsor block is atleast 50# more. I can carry 302 block no problem but a Windsor is borderline my limits of carrying lol


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THere's a BIG difference between a DART 302 block and a stock one. Like 60-70lbs.

When you figure the increased rotating weight, I'd bet the 408 and the Dart 347 were similar in weight.

1984 GT, 363 -RHS215 heads & Super Vic intake by MCRP, FTI cam, Carbureted, Glide, 4.30's, pump gas, street legal, N/A
Bests:1.35 60' / 6.21 /9.76 and 138.8 mph.
Thanks MCRP, UCC, FTI, Sepanek, Braswell, Racecraft, and Team Z
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post #8 of 17 Old 03-04-2016, 03:03 PM
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hard to beat the extra torque from .6" more stroke

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post #9 of 17 Old 03-04-2016, 06:57 PM
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Have u held a 3" main 4" stroke Windsor crank before lol? I assure u that 408 is heavier than a dart block 347. I know for sure a stock stroke 351w in my car weighs more than 70# more than my old 302 an it is a stock crank not a forged stroker


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post #10 of 17 Old 03-04-2016, 07:03 PM
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Pretty sure a Windsor block is that much heavier than a stock 302 as well. I'm sure Ed or woody can confirm. Or I could take my lazy but outside an put one on a scale


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post #11 of 17 Old 03-04-2016, 11:49 PM Thread Starter
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Not bad at all for a 408 choked up on intake an exhaust both.


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Agreed. My 438 is plugged up too on both ends, heads specifically (AFR225), but at the point where I'm at with this deal, to get any more out of it I'm looking at $3500+. There comes a point where most traditional inline valve heads will only do so much. If I were looking for more, I "could" look into the big TFS hi-ports but then we're looking at some serious cash outlay. That or Victor Sr's, or canted valve, and generally speaking with the latter two, piston, header, and intake changes go with it. Just out of our budget.
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post #12 of 17 Old 03-05-2016, 07:05 AM
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I'd be happy with those numbers u got for sure. Having the Vic jrs worked by someone good along with a super Vic an bigger headers alone in any order would probably help dramatically


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post #13 of 17 Old 03-05-2016, 07:49 AM
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toddturbo - what was the mph with the 347 vs 408? When I moved the same induction (including heads) from a 306 to a 363 I saw effectively no change (10.55 @ 129 vs 10.54 @ 127); just the rpm band shifted down.

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post #14 of 17 Old 03-05-2016, 11:26 PM Thread Starter
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I don't have the timeslip in front of me, but the 347 was in the 108 mph range and the 408 is in the 111-112 range. They were at the track earlier today tuning the injection, but I did not think to ask what it was running for ET and MPH. Got a call about tuning the barrel valve, then another about the pill and effect on barrel valve, but that was the last I heard. I have been at work all day; back hurting and not feeling well. Came home and went to bed.

That same exact 408 that they're using went 1.25 60', 5.79 at 120, in my car--but my car (and myself) are lighter by about 200 lbs.

I think his car should be a solid 6.0 car flat out. He and I may have some competing to do amongst each other on a 6.0 index race
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post #15 of 17 Old 03-06-2016, 04:32 PM
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toddturbo - what was the mph with the 347 vs 408? When I moved the same induction (including heads) from a 306 to a 363 I saw effectively no change (10.55 @ 129 vs 10.54 @ 127); just the rpm band shifted down.
wow, really?? na? what hci setup was on that 306?
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post #16 of 17 Old 03-07-2016, 08:15 AM
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way faster than i expected. #### i need to finish my motor.

working on motor
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post #17 of 17 Old 03-13-2016, 10:51 PM
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Very cool thanks for sharing.

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