Considering a DSS 331/347 longblock instead of building my 351


Founding Member
May 1, 2002
Granada Hills, California
I’m considering using a DSS 331 or 347 long block instead of building my own 351w. The advantages are obvious, but basically, for about 1-2 grand more than I would spend to build the 351w mostly myself, I could get a DSS 347 long block that would be:

a) built, perhaps warrantied and at least supported by a shop that knows what they’re doing
b) allow me to re-sell my old engine to recoup some of the extra costs
c) be about 100 lbs lighter than my current engine without some of the space-related issues I run into now and then
d) be a roller engine
e) would be a lot less work on my end.

A few questions:
1) That whole pricing argument is dependent on me being able to re-use many of the little parts on my 351w. I might replace the water pump and balancer anyway, but do things like the oil pump, oil pan, timing cover, distributor, headers, water pump and balancer that I have on my 351w fit 302-based engines? My current power steering setup, alternators and other accessories and their mounting stuff will continue to fit, right? Will my exhaust bolt right up or will it need to be modified?

2) Whats everyone stance on 331s vs. 347s? Both seem to be pretty popular.

3) 302 based engines don’t have a problem fitting in 66’s with intakes like Performer RPMs, Weiand Stealths, and RPM Air-gaps, right?

4) When using a roller cam, I’ve heard the principle advantage is that more aggressive cams are easier to drive around on the street. Anyone have a recommendation for a roller cam grind that is easy to drive and makes power from idle-ish to 6 grand?

5) If anyone knows some good engine shops I should cross-shop DSS’s offerings against, let me know. I know about CHP and am looking into them as well.
  • Sponsors (?)

1. a 331/347 block is a 302 block, so anything that bolts to a 302 is OK. Generally, these questions/costs end up being a wash...the 351 block is somewhat stronger at the cost of ~100 lbs of weight and a bit wider/taller. Your 351 distributor will not fit a 302; shaft is too long. Your accsry brackets may not fit due to the wider 351 block, but I dont know that for sure w/o looking.

2. If I were a dragracer, I would get a 347. If I were a roadracer, I would get a 331. 331 has a bit more rev potential at the cost of a smidge of torque...but weight and its distribution is key in roadracing. But you may never see the difference. IMO they are equal in reliability if competently built.

3. No.

4. Too many variables for a pat answer, I gave up years ago trying to recommend cams on car forums. I would aggressively use the 'help line' that every cam vendor has and get recommendations. You cant answer this question without factoring in your heads, trans, gears, intended usage, etc.

I will say that several years ago the roller cam was the hot ticket..but in recent times (esp for mostly street usage) the ole flat-tappet has made a comeback. I wouldnt automatically assume that a F-T was a bad option.

5. I have not used DSS but have heard nothing adverse about them. My last 347 was from CHP and I had no complaints about the parts quality or machine work (although I assembled it, it was not a shortblock).
First off you can't go wrong with DSS, there are several members on this board including myself who have one and are more then happy.

1. Pricing- I was able to afford the DSS package by selling of parts from my 289 that I wasn't planning on using on the 347 like the cam, water pump and balancer. I don't know about what parts will interchange, but a DSS longblock will come with an oil pump & pickup and a timing chain. To go along with what cam you pick.

2. I think the difference between a 331 & 347 is negligible - you may get a FEW more RPMs out of the 331 but you get 16 more cubes with ends up being 20+ more horsepower and better low end torque. They are both reliable and as the old saying goes "There is no substitute for cubic inches."

3. As said already no problems with fitment, I have a Victor Jr, a drop base air cleaner with a 3" element.

4. Look at the Comp Extreme Energy 274HR, great cam, lots of lope, enough power down low with tons of power up top. its a very popular choice and in a well built 347, it will put you into the ~425hp range. I have this and its much easier to drive then the Edlebrock RPM was in my 289.
Would you recommend a Vic Jr. or a dual plane like the Performer RPM Air Gap? I heard great things about the Air Gap but never could really consider one for my 351w. I was also pretty set on a dual plane because this was/is going to be a street car primarily, but if drivability/economy are still decent with a single plane it might be worth considering (if for no other reason than the drop in off-idle torque might keep my T5 breathing a while longer).

Where are the power/tq peaks and shift poitns with that cam? But yeah, thats about the cam I was looking at.

As far as the conversion from a 351w goes, does anyone know if those p/s brackets, pulley setups, etc still work?

Also, what do you think I could get for a 72' 351w long block with about 3,000 miles on it?
The 351's distributor won't fit a 302, due to the oilpump shaft size. The 302's is 1/4", the 351's is 5/16". Timing covers are the same, ditto for accessory brackets (usually) Ford used an adapter bracket to interchange accessories between the two engines. Oilpans are different. As for roller cam choice vs driveability---- My 331 has Canfield heads (AFR165 equivalent) topped with a 3x2 high rise dual plane. Cam is a Ford Racing 303 (228/228* @.050 .587/.587 lift) Power comes in at 1500 and pulls to 6500-7000. VERY streetable with the dual plane intake. I had this in my 89 Ranger for a year and at one point was driving it daily on a 50 mile r/t commute. It's now in my 77 Comet with a C-4 (Ranger had a Toploader 4 speed) mild stall converter (don't know which, but the stall speed is less than 2 grand) Still no driveability issues. Powerbrake it lightly and it'll instantly light up the rear tires. I could have gone with a 347, but don't regret the 331 at all. PLENTY OF POWER.
Valve covers, water pump, timing cover

Not swapable:
Intake(wrong width)
Oil pan
Distributer (different height/oil pump drive)

All 351s balance at 28oz
Early 302s balance at 28oz, Late 302s balance at 50oz
The change happened around '81 if I remember correctly
I went with the Victor Jr because the 347 already has enough low end power, and being that early mustangs already have enough traction issues I didn't feel I needed the small amount of low end gain from the RPM and opted for the top end gain of the single plain Vic Jr. Drivability is definately not an issue it drives fine- WAY better then my old built 289. As far as economy, not bad on the highway as it gets 21-22 mpg but I have never measured it around town.

I haven't dyno'd the car yet so I can't tell you where the power peaks are at, but I was shifting at 6000-6200rpm on the drag strip.
On a related note, if I did decide to sell my 351w, what would it be worth (complete)? It was purchased as a rebuilt crate motor in 2005 for $1400, has a couple thousand miles on it, and has no major issues and runs great. I was going to say 700 or 800, but maybe I'm way off.
You may want to pose this question to the 5.0 community too. Both options would be great 331 typically responds better to boost if that is a consideration, Both typically get about the same HP but the 347 does have better low end but cannot rev as high. Another great option for an engine builder is Rick91GT. He runs and has a great reputation in the 5.0 area. Unfortunately I doubt many of the accessory items can be swapped over but there are a lot of 5.0 stuff out there you can swap to a serpentine pretty easily and cheaply. I would talk with the engine builder about the cam.
The only thing bad I can say about the DSS setup is the block they use. OEM 302.

This will be fine for a NA motor, but if you install a power adder down the line you risk cracking the block at anything over approx 450HP (general rule of thumb is that the 302 block is only good to 500HP max)