Hi. I have a 70 351w block at the machine shop at the moment being built for boost. I have a blow through 302 that it'll be replacing. I have found a well priced 393 crank that I could use, however my question is am I better to stay as a 351 turbo or step up in cubes to the 393? I have read that the 393 will need at least an 88mm turbo. Here in nz a precision 7675ls is around 2k, a decent 88mm would be 3-4k. Im hoping for 650rwhp, more if the stock block will let me. Is going 393 worth it or will the 351 perform just as well? Thanks

 

If staying 351 cubes fits your budget better go with it. You can easily exceed 650rwhp with one.

 

I agree stick with the 351. A better breathing stroker will require a bigger more expensive turbo. Check out VS racing for turbos too if you wanna save some money

 

I have a 388W with a PT8285 turbo. It has a small hyd roller cam 228/232@ .050" and I tried running a VS racing Next Gen 7875 with a 1.25 A/R exhaust housing and had serious back pressure. The instant torque is nice but you will need a turbo with a large turbine wheel. A PT88, an S480 Borg Warner or some of the VS racing clones with a 96mm exhaust wheel would work OK if you can find room for them. Probably easier to stay with the 351.

 

Thanks. Would a the 76mm turbo be the minimum size you'd run on a 351? My 302 has a 70mm with a .68 housing. It builds good boost but will be too small on the 351. Im thinking a 76-80mm turbo but unsure which size to run on the exhaust side?

 

I'm going to run a 78mm on3 turbo on my 358. Should make 850+ pretty easily. I was in the same boat as you, and I already have both a 393 stroker recip assy and a 358. I chose the 358 just because I feel a pound or 2 of boost will make up for the cubes and I won't have to try and manage all that torque from a stroker. A windsor turbo has plenty of torque

 

I'd be more concerned about the turbine size. I would want at least a 75mm turbine. The cold side depends on how high you plan to rev it and how much power you want. I briefly ran a PT7675 Gen 1 ballbearing unit on a 351 and it was a nice responsive street setup.

 

As an aside the main reason I built my 388" was that I had a NA 393 in the car before I went turbo and I always wondered what would have happened if I had simply added boost to it. I was buying rods and custom pistons anyway so buying a cheap chinese forged crank didn't add much to the bill. My car has 3.00 rear gears so the extra torque is nice. What nxcoupe said is true though, a couple more lbs of boost will more than make up for the cubes and you won't need such a big turbo.

 

Looking back on that setup would you run the same turbo again or larger? I'll be running a stall converter 2800-3000rpm approx. Max rpm im not sure on yet

 

Yes I would, it was a nice combo. That said the 7875 that nxcoupe mentioned or a VS Racing 7875 would work well too and for less money if that is an issue. Those Precision ball bearing units have an extremely unpleasant price tag. I have a friend who is a dealer so I get somewhat better pricing but it is still ridiculous.

 

A 7675 precision gen2 is over 5k here in nz. I can buy from the USA, conversion rate is approx 50% on top of the USA price to nzd. Plus 15% gst tax at this end for anything over 1000nzd including the shipping cost. The turbos on vs racing certainly look quite good. There are Chinese 76mm turbos available here for 800nzd but I've already blown up two 70mm Chinese ones on my 302w, one due to a piece of fibre blocking the oil feed and the other just packed a sad one day destroyed itself on the housing

 

Borg warner s475 or s48o would do everything you ask. New Zealanders must have semi trucks, there should be something available for them. Small industrial turbo diesel engines will have something in the s200 size, 52-58mm a pair of those would work as well.

I'm not sure why your under the impression you need an 88mm turbo for a 393, unless your trying to make well over 1200hp that compressor is excessive. But a 351w will make a ton of power turbocharged without being stroked.

With a goal of 650hp run the 351w with an s400, 72-80mm you will have more than enough compressor. You could even get there on an s366. With a good set of heads and a modest cam you will easily surpass 650.

@Briansshop did a bunch of work with a 351w

https://www.theturboforums.com/threads/gen-1-lightning-single-66mm-build.378494/

 

There's more to this than just cid as well. Both engines with identical cylinder heads and cams (air flow) will have roughly the same hp potential, just at a lower rpm with the larger engine. The larger cid will of course have more torque under the curve. Turbo selection based solely on cid isn't the best route.

 

I was concerned that a t4 turbo would create too much back pressure on the 393? I'm limited to a 3" downpipe off the turbo because of the steering arm etc

 

It depends more on na hp/tq production than cid. What cylinder heads?

 

Pro comp 60cc, 210 intake, 70 exhaust. Not great heads, they have had some work done to them and they were well priced

 

I'm with the others, 351.

 

Thanks. I might still buy the crank and put it aside to use in the future since its available at a good price. For the 351 would a 7875 with .96 exhaust side suit well? Or 80mm with 1.10ar exhaust? Quite likely that I'll buy the turbo from vs racing if anyone has a recommendation on that website? I'll run a stall around the 2800-3krpm range, undecided on cam as yet

 

Either will make the power you want.

 

7875 still wants a 4" downpipe. If you really are restricted to 3" twins might be a better bet.