Hey guys I have my twin turbo setup sized for a 350-383 engine. I'm in process of building a new engine and considering going the route of a 377 (400 block/350 crank/6"rod) with my 190 AFR heads & Superram instead of another 350.

I'm thinking 377 because the bigger bore is supposed to unshroud the valves and I'll be going with a 8.5:1 compression to keep it street friendly.

Any thoughts? Looking for some quick feedback.

 

Compression is in the right area. If you plan on running high boost, definitely spend the extra money on a forged bottom end, arp hardware, and well worked heads.

 

Yes going Dart block, eagle crank & H beams, JE Pistons. I want to run lower compression and high on the boost.

Any other comments on engine combo?

 

This is usualy a given when building a 377, but buy a crank with the 400 mains, rather then using the spacers on the mains. while spacers work fine, they're just one more thing to go wrong.

I dont think that extra 1/16 of an inch will make a huge difference in unshrouding the valve because in the chamber on the head is where you want to grind to unshroud it... but the big bore short stroke combination makes for a quick/high reving motor...

 

I prefer a single plain intake over the superram for more power with less boost(+easier to work on).

 

be careful with that setup haha.....my buddy has one in a heavey car. im talkin some big rpm....don't forget the stud girdles and a rev kit.

 

Rev kit?

You dont need a girdle... we have ran 377's in our stockcars and built a few other ones with out a problem the sbc blocks are pretty strong. Billit caps would be nice but not necessary. At the shop my dad owns and where I have been working for 6 years we have built many racecar engines for customer and our personal cars. 7500rpm every lap and never had a problem. None of those had girdles and many had stock main caps. Now we have a 362ci limit.

 

So is that in a good way or a bad way (as in not a good combination)?

 

"Hey guys I have my twin turbo setup sized for a 350-383 engine."
That sounds alot like the BBSDesigns street/strip TT kit description, heh. Is that what you have?

It's not going to have to ability to rev any more durably than a 350, as they have the same stroke, 6" rods don't help too much. Some of you are thinking more along the lines of 347 destrokers or 302 destrokers, with their smaller strokes. With those parts it should make power up there though.

Anyway, what has been mentioned otherwise is a decent guideline to go by. Try to keep your quench somewhere around .040, not less if you'll be revving it high, not too much more. This will help even more if the piston's you'll be using have a D-cup shape, as well as the heads having a D-shape chamber.

 

Nope B&G custom fabbed a kit for me. I decided to go ahead and do the engine before I bolt everything up. They did a sweet job on the kit.

 

Okay, that's cool. I was just curious, as the BBS kit is the one I have.

Good luck with it.

 

Well, I’ll be the lone “I don’t like that…” I guess…

Big bores deshroud valves and increase air flow, though I’d be very surprised if you saw a big difference with something semi standard, designed to work with a 4” bore like AFR 190’s.

Smaller bores tend to control detonation better.

Supercharging in any form tends to give you all the airflow that you size the turbo for, so breathing (within reason) isn’t that big a problem, just turn up the boost. It also heats up air and forces a much more dense a/f mixture into the chamber which is more likely to detonate… See where I’m going?

Second thing that a larger bore lets you do is get the same displacement with a shorter stroke so you can rev higher with the same quality parts then you could with the same displacement and a smaller bore. OTOH, you don’t really need to rev a boosted engine to the moon to make very significant power and boost puts it’s own strain on parts…. The only time you’re going to see an advantage here is if you’re trying to keep the compression reasonably high and still run significant boost on the street, the trick then is to build the boost up top past the torque peak where it’s less likely to cause problems with pump gas and high compressions. Of course, you look to be thinking of running reasonable compression and for overall longevity I’d gladly give up a few hundred rpm.

I could think of reasons that you could really justify a 377, but for a fast street/strip or even fairly serious drag car, if you’re going to start with an aftermarket block, crank… I’d probably more seriously look at building a 400, or maybe something like a 417 than a 377, or a 383 if you’re sticking with a 350 block. OTOH, I’ve also seriously considered building up a boosted 305 with a 3.85” crank in it for 343ci for a street going toy or even my truck… but I’m weird that way, and again, I wouldn’t do it in a race car or even a serious street strip car.

 

ok I have the 377 short block done, heads are in the shop getting freshened up, and Cammotion is doing a cam grind for me. Any suggestions if I should go high volume oil pump or regular with the twin turbo?

Dart SBC 400 block (o ringed)
350 Eagle crank (400 bearings)
Eagle 6" Hbeams
JE forged pistons (good for 8.5:1 compression)
64cc AFR 190 heads
Cammotion retro roller 222/214 .541/.531 w/ 1.6 roller rockers
Two Precision 6031 ball bearing turbos w/ AR.58
Moroso 6qt oil pan

Also, repainting the engine compartment while I have the engine out.

 

I can see what you mean, but don't forget that with a larger bore and shorter stroke coming to the same displacement (for example, a destroked 400 to 347 vs. a conventional 350), you can stuff much longer rods in there and get a very favorable rod/stroke ratio, which helps control detonation to a large degree as well. Of course you have to really raise the ratio to make that difference, but it's pretty easy when destroking like that.
I don't know which one helps more overall, a smaller bore or a larger rod/stroke ratio, but don't forget about that. Of course you could use a small bore and a small stroke and just run a lot more boost to make the same power, but more boost also = more detonation. I think someone would really have to build those different combos while isolating other variables to get definitive results for a particular comparison.

Sorry to hijack, 87IROC350.
It sounds like your combo will be very fun and powerful when it's all tuned. If you're going to be revving relatively high which it sounds like you may, since you'll have a 6 quart pan, and with the slight additional oil demand from turbos, I don't think it would hurt to use a high volume oil pump.

 

Not looking for crazy high rev's. Probably no more than 6000 and will mostly likely shift around 5500. It has potential for a high rev combination but the cam is more for midrange.