Hey everybody, new user here. I have a Dart SHP block 350 main, 4.125in bore. I am new to the performance side of teching, and I'm looking for some advice on some specific engine specifications. I am very willing to learn and would appreciate being corrected if some of the information I provide is incorrect. My plan so far is to create a 400 and shoot for 600hp to the crank on pump gas N/A. Streep/Strip application. I picked out a Molnar crank and rods, 3.75in stroke and 6in H-beam rod. I am looking for some advice on which pistons I should go with, and some questions regarding how to come to that conclusion. To start, what compression ratio should I be looking for? I was told no more than 11:1 or I will have to use race gas (100+ octane). 93 octane is common enough around my area so that's what I'd prefer. I was looking at CP Bullet Pistons and Wiseco pistons, what type of piston head will be the best? Dome or flat top? Do I need valve reliefs on the pistons and if so how much? How much clearance should I have between top of piston and deck height? My block is standard deck height (9.025in). I'm assuming I'll need at least a 220cc 23degree cylinder head to hit power expectations? I was looking at some AFR heads but my machinist guy told me he doesn't like AFR heads. Head gasket thickness?
Any advice is appreciated, I just want to build this right the first time around!

 

Flat top with valve reliefs typically give near 11:1 with 64-65 cc head. Thats what id run. Brand dont matter too much the main players all have good pistons.

yeah 600 na will need a good flowing head, one of the bigger 220-227cc style heads will do it easy. The afr 220’s have been popular for this level, and have been good heads. Not sure why your machinist wouldnt like them? Can always order them bare and have him put in the components he likes, or at the very least inspect the shelf afr heads and touch up any machining or clearances as needed. You should do that anyway with any aftermarket parts.

Single plane manifold. Carb or efi you can get one for either application. Is it gonna be a carbed build or efi?

Cam you probably will be ok with a good hyd roller, mike jones cams can do it. Bullet racing might also be a good place for it. Martin Smallwood could too i believe although he is more turbo, but understands engines well. Lots of suitable ppl imo. Could also do a solid roller in a milder lobe and with proper springs, they can run well on the street with little maintenance

 

I’m not sure why he said he disliked them either, I’ve heard pretty good things too. This will be an EFI build. Thanks for the reply

 

Look for combo deals(rotating assembly kits). A few years back I bought a clearance forged BPE shortblock just for the rotating assembly, block is stock but rest was rated good for 1000hp

 

if you havent bought heads or anything yet, i would suggest contacting someone and have them put together a package for you to hit your goals. eric weingartner or chad spier are a couple of names that popped into my head.
basically, they could set you up with a set of pistons, heads, valvetrain, and intake that would hit your goal, and would take away the guesswork.

 

Chad Spier has got it going on, good dude.


I had a machinist tell me he didn't like afr either then I brought in my 245 sbc heads for him to look at. He changed his mind pretty quickly

 

600 HP at the Crankshaft is nothing for a 400 CID Build...

No need to go to a Builder for a combo.

I agree with Orr89RocZ that for 400 CI, an Intake Runner Volume over 220CFM that flows decently... Like an AFR or Trick-Flow Head.

You can go crazy with a more Track oriented Head, like Brodix... or go crazy with Porting, like going to Eric.
But it is not necessary for 600 HP... I used to do a Valve-Job and Pocket/ Bowl Porting to the old GMPP Fast-Burn Heads and make well over 600HP (400 CI).
And those GMPP Heads are small in comparison.

I like to run approx. 11.5:1 Static Compression in a build like this...
The Camshaft/ Valve Events that I would chose will bring the Dynamic Compression down to Pump-Gas 91 or 93 Octane Safe use.

I would recommend just having Brian Tooley Spec. a Camshaft/ Valve Springs for you.

 

https://www.chevelles.com/threads/42...esults.481081/

this was a 421 and a decent solid roller. Afr 220. Made 604 i think

 

the only things I have so far are block crank and rods. Will definitely look into contacting one of these guys. Thanks for the reply it helped a ton!

 

I have a coworker with a 406 sbc 10.3/1 cpr on 93octane and he swears that I’ll have detonation if I run any higher than 10.3/1 cpr. How did you get 11.5/1 on 93?

 

My 421 is 12-1 compression, and it runs on 91 pump gas no problem.
It's all in the cam.
Mine dyno'd at 657 crank hp on 91.
A 406, with 11.5-1 compression, and good heads will get your goals

 

Just as LB9GTA said...

The Static Compression Ratio can be that high, as the Camshaft/ Valve-Events essential lower the Compression Ratio (Dynamic Compression).

To simplify things, you can think of it as Valve Overlap (both Valves open at the same time) venting the atmosphere in the cylinders that would be otherwise compressed.

 

appreciate all the information, really helping me out.

 

Update: After hours and hours of research I think I have a good parts list together for the shortblock.
Here's what I went with-
-Molnar Forged Crank 3.750in stroke
-Molnar PWR ADR H-beam rods
-UEM Icon Forged Pistons/Mahle rings
-Clevite bearings

All of the reply's and advice is very appreciated, I will be posting more about the build as it progresses!