The 400 engine with the 3.25 crankshaft 11:1 CR? Destroked 400. I have "seen" and "read" about this is a real power house build but.... I NEVER talked with anyone who built one. It's suppose to make north of 400 HP and run on mid-grade fuel. What size heads & cam was used? Any actual experience?? Thanx 6sally6
I did a 350 crank in a 400 a few years ago. Had it in a Datsun truck, ran great! Had a solid roller cam, double hump heads and ran on pump gas. Drove it to work every day and ran 11.1's with ease. 3.25 crank would be fun also!
The 350 that GM should have built. Large journal 327 crank and a 400 block +.030. I have but there is a draw back now. No one makes thicker bearings any more and spacers are hard to come by. With bearing spacers you have a tendency to get hot spots. If you are willing to spend the cash, you can probably get a **** crank in 3.25 stroke and 2.65 journals. To run on mid grade @11.5:1 you will need to do two things, 6" rods and aluminum heads. Most people just use edelbrock heads. Or if you want to spend the cash brodix or trick flow both make excellent heads. The Trick flow heads will be a little less pricey. 6"rods are not as pricey as they once were, or if you have access to a good machine shop and can find them the Ford 300" 6 uses a 6" rod. you have to thin them out a bit on the big end of the rod. Choose a cam shaft to suit your build. Mild to extreme. I do not know about where you are but around here 400 blocks are as rare as hens teeth. The short track guys have pretty much used them up. Good luck with your build.
Here is an old thread on a board called Yellowbullet talking about that. 3.25 stroke in a 400? | Yellow Bullet Forums I'm thinking that circle track cl*** racers were trying the combo in low buck cl***es. On a lot of those tracks as long as your measurements work out to X ci or under life is good and you can't spend over Y $$ on the engine. -
I've often wondered this too. Seems like I hear about 400 cranks in 350 blocks all the time, which I'm sure makes more low end torque but I see those engines getting put into light weight vehicles, sports cars and T buckets and I wonder why? Wouldn't you want a big bore and short stroke in a light car?
I heard that the 355 c.i. limit, in Cup racing, was accomplished with a 3.25 stroke and a 4.125+ overbore as necessary. That is very doable with a dart or World products block and large journal 327 crank. For maximum benefit ,it might require cylinder heads with modified valve spacing. Not a problem for Nascar or any serious racer but good for 9000 rpm?
I am more intrigued with the Dart SHP block with a 4.125" bore and a 3.25" crank that Joel mentioned above. I have been pondering trying that one myself. I can't decide on that or a 4.125" bore and a 3.00 crank stroke. Which would work out to about 320 CID.
I have done 2 they were a**** the most surprising builds I've done The first used Off the shelf 400 6 inch for rod pistons and modified 300 Ford rods don't do that the amount of heavy metal to balance the engine was more than the cost of 6.25 after market rods . The engine ran a mild Comp hydraulic roller Edelbrock heads 10 75 compression on 89 obtain gas. The engine went in a 2900 lb Datson 240Z street car on 245 /60 15 tire through the exhaust 11.70s and 120 mph. As far as the Comp cam it was around 215 deg @ .050 on 114 lobe centers very street able. Without an over bore it's a new style 348.
Mine would be with all aftermarket parts. There would be almost no GM stuff in it, just because it’s cheaper in the long run.
Benefit would be big bore high rpm. Agree thick bearings aren't around and spacer bearings get far less reliable at higher rpm. Aftermarket crank and / or block would be the best way to get there. Ability to do your own machining also helps. Most custom engines shops don't want to deal with odd machining on factory stuff -they'll tell you to go buy a new crank. If you wanna go the other direction, I have a 4" stroke Cola crank with 350 journals, needs rear thrust repaired.
Back in the 70's we were running 350's in the sprint car. You could get a LT1 short block from GM for about $1200.00. It had all the good Chevy performance parts. To get more cubic inch I built a de-stroked 400. It had a 400 block bored 0.030 over, 350 crank and rods (same as in the LT1), special TRW pistons and the thick main bearings. I calculated it was 372 cu in. That was the best overall engine I had. I was running the Chevy performance angle plug heads, crane rockers, a Racer Brown roller cam, Hilborn injection, vertex mag and methanol for fuel. I did some USAC racing and they had a 355 cu in limit. I was swapping the de-stroked 400 for and LT1 short block depending on where we were running. I also built a stock bore and stroke 400 small block. It ran well, but the Clevite bearings wore the rod journals oval on the stock cast crank. Sold that short block to a drag racer who turned the crank and ran it for quite a while.
I think that a lot of the benefit of the combo is the long rod like Smokey said when ask on how long of a rod to run answer the longest that will fit.
ALWAYS a good discussion! I think Joe Sherman said....."long enough to connect the crank and the piston". 6sally6
This was a really popular engine to build back in the 1980's when the 400 blocks were easier to find. I believe it was a 377 c.i. once destroked, and they were pretty cool and fast. Then guys began building long stroke 350's and making the more popular 383 stroker. It was easier because there's no shortage of 350 blocks, and rotating ***emblies were fairly cheap to build these.
I had this discussion with a machinist I respected about 25 years ago. I liked big bore, short stroke, high winding motors. He told me "Don't de-nut a 400. The longer stroke builds more torque, and therefore more horsepower." Today I'd build a long stroke 400, probably 434. Parts are easily obtainable to make 550-600 hp. Devin
A common build around the KC dirt tracks was 4.125 bore and a 3.48 stroke. IE 350 crank in a 400. It came out to 377 and was a screamer or could be. I screwed several of those together in the '90s. There are so many combos for small blocks and limitless possibilities.
With availability of fairly low cost and lightweight high performance cranks, rods and pistons, I think a big cubic inch small block, 4.125 bore and 3.875 or 4.000 stroke for example, has more potential. I do agree if in a cubic inch limited cl*** racing, that the 4.125 bore 400 block and 307/327 large journal 3.250 crank was/is a great combo. But now you can get nearly 80 more cubic inches (427 with the 4.125 bore and 4.000 crank). With lightweight pistons and rods, it will rev plenty and make more power and torque; mostly because the additional 80 cubic inches. Use an aftermarket block to ensure crank clearance and a stronger base to build on.
Depends on what you are doing with it. Sure it will cost exactly the same to build 454 CID of sbc, but how will that work out for a daily driven street car? I have always wondered if you could get the same drivability out of a big CID small block as a small cubic inch motor. Taking into consideration the average cruising RPM is 1200-3500. Are you gonna get 8 mpg vs 16 ? Just thinking out loud here.
I had a 377 with a cross-ram, back when I was an idiot kid. Now that I am an idiot adult, I do miss the 8,000rpm redline, the manual transmission, and freeway gears. That was the first car that I lost my license in. That was the same day that the speedometer needle went past the line-of-sight, and never came back!
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