De-stroked Hemi possibilities?

For a racing class that requires pre 74 American production iron block and heads, with a 370 cubic inch limit, naturally aspirated, where maximum power is everything, how do you think a 4.25 x 3.25, high rpm Hemi would work out? I already have a set of iron heads that will flow 420i 315e. The Wallace calculator says these heads at this cid will make 900+ horse at 10,000 - 11,000 rpm. How high can this size hemi reliably rev, assuming all the best stuff?

What has been done like this already?

How would you build it?


Thanks, Joel

You would have to talk with either Ray Barton, or Charlie Wescott about this type of stuff, as SS/AH engines are turning those kind of RPM's.

John Hagen / Charlie Malyuke B-Block Pro Stock baby Hemi

There are a couple of engines still floating around. But I don't know if they are for sale or how much. It would be expensive to fix or duplicate.

Sounds like one of those classes where the deepest pockets win.

Also, no welding is allowed other than repairs. So I couldn't convert a low deck block. It would have to be a Hemi block.

Maybe a guy could convert a low deck without welding? I'd have to take a closer look

You're a smart man. You know darn well it takes more than money to win. The whole purpose for this class is to keep costs down by eliminating aftermarket blocks and heads, NASCAR motors, blowers, nitrous, turbos, and all that expensive stuff. But any real racing cost money.
Here's a topic that you will appreciate more:. bucks down racing

I’m pretty sure I know what your thinking is on this Joel.... you need to focus on one thing at a time.

One thing at a time? That train left about 40 years ago

Does that work though? Not sure if you are allowed the same mods but thought I read SS/AH hemi heads were something like 30k.

Those have a lot of welding/epoxy I believe however.

Are you allowed to do anything similar or need to keep original port locations?

The other possibility is the G1 354/392 Hemis....We have a couple of them around here in the gasser AA class running in the 4's in the 1/8th mile....Blown of course, but they rev them up there real good. They were supposed to come out with a new 392 G1 Hemi block last year, but it seems that's not happening. That would have been the direction I would have tried. You would need to call Oddy on his setup, its a wicked 4.8 car....

So if I were to attempt it with a G2, I would say a low deck Hemi block would be where I want to start if that's even possible. Wasn't one of the new block manufacturers making a block that could be machined as a Hemi or a Wedge? If he has a Low deck, that would be awesome. Use a billet center weighted crank, and go from there....Its the block that will be the issue I think...Barton already has the high rpm rocker train figured out, so its a great place to start with a SS/AH that's de-stroked...

One other thing....Lets just say you built it, and it worked, and you won a race....They would ban you as fast as they could.

I think the only thing that works to really hold costs down is a claiming rule like they have in circle track.
I've seen bracket racing cars that I'm sure are a strong six-figure operation.

from my efforts in my drag week hot rod coupe, I've learned a lot about the drawbacks of the first gen Hemi in naturally aspirated, mainly a small bore that hinders breathing. I know in naturally aspirated, it's a lot easier and cheaper per horsepower to build a Gen 2 Hemi.

It needs to be a production block, no aftermarket blocks. One thing I'm getting clarification on is if the Mopar performance iron replacement Hemi block is allowed.

What bore and stroke are you looking at?
I remember the destroke 366 C.I. Pro Stock gen 2 Hemi not running that good compared to the other longer stroke 426 hemi motors being used back then
I'm thinking a 4.310 bore with a short enough stroke to make your goal with ultra light good pistons may fit your needs

Late 70’s technology :

.030” over standard Hemi block, 6.96” NASCAR rod (can you say heavy?), standard 3.48” Direct Connection crank, DC race piston @ 12.5 to 1 (can you say heavy?) with Dykes rings, stock street Hemi heads port matched and bowls cleaned up, .750 roller, Rat Roaster manifold, auto trans, 10.5 x 30 tire. A/SM. Ran 10.30’s at 133+. Never could hook it up, but it ran out the back door like a freight train turning it 8500. Never broke anything and it was raced a lot.
This same package we went to a tunnel ram with 2 dominators, ported the heads - I think they flowed 350-370 back then, at 3400 #’s in B/MP went 9.70’s.

Current technology, light Diamond pistons, light rods, better valve gear, better intake, scrapper, who knows what that is worth.

You're at the bottom of the learning curve. Very little tune-up data crosses over.

That's why I'm asking.

Good info, thanks

Porting and milling of heads OK, epoxy OK, no brazing or welding on heads or block. Block can be decked up to .125.

What induction system is allowed, sheet metal ? Carb rules ?
Vacuum pump allowed?

That A/SM motor used a single 850 with choke tower in place.

By the way, I have one set of new .030” pistons and rods from the backup motor we never built. I also have good used 3.48” crank, full radius fillet if you want to try and build one on the cheap (cheaper).

I'm pretty sure this question or something like it was asked awhile ago. Bob George answered and I believe he said they were a hand grenade waiting to go off. Could be wrong though on his answer, Im getting old and my wife tells me I cant remember anything. I would check in it further if it was me. Although I like the idea.

Any intake, any carb(s), mechanical injection OK. No EFI. Points distributor or magneto only.

Transman, what is the rod journal dia on that 3.48 crank?

I'm not sure if you know Ron Flood...............North Branch , Mn. , but soon to be up Pine City way.
I believe he has a set of the B - RB to Hemi conversion heads , and Lord knows what else he has squirreled away , but he might be a good brain to pick for a project like this.
Cedar Machine.( 651 ) 674 - 8365
He is semi retired , but I think he would not be opposed to any project that was cool or interesting , and this sounds like both.

Unfortunately, I know Ron. Never again.

Standard B/RB - 2.375” with standard mains - 2.750”.
I also have a longer set of NASCAR rods at 7.06”.

I never learn.

That's good info to consider, Boff. What is the highest rod/stroke ratio that will still pull hard enuff on the intake to make big power?

Never mind, I'm sure it will be successful.

Good luck with your project

What about destroking/sleeving a 383/400 with Max-Wedge heads?
Custom/welded intakes allowed?

In the end, I think a destroked hemi....... done without reinventing the wheel...... would likely make as much of more power than anything else you could come up with using factory castings from the competition.

A slightly stroked Boss 351 would also be a good option.

All theory again. Empirical data. We tried a shorter rod versus the production long rod (6.960”) and the short rod lost power

In every situation. In the cas of both these engines it was solid tenth off the mark.

Stick with what works.

MaxWedge Joel just wouldn’t be right... I’d have to change my contact list in my phone then.

Can you move the lifter bores around? The Wescott and Barton stuff all has the lifter bores moved, to straighten out the pushrod geometry. They have done for years.

We tried that before the de-stroked Hemi. 361 block. 348 cubic inches, port matched maxwedge heads, single 4 bbl. Ran it way past 8500.
4 speed. I think you would be hard pressed to get close to Hemi power even with state of the art raised port maxies.

Valve train would be easier to sort out on a wedge.

Yes that would be legal. Big can core/can bearings ok too

You know me well, Jeff! Hemi Joel without a Hemi is like JericoGTX with a powerglide.

I had a 396 hemi a long time ago in my MP car. It never made the power that I thought, at least on my budget. I was better off with just running the weight to match the cubes.

Here's how you do it

You start with a 400 block because you want the B-engine mains. Make two 3/4" thick deck plates to adapt the Hemi heads to the wedge block while simultaneously bringing the deck up to standard RB height. You want that extra deck plate thickness so you have a better angle at grinding clearance for the pushrod in the block valley without hitting water. You also need the extra thickness for addressing the inner head stud mis-match, & oil drainback.

Bore the 400 block & the deck plates to accept sleeves pressed through BOTH the plates & block to get the bore down to 4.25". The cylinder walls will now be super thick & tied together nicely.

Next, take a B-engine crank & destroke/offset grind it down to big block Chevy size on the rods, taking it from 3.375" down to 3.21". This will yield a 364" engine with room to bore/hone during rebuilds.

With a 3.21" stroke, 7.1" rods, & a 10.725" total deck, the pistons can be a convenient stock or near-stock height, but will need a big-*** dome to make any compression. The typical 12.5:1 race hemi pistons might be a cheap route if you can come up with a 7.1" rod to handle the pin end at a price to make them worth it.

There you go, a wedge based 364" Gen II solution that might actually be cheaper than building the real deal. Go forth & go fast.

THE BIGGEST PROBLEM WITH THAT KIND OF RPM IS STABLIZING THE VALVE TRAIN. RAY BARTON AND JESEL ARE NOW GETTING A HOLD OF IT AT 10500. ANYTING MORE THAN THAT I DONT KNOW.

To bad they don't allow aftermarket blocks, Indy has or did have a short deck Hemi block.

Are the rules listed somewhere?

Interesting idea there, dad. I like it!

Lsp, the rules are in a book, nowhere online. Pre-74 iron production block and heads, block decking up to .125, 370 maximum cubes, no EFI, magneto or points ignition only, no welding on blocker heads unless it is for repairs. That's pretty much the rules for the engine.

#230 400 block, add bolt in head bosses for upper head stud retention, aluminum main caps, hat sleeve to 4.185" (best ring packages at that bore), 3.350" 8 CW crank, 1.777" rod journals, GRP 6.400" aluminum rods, Gibtech LW COM balanced vertical gas ported billet pistons, .866" x 2.000" x .180" DLC pins, .6mm, .6mm, 2mm Riken ring set, Jesel cam drive, largest cam barrel that will fit, Jesel lifters, 290/275 @ .050 cam - lift depends on heads, Jesel rocker gear, largest pushrods that will fit, largest box/kickout pan that will fit, std volume oil pump, 2"/2.125"/2.250" headers/merge collector, offset heads down .030".

That's a good start, similar to what set the NHRA PRO STOCK speed record in 1981 at 165 mph, when they were real Hemis and small, but with a few updates that would help hp.

Awesome detail, thanks I like the idea of the bolt in head stud bosses. I never thought of that. A dry sump is okay if that would help

Yes, used on BBC's in Pro Stock back in the day on blocks that didn't have the 4 extra upper head bolt bosses.

Yes 4 compartment dry sump by all means with 20ish inches of vacuum.

So the only reason that I can see to use the low deck block and give up the strength of the Hemi block is to improve the rod stroke/ ratio. Is it worth it?

Mechanical stack injection would probably be the hot ticket for induction.

How much horsepower will this thing make?

The low deck block is stronger than a RB/HEMI block. Thicker main webs, Shorter/stiffer cylinder wall, shorter pushrods. Shorter piston. It all just adds up to a better package.

What makes you think that? It's only two bolt main. The Hemi has better iron in it and I thought that the main webs were improved on the Hemi block.

I probably wouldn't phrase it exactly like that. Yes, most people feel the low deck block builds a better wedge for the reasons you stated. But that doesn't mean it make a better Hemi. The pushrod angle gets even worse if you make a Hemi out of a low deck. Thicker main webs don't make up for the cross bolted mains on the Hemi block. If he wants a Hemi, there are still some of the old Chrysler 366 cu in Hemi cranks out there. And new light weight rods and pistons are easily available.

So if you decked a hemi block to 10.6 and went with the 3.35 crank and 6.4 rods, would a 2.52 compression distance be a problem?

Maybe wouldn't be too heavy if a strutted piston?

Id have to check with the piston guys.

No to a Hemi block, waaaaay too tall, one of the reasons my combo specs the bore,stroke,and rod that it does. Uses a 1.785" compression height piston. 2.520" piston if anyone would even make it would be a heavy brick, bad idea.

Transman said the shorter rod lost power. Maybe the shorter deck with a shorter piston, gonna need a lot of meat up in the head

I'd fab up a main girdle out of aluminum to help tie the bottom end together, like the Milodon 426 Hemi block was.
That along with the aluminum rods and main caps will be plenty of structural integrity for a 370 ci motor.
Should be capable of 900 hp possibly, at least 9500, maybe 10,000 rpm