Peak HP from LA block w/ no problems

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tom340

tom340

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For anyone who has built a killer STREETABLE smallblock based on early 340 or 360 block. Up to what HP (no guesses, documented) did you make safely?
One reference i have says "no more than 450 HP safely" from a factory LA block. Im assuming they mean for extended durations like circle track or something, not street or occasional strip.
Im mostly interested from a reliability standpoint. I'd rather not build something I'll soon break.
 
use main stud girdle
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The nicest and most powerful I've built wasnt dyno'd...lol. But, with good machining, very good parts, and good assembly, 600hp is about the highest I've ever seen. NA anyway. Running a cast $330 crank, heavy rods, and decent pistons, and sticking in main studs, will be safe well past 500. The problem is cap walk. Mopars dont have enough meat to make a 4bolt conversion bulletproof. So the best design uses better caps, mains studs, lighter internals, and a strong crank. Reduce the flex and harmonics, and you increase the HP capacity of the material. You have to build to stay away from detonation or the caps will start to flex at the 500hp level. The one I built is 2 years old in CA, has 2 bolt Program caps on #1-4 mains, Callies crank, solid roller cam, Shady Dell ported Edelbrocks, ect. It should be making in the 550hp range on pum pas. But he wouldnt dyno it for me...lol.
 
question.... if i ever built another car liek a 360 but i followed one of the 318 400hp builds with better heads and more stroke will i make more power then what 318 makes by jsut following one of the pre built 318 builds?
 
OK, so I can assume its safe to say I will have no conceans using a "factory LA block" -1970 340- to build a mild, streetable stroker.. Im not looking to persue a raging 10 sec. 565 HP engine build by any means, but I thought what I read in this article that 430-450 was a "maximum allowable" figure and personally I thought was a tad conservative.
 
moper said:
The nicest and most powerful I've built wasnt dyno'd...lol. But, with good machining, very good parts, and good assembly, 600hp is about the highest I've ever seen. NA anyway. Running a cast $330 crank, heavy rods, and decent pistons, and sticking in main studs, will be safe well past 500. The problem is cap walk. Mopars dont have enough meat to make a 4bolt conversion bulletproof. So the best design uses better caps, mains studs, lighter internals, and a strong crank. Reduce the flex and harmonics, and you increase the HP capacity of the material. You have to build to stay away from detonation or the caps will start to flex at the 500hp level. The one I built is 2 years old in CA, has 2 bolt Program caps on #1-4 mains, Callies crank, solid roller cam, Shady Dell ported Edelbrocks, ect. It should be making in the 550hp range on pum pas. But he wouldnt dyno it for me...lol.
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Thanks for specifics...Im looking into the MP forged crank, unsure to go w/ the 4.00" stroke or the 360 stroke with 340 journals. Spending top $$ on good pistons, and a balance/blueprint. Also staying away from comp. ratio thats too high. Need to keep this cool with my factory cooling system which includes a nice 4 core and fan shroud. It looks like I'll be safe and wont need to get into a 340 replacement block or siamese block..
 
Tom, What do you want out of the motor ? Are you going to use the original block for your car ?

If your going to stroke it go with the 4" crank. Its the same price as the 3.58", no reason to give up free torque.
 
I agree with Adam if you are going to stroke it then get the 4" crank. If you are going to run the 3.58" crank you might as well leave your motor alone, store it and build a .040 over 360.

Chuck
 
AdamR said:
Tom, What do you want out of the motor ? Are you going to use the original block for your car ?

If your going to stroke it go with the 4" crank. Its the same price as the 3.58", no reason to give up free torque.
Click to expand...

Dis is da deal..motor is (secret) tired, and needs rebuild anyhow. I used to drag race my Challenger years ago and since technology has changed so much for the better since the mid 80's, I am looking for fast again-faster than what I even had.
Im using Hughes Engines for everything. They will put together a nice package and port match everything, instead of going ala-carte for parts they will do nice on the price. My brother has used their stuff for his BB Chally ,an extremely streetable 383 making over 500 hp-he's "sorta in charge" of my motor. He knows his ****..Anyhoooo, Im just trying to fit a stroker kit into my budget. He prefers I stay stock stroke and put the money into roller cam & rockers. He convinced me the stroker kit will add $2500.00, but in fact I found thats not the case as you can stroke it with no additional machining except for block clearance. I WAS concerned the 4.00" stroke would put it way over the top for power and possibly leave me open to damage the block. I prefer to have a motor w/ more torque vs. a screamin' high RPM 500+ hp.
Yep, Im using the original block. That is if the machine shop gives it a clean bill of health. My motor aint NEVER been apart, ever. Car has just over 100K orig. miles. Spending $$$ on a replacement 340, nah. I'll wait till I hit lotto. Will be fine, aint for strip use. Musclecar, streetable, fast & reliable.
Im just taking the side of "caution".
 
If 500 hp is the goal then you really need the 4" crank unless you can live with bad idle, No torque, race gas, low gears and a loose converter.

My 340 made 478hp with a stock stroke but its got well ported iron heads, 11:1 compression a 265 @.050" .580" solid cam and made peak power at 6900rpms. it will most likely be a pig on the street till it gets up to around 3500rpms. It barley made over 400ftlbs of torque and even that is at 5400rpms.

Go with the 4" arm, You wont be sorry. Dished pistons will keep compression down.

Are you going to keep the stock looks under the hood ?
 
I used a 360 block bored .040 with a forged 4" stroker kit. No girdles, Stock Main Caps, Stock Main Bolts
Graph below are the chassis dyno numbers add at least 15% for Flywheel HP/TQ
This car has been made about 20 1/4 mile runs and 15 dyno pulls along with several thousand miles of driving... never had a problem...yet....

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Also you an get the stroker kit for under $2500. Pistons will cost the same no matter what stroke they are form, You need to either redo your stock rods or replace them with something better anyway so that wont cost you anymore.

The only thing that will add price is the crank, $300 for a cast or $800 for a forged. I would ask around too and see what people have paid for balancing there 4" cranks. Mallory metal isnt cheap and I hear the cast cranks take more to balance out then the forged so the price difference between the two cranks may be a wash after ballancing.
 
Interesting post/thread.

I did one a while back but it was 408 vs procharger..Would be up in the same h.p range as some of these engines.A procharger alone would put you up and over the h.p of a stroker and have more longevity

Im going to be building a twin turbo 360.Should be over 600 h.p Im thinkin.Also reliability should be good as well.Turbo doesnt punish an engine like hi compression or more rod angularity from 4 inch stroke.

Chrysler did warantee thier little 4 banger turbo's after all!
 
Adam is correct about the mallory metal; I just had a 4.00 cast (Scat) crank balanced about three weeks ago and it took a couple of chunks to get it right. When I saw the bill I was shocked at the cost of the mallory metal. I don't have the bill in front of me as I post this, but I can get the specifics later today if you're interested.

Ray
 
Last I heard it was around $60 a chunk. And if you need a half piece to balance they will charge you for all of it. You can easily end up paying $150 for mallory. I think the Forged units dont need as much but I may be wrong.
 
Here's one of my favorites...

http://chucker54.stores.yahoo.net/340focrinbaa.html

Callies crank, Diamond pistons, Hbeam eagle rods, rings, bearings, internally balanced, $2050. It literally drops in, and you'll never break it.

A few notes: Cast cranks are always light in the counterweights. Mallory is up to about $75/slug, and you'll need at least two in most cases. Personal opinion, SIR rods will never be used in a build I do. I have used stock re-done rods over them, and I'm happy doing that. If you plan to use iron heads, and you can get away with them, the new Engine Quest Magnum heads are very, very nice for a street engine, about 2/3rds the cost of Edelbrocks when done, and with practice can run the old style valve covers. Get the dished Diamonds, set the quench right, and cam it right, and it will be amazing. Std open chamber heads can be used, but you'll be limimted to either dished tops down in the bore slightly with big chambers, or flat tops with big chambers and a big cam. Because the cylinder pressure goes way up with a 4" arm, and the smaller cams will ping. If you have power brakes, that is a big deal. Dont be afraid of overcamming, and dont be afraid of using too large a carb.
 
I have no "set" goal of HP. Like I said, I rather have a motor with more torque vs. a 500 hp screamer. Cant emphasise enough, Im not into putting a high RPM drag motor into a street musclecar. Its never been an option, and the thought has never crossed my mind. Not into needing to change plugs because i stopped for a traffic light. Been there, done that.
--My initial concern was just to be sure the HP figure quoted as a "safe zone" was conservative. {It must be, because if you take a stock spec '70 340, put good headers& exhaust, intake & carb, and a well matched camshaft you just added 80-95 HP over a"healthy" stock 275 hp motor. Hughes stage II heads with an airgap intake will add 50 or more HP. Your right at 425-435 already.}
--So just based on those facts, by doing a 4.00" stroker crankshaft the engine output wont diminish.. So knowing that it WILL be making MORE than 430 HP, brings me right back 3 paragraphs. "My initial concern"......I just dont wanna build something Im a gonna break :) .
--from the various parts list and specs ya'll provided for me (thanks!) looks like I'll be just fine. I have to say compared to some of the dyno graphs posted, Im looking to be a bit more streetable. I'll be letting the fine folks at Hughes Engines match me a good cam . The wildcard is IF we decide to stroke..will dictate what cam is best.
 
When i built my engine last year,i was on the fence on which to build 340 or 416 stroker,i'm so glad i went the stroker route..i'll stroke all my small blocks from now on,love the way this car runs consistent 11.0's and with a stock block too,and SIR rods..don't believe everything you hear,theres a set holding up quite well,in my engine and this after almost 2 seasons of beating the crap out of it at the track..
 
You can add me as another running SIR rods for almost 3 seasons now and also running low 11's



Chuck
 
The SIR rods are and arent bad. When you first recieve them, go over to your machine shop and have them take a look at them. Do this BEFORE you put it together, that way you can send them back and ask for a refund from Eagle, hopefully without any agruments.

You talk about Hughes alot and I like that. Hughes is a good shop for Mopar and I havent really heard anything to terrible about them. I suggest you take a look at there tech section. Look up the 360 "LA" Stage 1 Dyno Test, 360 Stage 3 Dyno Test, and 408 & 416 Stroker Dyno Tests. I would pick one of those builds and do it. I am some what following the 360 Stage 3 Dyno Test, but a little of my knowledge thrown into it. Good luck and happy cruising!
 
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