Best 273 and 318 builds (NO 360's please)

[Rat Patrol]

Couple of stroker builds - neither of these are "perfect - no port matching, very ordinary headers etc...,

Old "budget" stroker Motor

318/349
360 factory head with 1.88 valve - no porting.
Cast 360 crank journals turned down.
360 DC rods
Sealed Power Forged slug - .100 off the top. Zero deck, fly cut
Magnum 282S Magnum grind (.495 235@.50)
LD340 - 800cfm TQ modded.
Cheap TRi Ys / Twin 2.5" system, magnaflows
3.9 gears
904 - 3400 stall
Road tyres -

3650 lbs
13.18 @ 103.9MPH (1.91 60ft.........genuine road tyres!)
Dyno verified 247 RWHP - Est 320 FWHP.


# 2 Recent "semi-serious" street/strip

318/390
Ported 360 587 heads (243 @ .550, 2.02 valve)
4" crank
KB Forged IC846
10.3:1
Comp XS282S - 237 / .520
M1 SP, 800cfm AVS Thunder, 1" Super Sucker
Re-curved Dist
Cheap TRi Ys / Twin 2.5" system, magnaflows
3.9 gears
727 - 3600 stall



3650 lbs
12.3 @ 110.8 MPH - (1.86 60 ft - ET street radials - still got serious traction issues)
Dyno verified 333 RWHP - Est 420 FWHP.


So there's your apples...take your pick.

 

[benmopar318]

Sorry to disagree KO, but that result has been established as not just a "happy" Dyno result...but clearly "hysterical".....

I refer you to 71340 post - basically the same as SD and made 70 HP less.

No-one I know of has ever got near that 400 HP result with the same or similar build - and that includes using better heads.

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just a question??? the junk yard jewel has big notches on both sides of the bore and also on the chamber side out to gasket line (almost 4.150"???) is this the key??? I am going to do this on my next teen :burnout:

 

[Rat Patrol]

Sorry for the OP for the OT post.

Ben....here's some quotes from the JJ article -

Our plan was to find flow by porting the heads and upping the valve diameter to 2.02/1.60 with a set of Milodon street valves.

Valve shrouding isn't any more of an issue than with other small-block Mopar heads, since as part of the valvejob the chambers were cut concentric to the valve out to near the line of a Fel-Pro gasket. This makes the chamber quite a bit wider than the 318's stock 3.91-inch bore in the area adjacent to the valve.

To address this, the bores were chamfered (notched) to minimize shrouding by the shelf left where the chamber meets the bore. Contrary to popular misconception, 2.02-inch intake valves fit the 318's bores without a problem; in fact 2.08-inch intake valves won't hit.

..........so much for bore shrouding.....LOL!!

At the other end of the passages, the seat area was prepped with a Serdi-machined cut of the chambers out toward the head gasket line to minimize chamber shrouding of the valve. The oversized seat form was cut, along with a 75-degree bottom cut, which greatly opened the port bowls. After machining, the hand-porting involved blending the machined cuts into the as-cast bowls, streamlining the valveguide bosses, then blending and widening the short turn to a smoothly rolled form from the port floor to the valveseat, eliminating the various factory humps in the corners of the turn. The fully ported No. 302 heads with larger valves installed showed an intake flow improvement of nearly 60 percent to a respectable 215 cfm at a peak of 0.500 lift.

Are these low-buck heads? Getta grinder and learn to use it, and the answer is yes.

In other words - either learn to port or spend $1500 AFTER buying a set of 302s.....

Some "junkyard" deal...:wack:......

we employed four-into-one tube headers with 15/8-inch tubes, supplied by Hooker.

More junkyard kit........:shock::bs:

Skipping a low-rise dual-plane, we went straight to the Edelbrock AirGap two-plane intake simply because we know they really work

Must be some junkyard!! :-\"


Anyhow,..thats the flaws in the concept - but I still reckon with the Comp 268 and 215cfm heads will struggle to make 400HP ....

FWIW..Moroso says 400HP is a flat 12 in a 3500LB car/driver.....maybe that will put the dyno figures into perspective......

My 2c.

 

[lomchivok]

bottom end is stock cast crank with 360 floating rods on KB forged .040 over 1.81 CH pistons and chrome moly ring set. Block is squared & decked with the pistons .002 in the hole. Cam is a comp XE268H flat tappet on 1.5 stock rockers. Indy/RHS 62 cc quench heads from Hughes with no port work done but .192/.162 valves with multi angle grind and a .042 head gasket. On top is an eddy air gap with an eddy 600 cfm performer and pertronix ignitor II ignition.

I figure between 9.5 and 10 to 1 comp?? should be at least 350 hp with comparable torque?? I don't know...
The engine is assembled, installed and after addressing the extended accessory mount bolt hole boss issues in the heads for alternator mounts it should be ready to fire this monday...tomorrow Yippee... What kind of numbers do you guys think this combo should put up for hp/torque and 1/4 mile times in a 68 Barracuda 904 with an 8.75 and 3.23 suregrip on BFG 255/60/15's?

I cant wait to see this baby run....

 

[MuuMuu101]

Well, I've got a spare '68 273 block, spare connecting rods from my 360, my old 360 crank, crate engine 360 heads with 1.88" intake valves, a Mopar M1 intake, a Paxton supercharger, and a stock carb-to-pan 273 when my Dart is done. I've thought about building an engine for a pick-up or a wagon. Stroking a 273 would be strange and might provide costly difficulties (machining the crank, clearing the bores, custom pistons, etc.). But the heads with a dual-plane intake and Paxton should make for a fun setup.

 

[Infecteddog]

Well, I've got a spare '68 273 block, spare connecting rods from my 360, my old 360 crank, crate engine 360 heads with 1.88" intake valves, a Mopar M1 intake, a Paxton supercharger, and a stock carb-to-pan 273 when my Dart is done. I've thought about building an engine for a pick-up or a wagon. Stroking a 273 would be strange and might provide costly difficulties (machining the crank, clearing the bores, custom pistons, etc.). But the heads with a dual-plane intake and Paxton should make for a fun setup.

Turning the crank's same as for a 318 or 340. Might be about as much as a new 4" crank on the high end. Not uncommon for 360 cranks to be too worn to get away with a turn-down they could run in a 360. The pistons though- that's where it'd cost.

 

[MuuMuu101]

Turning the crank's same as for a 318 or 340. Might be about as much as a new 4" crank on the high end. Not uncommon for 360 cranks to be too worn to get away with a turn-down they could run in a 360. The pistons though- that's where it'd cost.

So, I've been told. I haven't priced out machining a crank, but I don't think you can get away with a 4" stroke in a 273 without major bore surgery. And I agree, pistons would be the high dollar item. We'll see what condition my engine is in when it comes back. With a 3.54" stroke and stock bore, you're only running 292 ci. The engine only had 8.8:1 compression, stock. With the 360 heads having larger chambers I'd imagine compression would go down to low 8:1 to high 7:1 on the stock stroke. Maybe the stock pistons with the larger stroke and bigger heads would be happy enough to allow everything to clear and compression to be reasonable?

 

[Infecteddog]

So, I've been told. I haven't priced out machining a crank, but I don't think you can get away with a 4" stroke in a 273 without major bore surgery. And I agree, pistons would be the high dollar item. We'll see what condition my engine is in when it comes back. With a 3.54" stroke and stock bore, you're only running 292 ci. The engine only had 8.8:1 compression, stock. With the 360 heads having larger chambers I'd imagine compression would go down to low 8:1 to high 7:1 on the stock stroke. Maybe the stock pistons with the larger stroke and bigger heads would be happy enough to allow everything to clear and compression to be reasonable?

Block's the same between 273, 318, and 340 with exception of bore. Running a 4" crank or the 3.58" 360 crank in a 273 will be just like running it in a 340 except for the pistons. Nothing special below the pistons.

Pretty much about the 360 heads. You're typically talking about 68cc+ chambers compared to 62cc+ chambers, then with thicker head gaskets common- down in the low 8s with stock 2bbl pistons. I'd be curious how easily you could get away with stock pistons in a stroker with the makings of big compression drops that are not uncommon.

 

[RAMM]

Sorry to disagree KO, but that result has been established as not just a "happy" Dyno result...but clearly "hysterical".....

I refer you to 71340 post - basically the same as SD and made 70 HP less.

No-one I know of has ever got near that 400 HP result with the same or similar build - and that includes using better heads.

I've personally done 360hp out of a 318 (321 cu .020") with Magnum heads and a small 205 @.050" cam , 9.1 comp. I dont see why 400+hp is difficult with good heads and a larger cam.

I have spoken with Steve Dulcich and met him several times. I asked him about this build, and why he would perpetuate this myth of the '302 cylinder head. He actually laughed and admitted that people seeking out the '302 head was mostly his fault, after I told him I thought they were total garbage IME.

Now for the good stuff: Those '302 heads were ported with an extremely high level of skill. I have no doubt that the JJ engine made every bit of 400+ HP. Those heads in the article didn't make it off the dyno ! They were ported so aggresively that they began leaking water in the short side. I have worked on those castings exactly once and managed 189 cfm from a stock level of 153cfm--BIG DEAL! They still didn't make any power. Everyone needs to forget these heads and move directly to a Magnum casting. J.Rob

 

[MuuMuu101]

Block's the same between 273, 318, and 340 with exception of bore. Running a 4" crank or the 3.58" 360 crank in a 273 will be just like running it in a 340 except for the pistons. Nothing special below the pistons.

Pretty much about the 360 heads. You're typically talking about 68cc+ chambers compared to 62cc+ chambers, then with thicker head gaskets common- down in the low 8s with stock 2bbl pistons. I'd be curious how easily you could get away with stock pistons in a stroker with the makings of big compression drops that are not uncommon.

I think the problem you'll find with a stroker is that the bores are so small, the rods may interfere. Assuming using the same pistons, but wouldn't the larger stroke raise the pistons in the bores causing compression to increase? Or do I have it wrong?

 

[duster rege]

Block balanced bluprinted 30 overfactory heads lilporting done bigger valves springs lunatti voodo cam double roolereddy 600 carb ceramic headers have no #s but it lights em up good runs idles drive anywere love it

 

[Infecteddog]

I think the problem you'll find with a stroker is that the bores are so small, the rods may interfere. Assuming using the same pistons, but wouldn't the larger stroke raise the pistons in the bores causing compression to increase? Or do I have it wrong?

Yes, and it could result in positive deck height too which would not work well. You'd have to start way with pistons way down in the hole or some folks shave them. The size of the bores won't matter much- you won't have perfect clearance stroking a 318 or 340 either. The 360 crank would likely be fine, but the 4" would need clearanced. As said- it'd take a lot to bring the compression down to something reasonable.

 

[MuuMuu101]

Yes, and it could result in positive deck height too which would not work well. You'd have to start way with pistons way down in the hole or some folks shave them. The size of the bores won't matter much- you won't have perfect clearance stroking a 318 or 340 either. The 360 crank would likely be fine, but the 4" would need clearanced. As said- it'd take a lot to bring the compression down to something reasonable.

I'm still learning about engines, but what do you suppose an extra 1/4" in stroke would increase compression by? 1-2:1 maybe? If I were to do this, and I'm not committing to anything, I would probably do a budget/junkyard build for fun and use what I have. Maybe find a wagon, convertible, or Colt for it. So, 3.54" crank machined down if reasonable, stock pistons if they're good, 360 heads, 360 rods if they're better than the 273 ones, maybe a 340 spec'd cam from Summit, cheap dual plane intake as I think the M1 I've got would be overkill, 500-600 cfm carb, etc. If the compression is low enough, I'd probably just top it off with my Paxton supercharger and throw 4-5 lbs of boost on it.

 

[66fs]

I'm still learning about engines, but what do you suppose an extra 1/4" in stroke would increase compression by? 1-2:1 maybe? If I were to do this, and I'm not committing to anything, I would probably do a budget/junkyard build for fun and use what I have. Maybe find a wagon, convertible, or Colt for it. So, 3.54" crank machined down if reasonable, stock pistons if they're good, 360 heads, 360 rods if they're better than the 273 ones, maybe a 340 spec'd cam from Summit, cheap dual plane intake as I think the M1 I've got would be overkill, 500-600 cfm carb, etc. If the compression is low enough, I'd probably just top it off with my Paxton supercharger and throw 4-5 lbs of boost on it.

If you are going to Supercharge it, you don't need to change anything. Just do it.

 

[MuuMuu101]

If you are going to Supercharge it, you don't need to change anything. Just do it.

Well, I'd need at least a 4 bbl intake as it currently has a 2 barrel and I have a blow-through carb. I have a Mopar M1, but that may be overkill on that little engine. But as the car was being driven, I was losing compression in one of the cylinders before I pulled it out. On very rare occasions, shortly after start-up at a stop sign, white smoke would puff out, but that only happened maybe once or twice. So it either needs head work due to a valve or maybe the rings on the piston gave way. If it's heads, I'll just swap them for the 360 ones. I just looked at Summit and it seems that cast 3.58" stroker cranks by SCAT with the correct journals can be had for less than $400. Probably be better than machining my current crank. Plus, I could say I stroked a 273 to 295 ci and supercharged it.

 

[vc318]

my combo
- 318 +.040"
- block zero decked
- kb167
- aeroflow alloy heads 2.02" intake/ 1.6" exhaust, intake flow 249cfm @ .500", exhaust 183cfm @ .500", 65cc
- 9.7:1
- LD4B
- Electronic ignition
- 273 adjustable rockers/shafts
- quick fuel or holley 600cfm
- looking to get a hydraulic cam at this stage xe268
Thoughts on hp? If I can get 1hp/ci I'll be happy

 

[Lelo Dart]

my combo
- 318 +.040"
- block zero decked
- kb167
- aeroflow alloy heads 2.02" intake/ 1.6" exhaust, intake flow 249cfm @ .500", exhaust 183cfm @ .500", 65cc
- 9.7:1
- LD4B
- Electronic ignition
- 273 adjustable rockers/shafts
- quick fuel or holley 600cfm
- looking to get a hydraulic cam at this stage xe268
Thoughts on hp? If I can get 1hp/ci I'll be happy

At least. No worries there.