My 340/420 Stroker Build

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YO7_A66

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20 months ago, I lost oil pressure in my 340 (70 Challenger numbers matching) and found that the oil pump internal components had many scars, the oil pump screen was full of crud, the thrust surface on the crank was ate up, and my main bearings were toast. (Please keep in mind that the bottom end has been together for at least the last 24-25 years and 4 cam changes.)

So, out came the engine and I stripped the block down and sent it to the machine shop as a bare block/main caps. At the time of drop-off, I was warned that there was at least a 12-14 month backlog. This shop I have used in the past and due to him losing some people during COVID, and another local performance machine shop going out of business during the same time frame, I knew I was in for a wait.

Now, about 19 months later, I received my new 340/420 rotating assembly yesterday. I spent last night cleaning the block and prepping it for paint. Next week I will start reassembling with as many parts from the 340 assembly that makes sense for the new block size.

This block was rebuilt to achieve a 10.7/10.8:1 comp. [pending head gasket selection] with my existing Promaxx/Sidewinder alum heads (63cc & ported to 280cfm], with the K1 4.00” forged crank and rods, +.050” JE Pistons, & ARP main cap studs.

I have two gasket matched intakes (Weiand single & a RPM dual), painted and ready to install and I am currently leaning towards the Weiand single plane. As for the carb, I am re-using my Quick Fuel SS-750-AN-DP and tuning with two FAST analog A/F meters.

I will be reusing my TTi 1-5/8” step headers, 2.5” x-pipe, and 2.5” Hooker Max Flows, then 2.5” exhaust over the rearend to a set of Classic Chambered 2.5” bullet style mufflers, then out through the 2.5” RT exhaust tips.

Since this is the numbers matching block, I don’t want to spin it up past 62-6400rpms. Plus, I don’t think my 280cfm heads and my two intake choices will allow the rpms to go up past that range on 420ci, as a guess.

Since I blew most of my budget on the rebuilt short block yesterday, I am now looking into a solid flat tappet cam. I am aiming for 515-525’ish range on the torque and hp if possible. I do not have AC or power brakes, and I never will. As long as I can tune this new combo to have a decent idle quality at a stop light (in D) with my foot on the brake, I will be happy.

The 727 has a 9.5” Dynamic converter. It flashed to 3800 with the 340 and a 226/238 hydraulic flat tappet cam. I did not get a chance to check the flash with my last 234/238 solid flat tappet cam, before I lost oil pressure, which caused the block re-build. I am assuming that the flash will move up a few hundred rpms with the 420. I am running 3:91 gears and Nitto 275’s on the rear.

I will have many questions to come, but for now, I’m just excited to have it back in my garage!
 
Thanks guys.
I have the later Weiand 7545 and thank you for posting that cam info and I do believe I know which member is running that cam.

This car is a streeter and the two solids that I have spec’d so far fall in between 247-250 and 252-254 with final lifts around .580” to .618” after lash and apx geometry loss with my 1.65 rockers.
But I will stay open for suggestions as I have a few more weeks before I order the cam.

Thanks again!
 
YO7_A66 said:
Thanks guys.
I have the later Weiand 7545 and thank you for posting that cam info and I do believe I know which member is running that cam.

This car is a streeter and the two solids that I have spec’d so far fall in between 247-250 and 252-254 with final lifts around .580” to .618” after lash and apx geometry loss with my 1.65 rockers.
But I will stay open for suggestions as I have a few more weeks before I order the cam.

Thanks again!
Click to expand...
The intake is a Weiand Excellerator? (If you can have it ported, do so!) What size carb will be employed? What mufflers? Who’s stroker kit?

I think your cam duration numbers are right in the ball park w/3.91 gears. I myself wouldn’t look any higher that that [email protected] intake. The converter will not be the best but it will work well for the street just fine enough. IF you dyno it, send in the dyno sheet with the converter to be reflashed. A dyno sheet seals it. My guy asked for one. Since I had none, not that it was a stretch for his mind, I gave him everything detail to everything about the engine, trans, rear gear and tires as well as weight of the car and what it is for and expected.

My guy Joe so “Nailed it!”
 
I advise taking the lifters to a reputable shop that can surface them properly. Poor machining seems to be a major culprit for failing lifters these days.
 
Dang, man! You're fearless with that numbers matching block....lol. I have a 70 A66 Challenger that I have owned since 1979, and it is all numbers matching. 99% of the parts are even date code correct, so when I get to it, it will be a boring stock type resto. Looking forward to seeing how yours goes and some pics. For what @Mean416 was saying about refacing the lifters, check out Powell Machines videos on You Tube. He's in Iva, SC and seems to really know his stuff on that subject.
 
JDMopar said:
Dang, man! You're fearless with that numbers matching block....lol. I have a 70 A66 Challenger that I have owned since 1979, and it is all numbers matching. 99% of the parts are even date code correct, so when I get to it, it will be a boring stock type resto. Looking forward to seeing how yours goes and some pics. For what @Mean416 was saying about refacing the lifters, check out Powell Machines videos on You Tube. He's in Iva, SC and seems to really know his stuff on that subject.
Click to expand...
Yep that's exactly what I was talking about. Look up what they say about the subject on YouTube.
 
Rumble,
The intake is the 7545 Excellerator, and if my budget opens up some I will look into getting it ported. My long-term plan was to end up with the TF Track Heat single plane on this assembly next year, so I am hoping they get them released sometime over the Winter/Spring.

Cam Duration:
I just got in a suggestion of 244/252 with .365”/.364” lobes on a 110 suggestion which falls within that rage too. I don’t feel comfortable with anything much larger at this time for a street car.

The converter was chosen for my old 340 combo at the time. I will run the 3800 and see how it reacts to the new combo.

Muffler Info:
2.5” Hooker Max Flows under the rear seat and a set of Classic Chambered 2.5” bullet style mufflers beside the gas tank.

Stroker Kit:
My machine shop selected the K1 forged crank/rod combination and then ordered the pistons from JE once the block info was known.

JDM,
Fear is exactly what I had when I delivered the block to the shop for this rebuild!! I asked the owner to inspect the block and fix what was needed to make it good for this upgrade. I don’t want this build to get too out of hand, so I am trying hard to keep the rpm expectation down. When I bought this car 23 years ago, the previous owner built the motor as close to OEM as possible. Then I slowly made changes to it over the years and now I just want the exterior of the car to look stock.

Thank you, guys!!
 
YO7_A66 said:
Thanks guys.
I have the later Weiand 7545 and thank you for posting that cam info and I do believe I know which member is running that cam.

This car is a streeter and the two solids that I have spec’d so far fall in between 247-250 and 252-254 with final lifts around .580” to .618” after lash and apx geometry loss with my 1.65 rockers.
But I will stay open for suggestions as I have a few more weeks before I order the cam.

Thanks again!
Click to expand...

I ran the cam mentioned above( the 260/264) on a 10 to 1 360, and now run the same cam on my 12 to 1 418.
It has proven to make excellent power on both motors. I have also had the wieand excellerator( an old stroker street strip favorite of mine) on the stroker I current run, and on previous engines I have had.
Very good street strip choice of single plane intake.
you are correct, you won’t need to run it more than 6200-6400 rpm with this cam and intake, it will make tons of power not much over 6000 rpm.
I ran my 10.70’s Eddie headed stroker shifting it at 6200, with fairly decently worked heads, and this cam and excellerator with the small Doug’s headers . 3350 pound street strip car.
Personally, and I say this as somebody who has used all these parts( and most of them recently) in a street strip car, with a stroker I absolutely wouldn’t go any smaller on cam than the one I am talking about. Certainly not if you are wanting to make true 500-525 horsepower.
 
B3422w5 said:

Personally, and I say this as somebody who has used all these parts( and most of them recently) in a street strip car, with a stroker I absolutely wouldn’t go any smaller on cam than the one I am talking about. Certainly not if you are wanting to make true 500-525 horsepower.
Click to expand...

100% this.

I just went through this with my 421 build. Strokers eat cam and duration. They love it. I went way too small with a 108* 236/242. It made gobs of torque but it wouldn't pull past 5800rpm.

I upgraded to a 110* 262/264 and oh boy did that wake it up! It's mean now.
 
Absolutely! The extra cubic inches along with the extra piston velocity from reducing the rod ratio makes the cylinder heads effectively smaller. Even a lowly 318 with stock edelbrock heads will absorb a whole lot more camshaft than it ever has a right to once you put a four inch crank into it.
 
It appears that a 236/242 is on the small side, and the 260/264 "seems" to be on the bigger side.

What about these two Hughes solids: 250/254 or the 254/260 for an in-betweener? I pulled out their 234/238 solid when I tore this engine apart for this rebuild.

STL5054AS.jpg


Hughes STL5460AS.jpg
 
I don’t think the 260/264 is on the large side at all. Ideally, because mine sees usually a good bit of track time, something 266-268@50 would be closer. Again I ran this cam on a stock stroke 10 to 1 360 previously, and drove it everywhere.
Howards makes all the cams for Hughes. Be careful, some of those lobes, especially the 904 ones, are very aggressive.
I like the cams Howard’s sells better for what you are looking to do.
As a couple of guys have mentioned, big stroke eats up duration.
Buddy of mine who bought my old stock stroke 360 is putting I think it’s a 246/250 solid in the 360. It’s a Howard’s. Again, stock stroke. He intends to drive it 15 miles each way to work in good weather.
I like the lifters with the oil hole in the face, worth the extra, they sell them.
 
JDMopar said:
Dang, man! You're fearless with that numbers matching block....lol. I have a 70 A66 Challenger that I have owned since 1979, and it is all numbers matching. 99% of the parts are even date code correct, so when I get to it, it will be a boring stock type resto. Looking forward to seeing how yours goes and some pics. For what @Mean416 was saying about refacing the lifters, check out Powell Machines videos on You Tube. He's in Iva, SC and seems to really know his stuff on that subject.
Click to expand...

At 500 hp or less with street suspension setup and quality components/machining, is there really that much chance of hurting a block than ~325hp 340 setup?

Limited traction, street stall converter, street gears...
 
If you use the converter in its present state it could even use more cam than the 260 degrees of duration. It’s going to stall and flash quite a bit higher than it did with the stock stroke 340.
 
It can use more cam except every time someone pushes up the duration there pushing up the rpm band the engine will work in which leaves the OP’s comfort zone and the 3.91 gear ratio.

Truth is, any engine you build can use, operate and work awesome with the very last cam at the bottom of the page of the race only list.

Considering he is using the 3800 converter, the cam he selected with the words of him saying he is not to comfortable with going larger is making a wise choice and one I endorse. The old saying of it’s better to error on the small side applies every time to a camshaft.

He can always step up later if he doesn’t like the top end charge of HP.
 
Here's a question for the experienced ones here. For a given converter rpm, where should torque peak occur relative to that rpm? Seems like you could then back calculate a cam selection that makes good sense. Obviously not the ideal approach but if you're stuck with a given converter that's a pretty significant constraint.
 
Mean416 said:
Here's a question for the experienced ones here. For a given converter rpm, where should torque peak occur relative to that rpm? Seems like you could then back calculate a cam selection that makes good sense. Obviously not the ideal approach but if you're stuck with a given converter that's a pretty significant constraint.
Click to expand...

Rule of thumb I have always used is converter flash 400-500 above peak torque
 
Mean416 said:
Here's a question for the experienced ones here. For a given converter rpm, where should torque peak occur relative to that rpm? Seems like you could then back calculate a cam selection that makes good sense. Obviously not the ideal approach but if you're stuck with a given converter that's a pretty significant constraint.
Click to expand...
It’s more along the lines in reverse. The converter should be stalled 4/5 hundred above peak torque. Min.
Actual stall flash will be altered as needed for the duties being asked of the car.
 
Cam Update:
I had a few phone calls this morning with Bullet, and I am going with a solid flat tappet. The cam that I pulled out of this block was a 234/238 SFT, so I might be able to reuse some of the valvetrain.

This cam specs out as a 252/256 @ .050, .365"/.365" lobes, 109 to be installed at 105. The spring specs are 145-150lbs / 350-360lbs for 6200rpms max. I am running Yella Terra 1.65 rockers, so after lash (before geo loss) this specs out right around .585". My Sidewinder heads were ported by Larry Smith (RIP) to 280 @ .550".

I'm getting excited to get this engine back together by Spring.
 
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