Safe RPM for a 408" Magnum?

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jbc426

jbc426

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I had my EFI tuner bump up the stock ECM rev-limiter by 500 rpm, because sometimes it hitting the factory rev-limiter just before my modified 200R4 would shift into 2nd at wide open throttle. I believe he told me the factory rev limit is 6100 rpm, and the trans should shift just above that rpm and before the new RPM limit is reached. I just reflashed it last night and have yet to test it.

The motor has a mild hydraulic roller (214 & 218 @ .050"), a balanced mid-compression Hughes reciprocating assembly with cast crank, I-beams and hypereutectic pistons. The heads are Hughes CNC Super-prep'd Eddies with some additional hand work in the bowls and ports. The oiling system consists of a blueprinted standard volume pump, windage tray and 7 quart pan.

It seems to me that the bottom end should be easily able to handle these moderate rpm's even though the motor is definitely nosing over somewhere in the high 5000 rpm range. Once it shifts into 2nd, it lands the rpm's in the peak power band.

Any information or experience with these motors and rpm limits would be appreciated.
 
if I'm not mistaken, your limiting factor is the valve train

but it seems you are coming at this from the wrong angle
you need to look at your drop RPM when you shift into second, and then look at the powerband
since you will be shifting AFTER peak power, the determining factor on where to shift is the point in the RPM range where the power is the same as the power at the RPM where it drops to after shifting

it might make more sense to get the transmission to shift earlier, rather then try to get a bunch of "empty" revs out of the engine before shifting
 
With that cam I would consider shifting it sooner, not raising the rpm limit.
 
Yeah, the over-rev is surprizingly strong with this little cam. I would still like more top end power, but I love the crispy off idle response and street manners of this current cam.

The transmission has some degree of adjustability with the Throttle Valve adjustment, and I have it dialed in to spec. It didn't hit the rev-limiter every time, so I think a few more RPM will eliminate it from hitting the rev-limit at all. I think the variation is related to temperature variation of the fluid. I'll do some testing over the next few days and verify the issue is resolved.

I love fast cars, so at some point within the next year; I'm pretty sure I'm going to pull the heads to have them fully CNC ported and hand massaged, and then bump the cam size up a few steps to the 230 & 234 @ .050 range.

I'm not sure how much the street manners will be affected, so I'll have to decide if the trade-off in top end is worth it for this particular car. It's my daily driver right now, gets decent mileage and runs very strong.

Alternatively, my compression is in the 10.2 to 1 zone and pumps around 200 psi on a compression test. but I think it's just too high for a Paxton style blower.
 
Now I've done it... the story of my life, spending more money, time and effort to get more power. I just ordered a set of stronger valve springs and a new custom ground roller cam with enlarged specs from Hughes .565" In, .575" EX - 0230* & 0234* @ .050 ground on a 108 degree centerline.

This is up from the current cam with .532 IN .539"EX -214* & 218* @ .050 on a 110 degree centerline. It will take a few weeks to get the custom ground cam, and I won't have to pull the heads to swap the springs. I may just drop the motor out the bottom of the car to make it easier to degree the new cam in and refinish the engine compartment while I'm at it.

With the current cam, the cranking compression is 195 to 200 psi. Dave recommended going to 108* centerline to reduce the compression bleed off their standard SER3034-10 cam would cause if I ran it with 110* centerline.

This bigger cam should idle with authority, maintain reasonable driving characteristics and add a significant amount of torque and horsepower acrossed the board. With an updated reflash, it should be a better combo for my build. More to follow.
 
That camshaft should make power to 6100-6200ish...
 
jbc426 said:
It was either shift sooner or change cams and rev it higher....the choice became simple at that point. :burnout:
Click to expand...

I would of rather fixed the problem with the trans. On your 200-4R, the governor is what controls the shift points. I'm not sure if anyone makes governor kits for the 200-4R now, but you can try this> The governor will have two weights on it. Tack weld a really small nut on each of the weights. This will make the trans shift sooner. If you remove material, the trans will shift later. I use to remove material when I had people swapping in a 200-4R from a grocery getter into their street machine. Same goes for people with the Buick T-types, GN's, Etc. when they blew their trans up. They would get a donor from a grocery getter and be disappointed with the way it shifted and performed due to the early light shifts.

Also, NEVER use your throttle cable adjustment as a way to mend a shift point problem. This will only force your trans into early retirement.
 
jbc426 said:
It was either shift sooner or change cams and rev it higher....the choice became simple at that point. :burnout:
Click to expand...

Yep. I meant the new cam choice should hit your mark...

Ought to run pretty strong! :D
 
diymirage said:
if I'm not mistaken, your limiting factor is the valve train

it might make more sense to get the transmission to shift earlier,
Click to expand...

Normally the valve train is except the cam isn't supposed to be turning that high of a rpm and the real limiting factor here is the stock oiling paths.
Shifting the trans sooner is the answer. If it doesn't do it by itself then you need to look into why and fix it/adjust it.
 
jbc426 - Your new cam specs are similar to the Mopar 380-horse 360 crate motor cam specs: 230/234 @ .050 on a 108 centerline. But you've got more lift.
How are you controlling the lockup feature on your new 200-4R. What type of switch and where did you mount it?
I hope to finally get my trans in soon.
 
My main concern is with the pistons. I will never, ever use a hypereutectic piston in a longer stroke engine because the peak and mean piston speeds in a 4" stroke engine get very close to the limits for them.
I can't see a cam that short making steam above 6K. Peak torque is probably down near 3500 and stays flat, with horsepower around 5500. Raising shift points is pointless givent he cam whether you think it or not. Fix the transmission shift point rather than adjusting the limiter.
 
With a cast lower end, I would recommend keeping it at 6K or less for shifts. Consistent 6K+ shifts will over work the parts you have and result in a shorter life.
 
Hughes 3844AL hydraulic flat tappet cam here, shifting at 6500 typically, I run anti pump-up lifters with nearly 0 pre-load...that does have a noticable 200/300 RPM extra...anyways, stock bottom end, mind you though all rebuilt with 3/4 main bearings.
 
Thank you for all the input guys. Lots of good stuff to think about. The shift point issue when going from first to second was really right on the fence with regard to the stock rev-limiter. I'm pretty confident that the shift point was just so close to the 6100 rpm limit, that around 50 to 100 more rpm will result in consistent shifts into second without hitting the now higher rev-limit. I'll need to do a bit more testing to see if the issue is resolved though. If not, I will definitely be adding weight to the governor.

The car very rarely sees full throttle launches through the gears at max rpm's. It is a street rod after all, though so it does happen on occasion. :blob:

If this was a dedicated track car or even a regular visitor to that rpm range, I would have had more cam in it to begin with and went with a forged bottom end. It is a street car 99.99% of the time and I don't abuse it, but it does need to perform when I mash the loud pedal. It's a small block after all. If it can't handle rev'ing to 6500rpm when needed, something's wrong with it. Heck, I spin my 493 inch Mopar to 6500 rpm regularly.
 
ocdart said:
jbc426 - Your new cam specs are similar to the Mopar 380-horse 360 crate motor cam specs: 230/234 @ .050 on a 108 centerline. But you've got more lift.
How are you controlling the lockup feature on your new 200-4R. What type of switch and where did you mount it?
I hope to finally get my trans in soon.
Click to expand...

Hughes states the cam should put my combo into the 490+ hp range at the flywheel. That should be pretty close to reality. The driveline combo 3.91's, 2.76 to 1 first gear, 3000 stall converter and 275/60-15's make the car pretty quick as it is. The best part is being able to shake it on down into overdrive and lock-up the converter.

I have a fourth gear pressure switch wired to the lock-up solenoid via a 12V wire to a toggle switch. It only locks up in 4th, and unlocks when the trans downshifts into 3rd etc. I normally drive around town with it in 3rd and the toggle switch powered up. Once I shift into 4th on the freeway the converter locks up a split second after. It will unlock as soon as I throw the toggle switch if I want.
 
Yup, further testing revealed that the issue has been resolved. It power shifts hard with no sign of hitting the rev-limiter. Even with a smallish cam, this thing gets up and frick'n goes.

I love the Hooker Aero Chambers. They are nice and quiet when you are cruising, but really let the thing breath when it's wide open. The sound of a 408" Magnum V8 at 6k+ is an awesome thing! I'm sure it could be heard for miles and caused a few smiles.

Now, I'm really looking forward to installing a more appropriate cam for my intended use. Thanks again each and every one of you for your insight and time.
 
besides the pcm flash, what have you done to injection/ignition ? What intake?

I am pulling parts to start a 5.9 with similar cam, just not split pattern. big EQ's, intake undecided, Edel SV EFI or Hughes AG EFI, Big TB etc. Simple drop in 67 GT Vert in place of 318 , Tanks Inc and fuel lines, to demonstrate how easy it is to go EFI with real HP.

Nice build BTW, you ever hit any of the cruises in S OR?
 
magnummopar said:
besides the pcm flash, what have you done to injection/ignition ? What intake?

I am pulling parts to start a 5.9 with similar cam, just not split pattern. big EQ's, intake undecided, Edel SV EFI or Hughes AG EFI, Big TB etc. Simple drop in 67 GT Vert in place of 318 , Tanks Inc and fuel lines, to demonstrate how easy it is to go EFI with real HP.

Nice build BTW, you ever hit any of the cruises in S OR?
Click to expand...

Thanks! I have a Hughes deep ported Airgap with their Big Gulp throttle body feeding a pair of Edelbrock Magnum heads that have been CNC Super prep'd and hand blended by Hughes Engines. The reciprocating assembly is the Hughes Mid-compression cast crank and Hypereutectic piston set-up.

I'm running 39lbs Ford Racing Injectors using a surge tank style fuel system. I currently am using a 3/8" feed and return line from a new stock tank, with a modified 3/8" pick-up and return sending unit that free-flows via a Carter pusher pump through aluminum tube and EFI rated rubber hose & clamps to a pair of Permacool fuel/water separators and then through the Radium Engineering surge tank with an internal high pressure Deutchwerks fuel pump.

The surge tank is mounted up front and flows through a pair of aftermarket fuel rails and back to the surge tank. I've had the fuel level down to less than 2 gallons at the Willow Springs road course with no fuel starvation at all. That is amazing given how easy this system is to convert a car to a high performance EFI rated fuel system with an inexpensive stock tank.

I used a '98 ECM for a 5.9 Ram Pick-up with manual trans from Solo PCM's in Florida without security and a HotWire Auto Hotrod harness. I had Chris at Performance Injection Equipment write the tune, which I loaded with an SCT Tuner. He knows what he's doing, and I can highly recommend him. It's really a cool way to tune a motor using a wideband to provide feedback to him, and then he emails me the updated tunes. I download them into the handheld tuner from my laptop and then load them into the ECM via the OBD2 port. The factory ECM can handle from mild to wild including supercharged etc.

Converting to EFI using this easy to build this style of system is about as plug and play as it gets. I don't have the time and patients to mess with a Megasquirt - figure everything out yourself style system or with custom "baffled" fuel tanks that hardly work better than a stock tank. Some of my buddies went that route and they still can't get below 1/3 tank without fuel starvation issues.

I'll be down in LA for Spring Fling in mid-April and will also hit Track Day at Willow Springs on the Thursday. It would be great if you guys would bring down one of your cars and hang out. It's probably the best hands on Mopar event in the world.
 

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Till it chucks a rod out the side. Then build anudun and don't spin thatun as hard.
 
The hypers should list a piston speed limit, or there should be some online info on that, I believe your cast lower end will survive with good rod bolts. I pulled the bottom out of a stock 340 piston at 6400 RPM just revving it. Yeah, stupid move on my part. I was showing a potential buyer the motor at the time! #-o

I would think a stroker would be cammed for torque more than top end.
 
RustyRatRod said:
Till it chucks a rod out the side. Then build anudun and don't spin thatun as hard.
Click to expand...

I hope not Rusty, but it happens. The rods and rod bolts are pretty stout units, and it was carefully machined and assembled. If it does happen, I'll build an even stouter 408" with lower compression and supercharge the thing with a belt driven, intercooled centrifugal supercharger.
 
jbc426 said:
Thanks! I have a Hughes deep ported Airgap with their Big Gulp throttle body feeding a pair of Edelbrock Magnum heads that have been CNC Super prep'd and hand blended by Hughes Engines. The reciprocating assembly is the Hughes Mid-compression cast crank and Hypereutectic piston set-up.

I'm running 39lbs Ford Racing Injectors using a surge tank style fuel system. I currently am using a 3/8" feed and return line from a new stock tank, with a modified 3/8" pick-up and return sending unit that free-flows via a Carter pusher pump through aluminum tube and EFI rated rubber hose & clamps to a pair of Permacool fuel/water separators and then through the Radium Engineering surge tank with an internal high pressure Deutchwerks fuel pump.

The surge tank is mounted up front and flows through a pair of aftermarket fuel rails and back to the surge tank. I've had the fuel level down to less than 2 gallons at the Willow Springs road course with no fuel starvation at all. That is amazing given how easy this system is to convert a car to a high performance EFI rated fuel system with an inexpensive stock tank.

I used a '98 ECM for a 5.9 Ram Pick-up with manual trans from Solo PCM's in Florida without security and a HotWire Auto Hotrod harness. I had Chris at Performance Injection Equipment write the tune, which I loaded with an SCT Tuner. He knows what he's doing, and I can highly recommend him. It's really a cool way to tune a motor using a wideband to provide feedback to him, and then he emails me the updated tunes. I download them into the handheld tuner from my laptop and then load them into the ECM via the OBD2 port. The factory ECM can handle from mild to wild including supercharged etc.

Converting to EFI using this easy to build this style of system is about as plug and play as it gets. I don't have the time and patients to mess with a Megasquirt - figure everything out yourself style system or with custom "baffled" fuel tanks that hardly work better than a stock tank. Some of my buddies went that route and they still can't get below 1/3 tank without fuel starvation issues.

I'll be down in LA for Spring Fling in mid-April and will also hit Track Day at Willow Springs on the Thursday. It would be great if you guys would bring down one of your cars and hang out. It's probably the best hands on Mopar event in the world.
Click to expand...

I was undecided about RPM AG EFI vs Edel SV EFI, I have both mag and la EQ's sitting on shelf so either way is easy. I have been looking for feedback on AG EFI in light car instead of truck. I will probably grab a AG and Big Gulp on my next order with Hughes. Racer Brown in working on my cam. I might consider using a SCT rather than just flash the pcm on this one so I can make changes. Wide band is almost like cheating:D. I plan on using a Tanks Inc tank and gpa 4 pump since they are sitting on the shelf. Had not figured out injector size yet but 34# seemed like good starting place.

I picked up a 67 GT Verrt thats been restored mechanically but somebody screwed up and the brand new rebuilt 318 knocks bad. I thought I would drop the 5.9 in to it for some fun with the 904 so I can concentrate on getting the 64 5.2/44 RE swap done first. I plan on turning my 69 Dart HT into my "track" car but that project is 6 mo down the road and I need to spin some tires sooner than that.

I will make a Willow run soon, havent been out there for 25 years when I was pit crewing on SCCA Endurance Series RX7. I drove SCCA solo for many years while in So Cal, looking forward to getting back on the track in a cool old Mopar. Thanks for sharing, Evan
 
"It's a small block after all. If it can't handle rev'ing to 6500rpm when needed, something's wrong with it. Heck, I spin my 493 inch Mopar to 6500 rpm regularly."

Couple notes on that line of thinking... The 493 will have forged pistons, and the 408 has a longer stroke and shorter rod than a 440, or 383 for that matter. It is, for all intents and purposes, no longer a small block.
 
493 BB has a 4.15 stroke doesn't it?

4.35 x 4.15 stroke
 
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