Good gen 3 hemi NA street power?

[Grant]

On paper these motors look great vs. an LS: rail mounted rockers, better oil drains, dual spark plugs, better flowing heads, etc. In practice though everyone makes more power with the LS.

I tried my best with a 449 ci aluminum block hemi in my manual transmission Magnum, and only made 540whp on 93. On that same dyno I'd done 567 with a mild cam-only LS7. Details on the build and a dyno graph are below; looks like everyone else has had the same experience as me with NA hemi power:

https://www.challengertalk.com/threads/ ... ld.685799/

Any thoughts as to why no one has made good NA power with these cars? My thought was the intake manifold was not designed for large displacement. The runners are 12" long measured by the inside curve, and 15" measured by the outside. I'll get their inlet and outlet sizes shortly. I did have to open up the end of the runners to match the larger Thitek heads.

One interesting thing was the motor made almost the same power (7 hp less) with a 224/232 +2 117 LSA cam and as it did the current 237/249 +5 117 LSA. Drivability was far better with the smaller cam.

The motor saw significant oil starvation on a road course, and we pulled it yesterday (it needs some refreshing; so any suggestions on where to send it would be great too). I gave the intake manifold to a mechanical engineer buddy of mine to CAD up; we were thinking about 3D printing some different designs to try, in case the intake is what is restricting power.

Thanks for any help.

Oh please don't say "go FI". I have a lot of fun chasing down sports cars on road courses with my Magnum, and sorting a big-power FI car for track use is a big pain. It was originally built for Hellephant power, but I'm having too much fun tracking it. I'd be happy with 600+ whp on 93.

[ProPower engines]

We see a good number of the modern hemi's and there is tons left on the table if your just trying to run a carb program!
I don't get why some guys think for any reason a EFI tune is complicated for race use or street. Again there is tons to improve on them but there are some basic things.
Like what heads and what mods regarding ports chambers valve size etc.
And did you get rid to the VVT set up?? or just using it to turn the cam??
What cam profile?? The 6.2??
Compression ratio are you anywhere near 11-1???

[Grant]

The car is EFI and going to stay that way. It needs to communicate with the PCM over CAN to run things like the air conditioner.

The original cam was CRH57 3722Q / 3726Q. That's 224 / 232 duration, 0.55 / 0.56" valve lift, 117 LSA and 2 degrees advance. The current cam, specced by Lil John, is CRH57 13780 / 13792. 237 / 249 duration, 0.58 / 0.58" lift, 117 LSA, and 5 degrees advance. Both were degreed. The heads flow very well at lower lifts, maybe that's why lift was kept low?

The motor never had VVT because it's one of the old aluminum blocks made by Arrow which were copies of the 6.1 SRT8 engines. The shortblock weighed in at 185 lbs, which I was happy with.

This was the power difference between the cams on a very similar super-conservative road course tune. I don't have a maxed out dyno for both cams, but the newer one made 30 more hp with more timing:

old_v_new_cam.jpg

I vastly prefer the original, smaller cam. I thought it was interesting how similar the torque curves were past 4,000 RPM. I also found it interesting how no one (see the Challenger Talk link above) seems to make much more power than this. The most I've heard of out of a 449 was 570whp in a Challenger on E85. Shops like HHP and Arrington tell me that's all they can make.

Full specs, maybe some stuff I forgot to mention in the link:

• Untouched Thitek heads with the largest (2.2") intake valve
• 4.185" bore, 4.08" stroke
• 11.6 CR (seems a bit too high)
• Ported and port-matched 6.1 intake
• 2" Kooks headers
• 90mm Arrington throttle body. I see 98 kPa at redline, so it could gain a few horses with a 100mm.
• TR6060 manual transmission
• HPTuners
• 12:1 AFR (it's very insensitive to AFR changes so I left it safe)
• 18 to 20 degrees timing advance on my aggressive tune, knock-limited on 93 octane, as measured by plug reading and a Plex Knock Monitor
• Demon injectors
• Piston oil squirters deleted (I want to put these back in during the refresh)

[englertracing]

What's with the massive lsa?

[Grant]

What's with the massive lsa?

I don't know but I didn't spec the cams. I'm told the hemis like a wider LSA than the LS. Despite trying every tuning option imaginable the idle quality on the current cam is pretty bad so I don't think I'd want more overlap.

The stock PCM LS guys have an advantage because they can tune injector timing, which helps smooth out cam lope and surge during excessive overlap.

[BLSTIC]

Out of curiosity, how does the average port area compare between the two heads? And what about mixture motion? How does ignition timing compare between the two?

[Bryan Maloney]

A stock 6.1 manifold will knock 40 cfm off of a 370 cfm intake port. The typical port matching and injector boss streamlining cuts the loss to 30 cfm. With specific reworking of the runner entry short-turns, I've gotten it down to a 20 cfm loss.

It may be time to consider a Drag Pak type manifold. I prefer the Ritter copy, as it has more material externally, and is way cheaper than the Mopar original.
The Ritter version still needs external welding to get more CSA in the end runner entries.

Your heavy steel valves, hydraulic lifters, and too-short stock rockers are not helping your situation.

The 7 liter NA Drag Pak development engine made 790 hp initially on Chryslers Dyno, then was given to Ray Barton who claimed he got it to over 820 with a cam change.

[englertracing]

https://www.holley.com/products/engine/ ... ts/300-650

Wonder if this would be any good?

[Grant]

Out of curiosity, how does the average port area compare between the two heads? And what about mixture motion? How does ignition timing compare between the two?

Between stock 6.1 and the Thiteks? I'll take those measurements and get back to you. IIRC optimal ignition timing was pretty similar, but I don't have any of my old 6.1 maps.

A stock 6.1 manifold will knock 40 cfm off of a 370 cfm intake port. The typical port matching and injector boss streamlining cuts the loss to 30 cfm. With specific reworking of the runner entry short-turns, I've gotten it down to a 20 cfm loss.

That doesn't sound bad at all? Doesn't a ported FAST 102 lose about 20 cfm @ 0.6"?

It may be time to consider a Drag Pak type manifold. I prefer the Ritter copy, as it has more material externally, and is way cheaper than the Mopar original.
The Ritter version still needs external welding to get more CSA in the end runner entries.

Your heavy steel valves, hydraulic lifters, and too-short stock rockers are not helping your situation.

The 7 liter NA Drag Pak development engine made 790 hp initially on Chryslers Dyno, then was given to Ray Barton who claimed he got it to over 820 with a cam change.

The LS guys make 600+whp work with all of that minus the heavy intake valves, and super-short intakes which fit under Corvette hoods. The Magnum hood isn't as restrictive but a normal drag pak isn't going to fit. Sounds like you can cut down and make it fit though:
https://www.lxforums.com/board/at-the-d ... ost4744081

drag-pak.jpg

When we get the flange in CAD I was thinking of designing something similar (in terms of runner layout) to the 6.1 manifold.

Do you know what people with drag paks do for crankcase evac? The evac ports are usually in the intake, which connects to the head. There's no direct crankcase port on these motors.

[Grant]

https://www.holley.com/products/engine/ ... ts/300-650

Wonder if this would be any good?

I took measurements when Holley first released that. Never going to fit without a big cowl which will impact sight lines. I need to be able to see right-hand turn apexes.

[Ron E]

I understand the IR 8-stack intake by Speedmaster is a big boost over what you have . All I remember is 30-40 more peak HP with more everywhere. I think the closest intake was -30 to it. Several were tried. It was a milder engine than yours. A 40 CFM loss by adding the intake "concerns me.

[Bryan Maloney]

Do you know what people with drag paks do for crankcase evac? The evac ports are usually in the intake, which connects to the head. There's no direct crankcase port on these motors.
[/quote]

Metco makes -10 an adapters that fit the oil fill tower on the manifold. The right side manifold flange can be machined for a
-10 ORB to -10 male adapter.

[Grant]

Thanks Bryan, I was hoping there was a better solution like the valley cover AoS on LSes. However looking at the motor I don't see where I could pull directly from the crankcase. When you start pulling over about 1.1 g the factory AoS in the 6.1 manifold turns your catch can in to an oil grenade. I think a taller, vertical-path (factory is horizontal) AoS is needed.

I understand the IR 8-stack intake by Speedmaster is a big boost over what you have . All I remember is 30-40 more peak HP with more everywhere. I think the closest intake was -30 to it. Several were tried. It was a milder engine than yours. A 40 CFM loss by adding the intake "concerns me.

Any idea where you saw that test?

Richard Holdener has tested the Speedmaster stacks (https://www.youtube.com/watch?v=G_DZSvJiFaA) and an unported SRT8 intake (https://www.youtube.com/watch?v=O6_GeHl-77U), but on slightly different motors (5.7s with different cams).

Speedmaster uses 50mm throttles; those come out to about 80% less surface area than my port opening. From what I'm gathering this is probably too small for me? I'm also kind of skeptical ITBs are meaningfully different from plenum intakes, once you put filters on them and route cold air to them.

I've been playing around with CodeQuery and may see if I can print an intake to test with.

mag_intake.jpg

[Ron E]

I'll try to find and get back tonight.

[Ron E]

Grant, I still haven't found the test. But, I share your concerns with the area of the Speedmaster deal. It's been my impression that IR manifolds have more area at the butterfly than the intake valve to feeds. I'm still curious about this. I'm sure you're ahead of me on this. But, Holley has a "Sniper" line of intakes that looks promising with runner lengths that should tune up to a higher RPM. But, I didn't see any reference to how it stacks up as far as hood clearance is concerned. But, it looks like it may be no higher than the stock one.