Hot rodding at high altitude?

SteveSS · Sep 12, 2018

We took the Mopar 408 into a race shop to see what could be done to improve its performance. It is a small-block stroker from Blueprint Engines. All the stuff I thought, the normal stuff like heads and cam, actually hurt performance at our elevatiom. Our average elevation is about 6,500 ft. I knew we had the 750 jetted down to the smallest we could but it was still really rich.

In talking to Steve Mills of Steve Mills Racing here in Colorado Springs the big thing here is loss of compression. It's still in the shop so I don't know the answers yet but I was surprised all the normal tricks don't work here.

Steve said he actually called Blueprint Engines and asked for a smaller cam on a customer's build and they wouldn't do it.

dvw · Sep 13, 2018

Adding compression will crutch the cam and the altitude. The idle air bleeds may be missed causing rich idle.
Doug

69L48Z27 · Sep 13, 2018

EFI would be a good solution.

beanhead · Sep 13, 2018

SteveSS said:
We took the Mopar 408 into a race shop to see what could be done to improve its performance. It is a small-block stroker from Blueprint Engines. All the stuff I thought, the normal stuff like heads and cam, actually hurt performance at our altitude. Our average altitude is about 6,500 ft. I knew we had the 750 jetted down to the smallest we could but it was still really rich.

In talking to Steve Mills of Steve Mills Racing here in Colorado Springs the big thing here is loss of compression. It's still in the shop so I don't know the answers yet but I was surprised all the normal tricks don't work here.

Steve said he actually called Blueprint Engines and asked for a smaller cam on a customer's build and they wouldn't do it.

@Garys1969RR would be a good one to ask, I believe he runs at higher altitudes. I know it does kill compression ratios though

Darter6 · Sep 13, 2018

This is all I can remember as I raced in Denver over 15 years ago. Normal for me was a density alt between 3200 to ruffly say 4000 ft.My guess there it was over 7000 ft. I was off my number by a full second or more.The locals said to advance the timing.It picked up some but still off. The cars CR was 11.4 to 1. That's all I know. Interesting topic.

Garys1969RR · Sep 13, 2018

beanhead said:
@Garys1969RR would be a good one to ask, I believe he runs at higher altitudes. I know it does kill compression ratios though

Altitude can be a power killer, if you don't have the right combo, and LOTS of compression, coupled with good flowing heads. A 408 can be made to run GREAT at this altitude. I saw a 72 Duster at Bandimere last week, and it clicked off a 10.76 ET! I thought for sure it would be a big block or Hemi. Got over there, and it was a 408! I remembered the guy, Dennis Mauer from back in the 70s. He was married to Judy Lilly, and was also her mechanic. She was a famous SS racer back then when Shirley Cha Cha Muldoney was competetive in Top Fuel. Ah, the good ole days! Both of those ladies were national record holders at some point. Judy Lilly with her 72 Duster 340, and her Chief mechanic/husband, Dennis Mauer. I talked to a guy here, and he said that 408 was running Trick Flow heads, with extensive porting, and 14 to 1 C Ratio. So find Dennis if you can, and maybe he will divulge a few secrets on how to make a small block scream, while there is still time. LOL

451Mopar · Sep 13, 2018

Altitude kills power (compared to sea level) and there is not all that much that helps except maybe a power adder. You can optimize the engine a bit with higher cylinder pressures (compression, advanced timing, earlier intake closing point, and watching port velocity more than maximum flow numbers.) It is pretty common for an engine to loose 18-20% power when your around 6,000+ ft. Summer air density at Bandimere can be close to 9,000 ft. Carb tuning is a bit strange at altitude. Compared to sea-level, the main jetting needs to be a bit leaner, but the idle / transition may need to be richened. The two carb circuits operate differently. Main jetting is a siphon from the low pressure created in the carb venturi when there is a good amount of airflow passing the venturi, but the idle / transition is more of a metered leak (there is a small siphon effect), but the main pull is the engine vacuum where atmosphere pressure in the fuel bowl is trying to push fuel into the lower pressure (vacuum) intake manifold. At altitude there is less atmosphere pressure (and less engine vacuum), so a idle / transition restriction that is good at sea-level is usually too small at altitude. This seems to be more of an issue with "street" carbs like the Avenger. Race carbs usually have a rich idle/transition which seems to work at altitude.

SteveSS · Sep 13, 2018

I think I found him, Dennis Maurer, in Arizona. http://www.maurersperformance.com/History.html

If you see that 408 Duster again at Bandimere would you mind getting his number?

Garys1969RR · Sep 13, 2018

SteveSS said:
I think I found him, Dennis Maurer, in Arizona. http://www.maurersperformance.com/History.html

If you see that 408 Duster again at Bandimere would you mind getting his number?

Yes, I'll look for him. That's the guy! Quite the engine builder. I'll be out there 1 more time this season. In the meantime, have you tried contacting Maurers Performance? Are they still around?

Garys1969RR · Sep 13, 2018

I just called the number at Maurer Performance, and that IS his current number.

Garys1969RR · Sep 13, 2018

Just curious Steve, what kind of 1/4 mile times are you getting with that motor? And what have you been running it in? Are you racing at a strip around here in Colo?

SteveSS · Sep 14, 2018

The 408 is in the Challenger. It has 391 gears and never drove it to Denver, too far revving that high. We took it to PPIR's 1/8th mile race and it was falling on it's face after 3600 rpms. Making some funny noises on the top end. Called Triple A and towed it to Steve Mills Racing. The '69 Charger has a 383 and highway gears, not a 1/4 mile car. Someday we'll pull the original stuff on the '69 set it aside and go ripping with a built big block. Maybe from your friend Dennis. We race the '97 Camaro SS a lot. Bone stock it does low 14's.

The car that freaked me out at the 1/8th mile race was the Lincoln MKZ 3.0T AWD 0-60 4.8 seconds!

I've been noticing some built 4th gen GM's for sale under $8K that can run 10's. I think there will be lots of cheap Hemi cop-car hot rods around soon.

Garys1969RR · Sep 14, 2018

I think you're right on that! I'm seeing SRT8 CARS like the 300, for sale around $8000. Is that what you mean by Hemi Cop Cars? Or ?

Garys1969RR · Sep 14, 2018

Dennis like the small blocks. But im sure he could build a great running big block too! If you're having problems getting your 408 to rev, I would say its possibly valve springs or an ignition prob.

Hot rodding at high altitude?

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