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Search found 2447 matches

by ptuomov
Wed Sep 15, 2021 8:16 am
Forum: Engine Tech
Topic: Ram induction question
Replies: 11
Views: 551

Re: Ram induction question

Modern motorcycle intakes are just like four cylinder tunnel rams. B4DD31F4-5C55-462D-AD5B-03B4170B63A2.jpeg The longer and narrower trumpets tune to lower rpms and the way they do it has relatively little to do with acoustic wave formulas, especially if the exhaust pulls a good vacuum during the va...
by ptuomov
Mon Sep 13, 2021 8:40 am
Forum: Engine Tech
Topic: Ram induction question
Replies: 11
Views: 551

Re: Ram induction question

In my opinion, you can’t consider the length independently of the diameter. This is not just acoustic waves. I worked on intake trumpets this summer, with both a simulator and live engines. A smaller diameter shorter trumpet and larger diameter longer trumpet gave almost exactly the same torque curv...
by ptuomov
Sun Sep 12, 2021 10:52 am
Forum: Engine Tech
Topic: Exhaust Duration, Boost and Elevation
Replies: 19
Views: 390

Re: Exhaust Duration, Boost and Elevation

If you overdrive the blower to get the same pressure in the intake manifold, the pressure in the exhaust would be the same. The lower tail pipe exit atmospheric pressure has to impact the exhaust port pressure at least to some extent, but the question is whether that’s practically relevant. You're ...
by ptuomov
Sun Sep 12, 2021 10:37 am
Forum: Engine Tech
Topic: Exhaust Duration, Boost and Elevation
Replies: 19
Views: 390

Re: Exhaust Duration, Boost and Elevation

With a Turbo, or a blower, the engine doesn't know it's at high altitude. It only knows the "Altitude" in the plenum. You would cam them the same way you would at sea level. If the pressure in the plenum is 46", that's what the engine sees. Would the lower pressure seen in the exhaust system at alt...
by ptuomov
Sun Sep 12, 2021 10:21 am
Forum: Engine Tech
Topic: Exhaust Duration, Boost and Elevation
Replies: 19
Views: 390

Re: Exhaust Duration, Boost and Elevation

I agree with almost everything that was said. I see there being some hardware questions and then some control questions. For high altitude operation, I think you need a big compressor inlet piping and large air filters. You likely also need big intercoolers, at least for the ambient air flow side. T...
by ptuomov
Thu Sep 09, 2021 4:54 pm
Forum: Engine Tech
Topic: The first exhaust collector in 4-2-1
Replies: 18
Views: 1137

Re: The first exhaust collector in 4-2-1

Outside the motorcycle racing series where the flat torque curve appears to be very important, do any racing engines actually end up using balance tubes instead of simpler 4-1 and 4-2-1 exhausts?
by ptuomov
Tue Sep 07, 2021 8:11 pm
Forum: Engine Tech
Topic: The first exhaust collector in 4-2-1
Replies: 18
Views: 1137

Re: The first exhaust collector in 4-2-1

“Take a look at some of the exhausts of the V8 era cars, and you’ll see some of them have collectors the size, or very close to that, of their final primary diameter.” I did take a look at those, and it’s a good a good idea to do so as the 2.4L flat plane V8 exhausts are just like two separate 1.2L ...
by ptuomov
Tue Sep 07, 2021 5:49 pm
Forum: Engine Tech
Topic: MERGE COLLECTORS,WHEN TO USE,HOW BIG A CHOKE AND WHY
Replies: 16
Views: 6157

Re: MERGE COLLECTORS,WHEN TO USE,HOW BIG A CHOKE AND WHY

You only have 6.25x primary tube area to work with. What do you mean by 6.25x? Oh according to sources like Gordon Jennings regarding 2 stroke exhausts, and Gordon blair on 4 strokes on any diffuser or megaphone going any more than 6.25 * the primary area does not provide any useful reflections. In...
by ptuomov
Mon Sep 06, 2021 11:33 pm
Forum: Engine Tech
Topic: MERGE COLLECTORS,WHEN TO USE,HOW BIG A CHOKE AND WHY
Replies: 16
Views: 6157

Re: MERGE COLLECTORS,WHEN TO USE,HOW BIG A CHOKE AND WHY

With a proper firing order like a 4 cylinder you can go real small like just bigger than a primary tube and then you can attach something like a megaphone and it will run good. You see abrupt large changes in area reflect strong scavenging effect over a narrow rpm range.... Small gradual changes in...
by ptuomov
Mon Sep 06, 2021 12:45 pm
Forum: Engine Tech
Topic: The first exhaust collector in 4-2-1
Replies: 18
Views: 1137

Re: The first exhaust collector in 4-2-1

Thinking of restrictions, here’s the following idea for four cylinder engines. Take the engine bore spacing and multiply it with the redline rpm. Lower the number the better suited a 360-degree 4-2-1 header is. Higher the number, the better suited a 4-1 system is. Since I’m working with a 80mm bore ...
by ptuomov
Sun Sep 05, 2021 10:19 am
Forum: Engine Tech
Topic: The first exhaust collector in 4-2-1
Replies: 18
Views: 1137

Re: The first exhaust collector in 4-2-1

After playing with a four cylinder simulation with independent zoomies, dual 360pdegree 4-2 system, and 360-degree 4-2-1 system, I've come to the following tentative conclusions (thinking out loud here): When the primary diameter off the head is the limiting factor on power at peak power rpm, the zo...
by ptuomov
Sat Sep 04, 2021 11:40 pm
Forum: Engine Tech
Topic: Duratec 2.5 - Torque / VE Dip
Replies: 3
Views: 336

Re: Duratec 2.5 - Torque / VE Dip

The fact that the intake cam timing doesn’t change the torque hole size or location does indeed suggest it’s more likely a plenum resonance issue than an exhaust blowdown interference issue.
by ptuomov
Sat Sep 04, 2021 8:57 pm
Forum: Engine Tech
Topic: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era
Replies: 65
Views: 10773

Re: 2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era

What I tried in the sim was instead of going from 48mm ID to 60mm ID on the last step I had a cone that went from 48 ID to 60ID over 375mm:s. That was better everywhere according to the sim and since my exhaust is modular I can easily change the last collector to see if it works in the real world t...
by ptuomov
Sat Sep 04, 2021 6:24 pm
Forum: Engine Tech
Topic: The first exhaust collector in 4-2-1
Replies: 18
Views: 1137

Re: The first exhaust collector in 4-2-1

I think the fastest way to see the difference would be to look at the pressure traces of the different arrangements of Y. Just one cylinder test would be enough to see what happens. If your simulation cannot do this then perhaps you can get one that does, or maybe I do it, but I need to mow the law...
by ptuomov
Sat Sep 04, 2021 2:45 pm
Forum: Engine Tech
Topic: Duratec 2.5 - Torque / VE Dip
Replies: 3
Views: 336

Re: Duratec 2.5 - Torque / VE Dip

Not pretending to be an expert, but that sort of big VE dip would likely come from intake manifold plenum resonance going the wrong way or exhaust blowdown interference during the overlap period. If you buy a EngMod4t license and program the engine into that simulator, you can likely identify from s...