Well, maybe not max out but at least when is it benificial to run a 3.5-4" IC pipe?

Also, When running a IC pipe that large how large would the intake need to be? After all the intake is uncomressed air so I'd imagine it needs to be bigger

Any info is appreciated,
STEPHEN

 

How about how much air do you want to flow? HP? Lbs /min

 

Corky Bell suggests a maximum air speed of Mach 0.4 (440 ft/sec) in Maximum Boost before things start to go bananas in the pipe. Here are some approximations in how much CFM and flywheel HP (assuming 1 HP = 1.5 CFM) would be supported by various sizes of IC pipe at the limit of 440 ft/sec:

2.50" --> 900 CFM --> 600 HP
2.75" --> 1089 CFM --> 726 HP
3.00" --> 1296 CFM --> 864 HP
3.25" --> 1521 CFM --> 1014 HP
3.50" --> 1764 CFM --> 1076 HP
3.75" --> 2025 CFM --> 1350 HP
4.00" --> 2304 CFM --> 1536 HP

Now, that isn't to say that you wouldn't benefit from from less restriction running 3" pipe on a car that was only making 600 HP at the flywheel, but adding volume has a downside, too. There is no sense in adding it needlessly.

I did always think it was kind of strange that the FD had 2.75" pipes in stock form and most turbo compressors capable of substantial power gains on the 13B have 2.5" outlets.

-Max

 

Thanks Max, I was too lazy to post that

 

Thanks Max, the cfm numbers are pretty much exactly what I was looking for.

One more question though. Why is it that some people run a smaller IC pipe on the hot side of the IC and a larger on the cold side (like 3" on hot side and 4" on cold side)? Really, it seems like if anything it should be the other way around cause the cold air is more dense than the hot air. Seems like the larger pipe would need to be on the hot side so that it can suppost the flow of the cold side.

Interesting point you bring up about the turbo outlet on most turbos, and how they are typically smaller than the IC pipes, isnt that cause the air is much more compressed inside the turbo then as it leaves the outlet it uncompresses some?

Thanks for all the info,
STEPHEN

 

I would think having smaller pipes for the intercooler would be more efficient anyways. There would be less volume for the turbo to fill while building boost. Thus building boost faster. Also, smaller diameter tubing would increase air velocity thus enhancing air and fuel ingestion/atomization.
if 3" pipe can handle 864 hp worth of exhaust, 2.5" would probably be a substantial size for i/c piping for any rx Ive seen.

 

Not to hijack your thread Stephen but could this same formula be used to calculate the pipe diameter on the exhaust side? I would like to know the max 3" piping will do for hp output without being restrictive.

 

For some applications, 3" will be too small.

 

I'm not sure guys, but those HP numbers might be for piston engines cause they look a little high to me based on the cfm. Maybe Max can post and let us know.

Also, I'd imagine these cfm/HP numbers are based on a certain air temp. What that temp is I have no idea, the hotter your actual temp is the less hp your going to make with that flow.

Thats 2 pieces of info you should look at when using these numbers......is it based on a piston or rotary? And what air temp is the hp figures based on....if they are even for a rotary.

I was mainly just after the cfm rating.

STEPHEN

 

it might just depend on pressure drop? i have some pics of a porsche 917/30 engine and they are making 1500bhp with 2x 60mm pipes, but no ic to restrict flow.

 

Yes, those HP numbers are a rough estimate for flywheel (not wheel) HP for a piston engine. The rotary will make a little less power for the same flow.

-Max

 

Yea, with those being pistons engine numbers I'd take about 10% off them. Then another 15% to get it to rwhp instead of flywheel.

STEPHEN

 

Are you talking on the exhaust side? If so what would be the max for a 3' pipe?

 

I'm not sure what you mean by "exhaust side" since we are talking about intercooler piping.

Intercooler piping and tuning is not my forte (sp?). I'm just pointing out that 3" could be too small for some applications (some drag cars, maybe some SERIOUS street cars!) but I do not have the experience or knowledge to know exactly what level of performance would require addiational size.

 

My rule of thumb is up to 600hp (rear wheel) for 3" IC pipe.
This should cover almost all 13B street applications out there.
Only some of the real big 20B applications can warrant large IC pipes.

The smaller IC inlet pipes would be warranted by the turbo compressor inlet?  Would you like to run some kinda expansion joint in that section?  Plus, the turbo is "pushing" the intake charge into the IC.  Giving the intake charge an easier path to exit the IC core would expain the larger IC exit pipe sections?


-Ted

 

What about IC inlet and outlet size, if I have a 2.5 inlet and outlet would I still benafit from 3 in ic pipes at high HP? I wanted to use the same size ic pipes as my intercooler, can I use 2.5 for 600hp?

 

Off topic....Ted would you have a rule of thumb for 3" exhaust pipe? About how much hp could 3" exhaust piping support before needing to go larger?

 

I know of diesel applications that use 3" pipe and get well over 1000 RWHP ..... There is more to it than just CFM.

 

Note also that the Mach 0.4 maximum speed was just a guess by Corky Bell. It certainly isn't a hard limit, and I am not even aware of any tests that quantify the effect.

-Max

 

My friend has calculated air speed of his setup to be right around 450 ft/sec.

 

So basically if someone is running 3" pipe it really shouldnt be a major restriction till your getting WAY up in the rwhp (700range). Guess I'll go with some 3" then haha

Since we kinda got on the topic of exhaust you guys have any educated guesses as to when it would be benificial to go to something larger than 3" exhaust? I'm sure someone can make 600rw no prob with 3" but who knows, maybe they would have made 650rw with 3.5-4"

STEPHEN

 

I think Corky Bell has limits of about 600hp for 3" exhaust pipe...?


-Ted

 

Thx Ted, I guess that answers both of our questions Stephen.

 

Well, I can't really give any scientific theory as to why the bigger piping is better, but I can give you my experience. I changed my piping from my IC from 70mm to 100mm. Nothing else was changed on my car. My setup is a sideported motor, 67-1 AR 1.15 P trim, Trust 4 core FMIC 70 in 100 out. I originally changed the piping because I was going to go with a different intake manifold/throttlebody setup, but the plan changed. I modified the end tank on my IC to outlet 100mm and my Greddy elbow was hacked as well. Initial feeling was that the car picked up alot of midrange response/got really peppy. I datalogged the car with the new piping and found my AFR's to be around .5 leaner at part throttle normal vaccuum driving. When I let her rip I found that there was very little change up top, but the turbo did spool up about 200 rpm's earlier(required some tuning).

 

damn, you Igy....had to throw a wrench in my plans didnt you lol

BTW - that 70 and 100mm is that inside or outside dia?

STEPHEN