Air intakes & ducting

asahartz · Post by **asahartz** » Fri Jan 16, 2009 6:11 pm

Hello, my first visit here. I've just put a Rover V8 in my VW T25 camper, my first foray into the world of V8s.

This engine is a touch high for the engine bay, and the original cylinder airbox is even higher. I was thinking of getting some ducting as is common on modern vehicles and routing it to my original VW airbox.

Question is, how important is it that the ducting is the same length to each carb?

Post by **Rossco** » Fri Jan 16, 2009 6:19 pm

Hi welcome to the mad house.

Differences in length wont make any noticeable difference.

Rossco

Post by **Coops** » Fri Jan 16, 2009 6:27 pm

welcome mate.
glad we got you signed in ok in the end

Post by **katanaman** » Fri Jan 16, 2009 7:22 pm

Ducting wont be a problem as Rossco said but the size of the original air box might be. I don't know these vans at all so have no idea what its like but thought it would be worth alerting you just in case.

asahartz · Post by **asahartz** » Fri Jan 16, 2009 7:28 pm

The original air box is rectangular, almost cuboid, with a filter about 9" square IIRC. The ducting from it is about the right diameter. I would expect that to give enough airflow?

ChrisJC · Post by **ChrisJC** » Sat Jan 17, 2009 8:39 am

Sounds like you might need two of them....

Chris.

asahartz · Post by **asahartz** » Sat Jan 17, 2009 9:51 am

The filters in the Rover airbox are pretty small. Are there any figures anywhere for filter area and airflow rates?

Ian Anderson · Post by **Ian Anderson** » Sat Jan 17, 2009 12:15 pm

Decide how many ponies your engine is making

Have a look at this
http://www.knfilters.com/universal/universal.htm

and from that you can see what airfilter will fit and allow enough air for your application Do not go small or at higher rpm you WILL lean out and do damage to the motor.

Filters do not need to be that big to support a fairly mild engine

Ian

asahartz · Post by **asahartz** » Sun Jan 18, 2009 12:49 am

From that it appears that the K&N filter for the V8 has a slightly bigger area than the VW - but there are two of them!

I'll have another think through this - I'm sure I have a Toyota airbox in my shed too, but there has to be a neat way to do this job.

My engine is not highly tuned, and in a T25 I'm hardly likely to be thrashing it, but towing might be more demanding.

Ian Anderson · Post by **Ian Anderson** » Sun Jan 18, 2009 8:02 am

The info on that link has changed slightly since I used it as each filter used to have a "for use on engines up to x hp"

Probably worth giving K&N UK a call and asking their advice.

Do you have 1 airbox or 2?

Ian

asahartz · Post by **asahartz** » Sun Jan 18, 2009 12:09 pm

Currently there's one big cylinder over the top, but that's too high and I'm looking to duct it off to the side of the engine.

Post by **katanaman** » Sun Jan 18, 2009 12:24 pm

a basic rule of thumb for matching airfilters is generally put like for like. A 1.9 diesel filter is unlikely to support a 3.5 petrol engine type thing as the 3.5 probably moves something like 2-3 times the air volume. Other things to consider are if the filter is too small it will clog far quicker needing much shorter replacement intervals.

asahartz · Post by **asahartz** » Sun Jan 18, 2009 2:23 pm

This is getting to be interesting. The VW, which was a 1.9 petrol, actually has a larger filter than the Toyota 2.4 petrol. The Toyota engine returns about 125bhp with that filter, which isn't that far behind the estimated 150bhp that I anticipate from the V8.

The only significant difference is that the Toyota is injected while the other two are carb engines, but that shouldn't be significant as the only important thing is the fuel/air mix, and if anything I would expect the injected engine to run leaner than the other two, so requiring more air not less.

I suppose it would be good to find airflow figures to compare.

Post by **katanaman** » Sun Jan 18, 2009 4:34 pm

There is more to it than mixture settings and air flow. You would have to look at service intervals as well. Something that is meant to go a long time between services usually has larger filters all round. Same applies to something that is expected to work in harsh environments. The RV8 also isn't the most efficient engine in the world but still moves a lot of air because of its size. There isn't really any simple answer but if you manage to find a modern say 4.0 engine its filter should be capable of flowing for the Rover. Something like a Lexus or Audi, they also tend to have nice box shaped filters that are easy to package and stash somewhere.

asahartz · Post by **asahartz** » Wed Jan 21, 2009 5:38 pm

I just looked at the vehicle cross-reference list for the original VW filter : http://www.knfilters.com/search/applica ... od=33-2003.
That includes engines such as the Audi Quattro and Jaguar/Daimler 6 litre V12!
Sounds more than up to the job to me.