Dyno testing with an airbox system

[dive!dive!]

Hello Folks
Thought this might be of interest to some, as I know the question has been asked before.
I spent some time on the chassis dyno yesterday doing some final tweaks on my EFI map and had the chance to see what effect the airbox systems has (I have a GWD airbox, similar to the CSP ones).
My engine is a 1776, Bugpack4062-10 cam, 1.25 rockers, 044 Heads 40*35.5 (they flow 163 at 12.5mm lift 25"H20), 38mm IDF throttle bodies, 1.5" exhaust, 9.5 CR.
Best run with the airbox on was 99RWHP @5900, 1151b torque@4900. Taking the box off gained 3-4 HP but the peak dropped back to about 5400, torque was about the same but the torque was sustained into the lower RPM (flatter curve). Just removing the air horns from the main airbox gained about 2 HP.
So, yes, the airbox does rob some power, but frankly not noticeable on the road and it does really reduce induction roar (nice on longer journeys!). I was  little surprised how much it moved the peak power rpm though. This combo drives very nicely on the road and I'm trying to resist putting more cam in it! Its the age old question of how much is 'enough' ? :-)

I've had various iterations of this engine, for interest :
Same motor, less headwork (144 flow), 8.9CR, twin 40DRLA, made 84RWHP , same dyno.
1776, stock TP heads home ported, 8.3CR, 4062-10, 1.1 rockers, 1 3/8 exhaust, twin 40DRLA, 76RWHP different dyno
As above but twin 34ICTs , 62RWHP , different dyno

On a related note : next job is the gearbox. For a street only car, what would be the recommendation for my current engine ?

Thanks for reading
Steve

[Zach Gomulka]

Nice results! With peak power that high, I would resist installing a larger cam. Consider swapping the 90.5's for 94's and adjusting the headwork accordingly. That will make a huge difference everywhere.

What year car, what size rear tires?

[dive!dive!]

I'm sticking to the 1776.... I have the same disease as Peter Shattock!

The peak power RPM is deceptive - its actually almost a flat line between 5000-6000rpm, marginally higher at 5900. Its not below 95RWHP from 5000 till well beyond 6300

Its in  '71 full weight Beetle 1300. Rears are 195/65 R15. Currently has the std 1300 box.

Steve

[alex d]

Those are great results...I wouldn't change a thing!!

I know that's easier said than done 

[Zach Gomulka]

If the stock ratios work well for you now, don't change it. Do you want it to be more aggressive, or lower rpm on cruise?

[dive!dive!]

I'm gentle with it in 1st of the mark, as I know I have the potential to break the diff if I'm not sympathetic to it......

The thing I like least is the gap 2nd/3rd. And a few RPM less on the highway would be good. So maybe a 4.125, shorter 3rd, keep the same 4th ?

[Zach Gomulka]

Do you know what ratios are in your box now? I'm not familiar with the Euro 1300 trans.

[dive!dive!]

Stock 1300 is 3.80/2.06/1.26/.89 final drive 4.375

Steve

[modnrod]

My gearbox ratios are 3.78/2.06/1.35/0.93, only changed 3rd ratio the rest is stock. I got the 3rd gear set from Weddle.
It fixes the big rev drop going into 3rd, and closes up 4th as well.
A 4.125 diff with these ratios on your car would work fine without losing highway cruise manners.

[Zach Gomulka]

Ok, you're on the right track then. 4.125 will make acceleration less agressive, but it will cruise better in 4th. It is also stronger. Use the 3.78 2.06 mainshaft for a stronger 1st gear. 1.32 is the early 3rd gear, it will tighten up the 2-3 split, but it will also make the 3-4 drop a bit larger.

[Martin S.]

Do you have any pictures to post of the car, motor, airbox, dyno, etc.?

[dive!dive!]

https://www.youtube.com/watch?v=ph3wwTLdNZg&feature=youtu.be

[dive!dive!]

[Jeff68]

Thanks for posting this. I've never seen that airbox assembly before.

[javabug]

The thing I like least is the gap 2nd/3rd. And a few RPM less on the highway would be good. So maybe a 4.125, shorter 3rd, keep the same 4th ?

I'm going to take a gearbox stance different from the masses: don't wimp out on selecting gear ratios just to be "safe." Spend some time with a gear ratio calculator. I like the one on John Maher's site. http://johnmaherracing.com/calculators/gear-ratio-calculator/

When I had my 'box built, I went "safe" with a 1.31:1 third and 0.89:1 fourth. After driving my car for a few years now, I realize that the engine speed it likes on the highway (3,700 rpm) would have yielded 70 mph with a 1.04:1 fourth. That would have been totally livable to me, and at a reasonable highway speed. So now I live with the disappointment that I could have gone with an actual close third and fourth, and been fine with it on the highway (as my builder even suggested).

Crunch the numbers, know your car. Don't end up disappointed ...

[max, Der Bahnstormerz]

Just my 2 cents worth, and if you have the time.

It'd be interesting to find out how the thing performs. If you were to remove the air horns, replace them with K&N cones and remove the filter from inside the airbox (just run the rubber sealing edge from a stock filter)

I'm wondering if the fan may be robbing the motor of some air.

[dive!dive!]

Just my 2 cents worth, and if you have the time.

It'd be interesting to find out how the thing performs. If you were to remove the air horns, replace them with K&N cones and remove the filter from inside the airbox (just run the rubber sealing edge from a stock filter)

I'm wondering if the fan may be robbing the motor of some air.

That's sort of what I did. Just taking the horns of was about 2hp. Removing the horns, filter box top and filter was 3-4hp. Not sure if its the fan robbing air from the horns or just the restriction they provide that accounts for the 2hp. No plans for more dyno time just yet...it gets expensive, even if it is interesting stuff !
Steve