Change in intake runner length

Rebuilt the motor during December and fitted 1444 cams, timed them to spec 104/106 I think it was, Spent some time mapping the car and it produced no more power and had some serious valleys in the torque curve which was nice and flat previously. We decided that we needed some longer trumpets as the Jenvey SF bodies and manifold are pretty short. I decided that due to the expense of purchasing a bunch of different trumpet lengths and only using 1 set from them I would do some research and mock up something for the time being, once happy with the length a final part will be made.

Started with an extension of 150mm including trumpet length, felt better but not great using the bum dyno and terminal speeds on my usual test route. Not very accurate but I know the car quite well. Then installed the 210mm extension, giving me a total intake runner length of 16" putting the pulse tuning effect within the useable rev range with my max of 8500rpm. Felt much better, so today I took it to the dyno for a power run comparison, well not really a power comparison more a shape of curve comparison. the reults were quite good:

[image] MWEB Homepage [/image]

Although the power and torque are Poo below 3000RPM it does not really worry me as I have the UCR box and seldom, if ever, drop below 3000rpm on the track.

Still I was hoping to havepower climbing above 8000 but some timing on the cams might help. Just pleased I got the torque spread better which is far more important than peak KW figures.

Forgot to add that no setup was done today only a power run, so better results could be expected.

What are the units on the left axis Jason?


Power in KW’s and NM’s at the wheels, bare in mind it is at altitude and 32 degrees here today so figures will be far less than most but consistent enough with what I am used to seeing up here.

I would try setting your cam timing using lift at TDC rather than lobe centres, 140 thou lift at TDC on the inlet and 120 thou on the exhaust should do it.


That’s about 185 BHP at around 6K. Assume at the wheels, which is good.
Amazing that it took some power down below. In my experiments, it seemed to shift the power slightly down until a certain point.
Tried max with 135mm on top of the standard Titans, but didn’t go further (no way to physically fit longer trumpets inide the airbox, even if it’s a modified, longer one)

But agree, longer trumpets is a mod that everyone should have, it’s free power.
More air being crammed in the cyls means more fuel is going to be needed, and not evenly across the rev range, so unfortunately I don’t think this will go well with a std ECU.
Somebody should try that on a 190 ECU and lay on to an AFR curve to see if there is any zone that is dangerously lean.

Check out my power graphs here

Note that the EmeraldPSS-EBDLT.gif is the one that shows the effect of only adding the 100 mm trumpets. They fit inside the original airbox.

The JV3 is the one that I’m using now.

Thanks Dave will give re time the cams using lift at TDC. Will save alot of trial and error so info is much appreciated.

Uldis, unfortunately the airbox situation is limiting, what I have done is spaced the airbox out so it mounts in the same way to the backplate. But it negates all boot space, will take some photo’s of my temporary solution tomorrow.

My calculations of the std VHPD +/- 11" (could be slightly out I never measured it on the car, measured bodies + tubes on the shelf, then added distance to valve)

For 2nd harmonic, RPM range is from 10680 to 12960 with a pulse strength of 10 percent
For 3rd harmonic, RPM range is from 8025 to 9171 with a pulse strength of 7 percent
For 4th harmonic, RPM range is from 6256 to 6996 with a pulse strength of 4 percent

For my current setup with extensions:

For 2nd harmonic, RPM range is from 7342 to 8910 with a pulse strength of 10 percent
For 3rd harmonic, RPM range is from 5517 to 6305 with a pulse strength of 7 percent
For 4th harmonic, RPM range is from 4301 to 4810 with a pulse strength of 4 percent

Certainly does need setting up and I don’t think that the std ECU would cope, I am really keen to see what it is going to do with cams re timed, proper mapping and a decent extension setup, might find some power below 3k.

Glad to see somebody else has been playing with the formulas

In my case, the length turns out to be head to edge of trumpet about 293mm which is about 11.5"
Consider about 10 cm still from the head to the valves bt we’re on the ballpark
If you check my graphs the gains were actually everywhere.

But my setup is slightly different than what DVA mentioned: 110 thou exhaust as opposed to 120.
I guess in theory 120 would gain a little midrange.

But can’t figure out what you say about the ECU can’t cope. What do you mean?

And I think you’ll find the 3K dip is not intake related, but exhaust.
Check out in my graph the <3K dip dissappeared when comparing the EBD with the JV3.

Just been having a look at your graphs, seems on the change to 100mm trumpets you also lost some power below 3k at about 2600 there is a noteable dip as well, perhaps not as much as mine but a definite correlation, i am looking at the bold blue line, is that the right one? Seems to me that the longer length has a very dramtic effect above 3k in my case and above 2.5k in your case, so it seems that the trade off is alot less torque below +/- 3k for a whack more torque everywhere else. The longer the length the more dramatic effect below 3k, only factoring in trumpet change here not exhaust which will help smooth it out.

I mean going to 16" runners with a std 190 ECU would propably not be of much benefit, personally I think it would run pretty lean, although can only go to 7800 so maybe it would just be ok.

This is the one that I was talking about:


And yes, you’re right about the observations on the dip.
And now I see about the ECU, yes, in fact if you keep the std ECU, lean is a conditon you might have almost all across the rpm range.
A workaround this (if you can’t have an Emerald) would be to probably up the fuel pressure, but this would make it far richer on the dip zone.

Fitted new extension piecs with nicer trumpets, never been a big fan of the ultra thin ali ones they bend and deform far to easily, so I go some machined ali trumpets that are alot stronger.

[image]MWEB Homepage

Also did some playing around with the air filter arrangement, going from sausage type ITG to BMC cone filter produced the following results:

Same road, same style of launch to keep things consistent, within a few hours of each other:


0 kph
0 kph == ==
10 kph 0.42 0.42
20 kph 0.82 0.84
30 kph 1.19 1.21
40 kph 1.86 1.76
50 kph 2.44 2.32
60 kph 3 2.87
70 kph 3.6 3.43
80 kph 4.62 4.48
90 kph 5.29 5.14
100 kph 6.11 5.89
110 kph 7.03 6.75
120 kph 8.17 7.9
130 kph 9.46 8.95
140 kph 10.82 10.2
150 kph 12.54 11.77
160 kph 14.31 13.29


0 kph
0 kph == ==
10 kph 0.65 0.61
20 kph 2.35 2.39
30 kph 4.95 4.97
40 kph 11.41 10.41
50 kph 18.64 17.44
60 kph 27.22 25.85
70 kph 38.1 36.01
80 kph 59.69 58.26
90 kph 75.67 73.98
100 kph 97.34 93.83
110 kph 124.23 118.98
120 kph 160.76 155.85
130 kph 205.41 192.34
140 kph 256.5 239.3
150 kph 325.9 302.57
160 kph 402.2 368.1

The only difference to the car was the addition of the BMC cone filter which gave the trumpets some more room to breathe in the airbox. The 0-160 km/h shows a marked improvement especially in distance taken to achieve the speed. Can’t wait to get the car on the dyno later this week to optomise the fuelling, then I will go out and do a decent launch, might even break 5 seconds at altitude which is not shabby for a N/A 1800.

Same clutch!?


Same clutch!?


Of course they’re indestructible was very sympathetic with the last one which lasted 3000’km’s, abused this one beyond belief for the last 5000km’s and it’s still good, didn’t even bother replacing during rebuild. But now that you have mentioned it will more than likely have to soon

Uprated AP?


Yep std AP ugrade, Logan couldn’t believe it when I told him I was running virtually a road clutch in the car, said the way I drive it he thought I had the carbon AP clutch in there. I must say that I always match on the downshifts on track which saves clutches beyond belief, I did not do this religiously with the one that only lasted 3k.

I do too, but at 15k the original welded together, no warning.