Need some 3.2 build camshaft opinions

[Gabe.]

Hi all!

I've been scouring the search tab for a while now and figured it's time to just post up.

There will certainly be a lot of opinions, made more difficult by my desire to keep the budget low and find deals rather than get something new.

Build specs are as follows:

• 3.2 Carrera base
• 10.5:1 JE Pistons
• twin plug heads
• TI retainers, slightly uprated valve springs
• Triumph ITBs, running megasquirt with coil on plug

The car will be driven on weekends, in the canyons, track days, and autocrosses. Looking for suggestions on cam grinds now that I'm not subject to the limit of stock pistons.

Thanks for all your help!
Gabe

[stownsen914]

Keep an eye on this thread => 3.4 Dyno Chart

Similar engine, and some engine details being discussed.

[Gabe.]

Thanks! I've been following that one, waiting on cam specs to be shared.

[Litle brother]

Webcam 120/104 grind is a great choice.


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[Trackrash]

IMO, mod S.

However, if you send a message to John D, AKA camgrinder, his opinion would be one to consider.

[Peter M]

Originally Posted by Gabe.

Thanks! I've been following that one, waiting on cam specs to be shared.

DC44 108 according to Jeff

[Gabe.]

Ended up going with a DC44 110 LSA. Once I have some dyno charts I'll upload them to my build thread! Could be a few months though...

[Jeff Alton]

Good choice. Your results will depend on intake, exhaust, timing and tuning, but you are off to a good start!

Cheers

[Mark Henry]

Originally Posted by Litle brother

Webcam 120/104 grind is a great choice.


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I love them on my 3.0 twinplug with webers. Absolutely no bad habits, except for cold starting you would swear it's FI and just a hair of loping at idle, almost a linear power curve. Truly a pleasure to drive on the street but a torque monster when you push it harder.

[Litle brother]

Originally Posted by Mark Henry

I love them on my 3.0 twinplug with webers. Absolutely no bad habits, except for cold starting you would swear it's FI and just a hair of loping at idle, almost a linear power curve. Truly a pleasure to drive on the street but a torque monster when you push it harder.

I agree My engine is a 3.2 short stroke with PMO ITB’s. Makes 290+PS and 345Nm torque. So yes, a real torque monster


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[Jeff Alton]

Have used the 120/104 in a 3.4 as well with decent results. A little less lift with a touch more duration and a much narrower lobe center. We also used a 171/149 in a 3.5 and got decent results as well.

Cheers

[jpnovak]

There are some good suggestions here.

Just MHO.

With EFI you will not want the standard cam grinds with high lift, duration and narrow lobe center. With ITBs you will have poor vacuum characteristics at low rpm which will be less than ideal for your MAP signal and fuel metering at low rpm.

I would suggest 108 deg minimum for EFI applications. Many of the cam grinders can adapt their standard modern cam shaft profiles with wider lobe centers.

[Trackrash]

Originally Posted by jpnovak

There are some good suggestions here.

Just MHO.

With EFI you will not want the standard cam grinds with high lift, duration and narrow lobe center. With ITBs you will have poor vacuum characteristics at low rpm which will be less than ideal for your MAP signal and fuel metering at low rpm.

I would suggest 108 deg minimum for EFI applications. Many of the cam grinders can adapt their standard modern cam shaft profiles with wider lobe centers.

Interesting. Good to know. I would have thought that the ITBs/EFI would want a cam similar to what is used on a carbed motor.

[jpnovak]

Gordon, If you are using an alpha-n fueling calculation (TPS only) then you can use a narrow lobe center cam. If you are using a speed-density (MAP signal) or often a blend for the fuel calculation the reversion pulse can cause noise on your MAP signal. Since ITBs have a highly minimized volume between the intake valve and throttle valve the reversion pulse has a higher contribution to the overall pressure wave that is measured by the MAP sensor. Basically, you get a sawtooth pattern in the pressure signal. This can be smoothed out using a larger vacuum accumulator manifold, or a variety of other methods. A common plenum can also help dampen pulse noise quality due to its larger overall volume.

The wider lobe center also broadens the torque curve and can give more area under the curve of power delivery at the slight expense of lower peak power numbers due to scavenging at higher rpms.

I am not saying that narrow lobe center cams can't work (98-105 deg). However, tuning can be easier and give you smoother drive quality if the entire system is thought through carefully.

Just my $0.02

[safe]

Don't use MAP with ITBs. Using alpha-n you can use whichever cam choice you want (well, as long as they don't interfere with the pistons...).

[Mark Henry]

On my"67 VW beetle conversion, 2.6L type 4. SDS EFI, 914 heads and a high duration cam I have 46mm suzuki TB's and yeah I can only run in TPS only (same as alphaN) mode. Big duration cams with ITB's have crappy vacuum signals.
This is why Porsche uses a single TB/plenum system in all of it's NA EFI production cars, it cleans up the vacuum signal for the MAP sensor.

[jpnovak]

Originally Posted by safe

Don't use MAP with ITBs. Using alpha-n you can use whichever cam choice you want (well, as long as they don't interfere with the pistons...).

I wholly disagree with this statement. A good tuner can make either system work. But yes, there can be compromises.

alpha-N makes thing easier but creates other issues of overlap areas in tuning at low TPS inputs where load can change dramatically. Think off-idle vs cruising at 1500rpm. It can be solved but not the best way to run things.

There is a difference between low vacuum caused by cam overlap and reversion and noisy vacuum signal caused by poor ITB vacuum pickup design and the combination of vacuum signals. The former is solvable by proper scaling of the MAP-based load rows. The later is solvable by proper mechanical coupling of the vacuum signal to the MAP sensor.

[Neil Harvey]

A couple of things to maybe consider.

Why would you not want the signal to the ECU that changes the quickest to be what the ECU sees first and makes changes to the fuel map. What changes quicker? TPS or MAP?

Two things we do with or without Individual throttle bodies, NA or Turbo.

No 1. We tap off each runner below the butterfly or without any butterfly's and feed into a common vacuum chamber. The signal to the MAP sensor/FPR etc is taken from this.

No2. We always run TPS as the primary map for fueling with a MAP overlay correction, NA or Turbo. MAP only is used for the Ignition map only.

If you think about these small less powerful engines, the difference in MAP from 3/4 throttle to WOT is so small, the throttle response changes in performance are almost zero. Add in head flow numbers stall out typically above a certain valve lift, torque production is limited above 6800 RPM and weak ignition, you need all the help you can find.

I think results are easily blamed on EFI tuning but often the engine is assembled with lots of different bits, none of which work well together. Don't blame the EFI control for bad choices.