7a cam timing

[S2central.net]

I thought the considered view, proven out by Doug and others was that the 7A inlet cam (in conjunction with 7A exh cam at least) reduces torque in the mid range, increases lag and spool times and made the car generally less tractable on the road...

I think there was a view that the 7A inlet could create more power at the top-end of the revs and Dougs buttdyno perhaps proved that. Be interesting to know if there was any real world tests on the same engine with different cams - mapped accordingly.

[prking53]

i have noticed 1 thing since the 7a,s .................i have a leaner fuel burn ............and rev,s roar up at mid range ............................. cant be bad or what? ........... ps im still using the standard 3b injectors

[prking53]

ignition timing.7a,s on 3b

as u know lads i have installed the the head busting 7A,S ................. a 3b lump.................the quetion is do i now change the ignition timing/...........AS IT A BIT ROUGH AT 2000 YES 2000 REVS .................CHEERS

[prosty]

Ignition timing is set with the distributor, but it MUST be set to 0 at TDC. Then you can remap the car, MRC tuning can do that for you in the UK. Or buy a "custom" chip that's designed for 7a cams with stock injectors and MAF and turbo and so on.

[prosty]

7a cams is not ideal for stock engines with smaller turbos imo. The exhaust cam is good for increased top end performance though. I'm using machined 7a cams, before we machined them, the spool was 750 rpm slower. So it's a big difference in spool, considering my turbo NOW kicks off at around 5000-5500 RPM.

[Audi_CQ]

I thought the considered view, proven out by Doug and others was that the 7A inlet cam (in conjunction with 7A exh cam at least) reduces torque in the mid range, increases lag and spool times and made the car generally less tractable on the road...

I think there was a view that the 7A inlet could create more power at the top-end of the revs and Dougs buttdyno perhaps proved that. Be interesting to know if there was any real world tests on the same engine with different cams - mapped accordingly.

They tested it and got that result, but why? That's the question people should try to figure out
What was "wrong" with the setup they used since the cams did little or nothing for them?
It's always important to get the right mix of parts and when something doesn't work you have to figure out why. If you find the answer you get results, if not you get left behind by they who does

[philip walker]

N/A cams have a greater duration/overlap to enable the engine to produce a vacume to draw the air/fuel in to the cylinder.
On a forced induction engine cam, greater lift it needed but not the duration as fair bit of the charge air/fuel will pass through without combustion.
When n/a cams are fitted to forced induction engines owners report their cars feel more laggy, the power delivery is more focused.
The challenge it to design a cam that will suit a modified engine giving revs to produce BHP whilst still keeping the gas speed high at low revs for torque. This is why some engine producers have variable valve timing S4 2.7 T etc. Others have exhaust valves fitted into the manifolds Yamaha Exup etc.

[Audi_CQ]

N/A cams have a greater duration/overlap to enable the engine to produce a vacume to draw the air/fuel in to the cylinder.
On a forced induction engine cam, greater lift it needed but not the duration as fair bit of the charge air/fuel will pass through without combustion.
When n/a cams are fitted to forced induction engines owners report their cars feel more laggy, the power delivery is more focused.
The challenge it to design a cam that will suit a modified engine giving revs to produce BHP whilst still keeping the gas speed high at low revs for torque. This is why some engine producers have variable valve timing S4 2.7 T etc. Others have exhaust valves fitted into the manifolds Yamaha Exup etc.

God points here , but what if we look at it this way:

Instead of a turbo producing 1bar boost we run the engine in a room were atmosphere has 2bar pressure instead of 1.
What cam would be best: the turbo one or the NA, and why?

[philip walker]

N/A cams as the ambient pressure would remain a constant.
In the same way as we live in 1 bar of pressure.

Do I get a prize?

[4WheelDrifter]

7A cams are bad enough below 4k rpm even with 2309cc. Better with ~2500cc though.

[Audi_CQ]

N/A cams as the ambient pressure would remain a constant.
In the same way as we live in 1 bar of pressure.

Do I get a prize?

Yes I agree, but why?

As you posted earlier:
"On a forced induction engine cam, greater lift it needed but not the duration as fair bit of the charge air/fuel will pass through without combustion.
When n/a cams are fitted to forced induction engines owners report their cars feel more laggy, the power delivery is more focused."

What's the difference between a 2bar atmosphere and a turbo with 1bar boost?
What made you choose the N/A cams now?

[prking53]

7a cam ..good or bad

hay! guys ,..........forget the science,... behind it all ..is using the cams good on the 3b or what. eexplain someone in laymans terms please............

[philip walker]

hay! guys ,..........forget the science,... behind it all ..is using the cams good on the 3b or what. eexplain someone in laymans terms please............

Sorry to go off topic,
You would be better of looking for some Rs2 cams or having a spare set of cams reprofiled to get the desired lift without long duration for around £100 ea

[Audi_CQ]

hay! guys ,..........forget the science,... behind it all ..is using the cams good on the 3b or what. eexplain someone in laymans terms please............

I'm also sorry to go off topic , but my intension was just to make people think for themself and not just believe everything that's written on the web
I often ask myself WHY? when reading on forums.

First to try to answer your question
If your engine is stock or just chipped, don't use 7A cams. If further mods are planned try this:
If using std parts set cams on std marks.
If using 7A cams with adjustable cam pulley, try to set them 5 degrees adv.
If fully adjustable "chainwheels" is used set ex 5 deg adv , and inlet at std timing.


In this case of 7A cams you get a lot of different answers. Why? Different engine setups give different results. You always has to find the weakest link in your setup. If cams isn't the weakest link you get little or nothing out of changing cams.

In a stock/near stock(chipped) engine the weakest link on the exhaust side is the restrictive EM and turbo. Since they create a lot of backpressure you have to use cams with little or no overlap to avoid exhaust blowing into intake at overlap. 7A ex. cam has the same cam timing as std cam, just more lift, so doesn't harm. Very little gain so if not planning for further mods I wouldn't change it.

On inlet side the problem is again the turbo. It just doesn't have a lot of capasity, and when the turbo can't deliver anymore it doesn't help what intake cam you use. Turbo is maxed out anyway. Limit is about 270-290 real hp on a chipped but otherwise stock engine. The turbo will be empty long before you get to the kind of RPM where the 7A inlet will help out (~5k) so no use for the extra duration here so stay with the std inlet.

Just my 0.02$

Cheers,
Roger

[prking53]

is my set up suitable

hi roger,is my set up suitable for the 7a cams im running 3b standard lump rs2 ex..rs2 turbo .....the rest standard.............. the valve timing/ ignition ...standard..........?