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-5's Vs Rs's On A Larger Then Stock Motor

Piggaz

By Piggaz,
in Engines & Forced Induction

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HYPED6
HYPED6

Here is my little story. I have been wondering the same thing the last 6 months or so. This is what I have found. I bought my gtr with plain bearing -5's. Now with Cams, 10.25 @ 292 Good after mar

JAGR33
JAGR33

Did you put your car on a 4wd dyno? That usually shows a lower figure than in 2wd mode. I can understand your frustration but let me tell you this, don't take dyno figures as gospel, they are a tunin

R31Nismoid
R31Nismoid

Nothing I haven't told him on 3 occasions now since Aug 2010, even earlier it think. So basically what you are telling us is that 6 months down the track. You haven't taken it to the track yet? O

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wolverine Grand Master

wolverine

Posted
Posted

Cams is always an interesting debate, long argued, no real end result.

There are basically two ways of thinking.

- Larger cams, combined with a LOT of head work, oversized valves and all that $$$ jazz - works very well great power overall. You do seem to take a hit in lower RPM however.

- Smaller cams, combined with a minor tidy up - works well but gives better off/on throttle response & low RPM performance as a result.

Obviously the is about as gross of a generalisation as one can make without typing a thesis.

The bigger/flow will obviously be more efficient as RPM and perhaps make more power. Yet the smaller option will perhaps not make quite the same peak yet give you more gains on/off the loud pedal.

Depends what you are after really. Most Racepace GTR's here in Melb 2.6-2.8ltr run factory cams from what it appears. Bigger than that the advice is the 3ltr does like a little bit of larger cam love given the displacement alterations.

Syd seems a different view where everything is oversized (valves, cams, porting).

Issue is - all the results are on a dyno for both states. Now as my RB26 comparo from Racepace showed... The turbos virtually have identical boost/power graphs (-9 & -5). Yet on the street/circuit it is markedly different. It would be up to the owner to decide what they are after I guess.

Pity you weren't about over Xmas. I do intend to come up again in a month or two so I can show you the Mexican build lol.

Yeah and we all packed in the trouser department too. :nyaanyaa:

Ash are there any of the examples using OS valves at Racepace or do they prefer using stock sized valves.

Piggaz Grand Master

Piggaz

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Rightio. Another cheeky question.

Would a 90 mm exhaust from the front pipes back (twin 3 inch into a single 90 outlet) be big enough.... or do we "really" need a 4 inch.

3.5 inch (90 mm.. close enough) vs a 4 inch (101.6mm)

JAGR33 Grand Master

JAGR33

Posted
Posted

Rightio. Another cheeky question.

Would a 90 mm exhaust from the front pipes back (twin 3 inch into a single 90 outlet) be big enough.... or do we "really" need a 4 inch.

3.5 inch (90 mm.. close enough) vs a 4 inch (101.6mm)

I'd say the 4 inch exhaust will benefit throughout the rev range.

It's just trying to keep the sucker quiet!!!

Tangomatt has a 4 inch cat back exhaust with custom Racepace mufflers, quiet on idle but oh the sound at high rpm!!!!!

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

Paul - 4" mate for 400rwkw.

3.5" for 350

and 3" for 300

See a theme? :D

Yeah and we all packed in the trouser department too. :nyaanyaa:

Ash are there any of the examples using OS valves at Racepace or do they prefer using stock sized valves.

Stock is the common choice :)

NickR33 Grand Master

NickR33

Posted
Posted

yeah but 4" exhaust and 10.8mm lift cams sounds awesome :thumbsup: ... love it when the whole car shakes at idle hehehe... even though its bottom end and mid-range sucks compared to most of the other Racepace cars... but that's more to do with the truck turbos than anything else

oh well nearly time to run E85, up the boost and see if I can't break the turbos so I can change to -5 :pirate:

Nee-san Grand Master

Nee-san

Posted
Posted

yeah but 4" exhaust and 10.8mm lift cams sounds awesome :thumbsup: ... love it when the whole car shakes at idle hehehe... even though its bottom end and mid-range sucks compared to most of the other Racepace cars... but that's more to do with the truck turbos than anything else

oh well nearly time to run E85, up the boost and see if I can't break the turbos so I can change to -5 :pirate:

I like it when I'm at the lights and everyone gives me a dirty look and winds up their windows hehe.

NickR33 Grand Master

NickR33

Posted
Posted

yep... with the uprated springs, retainers and lifters... a credit to racepace tuning it actually runs really smoothly, just a lope at idle... I think if you are going to upgrade cams go for as much lift and as little overlap as possible... so you get the most torque benefit you can without moving the powerband up too much

Piggaz Grand Master

Piggaz

Posted
  • Author
Posted

yep... with the uprated springs, retainers and lifters... a credit to racepace tuning it actually runs really smoothly, just a lope at idle... I think if you are going to upgrade cams go for as much lift and as little overlap as possible... so you get the most torque benefit you can without moving the powerband up too much

Well I have 270's @ 10.25 so more duration and less lift. I only rev mine to 8 - 8.5 so i could get away with the 260's...

Rolls Grand Master

Rolls

Posted
Posted

Ive noticed how big overlap cams bring boost on sooner with turbo cars, this is no doubt due to the extra exhaust energy being delivered to the turbo instead of crank.

Could a similar thing be achieved with stock cams, just retard the ignition when coming onto boost, whether or not the extra torque the boost gives cancels out the lack of power from the ignition I can't imagine it'd be any different from just running big cams. You would only need to do it from say 1500-2500 rpm to get it spooling a little earlier.

What do people think?

I found this out due to a bug with my nistune ecu where occasionally the cold start map would shit itself and put max retard on the timing. Could get 4psi in neutral and it would make the stock turbo surge like crazy at 2000rpm due to it building 10psi with the throttle barely cracked open. Made the car undrivable as it was so doughy but so much boost that it would kick back and forth from no power to loads of power as it came out of the map.

elrodeo666 Mentor

elrodeo666

Posted
Posted

How much difference does that Vcam make?

A lot !!

Standard idle feeling, boost on quicker and at lower rpm.

Can run laggy turbo / turbo's setup and lose the lag.

Its a shame theres not more being used in Oz.

Driven this setup a few times now and its response and power is bloody awesome.

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