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Discussion Starter #1
It's probably been asked before, but whats the highest lift cam that can be used with STD,valves,springs etc.
Will 10.2mm lift bind up?

Ta

Andy
 

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The maximum lift Tomei offer, on standard springs, is 9.15mm at 260° duration or 9.25mm at a slightly reduced duration.

My advice would be to keep within the above boundary's
 

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How

about JUN 9.7 mm lift 264 or 272 stage 1

Gary
 

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Discussion Starter #5
HKS

I was looking @ 280deg HKS cams with 10.2 lift. You advise this is too much lift. HKS's 272deg cams are 8.7mm lift.

Are there any 280deg cams that are near the max lift(9.15) on the market?

Basically, im looking for cams to suit my HKS T51R turbo conversion. The head if fully flowed and ported with bronze guides but STD valves. Im not looking for a high RPM engine. Say a 7500RPM limit. Im not that clues up on cams hence the questions. Which cams would suit my application?

Cheers Chaps

Andy
 

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R32 Combat,

The valve spring rate requirement increases as the lift goes up to close the valves after they have been opened.

Tomei also offer taller lifters to compliment their high lift cams.

The first valve spring-up grade Tomei offer, allows a lift of up to 10.8mm at any duration of their cam offerings.
 

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Discussion Starter #8
SteveN

Why don't you ask Ron @ RK why you run longer duration and more overlap with larger turbos? Ron has forgotten more than you know about engines. He doesn't get bogged down off the line nor does he have massive lag between gearchanges and he runs 280's I believe.

Hugh

Thanks for the advise
 

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Also, apart from at TOTB3 (as running a sequential box i think), i remember for years, since Rons had the big single turbo spec, his cars 1/4mile times have always been hampered by the fact it used to have massive lag (that was easily noticable when watching the car) between gearchanges... ;)
 

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Discussion Starter #11
Confused.com

I've gotta take someones advice as I know not to much about cams. Sure, I've had quite a bit of practice tuning a 1380cc A series to 140hp @ rear wheels in a MG midget. But the RB26 is a different kettle of fish. Both Abbey and RK have told me that longer duration cams with more overlap will suit my turbo better than what I've got and that 280deg cams are a good choice.

I asked a question about what lift the STD spring will take before it binds up. Hugh gave me some advice and you jump on board saying

'why does everyone want such huge duration/overlap with such massive and unrestrictive turbos?'

'no wonder you see these people running huge singles that has massive lag between gearchange and cant get off the line without bogging'

With one breath you suggest you dont know anything about cams(like me) by saying

'why does everyone want such huge duration/overlap with such massive and unrestrictive turbos?'

Then you suggest that you do by claiming that longer duration cams mean massive lag and bogging down.

I've got the info I asked about thanks and am now off to the moon to play cards with Hitler and Elvis Plesley :rolleyes:
 

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Hi Andy,

One problem you may have is keeping within your desired
rev range (7500rpm) with a more lairy profile (280ish)

My peak power is at 7400rpm with 264in / 272out.
So yours may well be higher with 280's.

I believe the Ron's problem between gears MAY have been high
rpm changes with a standard box and it's reluctance to engage gears.
I believe the new box sorted this.

Good luck with the car matey , sounds like it's gonna be awesome :)

Jay
 

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WTF you on about? HOW is that contradicting myself? Can you not read?

I say the same thing twice!

WHY does everyone use big duration (and hence overlap) cams on engines running big turbos that would give little or no backpressure, as this totaly ****s up throttle responce when coming back on the throttle, causing lag (i mean PROPER lag, not high rev powerband that some people think lag is).

The 2 people whos PMd me so far agreeing obvously understand what i mean, lol.

OK, as your the expert and i know nothing, lets have a lesson shall we...

The idea of long duration on a turbo car (ie DIFFERENT to a N/A car) is to an extent overcome exhaust back pressure - they work well with restrictive turbo's - allow them to rev more as you are keeping the exhaust valve open for longer allowing the gases to do one.
Disadvantages of this is it slows the gas velocity down, which gives less lowdown power and poorer idle, but neither is a terrible problem on a car that SUITS mega duration, ie one with a relativley restrictive exhaust side, mainly small turbo(s), but on a car with a massive unrestrictive turbo you will end up with shitloads worse throttle responce than if you used less duration/overlap, for usualy little worthwhile top end gains (Id rather have 15bhp less when ive got 700bhp than have the car bog to **** on ever gearchange losing me half a second a gearchange and letting a less powerful but less laggy car pull a few car lengths every time i change gear...)

The above is a very basic explanation, but ignore it anyway, i know nothing as im not the bloke with a sign above my garage that says "Racing" "Tuning" "Motorsport" etc, lol

Cams CANNOT be properly tested in their suitablility on a turbo engine by a RR or Dyno run, ONLY (IMO) by "seat of the pants" testing (The ASS DYNO, pmsl), ie going and fooking driving the car, as its NOT just about where the power and torque is on a dyno graph (tho most people think it is), its about how long it takes, when already in the powerband, for the car to be back on full power when you put your foot to the floor, ie REAL lag, not "lack of lowdown power" which most people think lag is, and a RR/Dyno sheet doesnt show this as its done IN GEAR.

Generally youl find, to keep an acceptable (ie not enough for everyone to pull away and totaly ruin your run/lap) amount of lag, the bigger the turbo, the less duration/overlap you can have...

Frankly id rather not share my help with people like this as its blatantly not appreciated, but as your so determined to shoot me down i had to...
 

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Gotta totally disagree with some of the points you made SteveN.

The longer duration cams are generally not used in turbocharged applications because of their larger overlap, for two reasons. Blowing all the intake charge through the exhaust port is one, reversion is the other.

If you used longer duration cams with restrictive turbos, some of the exhaust gases would try to escape through the inlet port as the pressure on the exhaust side is higher than the intake.

If you used longer duration cams with a large turbo, you would lose some of your intake charge through the exhaust during the overlap.

Saying all that, with some cam timing, you could alter the points where the inlet and exhaust valves open and shut, thus reduce the overlap. I know a few high hp GTRs running fairly long duration camshafts.
 

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Emre- I dont think long duration is a particularly good idea, thats my point, but UK GTR owners think its the thing to do it seems.

But about reversion...

Reversion is an issue, but in practice a small issue compared to what i mentioned, hence why i didnt bother.

I mean, you almost always end up with more backpressure than inlet pressure on turbocharged cars, so if reversion WAS an issue youd never be able to run any overlap on turbo engines, and thats simply not true.
 

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Just a quick question with regards to cam selection, based on the following facts:
1) Larger turbos are designed for more airflow, both turbine and compressor flow
2) Larger cams (both in lift and duration) are designed to flow more air through the head.

Wouldn't the combination of larger cams and larger turbos compliment each other?
 

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SteveN,

The point I am trying to make is that, longer duration cams with smaller turbos is totally illogical. It will not help overcome the exhaust back pressure as the cams are not the restrictive part of a factory setup. The back pressure will remain the same with larger overlap which in return will degrade the intake charge.

With a large turbocharger and cams, the response will be fairly dismal without proper cam timing. If small part of your intake charge is escaping through the exhaust ports, you will witness the increased lag. By reducing the overlap, this can be improved greatly.

Are you suggesting factory camshafts would be better suited for a T78 than a pair of 264s or 272s...? You have to be able to get the larger amount of air a bigger turbocharger supplies, into the engine, how do you suggest we manage this with small camshafts...? There are no cams with factory duration and 10mm+ lift out there, maybe there is a reason for it.
 

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DoughBoy_Au said:
Just a quick question with regards to cam selection, based on the following facts:
1) Larger turbos are designed for more airflow, both turbine and compressor flow
2) Larger cams (both in lift and duration) are designed to flow more air through the head.

Wouldn't the combination of larger cams and larger turbos compliment each other?
It goes a lot deeper than just that.

It is the complete marriage of the whole engine; port velocity, cam design (ramp rate, lift, duration, lobe separation), displacement, turbos, compression ratio, port size, injectors, ECU, timing, what rpm you want the power, what wheel size you have, what's you barometric pressure, you get my point.
 
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