Which Cam / Turbo combination?

[Yammer5]

Hey all

Just wandering what Cam / Turbo combo I should go for?

I'm having my engine rebuilt as we speak.

Fully stripped
New cylinder head
Uprated valve springs
New valves
New stem seals
Vernier pulley
New crank shaft
Glyco bearings
Wossner pistons
Wossner rods
Uprated head gasket
Lightened and balanced fly wheel
Stainless steel tubular manifold

Also I've got a Renault 19 gearbox with a Quaife LSD and Valeo uprated clutch going in.

My cam choices are : piper 270, 285 or 300
My turbo choices are : T2 with uprated internals (stage 1) or T2/T25 hybrid (stage 2)

I want fast 0-80 ish times, general road driving with some hill climbs possibly.

I'm leaning towards the 285, with the T2/T25 hybrid, but I'm concerned about the amount of lag and lack of responsiveness at low RPM's.

Any help would be appreciated.


Cheers

[Ian S]

IIRC, what 'everyone' settled on is the Piper 285 at 110°. Instead of Pipers 112°.

[Ian S]

From the buyers guide from 2011: https://www.rtoc.org/boards/showthrea...GTT-April-2011


POWER/TUNING

The Phase 2 5 GT Turbo left the factory with 120 BHP which does not seem very high now compared to many modern cars, however as the car is very light at 830kg the power to weight ratio is quite high and a moderate increase in power can give impressive results. Many people strive to reach 200 BHP and to achieve this, the RTOC recommend the following modifications:

• Correctly re-Jetted standard venturi’d carburettor set for 20 to 25psi of boost.
• Free flowing exhaust with larger bore from the turbo back all the way through to the tail pipe. Not one with a restrictor or narrow baffle.
• T25 or T28 Turbo set to 20 to 25 psi; a favourite is the ‘Tomcat Spec’ not the actual Tomcat turbo. The larger the turbo the more power and the more lag.
• Stronger actuator, preferably the T3 type with a -12 spring.
• Actuator piping changed to the ‘Cup Racing Series’ Modification.
• Delete the rest of the boost compensation mechanism as it has no effect once a decent low back pressure exhaust is fitted.
• Boost gauge to read manifold boost pressure or you’ve no clue what boost you have as the OE dash gauge reads the pressure before the carb.
• Larger than OE intercooler with alloy welded on end tanks and generally front mounted.
• Different camshaft profile, a favourite is the 285 @ 110°.
• Stronger clutch, normally the Valeo Volvo 480T, with 'soft pedal' conversion.
• Firmer engine mounts to check the extra engine movement.
• Normally silicone boost hoses and new OE or silicone water hoses as old OE items tend to split. For reliability this applies even if you’re keeping standard power.
• Oil pressure gauge to show you the reading at the inlet to the turbo.
• Adjustable bracket for top dead centre sensor to allow timing to be backed off a few degrees.
• Bottom pulley from a Campus engine; it’s smaller diameter turns the alternator / water pump slower and doesn’t throw off the belt on sudden lowering of high engine rpm.
• For long term turbo reliability, not noise, a double piston dump valve, possibly re-circulating for no noise at all. Double piston as they keep the inlet pressure up when off boost giving more responsive get up and go.
• A crankcase breather oil catch tank will probably be required.
• Taking the inlet air from a cold place near the font of the engine bay through a decent flowing filter, possibly trumpeted.
• For reliability, new valve springs, possibly longer, harder and in lowered seats to match the taller cam. Possibly new collets. Possibly rocker faces over the valve stems reground to remove the edges worn by the standard cam. No need for valve seats, throats, ports, matching manifold at this power level, it will yield little power for the expense.
• NB: Modify at your own risk! This is not a detailed list, just basic guide. It's not the RTOCs fault if your engine fails after only a few minutes because you didn't understand what to do and didn't ask the right people the right questions!

[Ian S]

The OE con rods are forged so why are you changing them?

There's usually going to be a trade off between power and lag.

It might make sense to have to have the valve spring seats lowered to allow for the taller cam. And have taller, firmer springs. That's what I had done with mine.

[R5MJH]

we used the bb cam(cat cams) on the engine i built we so it and the guy who now owns it had it on the rollers and got 231 bhp with a t28 before it bent a push rod lol

[Yammer5]

Thanks for the replies guys.

I'm afraid I don't know a great deal about this type of stuff, so I'm pretty much going off advice.
I'm not after chasing big power for bragging rights, I'm more after usable power.
I kinda want a middle ground, I'd like the car to be quick off the line with minimal lag, but I'd also like some power higher up, so I don't have to change gear every second and run out of puff quite as quickly as a standard GTT.

I was told not to get the forged stuff by the guys doing my engine, as they said that they aren't going to make a lot of difference, but I decided that I'm only doing this once and as I'm not capable of doing this stuff myself, I might as well do everything I possibly can now.

I'm pretty much replacing all of the mechanical items in the car with new/refurbished uprated items.

From what you've said, it sounds like the 285 with the hybrid Turbo would be a happy medium.

Cheers

Jay

[Yammer5]

It's turns out I really do know nothing about cams.
I saw cams as another mod to increase power, similar to an exhaust or air filter etc.
But my friend has explained that cams move the power band further up the rev range, so the 285 cams power band will come in later in the revs, so in order to use that power, I would need to always be high up in the rev range.
I'm guessing that is good for track use when always on the move, but I don't think that suits my driving style.
So I think the 270 might be the best for me.

I'm now second guessing whether I should go for a larger turbo or not, is the lag on a T2/T25 really that bad?

Cheers

[Ian S]

I had the Piper 270 and a T28 and the power band started at 5000rpm. To at least 7500rpm.

Anything beyond the T2 and standard stuff and you might have lag you don't want, even the standard car actually as a lot of lag.

People who had been doing this for years, eventually tended to pick the bigger power and deal with the lag as the end result is a lot more rewarding.

Hence people in general having the 285 @ 110°. Or maybe the Cat Cam. There's duration, overlap, lift. All have an effect and to get it right is where the tuning comes in. It not as simple as just bolting on power. You are using a low compression engine that is pointless without boost. In mine I raised the compression a bit as well as having 24psi available. I had the piston tops 'dished' and a smaller compression chamber volume in the head, the idea being to increase swirl and decrease detonation so I could run more boost with the higher compression ratio.

My recommendation to you is to have a bigger engine, say the Volvo 1.7 or the Megan 1.8, sort of thing, or the 2 litre. That, with low boost, will give you want you want and is what I would have if I had a 5GTT again.

[Yammer5]

Thanks for all the help Ian.

[Alex]

As ever it really all depends on what you want to achieve performace wise. From what you've said I would go for a T2/T25 or even a full T25. With a smaller turbo you don't really need to be changing the cam but if you've got the engine apart it makes sense to add something like a Piper 285 dialled into 112ish (mines at 114) so theres always scope for a larger turbo in the future if you want.

I honestly wouldn't bother with forged pistons and/or steel liners, they'll be more throuble than they're worth in your application.

For reference, my car has been running a T2/T25 turbo at 15psi with a Piper 285 @ 114d on track and it's proved to be very reliable and quick. O.k. it's not massively quick compared to people who chase SQM times but it's fun, and thats what it's all about!

If you want to go out in my car at some point just let me know

[Yammer5]

Thanks Alex

Im probably really over thinking this, but im spending alot of money and i cant afford to do it again if i get it wrong.

Ive had some info which is possibly abit extreme, people have said that the 270 cam will just run out of power far to early, but other people have said that the 285 cam will have no power unil high revs.

What i want is to be able to keep up (beat) the modern day hot hatches like Corsa VXR's, Fiesta ST's etc, so essentially have a 0-60 time in the low 6's.
Id prefer not to run out of power at 60mph, but im not interested in anything above 80mph, so im looking for the best Cam / Turbo combo that will give me what i need.

Ive heard similar info about turbos, where the T2's run out way too early and the T25 - T28 wont spool up for weeks due to lag.

Any help is really appreciated.

Jay

[michael tierney]

personnally i wouldn't bother with the cam either.....maybe a T2 with a 360 deg bearing which will run high boost.....an adjustable timing sensor and a rolling road session to make sure ur not detonating as this seems to be most peoples downfall at some time or other(including mine!!)

[Ian S]

people have said

Evidently people who don't know!

I don't see how you can get this right.

You need to get yourself some meaningful experience with these cars / engine before spending anything at all.

They don't 'run out of power' at 60 or 80mph. They don't stop accelerating. Some T25's do lag somewhat annoyingly then don't deliver much more than a T2 with a Nissan Silvia compressor. Others jolt the wheels straight into spinning at 5000rpm which is fun but doesn't make a fast car. A boring steady big turbo makes a fast car, with some, maybe mine, doing 0 to 60 in less than 5 seconds if the road and tyres have enough grip, which they usually don't.

Are you using the car in towns and want to overtake 30mph traffic? Or lanes and want to overtake 60map traffic? Or overtaking's not your thing, favouring the 'traffic light grand prix'?

On lanes my car overtook more of less everything. At the TLGP, before speed cameras every 200 metres, it could keeping up with, or soon catch up with, decent motorbikes, never mind cars. At 30 mph however, wheelspin all the way past with the steering wheel turned at 90° to keep going straight. And lag until 5000rpm in first, 4500 in second, 4000 in 3rd. It was loud, raw and hard work in town. I'd have a 2 litre next time for an easier and quieter life with traction from the off.

Who's doing al the engine work for you? Are they being honest with you? Don't they know what they're doing with this Renault C1J? Are they trying to make a 500BHP engine for you?

[Ian S]

Piper 285 dialled into 112ish (mines at 114)

Dialled in? The 110° was the Big Jim version that got the fast times and 240+ bhp, Mike Spenser, Lloyd Bush, Brad and others.

110° (or Pipers original 112° for their 285) is the camshaft lobes angle ground during manufacture, not that dialled by the user with a Vernier pulley during fitting, which can be that or either side of, depending of tuning choice. If I recall correctly.

[Ian S]

Im probably really over thinking this, but im spending alot of money and i cant afford to do it again if i get it wrong.

It's a mistake to believe that it'll last a log time because you have brand name pistons and rods. My engine, with standard pistons and con rods, failed due to a collet coming off a valve, or the valve stem breaking. My previous engine failed due to a collect coming off. At one point, some people where saying they wouldn't use Wossner in their C1J even if they were given them for free, I don't know anything about that brand.

A lot of engines fail due to poor oil quality, oil leaks, water leaks, overheating, detonation, turbo failures due to oil pollution with petrol or debris. Because your parts are new and expensive doesn't make them immune to these things.

Many people were having failures due to Piper cams regrinding on shafts with poor metal that wore away after a few months, but Piper blamed Renault for faulty new followers. People when over to Cat Cams instead.

A Renault 19 gearbox probably has the wrong ratios for a boosted 5GTT, or standard one.

You're just going to throw away your money with this engine. You're already throwing it away.

Possibly for vastly less money you can have a mildly boosted standard engine and bolt on's, have plenty of fun and learn some stuff. And maybe still afford to have it repaired a couple of times.

[Jimmy_GTT]

I have some experiences with turbos.
Standard T2
T2 hybrid with 0.35 than 0.47 AR turbine housing
T25 tomcat
and finally GT2056

The hybrid is ok till 160-170hp with low lag. With the T25 you can go over 200 but with increased lag.
In the last 4-5 years I'm running on the GT2056 and I can say it is perfect. Low lag and performs over 200hp.
I won't change to any other turbo.

[francob80]

The OE con rods are forged so why are you changing them?

Is that a fact Ian ?

[Ian S]

As far as I'm aware. It been a long time since I really knew all this stuff, seems like a decade ago, but I recall my graduate engineer pal had seen and worked on, and with, a lot of con rods, forged and cast, and said the 5GTT C1J rods are forged and showed me how to tell the difference.

If they were cast, would they take the abuse? 350bhp at least, or over 500bhp if those Scoff, and other, Nitrous people used them. And 9000 rpm, or whatever, with Sparkie.

Also recalled him measuring the thickness of the OE pistons tops as 13mm.

[Yammer5]

CBG are building it for me.
Ive decided on the 270 cam with a T2/T25 turbo, i basically want a really quick 0-60.
Im going to get Toyo R888R or similar to help with traction, these and the LSD should do the trick.

Cheers

[Matt Cole]

CBG are building it for me.

Cheers

Is this Bob at cgb?

[Yammer5]

Yeah, they have done some fantastic work, I'll have to post some pics of the engine build.

[Ian S]

He's a parts seller, not a graduate engineer who knows....

Whatever.

Lets have a look at some pics

And to 60MPH a set up like the list in my guide, with a 285 @ 110° and T28, etc, etc, will leave your new build in it's exhaust fumes. More than a decade ago I took a pal to another well know parts seller who called themselves a tuner. He'd bought £23,000 of their bulls**t and on the drive back, 0 to 60, he could do no better than to just about keep up with my car. And I maybe only had a standard cam and smallish turbo then. I went a lot faster later. So did he, once we took his engine out and changed all the nonsense for effective engineering. I seem to recall my car could do 0 to 60 in about 5 seconds if I could get good grip.

You'll probably still have good fun in it though.

[Alex]

Dialled in? The 110° was the Big Jim version that got the fast times and 240+ bhp, Mike Spenser, Lloyd Bush, Brad and others.

110° (or Pipers original 112° for their 285) is the camshaft lobes angle ground during manufacture, not that dialled by the user with a Vernier pulley during fitting, which can be that or either side of, depending of tuning choice. If I recall correctly.

You don't say, Ian

When I fitted my 285 and measured it on the dial gauge it was 114 degrees so I just left it at that. Works well to be fair.