R5 GTT Hill Climb Racer - Increasing boost.

[dalla]

Hi Guys

I realise this is a total noob question, that has likely been asked a thousand times. But i hope that you will help me anyways

I have this R5GTT Hill climb race car. At them moment it is running 130 hp, and of noticeble upgrades are an alloy intercooler and a Scorpion exhaust.

I do not now how the carb is jetted, but this is where i get to my question.

I would like to up the boost a bit, and maybe see 150-160 hp? (What is realistic?) I will run the car on my mates RR, and will naturally check the AFR.

But heres my question. Does anyone have an "recipe" for this? Whats required jetting wise? Any pointers where to buy the new jets?
Is an alloy lobster intake nessecary? Anything else to take into consideration?

Kind regards
Dennis
Denmark

[RussellT]

Hi Dalla
If you want to improve your times up a hill the first thing you need to do is get a limited slip diff. Then look at suspension set up and engine power.

Have fun

Russell

[dalla]

Hi Dalla
If you want to improve your times up a hill the first thing you need to do is get a limited slip diff. Then look at suspension set up and engine power.

Have fun

Russell

Hi Russel

Thank you for your reply. My car is built with full cage and so on, and the suspension feels quite good, at least I like the way it handles. It doesn't have a lsd however.
It is running in a standard class for now. I could just use a few More ponies, and would really appreciate some pointers on how to achieve this?

[Matt Cole]

Hi Dennis, Russ is your man as far as hill climbs etc. Do the diff,suspension and brakes then we need to talk about the carb. There's a great carb article, but this is what I would start eith:-

120mm main, 0.9mm a/c, 1.0mm first stage, 1.25mm second. Get and afr gauge and post up the results, idle, mid and full throttle.

[dalla]

Hi Dennis, Russ is your man as far as hill climbs etc. Do the diff,suspension and brakes then we need to talk about the carb. There's a great carb article, but this is what I would start eith:-

120mm main, 0.9mm a/c, 1.0mm first stage, 1.25mm second. Get and afr gauge and post up the results, idle, mid and full throttle.

Thanks a lot Matt. Any pointers on how much to increase the boost and so on? Also
Any tips to where I can buy various jets for the carb? Which AFR gauge would you recommend?

[Matt Cole]

Jets available in club shop. Dale Bigfoot may be able to help with any of the odd sizes. 160 -180bhp easily achievable with boost and a well setup fuel system.

[Ian S]

IIRC, 1.2 is the standard main jet. Changing that to 1.25 or 1.3 might be better.

0.9 might be too small for even a 1.3mm main. IIRC, the original is a 1.2mm or so.

I forget all the stuff about the enrichment jets. There's quite a bit of tweaking.

Do you have the 'cup mod' where the actuator pipes are altered such that the actuator is fed from the manifold instead of the carb top? That can increase responsiveness.

Those Scorpion exhausts might not be an upgrade at all if it's the type with the 35mm, or so, bore through the silencer, instead of 50mm.

A decent exhaust is key to getting more gas flow through the whole system, which can mean more power for the same boost, and a better ability for the engine to use more boost with appropriate fuel.

There were some good exhausts that were listed as 2 1/4 inches (56mm) bore all the way through from turbo to tail pipe. One of those transformed my 5GTT.

You should find a suitable AFR gauge at http://www.efi-parts.co.uk/

See this current thread: https://www.rtoc.org/boards/showthrea...t-etc&p=408401

https://www.rtoc.org/boards/forumdisp...mp-Information


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!

Above from here: https://www.rtoc.org/boards/showthrea...GTT-April-2011

[dalla]

Thanks a lot buddy. Think i might wait until winter and go for the full conversion?
How about the side exit exhausts? Where's the best place to buy these?

[Ian S]

I had a 2 1/2 inch (62mm) side exit made by Powerflow, sold originally I think by KTec in Bournemouth, UK. Was very loud inside the car, too loud really, hearing protection would have been a good idea.

I no longer know where to buy such parts 'off the shelf'. Someone here at the RTOC has made a few 'one off's' for the 5GTT: https://www.rtoc.org/boards/member.php?5843-Matty

I would guess with the number of 5GTT scrapped and the owners wanting to revert to standard there would be a at least a few used ones around.