Early GTA Atmo in at JL Engineering.

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Early GTA Atmo in at JL Engineering.

Postby John Law » Sat Jan 10, 2015 12:07 pm

Just a short and sweet one. Low mileage (30,000) atmo came in for suspected head gasket failure and all the doom and gloom that goes with it but it turned out the other garage miss diagnosed the issue so the happy customer decided to treat the car.

Amongst general service works as the car has been sitting for some time the car got a JLE holley conversion, stainless steel 3 branch manifolds and silencer, new water pump and thermostat, new aluminium radiator, JLE alloy engine bay water pipes, Magnecor leads and detailing of the engine bay.

How the car arrived. On a low loader and overheating..
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Engine bay looks dirty and unsightly. Standard carb setup and leaking hoses.
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Goodies!
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Trial fitting and bracket making while we clean up as we go. Fresh rocker covers are going to transform the engine bay.
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Bespoke alloy water pipes.
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Fitting the kit and fettling bits and pieces.
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Fitted the radiator and also had the front bumper mounts and tie bars blasted and powdercoated as they were beginning to look rough as they all do.
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And the final result! Really happy with how it turned out and the customer loved the transformation of the car both in looks and performance.
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Re: Early GTA Atmo in at JL Engineering.

Postby BIG_MVS » Sat Jan 10, 2015 12:31 pm

Nice one John thanks for posting. It's great to see these cars getting some love and upgrades.
1989 GTA Turbo - Stratos Blue
1994 A610 - Montana Red (For Sale)
Some GTA/A610 Parts For Sale:
https://www.ebay.co.uk/sch/m.html?_odkw ... e&_sacat=0
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Re: Early GTA Atmo in at JL Engineering.

Postby Trevor Skedge » Sun Jan 11, 2015 10:23 pm

Looks great Jon well done. I think the Atmo is as good as the Turbo, just lacks the glamorous badge and white is perfect too. Is this going on the rollers at some point so we can get an idea of the benefits of Manifolds and carb?

Trevor.
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Re: Early GTA Atmo in at JL Engineering.

Postby Custard » Mon Jan 12, 2015 7:44 pm

Trevor I think you're hundred percent right on that, in the 80s the word Turbo sold cars and people loved that wack of power when the Turbo came in. I personally Think that Renault D tuned the atmo so that it wasn't in competition with the Turbo, the Turbo is a whopping 40 kg heavier than the atmo which is over Six stone. So Lets heat the inlet manifold straight off the cylinder and heat the bottom of the carburettor to boil petrol. Also Great for hot starting as the fuel is vaporised away. When you liberate the atmo engine you get a fantastic linear power delivery which is welcome when cornering, and a fantastic v6 exhaust note out of that system.
I have done the above conversion albeit slightly differently, I would spend a bit more money and get the secondary metering block put on the carburettor before you put it on the Rolling Road so that you can rejet the secondaries, Which will mean you will get the best out of the conversion, also keep your old air cleaner and at later date you can modify it so the new conversion looks original and the induction air is taken from the outside, Cold air makes a big difference.
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Re: Early GTA Atmo in at JL Engineering.

Postby Custard » Mon Jan 12, 2015 7:47 pm

Original air cleaner
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Re: Early GTA Atmo in at JL Engineering.

Postby johnb » Mon Jan 12, 2015 8:18 pm

Custard,
So there's a Holley under the air cleaner in your photo?
Can you explain the reason for the twin air inlets to the air filter housing, if for other reasons than having a larger cross sectional area feeding the filter?
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Re: Early GTA Atmo in at JL Engineering.

Postby Custard » Mon Jan 12, 2015 8:40 pm

Johnb
That's it, plus to fit the original air cleaner is not that hard to do, had a thick steel ring laser cut to fit over the Holly exactly, flattened and then welded to the ring to the bottom of the air cleaner then welded up the holes from the old carbs,
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Re: Early GTA Atmo in at JL Engineering.

Postby johnb » Mon Jan 12, 2015 10:46 pm

Thanks but why the two air inlets. Is that the standard arrangement on the GTA? My A310 has a single air inlet to the filter housing, just interested why your GTA has two.
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Re: Early GTA Atmo in at JL Engineering.

Postby Custard » Tue Jan 13, 2015 7:14 pm

Johnb
No it is not standard on GTA I cut and welded in the second induction part from a secondhand Air cleaner I got from RATS so as you say increasing The cross-sectional area of cold air into the air cleaner.
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Re: Early GTA Atmo in at JL Engineering.

Postby johnb » Tue Jan 13, 2015 8:43 pm

Custard,
Thanks for that, should breathe better.

John,
Looks a well engineered upgrade, can see why the customer is happy with it. As Trevor commented, it would be interesting to know if the car is going on the rollers.
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Re: Early GTA Atmo in at JL Engineering.

Postby John Law » Wed Jan 14, 2015 10:01 am

Cheers guys, thanks. Yes I agree, a nicely tuned atmo will be quicker than a turbo. The throttle response is a much better which makes for a nicer experience in many ways.

I've had a couple on the rollers and also a few claims from international customers who have dyno'd their car after fitting and they range from 180 to over 200 crank horsepower. Essential its just a bragging number as dynos can be so easily manipulated to give a pleasing result. The best thing for anyone to do who is interested is go out in a car with the modifications or speak to one of the guys with the kit to see if they are pleased with the performance.

Hi Custard, great to see your car going well at Origine RS. Following on from what you were saying the Holley is very easy to tune for power as jets, metering plates, power valves and vac secondary springs are available off the shelf for very little money which means you can tailor the fuelling to any modifications you have done or plan to do with your engine.

Hey Johnb, the customer is planning taking it to the rollers with me at some point but is just enjoying driving it for now. Its surprising how many people spend a good deal of cash on parts but hold back on setup. :?
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Re: Early GTA Atmo in at JL Engineering.

Postby Custard » Wed Jan 14, 2015 7:47 pm

Yes as per my earlier post before you put it on the rollers put the secondary metering block on the carb, as the backset need much bigger jets than the front because when the secondaries open the air Speed through the carb reduces as the carb cfm is slightly too big for the engine so a bigger jet is required
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Re: Early GTA Atmo in at JL Engineering.

Postby Custard » Wed Jan 14, 2015 7:56 pm

Ragnotti drift
Have you thought about building the manifold with the centre partition this would make it much easier to tune, and also gives better low end power. Plus the key to the centre partition to get the best of both worlds is to leave at two or three mil gap at the top so that it balances between both sides.
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Re: Early GTA Atmo in at JL Engineering.

Postby John Law » Thu Jan 15, 2015 9:15 pm

Hey Custard, what size Holley are you running? We use the 390cfm having run a few on the rollers and with a wideband on the road we have been ok with just upping the mains a tad and running lighter vac secondary springs. I've messed about with power valves and secondary jets but monitoring the AFR's with just the first two adjustments alone we achieve 12 to 12.5 under load so left it at that. I have noticed that some of the Holleys have arrived with different jets from the factory which was odd. We start with 52's and go from there.

Funny you mention modifying the manifold further, I have plans drawn up for a duel plane manifold that I plan to fabricate sometime. Probably not any time soon unless a customer shows an interest. Things then starts getting more expensive and then you could go down the triple weber route, which I have a few pairs in stock if anyone is interested!

I really like that the atmos are getting played with, we should arrange an atmo shootout day!
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Re: Early GTA Atmo in at JL Engineering.

Postby Custard » Thu Jan 15, 2015 10:42 pm

Yeah that would be good fun. Yeah I made my manifold with the maximum height I could get so Making a large plenum, from memory I am running a 56 on the primaries and 62 on secondaries and running the second lightest spring, But I am running cold air from outside rather than from the engine bay. I tried to change the distributor to a programmable one but none were available for the PRV engine as I think there is a lot more to be had on the timing side.
The one thing that also worked well was disconnecting the vacuum advance and then advancing the distributor manually to what the vacuum did if you get what I mean, because the old timing set up on tick over was on TDC or just after from memory probably because the fuel from the old carbs was highly volatile being fully vaporised and 9 to 1 compression they must've suffered from run-on when they turn the engine off.
Although the overall maximum advance remains the same, now that the fuel air is colder it can be brought back to BTDC, this has had a dramatic effect on fuel economy on Tick Over the gauge no longer disappears when you are in traffic I now average 28 to the gallon and +30 on runs. The power of the ATMO :pint
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