87 GN octane and braking

[waldo786]

Hi all I was wondering if the 87 Grand National uses high octane gas or can be run on regular. I was also wondering how the braking is on these cars. Any help would be appreciated. Thanks!

[The Old Guy]

They require premium fuel, and they go a lot better than they stop!

[waldo786]

What is their compression ratio and do they have disc brakes at least in front and drum in back?

[2seater]

If you never get into boost from the turbo it will probably run happily on regular 87 octane, but if you use the engine anywhere near it's potential, premium will be required. At the least you will get spark retard from engine knock or at worst blown head gaskets or broken pistons from detonation.

[Turbo Loyd]

[color:\\"blue\\"]Regals have standard G-body brakes with disks up front and drums in the back. The compression ratio is 8 to 1. With the waste gate rod loose regular will be fine, but the car is no fun to drive. You could use alcohol injection to supplement the 87 octane when the need for a little boost kicks in.

[waldo786]

I'm new to turbos so excuse my dumb questions, but does the turbo only engage when accelerating then?

[Turbo Loyd]

[color:\\"blue\\"]While the intake streams and exhaust streams always pass through the turbo, it is usually spinning relativley slowly, a heavy exhaust flow is required to spin the turbine wheel fast enough for the compressor wheel to really compress the inlet charge.

Of course you control the amount of air passing through the system with the throttle. It is really difficult to resist the urge to mat the go petal thought, at least for me . . . . so that is why adjustment of the waste gate to provide a level of boost to support the octane of the fuel is necessary.

[Matt Harwood]

If you've got a turbo, use the high-octane gas--it's cheap insurance against potentially serious engine damage. The compression ratio is part of it, but the boost created by the turbo effectively crams A LOT more air and fuel into the combustion chamber than just vacuum does in a naturally aspirated car. Because of this, you'll see cylinder pressures far in excess of what the compression ratio would suggest. With all that pressure in there, if it doesn't detonate at exactly the right moment and with a sufficient amount of fuel, the pressure has to go somewhere. Usually, it's through the head gasket, but in severe cases, it'll put a hole through a piston or worse.

Yeah, staying out of the boost may let you run regular gas, but if you tip into it even once, and you hear it rattling away in there, it's too late. As someone who has built and raced a lot of super/turbocharged cars, the high octane is cheap insurance, believe me. You'll have a lifetime of premium gas upgrades (what is it, about $0.20/gallon difference--that's nothing!) for the cost of replacing your head gasket once.

Turbo cars are not like other cars. Respect the boost for its performance, but also its potential for destruction. Sometimes it's a very fine line, and good gas is definitely cheap insurance. You shouldn't ever have any problems with a stock GN's head gaskets if you run 92-94 octane in it all the time.

Hope this helps.