Performance ford 351 v8 build

[Millsy]

Hi all, please be kind as I am just learning the lpg side of things, and I want to make a bit of a guide for built motors and lpg.
just got a 71 mustang with a gas research set up and looking to optimise the power (and hopefully fuel efficiency too)

351cleveland, with a recent rebuild (not by me), has been built for lpg dedicated. So been stroked to 393 (6.3L), 2v heads (with possible milling to up compression, as a compression test indicated 230psi, higher than standard). I am guessing a gas research cam, twin B2 converters and twin intake gas research units (don’t know what size or specs) and a 70ish L tank, hei upgrade and single plane manifold. Exhaust headers, double valve springs, roller rockers. 3.00 rear gear ratio on a c3 transmission. Somebody did it well. 0-100kph in 4.9 and quarter mile in 13.1@170 (gtech, and wheel spin a bit due to 215 rear tyres)

Fuel efficiency is shocking. Around town I get 30-35L per 100kms (7mpg). I get it’s a big motor, and I drive it hard, but I want some input to see how I can get my car faster (and hopefully better on fuel)

Ignition, hei with flamethrower 3 ign coil, ngk cooler plugs, around “7” heat range
Timing was originally 10deg initial and 30deg cent (no vac), I have just changed it last week to 8 initial, 28 cent and hooked vac to it (about 12deg, so 20deg at idle)
Is it true higher compression engines like less advance? I now get my lpg “premium” at supagas, which don’t add any butane to their mix, and saw idle went up due to the efficiency, so I would say I have 110 octane, what timing curve would be best for “premium” lpg and high compression?

At 5500rpm, I start to hear the beginnings of backfiring, I am assuming I am going lean at those rpm, meaning not enough fueling, would I be correct in saying that? Bit of a blanket statement but is there some easy ways to fuel the top end with my dual “ohg x-1”/b2 mixers? I don’t think my line is 3/8th, it seems smaller than the filler line.

I will get an 02 reader soon. Any recommendations for that? Does innovate still work? (I have the obd unit but now you can’t get the app anymore)

Other things to consider? What rpm could I be capable of realistically with a 6.3L motor? I know the dual valve springs and even the cam will want to go past 6500rpm, and with my low rear gearing I need rpms to go fast.

Other things on my motor, I have my pcv valve venting into the manifold, so a “controlled vac leak” (still getting 20”hg of vac), should I just vent pcv to a catch can and vent to atmosphere?
And also, I find when pressing the button on top of the primary mixer, it hasn’t got a positive feel, still will make the motor stall from being rich, but I can’t hear a hiss or loss of pressure and can’t feel any resistance against the press of the button.

Would love to hear from you fast guys out there. Cheers. Jade

[storm]

1st question, where are you located? I assume Australia or New Zealand but it would be good to know so the correct advice can be offered.

Unless the engine was built many years ago I doubt it has Gas Research cam. GRA stopped selling cams years (it would be well over 10 years) ago.

A few things will affect fuel economy. Engine size definitely will but I doubt that is the whole problem. How are the GRAs set up? do they both come on at the same time? what jets and rods are in them? You need to be able to provide details of the size of them and tell us what RPM the engine regularly runs to.

Timing should be set for the individual engines needs. Setting it from advice found on the internet and expecting to have a "timing curve would be best for “premium” lpg and high compression" just doesn't happen. I tend to tell people to start at 14+14+14 qne adjust accordingly. Either get your engine dyno tuned by someone who has the equipment to do it properly or get yourself O2 sensors and knock sensors and other dataloging equipment (and Yes Innovate is still around) and start driving and see what happens and what you need to adjust.

PCV valve, in Australia, must not be vented to atmosphere. Engine crankcase gasses must, in Australia, be sent back into the intake stream.

That's all I have time to answer, I have to get ready for the day.

[Millsy]

Yeah no worries I’ll get some more details, yes I am in Australia, and the engine was built about 15-11 years ago, but only 4,000miles on it in that time.

It is a sequential set up, at around 50% throttle it starts to open the second throttle body, and both hit 100%wot at the same time.
No idea what jets or rods are in them.
And the engine runs to about 4800rpm, 5000 before it sounds like I should change up, but 5500before I start hearing minor backfires (obviously I have only don’t this once or twice) my auto in manual mode will hold the gear until stock redline or above I guess. So I don’t know.

[storm]

If I were to fit 2 GRAs to a Cleveland of 393 CI I'd fit a 350 as the primary and a 510 as the secondary. That will theoretically give you 860 cfm, which is more than enough for a 6500 rpm street Cleveland, but there is alot of debate on GRA cfm ratings. AFAIK GRA doesn't mark their throttle bodies with cfm rating so the only way to know is by the size of the butterfly (which I don't know). 2 B2 regulators is enough to feed approximately 600 crank HP (approximately 400 wheel HP). Take a look at the thread linked to in my signature and see what is required. The first thing I would do if I were you is check what lock offs you have on the tank and on each regulator. In Australia the GL30 is the most popular model and has the highest flow rating. Match that to a 3/8 (or 10mm) fuel line from the tank to the regulators. If you have 2 tanks you can feed 1 regulator from each tank, if you have 1 tank you may be able to get a "duo valve", which is a 2nd outlet, fitted to the tank and then feed a regulator of each outlet.

For the ignition get the best, highest output, coil you can and use the best, and largest (thickest), leads you can. Make sure you use good quality spark plugs like Bosch, NGK, etc. I, personally, wont use Champion plugs, they are good for a while but in my experience they break down much earlier (number of KMs) than Bosch or NGK.

With iron heads I'd be very careful with timing on an engine with over 11.1-1 compression (which you may have with 230 cranking PSI). Clevelands are a great engine ( I prefer Holdens but hey I like any good car and engine) with great heads but iron heads are a limiting factor when compression gets high. They simply do not disipate the heat of combustion like alloy heads do so they require different timing curves. Unless you have knock sensors and dataloging you are not going to be able to set up a timing curve that is nest for the engine without using a dyno.