Performance LPG

[steevo]

Hi,

I just recently had my 308ci Holden V8 motor rebuilt for use on straight LPG use.

The System i will be using is a Impco 425 mixer bolted onto a Holley 4 barrel squarebore baseplate(good for at least 300 horsepower) and the converter will be a Model "L" Impco.The motor has all the usual goodies and has a Gas research Voodoo camshaft and 10:1 comp.

Anyone else use LPG for a performance application and how did you go? and what system are you running.Also anyone have any info on who has the cleanest and highest octane LPG going around.

Who said LPG is only good for BBQ`s :D

[clemont76]

Check out fullboost forums too bcos some1 posted a similar topic, have u already bought the Impco system?

[steevo]

Clemont76,

Thanks for the tip about the other forums (BTW-What is the address?),Yep,I already have the Impco sytem as the car was dual fuel before the engine build so i thought i would use it as it is one of the better sytems to use for straight LPG conversions next to gas research.

Thanks

[clemont76]

http://www.fullboost.com.au - look under forums.

Have seen the Impco 425 on a 13B turbo rotary, was running ok but had problems tuning it. I am running the GRA S400 with B2 convertor on my 12A engine.

[VC V8]

Hi All,
I'm using twin GRA carbs that flow a total of 910 cfm, twin B2 converters on a Harrop single plane manifold with "cleaned up" EFI style heads on a 304 block stroked to 353ci, 9.8:1 cr and a Wade 1069 cam. Its putting out around 200Kw at the tyres.:D
Its got a nice flat torque curve, power starts at around 1500 rpm and its not worth revving it past 5500. I'm very happy with the set up.
Just gotta sort out the oil going into the inlet manifold on certain corners of Phillip Island race track (oil catch can plumbed up soon) and all will be right.

[hamish]

Steevo, I used to own an HQ with a worked 350 chev some years ago, which I ran on straight lpg. I had a very similar setup to yours, however at about 400cfm (on a holley 4 barrel rating) the impco 425 is a bit restrictive at higher revs. If I were to do it again I would run 2 impco 425 mixers for a total of 800cfm. You will have to make up a custom adaptor to mate the 2 mixers to the holley baseplate, you can turn these carbies on their side to clear the bonnet, I think they'll even work upside down seeing as they dont have a float bowl. If you are using a dual plane inlet manifold, you could set it up so that each mixer supplies one half of the manifold. Don't worry about the seemingly high cfm figure, these carbies are of the "constant depression" type, like an SU, and the gas valve in them will only lift as high as the engine demands, making it difficult to over-carburate with them.

Being as gas, LPG does'nt need any extra manifold heating to keep it vaporised, so keep as much heat out of the inlet manifold as possible, which is a real problem on V8s which use the manifold to cover the cam valley. Things like, blocking the exhaust crossover if it has one, insulating gaskets, and an oil splash sheild under the manifold can help, as well as a cold air intake to the carbies. The compession ratio you are running sounds about right, the camshaft is probably fine too.

In general I was pleased with the way my car went on LPG, bottom end & midrange torque, as well as driveability (from cold) were very good. Biggest negative was the lack of top end HP, but I'mm quite sure that was a result fo the carby being to small ,points ignition, and not having tuned it properly.

Hope this is of help.

[steevo]

Thanks hamish,

Yes i was worried too about the Impco 425 mixer not flowing enough and was seriously thinking about using dual 425`s on the adaptor (impco sells them) but im sure it would hit the bonnet due to the height of the adaptor.

I found a site from a bloke in the USA that has been working with impco products for years and he has more university degrees than ive had goood dinners!!, this bloke knows his LPG!

Basically what he told me is that he was running a single Impco 425 on a 460ci ford V8 and the impco 425 mixer never reached 50% of it`s flow potential so he said thast it would fuel my 308 with no troubles at all.Also the model "L" converter will flow 350 HP and 450 HP for 10 seconds.So i hold his recommendation in good faith.

Yep,you should run a electronic HEI dizzy with LPG as it is harder to ignite.Aslo did you have your dizzy recurved to suit LPG as you will never get the best out of it with a standard or petrol curve.

I did notice prior to having the 308 rebuilt (it ran a dual fuel impco sytem with a 425 and "L" converter)The engine was much smoother and better in the low and midrange compared with petrol like you said your Chev 350 .

Cheers

[hamish]

Steevo

I never got round to getting the dizzy recurved, too lazy, then crashed the car, same way I never got round to increasing the CR, fitting hardened exhaust seats, cold air intake etc. So the motor was a compromise. Doing it again now, I'm sure I could get a bunch more Hp (50+) out of it.


he was running a single Impco 425 on a 460ci ford V8 and the impco 425 mixer never reached 50% of it`s flow potential
??????????? Maybee if he was only revving it to 2grand.

Put it this way, would you put a 390 cfm holley on a 460 and expect it to perform to it's full potential? The single 425 will run well on your 308 as you already know, it's just that it will probably cost you a few,not heaps, of HP at full revs. Remember the more air you can stuff through an engine the more fuel you can mix with it, and the more power you can make, same rule applys for LPG as well as petrol.

Hamish

[DP13B]

There's not much more I can add as Hamish has explained it very well.
Just a couple of points that haven't been mentioned:
Not all holley square bore throttle bodies have the same size butterflys, in your situation it couldn't hurt to have the larger one.(off double pumper carbs I think)
If your engine has just been rebuilt and u intend to run it in on straight gas immediately it must be done correctly or it will forever use oil, see Gasreasearch's website for the procedure.
Also "425" does not relate to its cfm rating, they actually flow 460 @ 1 1/2" Hg

hope this helps.

[steevo]

Hamish,

The 425 Impco will flow 460 CFM as the other bloke stated and i think you can get away with using smaller CFM`s on LPG as it doesn`t need to be sucked out of a fuel bowl like a petrol carb does,but i spose if you rev the ring out of the 350 motor it might run into some troubles with air flow etc at the very topend but things such as tank type,wether or not you run a hi flow filter/lock offs and the size of the service line all play a part as well.I will ask that bloke how many revs he can pull with the 425 mixer on the 460 anyways.Just out of curiousity,Did you have the Holley 4 barrel baseplate modified so all the barrels open at the same time and make up a link so the secondaries open?,I say this because the Impco 425 mixer does not produce a vacuum to open the secondaries and unless you modify the baseplate to mechanicaly open them with a link bar from the primaries,The secondaries will NEVER open!!!(this only applies if its a vacuum secondaries base and not a double pumper as they have mechanical secondaries).

DP13B,

You are right about the butterfly size but i was informed that a Holley 600 baseplate is the best size as some of the larger size butterflies(maybe double pumpers) will actually be block the airflow to the mixer and cause shrouding and hampering airflow.My engine is currently being run in on Petrol so im going to be alright regarding the oil use problem.

Cheers boys

[hamish]

Steevo, I used a double pumper baseplate for the reason you mentioned.
I assume the oil use problem is a result of the rings not bedding properly on gas? Had'nt heard of that before, but can understand how it would happen.
Gas carbies also have to "suck" their fuel out of the converter, so really don't have any advantage over a petrol carby in that respect. I don't think your looking at the way they work in quite the correct way. A good rule of thumb I've seen from a couple of sources is to size the carby at about 2cfm for every Hp the engine should be capable of, eg. 300 Hp engine would work well with a 600cfm carby. Admittedly this was refering to petrol engines but I see no reason why it would'nt apply to LPG, I've even seen an article from GasResearch suggesting you should use even more cfm for gas than you would normally use for a petrol carby.

Anyway I'm nitpicking here, you probably would'nt lose much more than 5-10hp by not going with the maximum cfm possible. Commodore cup cars make over 300hp out of a 253V8 with a holley 450.

Hamish

[C0V3R]

Do any of you have pics of your LPG setups? Do you think I'd be able to keep my edelbrock 1406 (600cfm) carb if I were to convert to LPG?

[steevo]

COV3R,

No pics as of yet as im just gathering all the bits and pieces at the moment while i run in the new motor on petrol.

As for your Edelbrock carby,If you are going to use dual fuel,You most certainly can keep it as this will still open the carbies butterflies etc and supply the air to the LPG mixer mounted on the plenum above the carby,and when you switch over to petrol the carby will work just like it did before the conversion.Obviously if you want to go sole LPG you have to flick the Edelbrock carby.

Cheers

[C0V3R]

So if you go LPG only, you just have a gas mixer (eg impco/GRA) and no normal carb? Hmmm interesting. I've also been looking at getting a 2nd hand system off an XB or something similar, are there any issues with certification if you install yourself?

[steevo]

COV3R,

yes thats right,If you run straight LPG you will just have the mixer.If its an impco 425 it will need to be bolted to a holley squarebore baseplate but the GRA sytem has butteflies etc built into the LPG "carby" so you justr hook up your linkage or cable and your on your way.

As for self installations,best if you give your local LPG conversion mob a bell,As im not sure on particulars,

BTW-what car and motor are you looking to convert?

Steve

[C0V3R]

289w on a 68'stang.

[C0V3R]

Current mods are lotsa ignition goodies, single plane intake etc. I think the cam/heads are close to stock, but dont really know.

[steevo]

COV3R,

Mustang eh,nice!, Although a Holden man, The old mustangs have always been one of my favourite Fords.

If you are looking for a neater installation than your run of the mill dual fuel setups,I suggest you have a look at the Elko "Hi-Flow"mixer.It sits inside the aircleaner and makes for a neat looking install and dyno tests have been done to show that it will still retain 100% of its original output on petrol and achieve within 10% on LPG.

Check it out on this link
http://www.elko.com.au/page5.html

Single plane manifolds are recommended by Gas research so you will have no probs there and maybe you could slip in one of their Voodoo LPG cams.Usually the biggest cost in a LPG installation is for labour and the tank itself.

Cheers

[Tex]

I think if I ever convert the Riv over to dedicated LPG, I'll be going EFI!

Apparently Fuel Injection is very well suited for LPG applications, because it's made to flow very high volumes of gas.

I believe there is an Australian company who make EFI conversion kits for a broad range of cars. I have looked at their site before, they look quite good. I guess then you could then just hook LPG up to that.

www.efihardware.com (don't think it has an .au on the end from memory).

Might be worth a look?

Tex

[C0V3R]

The elco stuff sounds quite interesting. Im gona have to call their melb. office, as they neglected to put their Sydney details on their site.

[steevo]

COV3R,

I looked up elko on the yellowpages website and i got the number for Elko auto gas in Silverwater NSW.PH 02 96485222

Cheers

[C0V3R]

Wow... thanks!.

[steevo]

No problems mate,

Also,I found this number on the whitepages website and its a different number but you can give them bith a whirl anyways,

PH-02 96480444- (In Auburn)

[Cole-Trickle]

Hamish

i would like to ask a few q's about your gas setup on your 350 chev as i have just purchased a car with the same motor,

It was originaly set up on petrol where it made 289rwhp but now is running on straight gas which it has been for the last 3 yrs.

The motor has high comp (unsure on what tho) fuelie heads (not the lumpys), nascar spec cam (don't know any figures or size's) electonic ignition, standard headers and exhaust

I'm unsure whether to revert it to petrol or run it on straight gas with a Gas reasearch setup

If i was to keep it on gas would it be better to change cams to suit lpg?

Any input would awesome

Thanks Cole

Cheers

[muttaburra]

i have actually been talking info about turbo and LPG set ups in another thread.
i found this info for sizeing
**********************************

CID* RPM / 3456 * 0.85 = CFM required
CID is engine size, in cubic inches (CID = cubic centimeters (cc) * 0.06102), RPM is maximum engine speed. 0.85 is a close approximation of Volumetric Efficiency.

For turbocharged or supercharged engines:


CID * RPM / 3456 * %boost + 1.00 = CFM required
Normal inlet air pressure is 14.7PSI; supercharging merely increases inlet pressure. For example, 6PSI boost means 20.7PSI pressure, or 140% boost.

Vehicle applications



IMPCO Max.
Model CFM
50 91
50-500 108
100 170
125 202
175 210
200 276
225 329
300A-1, -20 348
300A-50, -70 432
425 460


**************************

i worked out that a 308 needs about 460cfm
its a very handy equation

[steevo]

Cole-trickle,

Im not Hamish but ill have a go,

Why not stick with the straight LPG setup?.With the right mods it will be as good as petrol if not better with economy to boot.

If you already have the Impco system,Do you realise you can run dual Impco 425 mixers on an adapter?Plenty of fuel for a 350!

The only drawback of Gas research stuff is the initial outlay cost of the equipment but if you have plenty of chaff go ahead

As for the cam,D you have the duaration figures for the inlet and exhaust?.As cams for LPG have much longer exhaust duartion than inlet (IE 214IN/224EX) and have a look at the Voodoo cams by gas research on there web page.

Cheers

[XDed]

hey :) the elko gear seems to be a almost exact clone of the impco stuff! im running a ford 250xflow on LPG using a holley carb and impbo 300A mixer, pics are http://nforsa.8m.com/car/index.htm

[hamish]

Cole, I'd pretty much agree with what steevo suggested re. using an extra Impco mixer. I beleive the way to check if your carby is too small is to run a vacuum guage off MANIFOLD vacuum, take the car for a drive, rev it out in 1st or 2nd gear, & note the peak reading at full load & revs, if it's more than about 1"- 1 1/2" of mercury, you probably need a bigger carby. Make sure it's the carby not the air filter thats restrictive. This is what I should have done when I owned my 350.

There is generally a small power & fuel economy loss 5-10% as compared to petrol when running LPG, even when you have it perfectly set up, according to the experts. LPG has less energy than an equivelant amount of petrol, so you have to burn more of it hence the loss in economy, and being a gas, it takes up slightly more room in the incoming mixture ( petrol goes into the engine in fine droplets), and being fully vaporised theres no charge cooling effect, this reduces the engines VE slightly and costs some power. It's also the reason to try and keep the intake air as cold as possible, any manifold heating is conterproductive for LPG, a real problem on most V8's. If you're using a chev use a manifold with an air gap, Edelbrock make a few, wish they were available when I did my engine.

Nascar spec cam? if it is, it's going to be way to big for any streetable engine, Nascars rev to over 8000 rpm, expensive. I really dont know if LPG requires different cam specs or what they are. I'd love to do an lpg engine again to see what really works, but I lack the $, time & motivation.

[Cole-Trickle]

Thanks guys

Yeah i think your right about the cam being a nascar spec,

I'm gonna get a expert to look at the setup to tell me whatwould be best

If possable i'll keep it on gas

What manifold and extractors would you recomend to suit LPG

Cheers

[steevo]

Cole-trickle,

Check out the link i provided and this should give you a idea of what works with LPG.

http://www.gasresearch.com.au/epg.html

Hamish,

My apologies,You are right about LPG needing slightly more CFM than an equivelant petrol carb,I read this in GRA`s new tech section.Also i have noticed they have added a single S510 carby that flows an actual 520CFM.I might look into this over the impco.Who knows! It falls within my maximum required CFM rating by using that well known CFM calculator formula.

Cheers