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Old 12-29-2004, 01:13   #1 (permalink)
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confused Advice needed for working a 351 on Gas

I have recently purchased an XE 4sp that has a 351 in it. It currently has a straight gas research single throttle body system. As far as I know the motor is stock.
Could people please let me know what they believe would be the best mods to the engine I can do and where I could get the parts, keeping in mind its on gas, I am based in Melbourne.
I plan on trying to do most of the work myself as my budget will be very small, only a few thousand.
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Old 12-29-2004, 01:21   #2 (permalink)
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Re: Advice needed for working a 351 on Gas

an increase in compresion would be the best thing to do , pos s ib ly with clo sed chamber heads
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Old 12-29-2004, 01:22   #3 (permalink)
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Re: Advice needed for working a 351 on Gas

Quote:
Originally Posted by MRESP8
I have recently purchased an XE 4sp that has a 351 in it. It currently has a straight gas research single throttle body system. As far as I know the motor is stock.
Could people please let me know what they believe would be the best mods to the engine I can do and where I could get the parts, keeping in mind its on gas, I am based in Melbourne.
I plan on trying to do most of the work myself as my budget will be very small, only a few thousand.
Only a few thousand? That should get you to the limit of one GRA carb without too many issues!

First up, can you let us know:
What manifold your running (i'm guessing its stock but it never hurts to confirm!)?
What exhaust system you're running?
What dizzy is in the engine?
Are you comfortable with doing a cam swap yourself?

I ask because they are the first things i'd be looking to get rid of/modify on a stock engine. If everything is 100% stock then all of the above replaced and, assuming its an un-modified XE electronic dizzy, having the dizzy recurved to suit LPG would give you a serious kick! After that it starts becoming a bit more complicated, like raising the comp, converting to a dual GRA setup, diff ratio swaps (not a bad idea anyway) and headwork.

Cheers,
Greg
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Old 12-29-2004, 02:45   #4 (permalink)
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Re: Advice needed for working a 351 on Gas

Quote:
Originally Posted by xdc351
Only a few thousand? That should get you to the limit of one GRA carb without too many issues!

First up, can you let us know:
What manifold your running (i'm guessing its stock but it never hurts to confirm!)?
What exhaust system you're running?
What dizzy is in the engine?
Are you comfortable with doing a cam swap yourself?

Cheers,
Greg
The engine has pacemaker extractors and 2 and a half inch exhaust.
The dizzy and intake appear to be stock.
Could you reccomend a few of the cam's, dizzy's etc you think are good.
I am planning to change the cam with my dads help, and if i get stuck ill have to get some mechanics from work to help.
I also want to get the Dual GRA setup, but will have to wait till I can source some second hand parts.
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Old 12-29-2004, 03:32   #5 (permalink)
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Re: Advice needed for working a 351 on Gas

OK,

Well a few things I've found out about the GRA setups is 1. They are widely disliked when it comes to tuning them. 2. They are hard to build an engine around. 3. They are the best of all the LPG systems around (I'll explain myself in a minute).

Back to point 2, the biggest single GRA throttle body I'm aware of is the 440cfm, where as the smallest dual system I'm aware of is the 400+400cfm (800cfm minimum) system. Thats a huge gap in the middle and makes things hard to build around. An engine that needs 800cfm of carb is a monster, needing well worked heads (roller rockers, screw in studs, guideplates, double valve springs, etc), a cam on the huge side, big single plane intake and a big exhaust system at the least. Then you need to start looking at the fact your running a stock bottom end.

Now to point 1... if your running a dual system on a stockish setup the tuner now has to try and lean the carbs out to what you need, which is a lot easier said than done, then of course there's the throttle linkages which are not widely liked either. Expect to pay lots for this work to be done properly, if they can get it to work at all. Failure to do so will see your engine running so rich you'll actually lose power.

But to point 3, the GRA kit is the superior setup on the market unfortunately. The Impco setup's are not suitable for big HP engines, although they do fill the gap a little better because they can be ported up to 550-600cfm. The GRA's simply offer better throttle response and have the ability to expand with your engine. Something the impco carbs just can't do.

Basically you need to decide exactly what you want from the engine before you can start. The more power you want, the more $$$ your going to need to get there (same for petrol too). I can tell you from experience that starting small then adding bits as you go will only cost you twice as much to arrive at the same point.... but you'll be 10x more frustrated trying the add on method! LPG is a great fuel when its running right, if you have an XE and want a decent 351 in it then your pretty much straight LPG or hoping the cops don't pop your hood everytime you drive it.
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Old 12-29-2004, 04:04   #6 (permalink)
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Re: Advice needed for working a 351 on Gas

But what Cam and dizzy etc should I be looking at getting for it??
I have read a few times about putting a 302 2v closed chamber heads on it.
Would this be the go?
Or is it better and cheaper to work with the heads I already have?
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Old 12-29-2004, 04:11   #7 (permalink)
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Re: Advice needed for working a 351 on Gas

I was speaking to a young bloke out at Calder last meet. It was his first time out, and he was driving an XD as was I.
He said his motor, although rebuilt was near stock but did run a dual GRA set up.
He ran 14.5 on his first pass!! Unfortunatly it was so crowded we got very few runs in.
I spoke to him later and tried to find out all I could for you xdc351.
4.11:1 diff, stock C4, extractors and single 2 1/2inch system and may have had a mild cam, didn't sound much, and the dual GRA of course.
I'm sure he would go quicker with practice. I was very impressed as was he with such a mild combo
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Old 12-29-2004, 04:16   #8 (permalink)
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Re: Advice needed for working a 351 on Gas

a cam would be a huge improvement and the best bang for your buck atm.

after that get the dizzy recurved- is it electronic?

go to crow cams etc website, or even better go see a tuning shop and ask if they have done any straight gas 351 motors and ask to see dyno results/ a pic of the car. etc. ask a lot of questions if they dont have any proof. Ask them after that if they can fit/supply u with a good cam and a warranty if it does nothing (presuming it has a stock cam)

i know an engine builder, and hes built a few straight gas motors. both of which go very well. he said gas likes low duration and high lift (in comparison). gas also likes more lift and duration on the exhaust side than a petrol cam.
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Old 12-29-2004, 04:19   #9 (permalink)
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Re: Advice needed for working a 351 on Gas

yeh them dual GRA throttle bodys are the way to go when ya get the dollars. look sweet too
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Old 12-29-2004, 15:33   #10 (permalink)
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Re: Advice needed for working a 351 on Gas

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Originally Posted by needturbo6
i know an engine builder, and hes built a few straight gas motors. both of which go very well. he said gas likes low duration and high lift (in comparison). gas also likes more lift and duration on the exhaust side than a petrol cam.
I've found the exact opposite. Gas likes low lift but long duration for the sole reason it needs to be sucked into the engine.... not pumped in. High lift but low duration tends to have nothing up high (my old cam was like that) where as the new cam put the gas system at its limit 1000RPM earlier that the old one! Dual pattern cams are good, they work perfectly well on petrol cars too.

The dizzy recurve costs SFA ($100-$150) and will make a huge difference over an unmodified dizzy. A cam is much more work.

As for which cam, I can't really suggest an exact cam until you know how much you want to spend. I'm a big fan of building the engine to suit a cam as the cam is most important part of your combo. Get it wrong and it'll never run right.

My combo (unfinished):
351C - 10.5:1 comp
Weiand x-cellerator intake
Pacemaker 4-1's into a dual 2 1/2" exhaust
Ported and polished 2V heads, dbl valve springs, RR's, etc
Custom Wade solid cam focusing on large duration and mild lift (very easy on the valve train too).
Ported impco 425 on a 700 Holley base with a 1" alloy spacer.

That combo currently makes 148rwkw@ 4300RPM. After that its lean, really, really lean. Pretty much, I need to get the LPG system replaced. It was also run with only 22 degrees total timing, with everything sorted i'm expecting to add at least 10 degrees more timing into it. The cam should run to just over 6200RPM so peak power should be up around the 190rwkw mark. With a larger cam and a dual GRA setup I can't see any reason why more power wouldn't be possible.... but its not cheap building an engine to that level.
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