Cheap power mods for a vk 5 litre on straight gas.

[M3ZZA]

Hi i have a Vk 5 litre on straight gas with a rebuilt motor to suit straight gas it also has a high stall converter and a sports system on it.

What else can i do to extract more power out off it with the 5 litre thats in it. Could i put vn worked heads and bigger cam and valve springs and upgrade the manifold and carby ?

And with the gearbox can you fit a stage 2 shift kit or would i need a different kit since its a 3 speed trimatic.

And i have a 2 1/2 exhaust on it already would it be worth it if i went 3 inch.

[Cane_It]

what carb are you running now?
an impco 425 is an improvement over the snorkel set up.
open up the divider in the intake manifold for LPG.
you'd gain nothing more from upping the exhaust to a 3" unless you went a big cam and a lot of headwork.
a crane 286 is a decent lively cam in a 308

[75hjprem]

shave the heads mate gas runs better on higher compression

[M3ZZA]

Hi guys i am not really sure i just picked it up all i know is the motor was rebuilt not that long ago to suit gas and it has a high stall.

Exhaust is already a 4 into 1 setup with duel 2 and a qaurter i think going into a single 2 1/2 then into what looks like a hot dog and then into a single rear muffler.

But i want to get the exhaust changed to duel 2 1'2 complete into either a 3 inch single or 2 1/2 single with no hotdog and rear muffler.

Would it be worth wild going with either vn cast heads or l34 heads and getting them shaved,milled,port and polished ?

I want to go with a duel plane manifold with a rebuilt qaudrajet with a 1 inch spacer and with the cam i cannot decide if i should go with a solid cam or a hydaulic roller cam ?

I want to get atleast 180rwkw to 200rwkw and a tuff as nails sounding eight which can fry the tyres off quite nice. You guys know what i mean ; )

[4wheelinls1]

The VN heads are far superior but require cam, inlet manifold and extractors due to the different valve spacing. If you want a genuine 200 rwkW you will need a better cam than a crane 286, they are oldschool and better camshaft profiles exist now. As you would need a manifold to use the VN heads a single plane is a far better choice than duel plane (divider). You will need a cam of at least 235 degrees at 050 to come close and compression to match, 10.5:1 or so. Personally I think you will struggle with a 425, I ran twin gasresearch carbies on my VN headed VK about 10 years ago and made 218 rwkW and ran 12.7 at 108mph with a T5. I was using a small mechanical camshaft and peak power was at 6500 rpm.

[M3ZZA]

Thanks for that mate.

I am thinking Vn heads since ################ say that there the best flowing heads but i am considering either getting the current heads worked or getting brock L34 heads or something like that.

So a duel plane manifold is worst then a single plane ? And isn't the inlet the same thing ?

I am only chasing 200rwkw at most on straight gas. I dont want to go more because i don't want to beef up the gas system for it.

Whats the best sort off setup i could go for because at the moment i am happy with how it sounds but i want it to have more up and go i cant even get it to wheel spin due to the highstall in it. And it has f**K all go.

I am considering removing the clutch fan and replacing it with twin Au thermo fans and also deleting the power steering pump so that i can have less off a load on the motor and be able to run Gilmer belts.

Also if i was to go with a cam and get other things like bigger valves and valve springs what sort off cam type would i need ?

[75hjprem]

mate if ur gna spend the money on l34 heads or getting some work done
its probably just worth getting the stuff to wack the vn ones on
from what ive seen from peoples flow figures and the such the red heads will always be outmatched by the vn heads, it takes alot of work to get a red head to flow asmuch as a vn head

[the_boozer]

you going to use a single plane inlet manifold?
my experiences with straight gas and a twin gas reaseach throttle bodys cost a bit but didn't make huge amounts of power and ended up with a car take couldn't go too far without going to the servo.
hope you got two big gas bottles

[M3ZZA]

Hi thanks for that at the moment i am planning on going with vn heads and getting bigger cam and the rest off the top end gear to avoid issues.

Is it worth it getting the vn heads worked ?

Also if i went vn heads do i need to go with a double row timing chain ? How much do they usualy set you back.

And can you get gilmer belts that work with a powersteering pump ?

At the moment it used 1 tank off gas for 260 to 280km's roughly with a few little pokes on the throttle here and there.

I would preffer to avoid using twin carby's and upgrading the lpg system what mods can i do to atleast get another 50 - 100rwkw.

[anfo]

would the 'bunch o bananas' manifold be anygood here? from memory dual plane manifold is better for higher up in rev range and the single plane better in the lower half

[Cane_It]

would the 'bunch o bananas' manifold be anygood here? from memory dual plane manifold is better for higher up in rev range and the single plane better in the lower half

the bananas manifold is too restrictive for the power he's chasing.
I can tell you that even with the impco 425, you'll need a very big vapouriser to feed a genuine 200rwkw engine. Mine would lean out beyond 5000rpm, that was with headwork, cam, compression and a good exhaust.

dont waste your time trying to graft the AU fans into a VK, the rad support isnt wide enough to take them. Mondeo twins fit up very nicely or if you absolutely have to have falcon ones go the EL, but be prepared to have to do a bit of work to get them in there.

go the VN heads, you'll make power easier, you're going to need a cam, and manifold anyway, so match them to the better heads. 200rwkw is a big ask out of a 308 on LPG....

[4wheelinls1]

The issue with poor take off isn't the Gasresearch its one of two things, poor camshaft choice or lack of initial igniton timing or both. Simply put LPG burns slow at low rpm so requires higher amounts of inital timing than petrol, this requires the shortening of the distributor advance, 10 degrees of mechanical advance in crank degrees is a good start point with the initial timing set around 18 degrees. LPG is also very lightweight and has no accelerator pump, if the camshaft design opens the inlet valve too early relative to the exhaust valve closing then manifold reversion pushes the incoming charge of air and LPG out resulting in poor efficiency, low volumetric efficiency and low power. This is why at Gasresearch when I was there we did a lot of camshaft developement, as a general rule you want about 10 degrees more exhaust duration than inlet. Choose your camshaft size based on the inlet duration. A 425 impco will suffer less of this low take off perfomance as it is a variable mixer and it uses manifold vacuum to open it, this cancels the reversion characteristic to a large degree, this design is also more restrictive which results in lower peak power and reduced mid range torque.

[M3ZZA]

Ok thanks for that mate but you just got me lost about the degree's and inlet and so on. Sorry i am not that mechanical minded about these things.

For example if i now reduced my goal for the vk to be a 200rwkw tyre frying machine what mods could i do to get it sounding really tuff and to atleast be able to smoke em up some what.

Is it worth it going vn heads plus all the other goodies or is there a way to make the stock 5 litre go atleast 30 to 50rwkw harder for example is it worth it shaving,port and polishing the current heads and throwing in a suitible cam for the straight gas system and getting the rockers and valves and valve springs to match it.

Also if i was to retain the standard inlet manifold can you get these worked aswell and would i benefit from a 1 inch spacer for a little more air flow.

I am thinking off using el thermos and possibly ditching the power steering so that i can use a gilmer belt drive.

Speaking off gilmers does anyone know if they drain power from your engine ?