street 250 on LPG

[Anonymous]

I am currently planning to build a straight gas 250 with performance in mind. The below is going into an XE.

Currently thinking of:

larger cam (hydraulic)
valve springs
pushrods
worked alloy head
possibly 200 rods with ACL pistons
backed up by C4 with 3000 stall & 3.23 eb series 2 diff

1. Now, if I were to go the 200 rods & ACL piston combo, will the higher comp version (11.8 from memory?) be ok to run with straight gas?

2. With the higher rev range with 200 rods, what type of cam should I be considering? Durations/lift etc?

3. How reliable will the 200 rods/ACL piston combo be? It wont be seeing 7k RPM daily, but I will definately be hitting 5k RPM daily... stretching it to 7k occassionaly.

4. Rough price of the ACL pistons?

5. What else should I be considering through the build?

 

[lyonsy]

hey
if by worked head you mean off its rocker and ported to the max you might make power to 7000rpm
if not about 6000
use arp rod bolts from a 289 balance the bottom end it will hold together all day at 7000.
gas octane is much lower now only about 98/96 so safe bet is 10.0:1 comp now.
if driving it every day nothing to wild prob 30/70 280deg dur 500+ lift depending on rocker gear.
rough price about 100 bucks a piston with the full rebuild kit.
to have built all up about 5g with machining and assembled
drift

 

[Anonymous]

sweet thanks.

do the rods need to be prepped, i.e. shot peened etc? or just get the rod bolts in there?

 

[lyonsy]

hey
rod bolts and resized caps and re sized rods (make sure there all the same length)
for an every day with no boost i whouldent bother with shot peening
drift

 

[Anonymous]

are the long rod (200 rods) 250s ok with straight gas? anyone tried it yet?

 

[Anonymous]

wade cams has a decent profile, big cam by the look of it:

PROFILE: 1147
Lobe Lift
Ex .316
In .304

Timing Ad
Open Close
Ex 81-41
In 37-74

Duration @.050
Ex 232
In 226

Valve Lift
Ex .547
In .526

Lobe Sep
110

Needs springs, anti pump up
lifters 3000-6500

(http://www.wadecams.com/)

what do you think?

driveability might be a bit 'how you going', but will be sweet when it comes off the convertor.

 

[lyonsy]

hey
yeah it should be pretty good.
i ran the 1447B speedway grind and was really strong at 4500 but on a stock head manifolds.
wasent to bad with the manual but dident like going below 1500.
drift

 

[Anonymous]

I have emailed crow, and they have recomended their 14619 cam which looks a lot better.

I am just trying to work out a good compression ratio now.

what will be a good static compression ratio for straight LPG? approx 10.0:1?

 

[aussie7mains]

Ive had a look at the Crow catalogue , thats a fairly strong cam, I would hesitate to use an auto tranny, its going to be pretty soft at low revs.
Id consider something like the Crow 14550 or 14686 and Id still say a manual tranny.
The CR should NOT go above 10:1 for LPG, Id be spending my money on a GOOD intake manifold like the ultraflow 2 barrel setup for speedway use. The stock style and most aftermarket ones a pretty poor.
The crossflow alloy heads are good, if a little small in the intake (designed for torque), you may think about enlarging the intake ports.
Dont forget that a C4 with a 3000rpm stall speed is going to be pretty loose and will really hurt fuel economy.
Dont worry about 200 rods etc for a street engine, a waste of money, just use good quality 250 stuff, the cam etc wont make power above about 5500 so exotic stuff is uneccesary, spend the money where youll get the most benefit.
A7M

 

[Anonymous]

thanks for the reply A7m.

the head I have has already been ported on inlet with 1.85 valves. its a HF5 type head and looks really

good. I will be changing the springs & valves anyway along with a reco.

I currently have a CAIN 4 barrel and will be using a gas research throttle body adapted to the CAIN with the special adapter.

should I be looking for 10:1 dynamic or static?

 

[Anonymous]

where can I can an ultraflow and what do they cost?

 

[Anonymous]

i run a supercharged hemi 6(9.5 comp and 8.5lb's boost)on straight LP gas and it will run well on the worst gas(98 octane)but the best gas-uni gas-is rated at 105 octane.we've run up to 12.5:1 on gas with no trouble.my brother has an AMC v8 with 11.5:1 on gas and he can run on 98 without any worries.the main thing is to get your dizzy recurved to have a good gas curve(15" mechanical advance in the dizzy at 2500rpm)and set up for 15"at idle-max advance(at rev's )should not exeed 30".some truck stops have pure propane(lp is a mix of propane and butane)and it is rated as high as 110 which really will make HP.i also run my own home mde water injection system just in case i can't get unigas

 

[Anonymous]

got info about your cam overlap etc? what effective comp are you running?