Outer Limits 4x4 Board

I have just put a deposit down and ordered a LPG tank and I’m a bit mixed up on which mixer to use?

Well the LPG shop’s (3 in all) all want me to use a NEWGEN mixer they say it will feed my 392ci motor
.
The guy who helped me build my scout and the motor swears black and blue that the IMPCO 425 mixer is the ONLY one to use.

I Have also heard OHG is the go, I have done some web searches and the OHG flows more CFM rated to suit higher HP motors ect. But a lot of people say the IMPCO 425 is great also.

My 392 wont see more the 4000rpm (3600 redline) so the 460cfm IMPCO 425 should fit the bill.

The mixer will sit on top of a Carter 625 carb if that makes a difference.

All feed back and recommendation wanted.

Eric

you running straight gas? if so go the impco 425

you running dual fuel? if so, go the impco 425

your not sure about straight or dual? Go the impco 425

did i mention that you should go the impco 425?

Jes

yes, the impco 425 is a great gas carb.

but the OHG stuff is just as good if not better........well certainly better for any performance type of work.....or bigger cube motors

but in all honesty, i have no doubt the 425 would do the job for u, esp. since its only going to see a redline of 4000. A 425 did well on a 350 chev of mine pulling 6500, but it ran better and produced more power etc etc when changed to the OHG. Also picked up another 500 or so revs while it was at it.

jessie928 wrote:you running straight gas? if so go the impco 425

you running dual fuel? if so, go the impco 425

your not sure about straight or dual? Go the impco 425

did i mention that you should go the impco 425?

Jes

X2. Impco is relaible and easy to tune.

OHG (over the Hill gang) are the guys that used to work for impco they left and started there own bussiness so they make the better stuff and the latest technolgy ived used both and consider them to be justg a good as each other and parts are readly avalable for both as well

From what i have been led to believe you cannot run an Impco 425 on duel fuel. I would like to know if this isnt the case so i can find out why they put the 300 on my truck!

In my experience the best LPG system is Gasrearch, but it is straight LPG on non-efi engines. The OHG is a similar copy to the 425, when tuning it though it tends to run lean under load at low rpm, the 425 is better although both systems if you dyno a data log of Air Fuel verses RPM at wide open throttle will go from lean to rich. There is a simple formula which is to convert CI to CFM. max rpm * CI / 3456 = CFM. So your inter would be 4000 * 396/3456= 450 cfm of thereabouts, this dosen't take your engine efficiency into account, assume 80% for an old inter or less, so 360 cfm is more likely. For a heavy vehicle you are likely to have better driveability with an impco 300A 70 series. The 396 inter is a truck motor and origionally was designed around a 2 barrel carby, it has small valves and ports for maximum torque at low RPM. A 425 may make more peak power but will not drive as well, also a 425 is designed to run upright and not on its side and will wear poorly internally causing mixture consistancy problems down the track if mounted on its side. Most importantly whatever you decide get it tuned and make sure your ignition system is in top condition as LPG is harder to ignite.

Personally I would avoid the new genstuff, complex mixers are more sensitive to fluctuating LPG quality.

mattsluxtruck wrote:From what i have been led to believe you cannot run an Impco 425 on duel fuel. I would like to know if this isnt the case so i can find out why they put the 300 on my truck!

this is total bulshite

i have run them upright and sideways for dual fuel. Currently on of the 40's with a 302 windsor dual fuel.

JEs

PGS 4WD wrote:In my experience the best LPG system is Gasrearch, but it is straight LPG on non-efi engines. The OHG is a similar copy to the 425, when tuning it though it tends to run lean under load at low rpm, the 425 is better although both systems if you dyno a data log of Air Fuel verses RPM at wide open throttle will go from lean to rich. There is a simple formula which is to convert CI to CFM. max rpm * CI / 3456 = CFM. So your inter would be 4000 * 396/3456= 450 cfm of thereabouts, this dosen't take your engine efficiency into account, assume 80% for an old inter or less, so 360 cfm is more likely. For a heavy vehicle you are likely to have better driveability with an impco 300A 70 series. The 396 inter is a truck motor and origionally was designed around a 2 barrel carby, it has small valves and ports for maximum torque at low RPM. A 425 may make more peak power but will not drive as well, also a 425 is designed to run upright and not on its side and will wear poorly internally causing mixture consistancy problems down the track if mounted on its side. Most importantly whatever you decide get it tuned and make sure your ignition system is in top condition as LPG is harder to ignite.

Personally I would avoid the new genstuff, complex mixers are more sensitive to fluctuating LPG quality.

i hear ya about the upright mounting being the best for thr 425, but it works well on its side aswell. In the long run, the effect of the wear is not much compared to the better flow, performance and adaptability of the converter.

Jes

Hey guys, this is not a contest of opinion or who's knowledge is better!!!
We are only making suggestions based on our own experiences.

Ditto what Ruggers said. But I was told it was the previous owners of Impco who sold up their share and started again not employees. Stiff. OHG is a copy of Impco for that reason. There are many other copies of Impco stuff and all are fine to use. Many parts are interchangable so you can't go wrong with your choice. Also PGS I thought the 392, not 396, only came with a 4 barrel. Either a Carter or Holley. Just if that's what he's got he may as well stick with it.

PGS 4WD wrote:Hey guys, this is not a contest of opinion or who's knowledge is better!!!
.

where did you get that idea from? look at the next post, that one s direced to you

mattsluxtruck wrote:From what i have been led to believe you cannot run an Impco 425 on duel fuel. I would like to know if this isnt the case so i can find out why they put the 300 on my truck!

Well you can run The IMPCO on a carb thus making it duel fuel.

Eric

jessie928 wrote:

PGS 4WD wrote:In my experience the best LPG system is Gasrearch, but it is straight LPG on non-efi engines. The OHG is a similar copy to the 425, when tuning it though it tends to run lean under load at low rpm, the 425 is better although both systems if you dyno a data log of Air Fuel verses RPM at wide open throttle will go from lean to rich. There is a simple formula which is to convert CI to CFM. max rpm * CI / 3456 = CFM. So your inter would be 4000 * 396/3456= 450 cfm of thereabouts, this dosen't take your engine efficiency into account, assume 80% for an old inter or less, so 360 cfm is more likely. For a heavy vehicle you are likely to have better driveability with an impco 300A 70 series. The 396 inter is a truck motor and origionally was designed around a 2 barrel carby, it has small valves and ports for maximum torque at low RPM. A 425 may make more peak power but will not drive as well, also a 425 is designed to run upright and not on its side and will wear poorly internally causing mixture consistancy problems down the track if mounted on its side. Most importantly whatever you decide get it tuned and make sure your ignition system is in top condition as LPG is harder to ignite.

Personally I would avoid the new genstuff, complex mixers are more sensitive to fluctuating LPG quality.

i hear ya about the upright mounting being the best for thr 425, but it works well on its side aswell. In the long run, the effect of the wear is not much compared to the better flow, performance and adaptability of the converter.

Jes

The LPG shop did mention the extra wear, but i would expect years of use before that became an issue.

Eric

BowTieGQ wrote:Ditto what Ruggers said. But I was told it was the previous owners of Impco who sold up their share and started again not employees. Stiff. OHG is a copy of Impco for that reason. There are many other copies of Impco stuff and all are fine to use. Many parts are interchangable so you can't go wrong with your choice. Also PGS I thought the 392, not 396, only came with a 4 barrel. Either a Carter or Holley. Just if that's what he's got he may as well stick with it.

The details on the 392

Here’s what I did

The heads shaved but only to make it true, a 3 angel valve job , the springs were tested then were shimmed up to give a little more pressure, the ports were also opened up.

The cam shaft was reground I’m not sure what the sizes are (lost the tag) but when we were discussing it I told him to give me a very small grind to keep the low down grunt but also should be good for 4500 rpm.

I had the block, crank ect hot tanked and board/honed to 30 tho over sized, with new flat top pistons, the crank was linished.

I run twin 2 ¼ pipes, electric fuel pump and standard steel fan Since the rebuild I have had the 625 carter tuned, changed to regraffted electronic dizzy

I have had it on the dyno 103kw at the wheels and 900 ft of torque. dose not sound like much but the dyno guy said it has about the same KW as a V6 commodor but with twice the torque.

Eric

NEWGEN (omvl) spend the rest of your days tuning it
IMPCO the go set and forget and u can get good power

TEAMRPM wrote:

jessie928 wrote:you running straight gas? if so go the impco 425

you running dual fuel? if so, go the impco 425

your not sure about straight or dual? Go the impco 425

did i mention that you should go the impco 425?

Jes

X2. Impco is relaible and easy to tune.

X 3

Your prolly right BowtieGQ about the manifolds, I've only played with a 1/2 dozen of these engines over the last 10 years and most were in international trucks, have put Gasresearch on a couple of Scouts in a past life, by the time I saw them you have no idea whats not standard and whats origional. I wasn't suggesting take the 4bbl off if it hasa one just that these aren't big HP big airflow engines as the dyno figure shows. I've dynoed heaps of bigblock Ford and Gm stuff, typical 460 or 454 only makes 120KW at the wheels if dead stock.
The only problem with all the gas stuff except the gasresearch is that it tends to be lean at wide open throttle(WOT) at low rpm compared to high, if you have the time by playing with converter springs you can dramatically improve this, if you want to run the 425 you will get better part throttle mixture, and this is where the car will spend most of its life, if you raise the primary pressure on the converter to around 3 1/2 tp 4 psi.
As most will already know lean LPG mixtures mean damaged heads.
I'm with eveyone else in whatever you do don't go NEWGEN, its cheap for a reason, mixture control is poor and converter reliability is poor. Some of the gas joints trying to sell it will tell you its better on petrol as the mixer lifts out of the way when running on petrol, you can also do that with the impco.

I'd be interested to know if HotRods car was tuned before and after fitting the OHG 450?? Rich LPG mixtures make very poor power, I had a lot of complaints about Gasresearch from fitters who were just putting the stuff on, without a tune it's all hit and miss, I've seen power figures nearly double when going from .77 lambda to .89 which I would run on a naturally aspirated LPG engine generally. Got to compare apples with apples when testing.
No one ever would consider putting on an EFI system without a tune yet LPG and petrol carbies will often bolt on and run so never get a tune and their full potential is never realised.

Prob the only reason Inter fitted 4 barrels was due to large airflow/volume needed for large cubes, not for power. They don't (shouldn't be more like it) rev hard. Too heavy reciprocating mass in them. Should see what the yanks do to them. Awesome stuff. Your right about low kw's but good ft/pnds. Was contemplating a 392 for the Patrol but it and the 345 weigh as much as a big block but are a small block size. Damn, as I've got access to all the Inter stuff I want. Was looking for a Scout Traveller before I got the Patrol too.

I'm building a GEN 3 with a TO4ZR for my new comp truck, trying to have torque and keep the weight down, don't know if I'll be able to drive it though

Well the inter petrol V8's are all Big block motors, 266,304,345 and my 392.

266/304's were all 2bbl carbs, the 345/392 came with both 2 and 4bbl carbs.
V8's Have Forged Rods, Crank and Pistons, As Well As Timing Gears Instead Of A Chain


Eric