Search found 34 matches

by Tom68
Sat Apr 04, 2020 11:53 pm
Forum: Propane Forum
Topic: Propane Tuning AFR and Lamda
Replies: 10
Views: 1155

Re: Propane Tuning AFR and Lamda

Sold all my cars etc when retired a while back Spent a lot time on Data logger dialing in SB chev. With a single 425 found lean out started about 4400/4500 then got more serious around the 4900/5000. In practice, passing a large cattle truck (they are long in NZ) maybe doing 80/90km/h , the whole m...
by Tom68
Sat Mar 28, 2020 7:20 pm
Forum: Propane Forum
Topic: Lean out at WOT. Fine at 3/4 throttle
Replies: 18
Views: 1333

Re: Lean out at WOT. Fine at 3/4 throttle

The high pressure lines are all copper-tubing. Both tanks are connected together in the trunk. I've fueled up the car yesterday and I'm noticing (as always), the car has some more power. But still everytime I depress the throttle-pedal fully, the AFR goes very lean after about a second orso. Everyt...
by Tom68
Wed Mar 18, 2020 2:07 am
Forum: Propane Forum
Topic: mkiv 454 big block and impco300 mixer too small?
Replies: 7
Views: 1816

Re: mkiv 454 big block and impco300 mixer too small?

thanks C3H8 thats a clear explenation. I also found this website, I could have found myself...since its a simple calculation as you stated https://www.widman.biz/English/Calculators/CFM.html Tom68 I have a air-gap dual plane ready to be swapped on. They told me that a single plane big intake would ...
by Tom68
Mon Mar 16, 2020 1:18 am
Forum: Propane Forum
Topic: mkiv 454 big block and impco300 mixer too small?
Replies: 7
Views: 1816

Re: mkiv 454 big block and impco300 mixer too small?

As advised you'll be able to trim the af ratio. That cams no baby for a stocker, you're running a baby mixer with a half decent cam. Cams costing you low rev power, the mid range and up is limited by your low horsepower mixer. A top end manifold with a mid range cam and a bottom end mixer, missing o...
by Tom68
Sun Mar 15, 2020 5:18 am
Forum: Propane Forum
Topic: Dual carbs with propane?
Replies: 26
Views: 8268

Re: Dual carbs with propane?

I did a compression test a few months ago. I remember all cylinders were 120 or 115. I forgot to hold the throttle open when I did it and I live at 4000 ft, so actual numbers are probably quite a bit higher. The engine still delivers good mileage and power and doesn't smoke or make any weird noises...
by Tom68
Thu Mar 12, 2020 3:46 am
Forum: Propane Forum
Topic: Dual carbs with propane?
Replies: 26
Views: 8268

Re: Dual carbs with propane?

Wouldn't the cam-induced-egr theory only work with a horribly restricted exhaust? Any sort of free-flowing exhaust system should provide enough of a reduction of pumping losses to offset any mileage benefit of egr Gas flows to lowest pressure, that's why the oil getting into your inlet tract gets b...
by Tom68
Wed Mar 11, 2020 2:27 am
Forum: Propane Forum
Topic: Dual carbs with propane?
Replies: 26
Views: 8268

Re: Dual carbs with propane?

I thought about the mile-a-more but was scared off my its 108 lobe center. I was reading another post on here on how propane doesnt like tight cams as it tends to suck the intake charge out the exhaust . It probably makes more power, but I drive this truck 60 miles a day so mileage is important. I ...
by Tom68
Tue Mar 10, 2020 3:30 am
Forum: Propane Forum
Topic: Dual carbs with propane?
Replies: 26
Views: 8268

Re: Dual carbs with propane?

For reference, my cam is a isky 256. 450/450, 202@.050 and 112 lobe sep. I just looked that up and I think you have lobe separation (LSA) and Lobe Centreline Angle (LCA) mixed up. In all honesty I think the MILE-A-MOR or the Turbocycle-A are better alternatives. Why? Mile-a-mor is a single pattern ...
by Tom68
Mon Mar 09, 2020 6:13 pm
Forum: Propane Forum
Topic: Dual carbs with propane?
Replies: 26
Views: 8268

Re: Dual carbs with propane?

For reference, my cam is a isky 256. 450/450, 202@.050 and 112 lobe sep. I think a important thing to remember with mileage is that its more about the whole truck than the engine. Replacing the 9 in axles with 8.8s and the granny 4 speeds with the mazda 5 speeds im sure helped with mileage. the bul...
by Tom68
Sat Mar 07, 2020 5:03 am
Forum: Propane Forum
Topic: Dual carbs with propane?
Replies: 26
Views: 8268

Re: Dual carbs with propane?

Im RV cammed and computer free, so I dont have those restricting me. Seems like the consensus is a single mixer for propane. I know the old school GM inline guys swear by dual or triple carbs for their sixes, and thats what got me thinking about it, but they dont have the benefit of dealing with pe...
by Tom68
Fri Mar 06, 2020 11:12 pm
Forum: Propane Forum
Topic: Dual carbs with propane?
Replies: 26
Views: 8268

Re: Dual carbs with propane?

Thought he meant poor mileage from timing restrictions with dual fuel and possibly from some odd camshaft designs. Never gunna be revvers with the limited valve area for the capacity, but you need at least enough mixer area to fill the cylinders at 3500 rpm. Can't see any need to seperate it into tw...
by Tom68
Thu Jan 30, 2020 2:17 am
Forum: Propane Forum
Topic: Status on High Performance 4-barrel Carbs
Replies: 13
Views: 3439

Re: Status on High Performance 4-barrel Carbs

Impco 425 mixers flow approximately 460 cfm. Using the formula CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456 you can work out what you need. If your engine is 416 ci, your max rpm is 4500, and your VE is 85% you'll need approximately 460.41666666666 etc cfm. If your VE is higher, e.g...
by Tom68
Wed Jan 29, 2020 2:50 am
Forum: Propane Forum
Topic: Status on High Performance 4-barrel Carbs
Replies: 13
Views: 3439

Re: Status on High Performance 4-barrel Carbs

There are two ways supplied by IMPCO for CFM calculations. The calculation storm supplied or a chart that IMPCO made up to forgo the calculation. According to the chart storms formula pretty well matches the chart. IMPCO does suggest rounding up the CI for over the road vehicles. In this case the c...
by Tom68
Wed Jan 29, 2020 1:12 am
Forum: Propane Forum
Topic: Status on High Performance 4-barrel Carbs
Replies: 13
Views: 3439

Re: Status on High Performance 4-barrel Carbs

Impco 425 mixers flow approximately 460 cfm. Using the formula CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456 you can work out what you need. If your engine is 416 ci, your max rpm is 4500, and your VE is 85% you'll need approximately 460.41666666666 etc cfm. If your VE is higher, e.g...
by Tom68
Sat Sep 14, 2019 3:00 am
Forum: Propane Forum
Topic: Help to identify the parts in this picture.
Replies: 12
Views: 3745

Re: Help to identify the parts in this picture.

Impco filter.
Image