having trouble with new install (SBC in boat)

Propane, Butane, LPG, GPL, C3H8, C4H10
ChrisR
Posts: 7
Joined: Fri Jul 09, 2021 5:11 pm

having trouble with new install (SBC in boat)

Post by ChrisR »

Hi, First post, so thanks for the add....

I've got a ski boat with a 3yr old replacement 5.7L based on a small block chevy, on petrol the builder estimated the power to be 350lbft between 2700-4800, peak at 370lbft@4100 and a max rpm of 5600, with a hp figure of between 335 (matching the torque figures) and 360 depending on tuning. Which I believe as the difference between the original 5.7 indmar tbi (275hp) was night and day.

Now the problem I've got is since the LPG conversion (about 20-25hrs of use now and around 300L of LPG) it is lacking power. It's a monofuel conversion but still keeps the TBI and ECU for ignition control (HEI), knock sensor, TPS/MAP etc

The mixer is the Impco 300A (I presume the 50-70) with the Model E vaporiser.

I'm using less LPG than when on petrol and it will only top out at 4000rpm on WOT and is now a gutless beast, I'm taking it back to the converters to try and sort it, but ideally would like some more background so they don't try and pull the wool over.

I've attached a picture of one of the plugs, it was used on petrol first, then the 20-25hrs on LPG so far. I've got new ones to replace with now.

Also, the video link is a WOT power run in the boat, on petrol it was 0-58kph in around 3-4s, on LPG its currently around 12s.

https://youtu.be/H-thL517lEM

Because its a boat, it has a wet exhaust (water jacket over around the headers) and no o2 sensor. I'm very mechanically minded and have built many many engines and cars over the last 20 years, and even done a couple of LPG conversions, but went to a "reputable" installer because of the lack of monitoring i.e. I thought they'd know how it's setup / tuned and also the lack of time (rather be on the water rather than tinkering off the water) - but that seems to have backfired!

Any ideas and all thoughts are welcome!?!

Thanks
Chris
Attachments
sparkplug
sparkplug

storm
Posts: 779
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: having trouble with new install (SBC in boat)

Post by storm »

ChrisR wrote:
Sat Jul 10, 2021 6:00 am
Now the problem I've got is since the LPG conversion (about 20-25hrs of use now and around 300L of LPG) it is lacking power. It's a monofuel conversion but still keeps the TBI and ECU for ignition control (HEI), knock sensor, TPS/MAP etc
There's your 1st problem
ChrisR wrote:
Sat Jul 10, 2021 6:00 am
The mixer is the Impco 300A (I presume the 50-70) with the Model E vaporiser.
There's your 2nd problem.

The TBI setup is restrictive and you have adapted (adding another restriction ) a 300A which will be another restriction for a "performance" 350. Change the manifold to a 4 barrel carb with a Holley bolt pattern and fit an Impco 425 with a Holley double pumper baseplate. You can get a TPS to fit to a Holley baseplate from Innovate Motorsport, you can use TunerPro RT to tune the engine as long as you have the correct ADX and XDF for the ECU. The only thing you will loose will be the ICS (Idle Control Solenoid).

Do you have a better view of the spark plug? The heat range appears ok (you can tell that by how far the heat goes down the threaded section), but I can't tell how the timing is because I can't see the back of the electrode. Ideally for a baseline you want the "timing mark" to be near or on the curve of the electrode as a baseline and then tune for best performance from there.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

ChrisR
Posts: 7
Joined: Fri Jul 09, 2021 5:11 pm

Re: having trouble with new install (SBC in boat)

Post by ChrisR »

Thanks, it's confusing as it seems one person will say the 300A is fine, and another it's not (or maybe in more colourful language) - the installers seem to be just saying, it's what we always put in and it always works. but anecdotally ski clubs reckon the engine is shagged after 1000-1500hrs on LPG

Hopefully the pictures are what you meant - not the same plug BTW! , I've never really had to read plugs before (not on LPG anyway) and even that extent was just colour i.e. lean/right/rich. If not, I'll take a full 360 of one of the plugs tomorrow.

I've just replaced the plugs with some iridium/platinum, minimal change in performance - little bit and maybe another 100rpm top end.
did a compression test at the same time and all cylinders are between 155-165psi (cold) , 9.5:1 compression ratio.

I read the logs from the old MEFI system on petrol and with the following readings holding steady rpm:
RPM: 3340
MAP: 68-69 kPa
Throttle angle: 40% (39.4-42.2)
Advance: 37.9 deg BTDC
Max poss RPM on super unleaded: 5600
Max poss RPM on regular: 5200


Now the readings are as follows:
RPM: 3330
MAP: 75-78.4 kPa
Throttle angle 48%
Advance 37.2-37.6 deg
Max poss RPM on propane 4100 (at WOT)

so 8% more throttle for the same rpm under same load conditions tells me the impco isn't feeding enough or either air or fuel or both

A few example load conditions :
1) Slalom - the boat would normally throttle up to 58kph (36mph) in a few seconds, then about 20s at 3800-4000rpm while the skier runs the course, then drop and idle for 40s or so, then repeat.
2) Tricks/wakeboard - 30mins-2hrs at 2300rpm
3) Barefoot - full throttle start, 4500rpm for 1min or so, drop, turn, repeat.
4) cruising/power run on the lake, 3km at 5000rpm (70kph/45mph or so)


I've been looking for ages for the ADX/XDF files for the MEFI2 ecu, but I think mefiburn chaps are keeping it under lock and key / paywall - and for the price, I could put an aftermarket ECU on it.

I'll post a picture of the whole install tomorrow once we've got light again!
Attachments
one side
one side
other side
other side

Tom68
Posts: 53
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: having trouble with new install (SBC in boat)

Post by Tom68 »

ChrisR wrote:
Sat Jul 10, 2021 6:23 pm
Thanks, it's confusing as it seems one person will say the 300A is fine, and another it's not (or maybe in more colourful language) - the installers seem to be just saying, it's what we always put in and it always works. but anecdotally ski clubs reckon the engine is shagged after 1000-1500hrs on LPG

300A isn't rated for your horsepower requirement by Impco and they only rate the 425 at 287HP, you won't have enough airflow with either of these on your inlet tract.
Plugs got ash on it from burning oil, wouldn't get to worried about that yet.

https://centuryfuelproducts.com/parts/i ... 5m-2-mixer

https://centuryfuelproducts.com/parts/i ... gines/300a

storm
Posts: 779
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: having trouble with new install (SBC in boat)

Post by storm »

When reading the plugs for timing you are looking for 2 distinct lines or 1 section of colour between 2 lines on the ground strap. @Tom68 mentioned the ash, while I do not agree that it is oil burning it is an indication of contamination and it makes it very difficult to see anything on the ground strap.

There is nothing really wrong with a 300A, my first LPG vehicle had one but it was a 4 litre Toyota 6 cylinder and even it was limited because of it. IMNSHO they are a good dual fuel mixer on an engine that isn't expected to go over 3000 rpm. The 425 should be able to feed a 350 to 5000 rpm but, as @Tom68 points out they are rated at lower than the output you are looking for. I'd fit a 425 with 2 regulators if I wanted more than 300 HP.

Regarding an XDF there is a program, I'll try and find a link for it, that may be able to read the bin and create an XDF for you.
https://www.youtube.com/watch?v=cjR4-Av ... e=youtu.be
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

ChrisR
Posts: 7
Joined: Fri Jul 09, 2021 5:11 pm

Re: having trouble with new install (SBC in boat)

Post by ChrisR »

Picture of rear of plug and current installation.
Attachments
2021-07-11 16.13.27-1.jpg
another plug - backstrap.jpg

storm
Posts: 779
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: having trouble with new install (SBC in boat)

Post by storm »

If you can try to refit the regulator so the vapour hose is at the bottom rather than the top. The reason for this is it helps drain the regulator of "heavy ends" which is like a thick oily substance that can block it up.

Plug looks good. I can only see 1 timing line which if its the idle timing line it is a bit far across the electrode for an untuned engine. I usually like to see them on the bend of the electrode on an engine that hasn't been tuned.

I don't really know alot about marinized chevs but is the mixer sitting right next to the exhaust manifold?
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

Tom68
Posts: 53
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: having trouble with new install (SBC in boat)

Post by Tom68 »

ChrisR wrote:
Mon Jul 12, 2021 4:39 am
Picture of rear of plug and current installation.
May pay to measure the area of your snorkel compared to the open area of your 300 mixer. I had a diecast Impco snorkel on a Q'Jet on a 307 and it would lay down at I guess 3500 rpm, realised the snorkel was smaller than the 300, welded a box on top and picked it up significantly. I can see your snorkel is sand cast which are usually bigger but it does look like quite a small area.

Having said all that, you won't make enough power with a 300 or a 425 for skiing.

ChrisR
Posts: 7
Joined: Fri Jul 09, 2021 5:11 pm

Re: having trouble with new install (SBC in boat)

Post by ChrisR »

Thanks for the help so far, the converters have replaced the 300a with a 425 mixer, it's gained a bit back but still not amazing or anywhere near what I believe its potential is (gained a bit in the low/mid and an extra 100rpm to the top end).

I have parts on order and a "cunning plan" so will post back once they're on :) being in the UK, its all being shipped from the US so will take a while :(

Tom68
Posts: 53
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: having trouble with new install (SBC in boat)

Post by Tom68 »

ChrisR wrote:
Thu Jul 15, 2021 5:43 am
Thanks for the help so far, the converters have replaced the 300a with a 425 mixer, it's gained a bit back but still not amazing or anywhere near what I believe its potential is (gained a bit in the low/mid and an extra 100rpm to the top end).

I have parts on order and a "cunning plan" so will post back once they're on :) being in the UK, its all being shipped from the US so will take a while :(
LIKE.

This sort of action would help in your higher rev ranges.
L03_Ported_plenum_1.jpg

ChrisR
Posts: 7
Joined: Fri Jul 09, 2021 5:11 pm

Re: having trouble with new install (SBC in boat)

Post by ChrisR »

while bored waiting for these parts to turn up (delayed again!) I thought I'd look at the timing and see what I could glean from the datalog

towing at steady RPM
1700 - 25deg
2000 - 29deg

WOT from stationary to max rpm (won't go above 4200 at the moment)
650 - 12deg
800 - 20deg
1280 - 30deg
1800 - 33.5deg
2050 - 35deg
2300 -> 3500 36deg
3500 -> 3800 37-38deg
3800+ 35.8deg

no knock detections

interestingly, the MAP readings I think show the flow restriction:

WOT run.
47-50kPa @ 650
80kPa @ 1280
92kPa @ 2300
95kPa @ 2500-2800
92kPa @ 3000
88kPa @ 4100

to me, it looks like the tbi ports and snorkel extensions are restricting flow from 2800rpm


Also, interesting was comparing it to the standard 14-14-14 map on another post the timing seems to be pretty advanced, I know I can't edit the timing table at the moment, but might it be worth trying pulling a few degrees out from the base timing? Say set the dizzy back 2-4deg from what it currently is(so the ECU would still think it's at 38deg but it would actually be 36 or 34deg btdc)

On this ECU, you need to put it in service mode, set the timing to 10deg BTDC so the ECU knows where the timing signals are coming from, so that would mean setting the ECU base timing to 8deg (or 6deg)

storm
Posts: 779
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: having trouble with new install (SBC in boat)

Post by storm »

The TBI manifold was designed and fitted by OEM at a time where economy was what most people wanted. The TPI manifold released alot of power from otherwise restricted engines. A good dual plane or single plane will perform very well compared to the TBI. Fix your restriction, which would have a negative effect on petrol as well as LPG, and then work on your timing. Doing that will enable you to optimise your engine for LPG rather than running a restricted petrol engine on a less than perfect timing curve for LPG.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

ChrisR
Posts: 7
Joined: Fri Jul 09, 2021 5:11 pm

Re: having trouble with new install (SBC in boat)

Post by ChrisR »

I think that's where mine differs, it's a dual plane with notch manifold + flat TBI adapter plate then the tbi thottle body rather than a factory tbi manifold with direct bolt on throttle body (the picture below was taken before the 425 went on
tbi close up.jpg
I've got at least 3 weeks until the new kit turns up now but I still need to use the thing

Tom68
Posts: 53
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: having trouble with new install (SBC in boat)

Post by Tom68 »

ChrisR wrote:
Fri Jul 30, 2021 4:20 am
I think that's where mine differs, it's a dual plane with notch manifold + flat TBI adapter plate then the tbi thottle body rather than a factory tbi manifold with direct bolt on throttle body (the picture below was taken before the 425 went on

tbi close up.jpg

I've got at least 3 weeks until the new kit turns up now but I still need to use the thing
Measure the area of your gas snorkel and compare it to the opening area of the 300, you'll find it is smaller. A bigger snorkel will greatly improve performance.

Got a brand on that manifold ?

ChrisR
Posts: 7
Joined: Fri Jul 09, 2021 5:11 pm

Re: having trouble with new install (SBC in boat)

Post by ChrisR »

Thanks to everyone who contributed and helped me out.

Finally, after months of waiting for parts, then a 2 week delay in customs, the Holly throttle plate & Innovate TPS are on along with a 1" spacer to help alignment and clearances with other parts.
20210906_101616-2.jpg
I think I've found a stepper motor idle valve that will work with the MEFI2 ecu so I'll get active idle control back.

Performance wise, I reckon I must have been down at least 150hp / 150lbft, it's certainly back up to, if not better performing than when on petrol!

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