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Penta AQ151 Engine Conversion

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Old Feb 17th, 2020, 11:08   #11
Laird Scooby
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Originally Posted by Clan View Post
ahh , thought he had a B230 🙄
First two lines of his first post on this thread :

" Afternoon, as some of you will be aware I have been pondering at length about what to do with the engine situation in my 1988 740 Hearse. Unfortunately, it came with a B200E, which whilst low mileage and runs quite well, is just not up to the job of hauling the extended wheelbase brick around!"

While the B200 is fine in something like a 360, it just doesn't have enough grunt to haul round even a basic 744, never mind one that has a tailgate on steroids and a chassis to match!
Even the B230E in a 745 felt underpowered at times so the B200 must be positively lethargic in terms of performance and thirsty on fuel because of the gross mismatch between expectation and reality.
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Old Feb 17th, 2020, 11:23   #12
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If it's still not got enough grunt then I'm sure at some point I will be breaking another 940 and you could use the lh2.4 from it and make a 2.5 turbo which will definitely have enough grunt then!

Just don't ruddy fit a lift kit!!!
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Old Feb 17th, 2020, 12:10   #13
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If it's still not got enough grunt then I'm sure at some point I will be breaking another 940 and you could use the lh2.4 from it and make a 2.5 turbo which will definitely have enough grunt then!

Just don't ruddy fit a lift kit!!!
Like the way you're thinking Luke!
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Old Feb 17th, 2020, 12:46   #14
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I didn't realise the plan was NOT to use a turbo....

Why would you not turbo it?

[starts dreaming of a 500bhp fire breathing Penta engined hearse going sideways around the local crematorium.......]
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Old Feb 17th, 2020, 13:11   #15
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I didn't realise the plan was NOT to use a turbo....

Why would you not turbo it?

[starts dreaming of a 500bhp fire breathing Penta engined hearse going sideways around the local crematorium.......]
Many good reasons not to turbo it, primary one is the "KISS" principle. Remember Tom is still learining about cars and very well he's done so far but splicing in an EFi loom, adding the turbo ECUs etc is probably still stretching his abilities.

Besides, a lot of it came down to cost. The biggest, simplest "bang for his buck" came from simply going to a larger, torquier unit without adding forced induction and EFi.

A big blessing is the K-Jet system can accommodate capacity changes very easily, just needing simple setting up after although that won't be far out anyway because it's simply 25% more airflow into the engine, lifting the metering flap and increasing the fuel pressure delivered to the injectors.
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Old Feb 17th, 2020, 15:31   #16
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If it had a B230, it would probably have been OK for the time being, with a +T planned in its future. However, the B200 is not up to the job.

Basically what Dave said.



My car knowledge is general but basic, and I've never messed with engine stuff before. Without going into daddy issues and all that, mechanical knowledge and skills etc is something that would have cool to be passed down, both my grandad and dad are very practical and handy, dad's a consultant engineer and my grandad more or less built his own house. So whilst I at least have a potential genetic predisposition for being handy, i'm mostly ignorant! Figuring stuff out on your own can be fun (also can be awful!) at least with the hearse there has, and hopefully will continue to be, excellent support on here!

Another issue is time, over the last couple of years I've had to more or less do another bachelor of science degree in my *spare time*, outside of a full time job. Also the house needs a lot doing to it, and the garden, family, friends... You get the idea? What i'd really like to be doing though is playing in the shed, building a better engine for the hearse, and learning all about it in the process. I'd nearly finished building the shed too, before this academic year kicked off.

I think/hope the 2.5 n/a will be all well and good for now, when the camper project is further along (or even started!) and we have LPG tanks, water tanks, carpentry and fittings etc it may very well benefit from a turbo to cope with all the extra weight. But that will likely be a way off.

If it's a relatively low pressure turbo, I don't have to worry about altering the compression ration, right? Not that i'm planning ahead for +T or anything...
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Old Feb 17th, 2020, 17:06   #17
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I think/hope the 2.5 n/a will be all well and good for now, when the camper project is further along (or even started!) and we have LPG tanks, water tanks, carpentry and fittings etc it may very well benefit from a turbo to cope with all the extra weight. But that will likely be a way off.

If it's a relatively low pressure turbo, I don't have to worry about altering the compression ration, right? Not that i'm planning ahead for +T or anything...
Up to about 4psi boost, as long as you run high octane (98) fuel, you will likely be ok with the compression ratio you have, that said it largely depends what the compression ratio ends up being.

The 2.5 pistons are 3mm shorter above the gudgeopn pin to reduce compression somewhat but i haven't been able to find a definitive number for the compression ratio. If it's built to run on low octane (88-91) fuel as a lot of marine engines are, the chances are an LPT conversion would be a spanner job to fit but you may have to consider going to EFi (LH2.4 comes to mind) to make it work properly.

See how the conversion is after it's done on the K-Jet, you may well find you don't need a turbo, even with the extra weight.
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Old Feb 17th, 2020, 18:40   #18
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I found a compression ratio figure from an FAQ thread on turbobricks. 9.7:1 seems to be the ticket with the 531 head. However, IIRC the 530 head has a slightly smaller combustion chamber, so will end up slightly higher.

Quote:
Aq151 = aka 250
-2.49l, or 151ci
-86MM stroke
-Forged crankshaft
-8v 1000531 head
-Dual Carb
-"V" cam
-CR 9.7:1. comp press 142-170psi
-Cast V pistons
-All Square Tooth T-Belt
-146hp
-551.2 lbs
-max speed 5500 rpm
What is the issue with compression and turbo forced induction? Without investigating my two guesses would be actually getting the fuel/air into the combustion chamber being difficult at such high compressions and/or too great a force on engine internals = bent rods or other ruin.
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Old Feb 17th, 2020, 20:44   #19
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Originally Posted by TomSaintJames View Post
I found a compression ratio figure from an FAQ thread on turbobricks. 9.7:1 seems to be the ticket with the 531 head. However, IIRC the 530 head has a slightly smaller combustion chamber, so will end up slightly higher.



What is the issue with compression and turbo forced induction? Without investigating my two guesses would be actually getting the fuel/air into the combustion chamber being difficult at such high compressions and/or too great a force on engine internals = bent rods or other ruin.
Sort of the right consequences but not for the right reasons Tom.

Primary problem is detonation aka pre-ignition, knocking, pinking, pinging and similar phrases. It can cause problems in the little ends but before that, it has a tendency to overheat the piston crowns, resulting in a big hole where the piston should be.

In extreme cases, con rods can get broken and make a bid for freedom through the side of the block.

As a side effect, it also reduces power output.

The forced induction pushes extra air into the cylinder so when the cylinder compresses, the heat goes up further. If the compression ratio is too high and/or too much boost or too low a octane rating fuel is used, it has a tendency to self-ignite the mixture before the time it should for maximum power.

If you remember Boyles Laws from your physics days at school, you'll get the idea fairly quick.
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Old Feb 17th, 2020, 23:31   #20
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Be aware that if the engine was used in a boat, and in a sal****er boat, there's a fair chance there's some heavy corrosion on the head, mainly exhaust port 4.
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