• From: Elverson, PA
  • Registered: 2017-08-15
  • Posts: 1,366

Topic: Bad ideas for engine mods

Impressions, please(?):


An engine from a 2004 Civic GX apparently has something like hardened valves, rods, pistons, and perhaps other things I know almost nothing about. (1.7l, CNG, maybe a SOHC w/VTEC? ~100 hp)


The listed compression ratio is 12.5 : 1;  _designed_ that way to use the energy from methane, which is considered to have an 'Octane' of 120. (from online information)


I'm scrapping this particular GX, since it looks like I could pull the CNG tank and lines, and put them into my CNG van to extend the range; which means I'll have an extra engine with relatively few miles on it.


It's probably (??? - definitely!)  an overreach, but I'm thinking about transplanting this engine into another Lemons candidate. Especially since this series seems to like bad ideas in race cars ;-)


I think the idea of hardened valves and other high-compression-ready engine things is a _good_ idea. Makes me want to put a turbo on it.


I've looked at the high compression, though, and a conversion to gasoline (CNG being a non-starter for Lemons racing) would likely require reducing the compression, because from what I've read, even full race gas likely would lead to premature detonation.


I've looked at the first few YouTube videos about reducing compression, so I know that's possible.


Or should I go the other way and fuel it with diesel?


And bring another engine for the race candidate.


Sell it for hardened parts for a different Honda engine?


Or just scrap it with the shell?

  • From: Camarillo, CA
  • Registered: 2021-03-26
  • Posts: 452

Re: Bad ideas for engine mods

The ND miata engine has a CR of 13:1 and runs on premium pump gas. I'm sure an engine designed for CNG that's 15 years older running on a garage tune will be just as successful as the ND engine.

Honestly though, this is awful idea, an insane amount of work for 100HP on a good day, and will probably be unreliable... please do it. I'm guessing that this 1.7 is based on the D17. I know the D16's were bulletproof and the only "issue" they had was the head gaskets tended to go out in the 150-250k range... and after replacing would go another 200k, with or without oil lol. I'm making a few assumptions that this is based off the D17 and the D17's were similar to the D16's.. and with all those assumptions in order you might as well do the head gasket while it's out and they do sell head shims for these engines. Add a shim (dare to run more than one???), shade tree sand the head flat, see if you can find a thicker head gasket, and you might be nearing a usable CR to run pump gas. You can easily calculate swept volume vs. total volume to get a rough idea on how much you'll need to space the head to get there. If the engine is a worn and you space the head you can probably get the CR to the low 11's. This is still pretty high, and won't be nominal, but if you're just trying to stay out of detonation this doesn't sound impossible.

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3 Reply by Lemon_Newton-Metre (edited by Lemon_Newton-Metre 2022-06-24 01:24 PM)

  • From: Elverson, PA
  • Registered: 2017-08-15
  • Posts: 1,366

Re: Bad ideas for engine mods

duthehustle93 wrote:

[snip]

Honestly though, this is awful idea, an insane amount of work for 100HP on a good day, and will probably be unreliable... please do it.

Thinkin' about it ...

duthehustle93 wrote:

... I'm guessing that this 1.7 is based on the D17. [snip]

I believe that to be the case. I think about 100k on it, originally a municipal vehicle. I never wound it up, have always had oil in it, and CNG engines run clean as a whistle.

Everything else you mentioned (shims, gaskets) I had read; glad to see I understood some of it.

If I put this in a light car it shouldn't be too bad, right?

I'm thinking when this blows up, maybe the engine mount configuration [I'll have to fab this]  would be close to many other small Honda engines, so a subsequent swap should be easy, right?

How hard could it be?

duthehustle93 wrote:

[snip] ... but if you're just trying to stay out of detonation this doesn't sound impossible.

That's what I was thinking.

Thanks for the input!

4 Reply by duthehustle93 (edited by duthehustle93 2022-06-25 12:59 PM)

  • From: Camarillo, CA
  • Registered: 2021-03-26
  • Posts: 452

Re: Bad ideas for engine mods

Coming from someone where 99% of their seat time on a track is in an array of stock powered miatas... yeah, if the car is light 100HP really isn't that bad. There's something fun about wringing the absolute piss out of an indestructible underpowered engine.

Yep, honda is pretty good about keeping bolt patterns the same. A lot of hatch guys (came with a D15) run the CRV engines (B20) and if I'm not mistaken that's a bolt in upgrade. I'm far from an expert on that swap though, I just know it's common enough to assume that it's mostly bolt in. Same thing on h series on our prelude. There's also a lot of gearing options for transmissions depending on options if you have a choice of the litter. You'd likely have a good shot at finding a few extremely common engines that will bolt in. But if this engine is based of the single jingle D series engines and your tune is half decent you may never need to shop for a replacement engine.

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  • From: Elverson, PA
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  • Posts: 1,366

Re: Bad ideas for engine mods

I'm thinking about also changing the engine orientation from T/FWD to L/RWD, and: a different manufacturer's chassis, because manual.

...

A sensible choice would be: drop this idea like a hot catalytic converter, and move on...

... but I keep pointing out the I.O.E. is the Grand Prize in Lemons, so I came up with this idea.

(... and a turbo ...)

6 Reply by duthehustle93 (edited by duthehustle93 2022-06-24 04:07 PM)

  • From: Camarillo, CA
  • Registered: 2021-03-26
  • Posts: 452

Re: Bad ideas for engine mods

Nice! But taking a T/FWD engine and mounting it to a RWD transmission is sooooo last year... why not get a honda manual trans bolted to your 1.7CNG gasoline-converted engine and make a custom driveshaft so that your FF engine/transmission is now L/RWD? I don't understand FWD transmissions, but there's a diff in there probably that can probably maybe be welded and possibly there is some chance that you can use a CV axle stub on the rear-facing end as an output shaft. Might as well combine a questionable engine with a horribly engineered drivetrain. Sounds great in my head and I don't see any issues with racing that for many hours on end.

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  • From: Elverson, PA
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Re: Bad ideas for engine mods

duthehustle93 wrote:

[snip] ... Might as well combine a questionable engine with a horribly engineered drivetrain. Sounds great in my head and I don't see any issues with racing that for many hours on end.

minutes on end; pretty sure you meant minutes there... 3 ... maybe 5 ... 10 ... like that.

I already have a RWD flood car with the manual tranny, stripped. The front end is going to be overloaded, regardless.

I'm not a mechanic. Lots will have to be moved.

"A man's got to know his limitations."
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  • From: Queens, NY
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Re: Bad ideas for engine mods

carb+magneto it and you are in business big_smile Might need to advance the intake cam a tooth though

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  • From: Camarillo, CA
  • Registered: 2021-03-26
  • Posts: 452

Re: Bad ideas for engine mods

Lemon_Newton-Metre wrote:
duthehustle93 wrote:

[snip] ... Might as well combine a questionable engine with a horribly engineered drivetrain. Sounds great in my head and I don't see any issues with racing that for many hours on end.

minutes on end; pretty sure you meant minutes there... 3 ... maybe 5 ... 10 ... like that.

I already have a RWD flood car with the manual tranny, stripped. The front end is going to be overloaded, regardless.

I'm not a mechanic. Lots will have to be moved.

"A man's got to know his limitations."
/Det. Harry Callahan., Magnum Force


Sounds like you HAVE to do this now...you can't fight fate!

Full Ass Racing (Captain)
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  • From: New York, NY
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Re: Bad ideas for engine mods

Lemon_Newton-Metre wrote:

Impressions, please(?):
The listed compression ratio is 12.5 : 1;  _designed_ that way to use the energy from methane, which is considered to have an 'Octane' of 120. (from online information)
...
I've looked at the high compression, though, and a conversion to gasoline (CNG being a non-starter for Lemons racing) would likely require reducing the compression, because from what I've read, even full race gas likely would lead to premature detonation.

If you're just worried about pre-detonation, you could use E85 - it supposedly has an effective octane rating of ~115.

DefectiveLemon's Website

  • From: Camarillo, CA
  • Registered: 2021-03-26
  • Posts: 452

Re: Bad ideas for engine mods

DefectiveLemon... that's some big brains... e85 will generally run at up to 14:1 IIRC. Only issue is it being a consumption rate and availability issue for endurance racing.

Full Ass Racing (Captain)
#455 Piñata Miata - 1990 Miata   |   #735 BMDollhÜr 7Turdy5i - 1990 735i (Sold)

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  • From: Elverson, PA
  • Registered: 2017-08-15
  • Posts: 1,366

Re: Bad ideas for engine mods

DefectiveLemon, duthehustle93:
Good suggestion about E85; since I'll be adding gasoline fuel features, I'll look for those.

DL:
Thanks for that reference! That's an interesting read, and I think I followed it, even though I've never taken apart an engine.

The technology in the MIT paper you listed reads similar to the Mazda SkyActive-G (or -X) engine technology.

My impression of that paper is this:

The successful reduction of pre-ignition in that MIT experiment was a result of reducing the temperature of the air-fuel mixture - using ethanol or methanol - but by separately injecting the alcohols into the combustion chamber at a certain part of the combustion cycle, which also acted to swirl the outside of the mixture (like the SkyActive technology), but NOT as the main fuel mixture per se.