William Leonard

Hi, I'm building a G23 (I know I'm late to the party lol) and I have some thechnical questions as I want to daily/weekend drive this setup and only 91 octane is available here.

The build consists of:
- F23 block, bored to 87mm
- F23 crank, balanced
- F23 crower rods
- Pro 2 cams
I'm shooting for around 11.6 to 11.8 compression to make power with these big cams while running 91 octane.

The problem comes when choosing pistons, because I've seen a lot of people having problems running k24 pistons with pro 2 cams. The valve angle of the H22 is 29 degrees while K24 is 25 degrees, so even with deep valve relief the valves hit the piston. So I have three options here, but cost is a major factor here as I'm still studying, so:

1. K24 pistons (the 12.5cr i think, in my setup yields around 11.9) with a slightly thicker Head gasket and fly cut the valve reliefs ($$$)

2. H22 shelf pistons with 7cc dome (with correct valve angle) and mill it a bit so i get 4.5cc dome to get around 11.7cr with 2mm HG ($$)

3.H22 pistons with whatever cc dome i need (shelf of course) with a stupid thick 3mm HG ($)

I basically want to know if i can run 3mm head gasket with the piston sticking out the block a fuckton on an all motor setup and expect a long life out of it.

Any cheap solutions welcomed!

Aradin

If possible, you would be better off using an F20B block bored to 87mm with H22 slugs or just using a 97+ H22 block with 55mm mains. "G" builds tend to have a fair amount of reliability issues and lots of unnecessary mixing/matching of parts to get everything to work as you're currently learning.

William Leonard

Yeah thanks you for the info, but i know what modification to do in order for it to run reliably. This is not my first engine build, just my first g23. I chose to go with the f23 block for the massive main girdle, whiche ties the mains to the block, helping with block distortion at higher rpm with a 97mm stoke.

Whats really bothering me is the P2V clearance ans camgear adjustment range with the k pistons. I'm trying to find a way to run shelf forged H22 pistons while having optimum compression ratio and good quench pad distance. I'm shooting for 250whp, so it's not a far stretch.

GhostAccord

Why do they need to be shelf pistons?

I got a set of custom 89mm Wiseco pistons for my build from Race Engineering for maybe $100 more than shelf. Then there would be no P2V or quench issues and no need to pay extra for thicker head gasket. They list a set of 86mm F23A 11:1 pistons that are $50 cheaper than a shelf K24 set.


Contact the guys at Race Engineering, they were very helpful with my setup. https://www.raceeng.com/t-contact.aspx

William Leonard

Thanks for your reply ghost! Been reading your threads since i had my first honda lol

To answer your question, the block will be bored to 87mm to eliminate any hotspot at the block/head interface (and to get a little more power too).

And to be honest, i considered custom pistons from diamond and wiseco but i was under the impression that they would cost me an arm and a leg. But yeah, that would be the better option i'm very aware, just didn't know the actual cost.

So since you're here, what's your take on the G23 reliability? I plan on building it to be solid with more oil pressure than usual, clearances on the loose side of oem specs for the bearings and a redline of ~7800 rpm

GhostAccord

Reliability depends on the builds quality and attention to detail. Choosing the correct pistons, rods, bearings, clearances and very important tuning will all weigh in on reliability. Hybrid builds can be just as reliable as an original if done correctly.

if you are planning to run a slightly looser clearance, such as that found in the H22 vs F22/F23, a higher oil pressure than OE F23 would be ok. Not sure that it is a necessity, but it wouldn't hurt. What are your plans for the car, strictly street or a little bit of strip/racing mixed in?

I know this may sound expensive, but I got my 89mm 11:1 pistons and H22 Carrillo ProA rods for $1250. The rods were $750. That being said I think prices have gone way up since then.....

William Leonard

The engine is going in my 5g prelude. I use it as a daily in the summer and i do take it out on the track sometimes (lapping, no drag) so it gets driven yeah.

As for reliability, I think the biggest issue will be the narrow rod journals which i intend to adress with increased clearance and oil pressure, and the rocker wear caused by the skunk 2 pro 2 cams. I plan to plumb an oil line to the head like an ls vtec and using high zinc oil but i've never dealt with this so it's only speculations.

Also, I already got some crower forged f23 rods so i won't be paying for all the parts all at once, which is good if i consider buying custom pistons.

Honderachinaldo

Starting to get excited about my g build now. I think the weak points in a G23 are those skinny rod bolts, which has been addressed with rod upgrade. My molnars are 35 grams heavier than stock, don't see a g23 being the smoothest motor but should have great longevity if done right. Not a superfan of h22 valvetrain but a properly treated cam lobe should resist wear at expense of followers. The rod big end width is the same as the k20, a somewhat rpm friendly engine, although K doesn't have a 97mm stroke-I guess it converts from 8k to 7.4ish for equiv piston speed with the h22 stroke.

William Leonard

Yeah i've heard the argument about the f23 rod journals being the same width as th k20's, but no one seems to know that the diameter is smaller on the f23 (48mm vs 51mm) so less crank material/strength and less surface area to distribute the force. This is why i dont think revving them like K's is a good idea, the crank being the weakest factor in a built f23/g23.

Regarding the rotating assembly, internal balancing and a good damper works miracles on any engine. Just look at the 99mm all motor k24 that revs to 10 000 and road race!

For the cam wear i agree the h series valvetrain is limited, but some people have had good results with high zinc engine oil, molly additives and external oil feed line like on the ls vtec engines. Running pro 2 cams i think is compromising a bit longevity but not that much with all the supporting mods i listed.

Anyway i hope your build will go together without problem! How much compression and what pistons do you plan on running?

Honderachinaldo

I can see a properly sorted G23 running up to 8k rpms reliably, people are supposedly exceeding that with stock rods, for however long. F23s are seriously over engineered for something intended to get Grandma to the bingo parlor, oddly thin rod bolts aside.
Was going to complain about piston speed but will have to see that 10k rpm K24 first.

William Leonard

Yeah 8k would be reliable with proper clearance and oil pressure. I think clearances on the loose end of the oem specs with a balance shaft delete to up the oil pressure would be a good combo.

Regarding piston speed, take a look at the 4Piston K400 here: K24-K400 2.5L Complete Engine - ROAD RACE / RALLY | 4 Piston Racing
Its a 2.5L 99mm stroke capable of 9800 rpm reliably. That means an insane piston speed of 32,34 meters per second, while the 97mm f23 crank at 8000 rpm does 25.87 meters per second (the f22c at its factory cutoff of 8200 rpm does 24.79 mps). So relatively speaking, piston speed is not an issue here, i think.

Again, i'm curious as what pistons you plan on running cause' I think of going custom but damn a shelf option would be perfect.

Honderachinaldo

F23/k20 ACL rod bearings fit well.
The Nippon Racing coated eutecs came with a 2cnd ring gap a bit large at 27 but match valve reliefs well and give 12ish c/r. I'm doubling F23 mls hgs for around 1.33mm and am expecting high 10s. .5mm generally drops a half compression point in these shitboxes. I'm just going to not reinstall balance shaft belt for now. Do the whole deal when I build an 87mm block.

Aradin

You guys are on the right track. I wouldn't have used an F23 block though. I'm doing something similar but with a boosted application utilizing an F20B block, F23 crank, forged rods and custom pistons. Same end result but better because the head fits like it should and no need to worry about valve clearance issues. No need to fiddle with the mismatched oil galleys either. There is an argument to be made about the girdle of the F23 which ties into the block casting itself but the benefits haven't really been proven one way or the other. All other H/F series have a very strong girdle design from the factory to begin with.

I initially had my concerns about piston speeds as well but it seems like it will be manageable as long as the stroke and geometry are taken into consideration when tuning. The crank is relatively light and the rod journals are a good design that are smaller/lighter but still robust. If other measures are taken to reduce reciprocating mass like removing the balance shafts and a lighter weight flywheel, the engine should rev relatively smoothly and operate well in the higher RPM range.

I am building my engine a little on the looser side of clearances due to the fact that the 97mm stroke will potentially be pretty rough on the bearings when combined with boost. High RPM NA setups will want to do the same. Another thing to consider when planning your build is the side-loading of the sleeves and pistons due to the big stroke. To combat this and minimize piston skirt wear/maximize engine longevity I recommend using a strutted piston if possible. However even then you will still likely see a fair amount of skirt wear under consistent high RPM operation. H23A blue top pistons are a good design and could be useful in an NA application, but are 87mm and can be hard to source.

William Leonard

It's been a little while, but after a lot of measuring I opted to retain the h22a4 block. I have rebuilt a bunch of those and the FRM lining is not that bad to work with. The incentive is that f20c and f22c pistons will fit the h22 block with the 97mm crank because of their 30mm compression height. They have the same valve relief angle as the k20 if i'm not mistaken (25° f20c vs 29° H22). This combo has the advantage of keeping the h22 block and head so the oil will flow as intended. It's more like a stroker kit than a frankenstein build.

With the zeal calculator, the f22c pistons and 97mm stroke put me around 11.7cr, which is enough for the pro2 cams I want to run and low enough to run on 91 octane. My only real concern now is the 23mm wrist pin found on the f22c pistons vs the 22mm bushings on my f23 crower rods. The bushings seems already thin as is, so I wonder if I can overbore the small end to fit new 23mm bushings? i have never tempered with rod bushings before.