Destroke or not to destroke?

Hello guys!
I am currently in the way of doing a big engine/transmission to my track mk2.
She will receive a 830 engine block which will be tuned with forged internals.
At this moment I have 421 cams, dedicated racing ecu, ITB's.. full exhaust etc etc.
In the future I think I will go with solid lifters and cnc head machining.
The plan was to fit 84mm hi comp forged pistons with proper rods now that I am rebuilding the block.
So here comes the dilemma.
I was thinking to fit a 90mm stroke crank with 150mm rods to reduce the stroke with obvious benefits.
Since the thing costs a lot, I am questioning myself if the gains in term of balance with the build and be more happy revving can be worth or not.
What do you guys think?

Think you need to start with deciding how much power you want to extract from the engine and then go from there.

Does it need to be N/A as Engine Dynamics do a bolt on 240 bhp turbo kit for a std 172 engine for £2499.

Seems like a cost-effective way to go to me.

200 hp is fairly easy from the F4R, north of that it gets expensive quickly,
if you want nearer 250 hp N/A then go down the K20 swap route and save yourself some money.

TheCAB said:

Think you need to start with deciding how much power you want to extract from the engine and then go from there.

Does it need to be N/A as Engine Dynamics do a bolt on 240 bhp turbo kit for a std 172 engine for £2499.

Seems like a cost-effective way to go to me.

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Yes it needs to be NA as I love its power delivery. At the moment with ITB's cams and so on I already have more than 200 hp and about 220 of Torque. Torque and power are delivered amazingly and already pulling strong from 5500 rpm.
My question was more about technical advantages and if it was worth the hassle and the money considering it in the build of the new engine.
Being the short stroke crank more than 2000 euros alone you can imagine I know the build will not be cheap.

bashracing said:

200 hp is fairly easy from the F4R, north of that it gets expensive quickly,
if you want nearer 250 hp N/A then go down the K20 swap route and save yourself some money.

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Its not hard to get.. but it also depends on the Dyno. Ive seen online some F4R dyno charts.. how can I say? lets say pretty optimistic to say least.
Anyway.. I have considered the k20 route but I already invested money on my head, the itbs, electronics and other things. so swapping k20 could be nice (and i would love) but bringing it at this stage would be very very expensive as i would need to spend the engine build money + the whole k20 block and gearbox + another dedicated ecu, the itbs and all the things i already done. I did some math and beside being tempty it would cost double building a forged strong F4R.

I am a big F4R fan, but the k20 is lightyears ahead both in terms of making power and being reliable at that power, my understanding is that a k20 with mild breathing mods and a map is making about the same power as a cammed and ITB f4R. I can only imagine an ITB k20 will make some mad power!

I don't believe that the stroke is the major factor restricting the development of power from the F4r engine.

The crank you mention seems an expensive way to go for unknown power returns.

Developing a hi-output N/A engine is more than just simply bolting together several different parts from various sources and hoping for the best and the F4r engine also gets very fragile the higher the state of tune it is in.

If its just a track toy then turbo it an develop that, easy gains really.

Martin_172 said:

I am a big F4R fan, but the k20 is lightyears ahead both in terms of making power and being reliable at that power, my understanding is that a k20 with mild breathing mods and a map is making about the same power as a cammed and ITB f4R. I can only imagine an ITB k20 will make some mad power!

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Don't make me think about it mate heheh!!
It would be crazy I know.

TheCAB said:

I don't believe that the stroke is the major factor restricting the development of power from the F4r engine.

The crank you mention seems an expensive way to go for unknown power returns.

Developing a hi-output N/A engine is more than just simply bolting together several different parts from various sources and hoping for the best and the F4r engine also gets very fragile the higher the state of tune it is in.

If its just a track toy then turbo it an develop that, easy gains really.

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I know, my post is not about the dream of putting a short stroke crank and see horsepower increase. I already have a plan about what to do for the new season engine. And as said it will be high compression, all forged, it will use my current itb, cat cams and so on and soon the head will be cnc worked too.

The crank is not a major restricting element. But being F4R a long stroke engine, it surely isnt super suited for high rpm because of high piston speed.
Reducing the stroke we can change the bore/stroke ratio and make it more rpm happy.
Doing so it can be tuned to have the powerband placed in higher rpm, which is the route usually used on NA engines.
Anyway..
As said Its NA and will stay NA.
I don't like turbo power delivery, and I never asked about easy gains or cost effective gains..

My interest is very technical about real advantages of that choice instead of keeping the std stroke. So it was more oriented to people who built or raced such engines (like the old clio Maxi to give an example).

I know somebody who destroked an f4r to 1.8 using a f7p or volvo crank from memory.

Totally different setup as the engine was turbo but you could maybe look to see If that could work for you.

It doesn't answer your question but I'd sell what you have and K24 it, 260bhp/200lbft without taking the head off. People always think Kswaps are £8k I did my whole swap for around £3k a few years back.

T3gav said:

It doesn't answer your question but I'd sell what you have and K24 it, 260bhp/200lbft without taking the head off. People always think Kswaps are £8k I did my whole swap for around £3k a few years back.

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All day long. Assume gearbox is a lot better too

T3gav said:

It doesn't answer your question but I'd sell what you have and K24 it, 260bhp/200lbft without taking the head off. People always think Kswaps are £8k I did my whole swap for around £3k a few years back.

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I don't know how are priced those parts in UK (I live in italy) but here a K20 in good conditions is about 5000€ + around 1500 for the gearbox.
Then we have to add the kit to install it on the clio (shafts, supports, water hoses and headers) which here is about 1600€
Then we need an LSD (as I Always had) which is another 1000€
Ecu 1400€
ITB's 1800€
And a lot of other little things.

Yea to be fair we have or had an abundance of K20 engines in the UK, the EP3 Civic was massively popular here, thanks to our salty winter roads many ended up in scrap yards or broken for parts.

No-one has mentioned supercharging? The benefits of additional power with the power delivery closer to N/A experience.

kurai said:

I don't know how are priced those parts in UK (I live in italy) but here a K20 in good conditions is about 5000€ + around 1500 for the gearbox.
Then we have to add the kit to install it on the clio (shafts, supports, water hoses and headers) which here is about 1600€
Then we need an LSD (as I Always had) which is another 1000€
Ecu 1400€
ITB's 1800€
And a lot of other little things.

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K24A or K24A3 around £1000 in the UK

Have you looked at Puremotorsports engine?
That'll give you a good idea of what's needed, and they're doing a version 2 as we speak.