2L heads on a 2.4

**croSSed** · 07-04-2025, 01:18 PM

Thoughts on this? Will I see any performance gain? Can I still run 92 oct pump gas? Will I need a jetting change?

**pcrussell50** · 07-04-2025, 01:59 PM

Originally Posted by croSSed

Thoughts on this? Will I see any performance gain? Can I still run 92 oct pump gas? Will I need a jetting change?

This has been discussed here before within the last year or so. I don't remember what the firm conclusion was, but IIRC that it made for some pretty racy compression. I'll let the legends finish this out, though.

-Peter

**ChrisCarsonMarine** · 07-07-2025, 07:47 AM

Uncut 2.0 heads will yield 145-150 lbs compression.Use 93 octane fuel(fresh fresh) and 22 Degrees WOT timing,prop to turn at least 6000.This is close to the edge,but on the safe side...but realize you have erased the safety margins the factory built in,don't over prop or use month old fuel.Read the Save your motor post,Chris

**mercrazy** · 07-07-2025, 10:13 AM

What would 2.0 heads yield on a 2.5 FF block ?
What would they yield on an o-ring head F block?

**croSSed** · 07-07-2025, 11:41 AM

Originally Posted by ChrisCarsonMarine

Uncut 2.0 heads will yield 145-150 lbs compression.Use 93 octane fuel(fresh fresh) and 22 Degrees WOT timing,prop to turn at least 6000.This is close to the edge,but on the safe side...but realize you have erased the safety margins the factory built in,don't over prop or use month old fuel.Read the Save your motor post,Chris

Thanks for this, Chris. I can't get 93 octane fuel where I live, 92 is the best I can get. Will this get any noticeable performance gain?

**ChrisCarsonMarine** · 07-07-2025, 11:45 AM

Much better accelleration,not much top end,you could use the 92 as long as its from a station that mover a lot of it,Chris

**LakeFever** · 07-08-2025, 05:53 AM

I put the small chamber 2l heads on my 2.5. It woke it right up. I run premium fuel 91-4 I’ve tried a few but I always add aces additive and only 23 degrees timing. One of my friends runs his stock 2.5 heads, runs cheap pump regular fuel ( whatever he can get cheap ) and 20 degrees timing. His boat is almost as fast as mine but it doesn’t accelerate as well. Just some info to help you decide what your goals are

**ctobias1984** · 07-08-2025, 02:25 PM

Originally Posted by LakeFever

I put the small chamber 2l heads on my 2.5. It woke it right up. I run premium fuel 91-4 I’ve tried a few but I always add aces additive and only 23 degrees timing. One of my friends runs his stock 2.5 heads, runs cheap pump regular fuel ( whatever he can get cheap ) and 20 degrees timing. His boat is almost as fast as mine but it doesn’t accelerate as well. Just some info to help you decide what your goals are

How drastic is the acceleration difference? These things suck enough gas. I have a set of 2.0 heads I have been debating on tossing on my 2.4 xr4. Near me I only have access to "premium" 93 or 90 non-ethanol fuel.

**KIRCHNER** · 07-08-2025, 02:40 PM

not as much as a light flywheel makes on acceleration. 2l heads on my 24 didnt do much.

**ctobias1984** · 07-08-2025, 03:27 PM

Originally Posted by KIRCHNER

not as much as a light flywheel makes on acceleration. 2l heads on my 24 didnt do much.

Do you know what the compression was? What gas did you run?

**croSSed** · 07-08-2025, 03:41 PM

Originally Posted by LakeFever

I put the small chamber 2l heads on my 2.5. It woke it right up. I run premium fuel 91-4 I’ve tried a few but I always add aces additive and only 23 degrees timing. One of my friends runs his stock 2.5 heads, runs cheap pump regular fuel ( whatever he can get cheap ) and 20 degrees timing. His boat is almost as fast as mine but it doesn’t accelerate as well. Just some info to help you decide what your goals are

I'm setting mine at the factory called-for timing: Throttle pickup - 7 deg. ATDC, max spark advance (at cranking speed) 18 deg. BTDC.

**KIRCHNER** · 07-08-2025, 05:48 PM

MY 24 calls for 0-4 BTDC, FIRST EFI motor 1987. i gained 10 lbs 120 to 130. are you sure on that ATDC#?? how far is your max timing stop screw from the actual block stop. motor off/sitting?

**croSSed** · 07-08-2025, 09:27 PM

Not sure what you’re getting at. I’m going off the sticker on the sound box and the factory manual.

**LakeFever** · 07-09-2025, 01:29 AM

My compression is 130ish per cyl. The acceleration was a very noticeable gain. I was running the same prop before and after too. I ran the big chamber heads untouched the same week same temps and prop to the small chambers and I was pretty surprised how noticeable the gains were. I then added an adjustable fuel reg to tune it and it really started to fly. The boat went from a solid 85mph rig that never bested 90 to a solid 90mph rig that has yet to see 95 but I’m getting close. The tuning is essential to get all the beans out of your set up but you have to be careful and prudent. Baby steps to keep it safe. I’m dropping fuel psi by half point bumps now and running at least 100 miles reading the plugs multiple times before leaning it out further. I know where to get it to if I want all of it on any given day but I’m working towards a max effort tune that’s day to day reliable. I’m not racing anyone so there’s no rush to dial it in

**KIRCHNER** · 07-09-2025, 07:49 AM

2.4? im at 80, running small changes, taking notes every outing. i cant change my mixture[efi] but props.engine height & weight location. also not in a rush. yesterday ran out of fuel,gauge read 1/3, tank bone dry. waiting on amazon today. trying for best rpm cruise at 50, skater18.