BradGTV
Gold
Gold
Posts: 133
Joined: Thu Sep 24, 2009 2:55 am
Location: South Australia

24v headwork - power gains

Post by BradGTV »

about time to start pulling the top end of my 3.0 24v, the donor car had a wiring melt down / fire. bottom end is fine but id like to replace all top end gaskets and seals to be safe. whilst its all apart im thinking about some possible modifications but without spending to much $$$

what modifactions are receomended? port / polish? bigger inlet? larger valves?

with these small mods, what sort of power would i realistly be able to see from a stock bottom end 916 3.0 24v with standard cams? (will also have decent extractors / exhaust and aftermarket efi)
79 GTV (sr20) 83 GTV (TS) 85 GTV, 76 GT, 84 GTV6, 91 164, 88 75 TS & 89 75 TS
Jim K
Verde
Verde
Posts: 1732
Joined: Tue Nov 30, 2004 12:10 am
Location: Athens,Greece

Re: 24v headwork - power gains

Post by Jim K »

I would say... don't touch it! Unfortunately, ports are unnecessarily huge in these engines and any enlargement and/or polishing would end up lowering velocity, resulting in power loss. If you have good fuel in your area, you can mill the heads for a bit more cr and maybe reprofile the cams with a bit higher lift but no more duration. Thing is, you'll need remapping after all this... With such mild mods, you can expect to see ~270hp, which is what I got with precision balancing/assembly/mild cams/11.3cr/remapping and very light port clean-up. Std intake flow is ~138cfm and I got 146. It looks like you can get these heads to flow ~165cfm or more, but you'd end up with a pig of a motor at anything under 4500rpm with impressive high power capacity; consider 320hp as a conservative number when other serious mods are executed at the same time! However, to exploit power at these rpm levels (over 7500rpm and up to 8500) serious bucks would be required for internal parts, cams, breathing improvements and aftermarket ecu...
On the simpler and more practical side, some guy in the UK is about to try bolting on 2.5liter heads on the 3liter block and that should be a very interesting exercise! Smaller ports mean higher velocity and better low speed performance which is the main detriment of the 24v 3liter. The biggest disadvantage of this engine in my opinion, is the ridiculous bore/stroke sizing. If it had 86x86mm (still 3liters) it would be an all-around great performer! ...And it would be, if some German had designed it! :mrgreen: :roll:
Jim K.
User avatar
Mats
Verde
Verde
Posts: 4059
Joined: Mon Nov 29, 2004 12:26 am
Location: Gothenburg, Sweden
Contact:

Re: 24v headwork - power gains

Post by Mats »

Or Japanese... Eg. CTR. K20
Mats Strandberg
-Scuderia Rosso- Now burned to the ground...
-onemanracing.com-
-Strandberg.photography-

GTV 2000 -77 - Died in the fire.
155 V6 Sport -96 - Sold!
User avatar
75evo
Verde
Verde
Posts: 944
Joined: Tue Oct 11, 2005 8:56 am

Re: 24v headwork - power gains

Post by 75evo »

The K20 is a pretty awesome engine. My K24 only revs to 7600 rpm as it has a 99mm stroke.

About the Alfa V6, maybe if they went with longer stroke on the same outer dimension of the block (based on the 2.5), then the rods would need to be shortened considerably. Because even with the 3.2, the last ring is close to the piston pin. Then I guess having too short a rod isn't too good due to increased piston acceleration.

Then there is the issue of block clearance. I'm not sure if stock rods and an 86mm crank would clear the block when the assembly rotates. I think a 3.2 crank with JK rods would be a pretty close shave.

I think they just made do with whatever block casting they had to save on development cost.
Duk
Verde
Verde
Posts: 531
Joined: Sun Aug 19, 2007 9:15 pm
Location: South Australia

Re: 24v headwork - power gains

Post by Duk »

You could try adding some material to the inlet ports to fill them up a bit.
Despite my other thread on here about adding material to the ports where I wasn't keen on adding epoxy (it was right next to the valve seats in an area that wasn't really cast properly), I have shrunk the ports in my Toyota 'big port' head on my MR2 using epoxy. My approach was to get port cross sectional area down to about the same as a 42mm diameter (still pretty big for a 1.6 litre 4).
The combination of small ports and my custom made inlet manifold gave the little twin charged 1.6 litre engine some impressive low RPM torque and drivability gains without then falling flat on its face as revs rose.

If I was building a 24 valve, I'd be seriously looking at applying the methods like http://mototuneusa.com/thanx.htm and how he added epoxy to the port floor.
Giving the engine higher average inlet air speeds will give torque advantages at all engine speeds. That will make the car faster and much easier to drive.

I loved this http://mototuneusa.com/power_news_--_th ... erbike.htm particular article where Motoman add clay/Plasticine to the port of a CBR600 while on the flow bench to see how much material he could add before it started to effect flow. Given the size of the port and the very high revving nature of 600cc bike engines, it's a real contrast to what you might 1st believe is going on and what is actually required for best performance.

"Most modern engines already have more than enough flow in the stock ports. What they need is more velocity. I've intentionally made the ports so small that they flowed 8% less than the stock ports. These high velocity ports always make the best midrange and top-end power !!"
Jim K
Verde
Verde
Posts: 1732
Joined: Tue Nov 30, 2004 12:10 am
Location: Athens,Greece

Re: 24v headwork - power gains

Post by Jim K »

While I totally agree with reducing port size, the only reason I don't suggest it is because I've seen first hand what happens when some of the stuff (invariably?) detaches... I have also measured the flow gains on the bench -impressive for both in/ex.
For Nord inlets, there's a very safe method to decrease port size: Build up with epoxy on a release-agent lubricated port floor. Then when hard, remove carefully and replicate shape out of alloy stock. There is just enough room to insert a bolt through the water passage underneath the head to clamp down securely the reducer lump. This is 100% safe and I've seen 134cfm vs 118 on the same head before the mod. If a similar securing technique can be applied in the 24v, I'm all for it, though I haven't checked feasibility so far. In the interests of longevity and daily driveability, I wouldn't want to take the 24v past ~7600rpm, so reducing the ports considerably should pay great dividends to lower rpm work.
Regarding hypothetical block dimensions, any increase past 78mm stroke would necessitate a wider crankcase. Block height could be increased by 12-15mm no problem, with the same or other rods, so there's the new engine! But, we are all aware no manufacturer would be willing to proceed with similar changes as it would mean millions in tooling, proofing etc, especially in these times, when most are cutting back on production and manpower. Its too late now anyway, as the initial 'crime' was perpetrated by Alfa engineers when they set out to increase capacity of the 2.5liter back in ~1980 -first modification attempt for the SA 3liter. Naturally, they were asked to keep as many components as possible from the existing engine and they sure did... Basic crankase, oil pan, rockers, valve covers, cams, rods, pumps etc. They were very successful as a matter of fact in financial savings terms -until some clowns, many years later, dared compare their 3liter gem with the Beemer 3liter six and some ricer lumps... :roll:
Jim K.
Last edited by Jim K on Sat Oct 20, 2012 7:54 am, edited 1 time in total.
Duk
Verde
Verde
Posts: 531
Joined: Sun Aug 19, 2007 9:15 pm
Location: South Australia

Re: 24v headwork - power gains

Post by Duk »

JimGreek wrote: dared compare their 3liter gem with the Beemer 3liter six and some ricer lumps... :roll:
Jim K.
^^^ LOL!
I would never have called you an ignorant person, until you posted that drivel........... :shock:
Jim K
Verde
Verde
Posts: 1732
Joined: Tue Nov 30, 2004 12:10 am
Location: Athens,Greece

Re: 24v headwork - power gains

Post by Jim K »

Hold on there!!!! How does aknowledging superior engineering make me ignorant?? :mrgreen: :wall:
Jim K.
User avatar
75evo
Verde
Verde
Posts: 944
Joined: Tue Oct 11, 2005 8:56 am

Re: 24v headwork - power gains

Post by 75evo »

Jk, surely you mean 78mm stroke right?

An M30B30 is as impressive as an Alfa V6 12V? The sack of iron #%#}£€!! isnt woth the iron itis built with.

Now if we are talking Motorsport S50/S52/S54 stuff in the M cars compared to the Alfa 24v then I'm all ears. Twin vanos in the EVO 3.2, ITBs, good ecu, nice engine!

Actually why arent we looking at the new Brera/159 engines? Roller tappets, twin VVT, 90mm stroke. PERFECT! If that thing can go into the 116....
User avatar
Giuliettaevo2
Verde
Verde
Posts: 790
Joined: Sun May 08, 2005 11:56 pm
Location: Netherlands

Re: 24v headwork - power gains

Post by Giuliettaevo2 »

What do you people think about the original 24v heads and cams + boost? That would solve the low-down torque problem and have massive amounts of flow available for good power then? :)

M30 beemer engine is very tough, except oiling system for camshafs... M50 modern 24v engine is a nice unit if the coolingsystem is perfect, they crack heads easily if overheated. M badge(or S in the enginecode) takes parts-prices to a hole new level... :(
Drive it like you stole it...
Jim K
Verde
Verde
Posts: 1732
Joined: Tue Nov 30, 2004 12:10 am
Location: Athens,Greece

Re: 24v headwork - power gains

Post by Jim K »

Yes, 78mm stroke -has been corrected.
I'm referring to the M3 3liter (286hp). As far as ricer power, I can't believe anyone will consider the 3.8 GT-R too shabby, as well as the NA 350Z. Simply better than ours; truth is ours is ~30 years old and that's our only excuse; or is it?
All in all, I respect daily drivers making >90hp/liter and >300Nm (216ftlbs).
Twin turbos would solve many performance problems and create a bunch of new ones, starting with money and heat!
Jim K.
User avatar
Mats
Verde
Verde
Posts: 4059
Joined: Mon Nov 29, 2004 12:26 am
Location: Gothenburg, Sweden
Contact:

Re: 24v headwork - power gains

Post by Mats »

78mm stroke? That won't impress many girls... ;)
Mats Strandberg
-Scuderia Rosso- Now burned to the ground...
-onemanracing.com-
-Strandberg.photography-

GTV 2000 -77 - Died in the fire.
155 V6 Sport -96 - Sold!
User avatar
Giuliettaevo2
Verde
Verde
Posts: 790
Joined: Sun May 08, 2005 11:56 pm
Location: Netherlands

Re: 24v headwork - power gains

Post by Giuliettaevo2 »

The 93mm bore could upset some girls however... :lol:
Drive it like you stole it...
Jim K
Verde
Verde
Posts: 1732
Joined: Tue Nov 30, 2004 12:10 am
Location: Athens,Greece

Re: 24v headwork - power gains

Post by Jim K »

Exactly the point Mats! This is the 3.2liter stroke! Not too clever for a daily! :(
It did correct much of the 3liter's low speed weakness but its still ...wrong!
Jim K.
User avatar
Mats
Verde
Verde
Posts: 4059
Joined: Mon Nov 29, 2004 12:26 am
Location: Gothenburg, Sweden
Contact:

Re: 24v headwork - power gains

Post by Mats »

Giuliettaevo2 wrote:The 93mm bore could upset some girls however... :lol:
Easily impressed, those dutch girls... 8) :wink:

The problem isn't the short stroke, it's the short rod... :lol:
Mats Strandberg
-Scuderia Rosso- Now burned to the ground...
-onemanracing.com-
-Strandberg.photography-

GTV 2000 -77 - Died in the fire.
155 V6 Sport -96 - Sold!
Post Reply