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(Post Link) post #1 of 15 Old 03-09-12 Thread Starter
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Cylinderheads V6

I'm rebuilding 3.0 V6 24v engine to go in my 156. It Will be long slow going project with all kinds of goodies to put in or on the engine.
Reading on different forums, it seems that the inletports in the 3.0 cylinderhead are way to big to get really good air speed Down in the chamber.
On the 2,5 V6 24v engines smaller intake valves are used with i presume also smaller intakeports.
The thing to investigate is can i put these 2,5 cilinderheads with the 3.0 intake valves on the 3.0 block and gain some extra pony's?
Also the dome shape combustion chamber in the 2.5 heads suppossed to be bit different compared to the 3.0 head.

My question what do you think of the idea and maby more important does anybody got info on the subject.

Tim

Last edited by tim0172; 03-09-12 at 20:36.
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I cannot see that the 2.5 head will be better than the 3.0 head...
The 2.5 head combustion chamber will have to be grind bigger to host the bigger piston for one.

There will be more benefit in changing the cams to GTA-1 spec and increasing the plenum air volume
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(Post Link) post #3 of 15 Old 05-09-12 Thread Starter
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Combustion chamber would't be the biggest problem i think because the piston wont reach so high to actualy get into the cobustion chamber of the cilinderhead. Ofcourse there will be some work in that area but not to much.
C&B cams are going in so thats sorted.
Once the carbon plenum is ready from ACT this will also go on.

Tim
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You are correct in saying the piston turns (TDC) pretty flush with the sleeve and won't touch the head, but the combustion chamber will mask some of the piston surface area. I am not sure, but I have a suspicion it might be prone to detonate in that area as the compression profile will have a step.

If you have the means to complete the exercise to put the 3.0 valves in a 2.5 head - DO IT! I would like to know as I also want to put 3.0 pistons in my 2.5 block (with the 2.5 stroke that will become a 2.8L)
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(Post Link) post #5 of 15 Old 05-09-12 Thread Starter
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Ofcourse will the chamber need some work and the 'step' obviously need to be removed to make sure it wont detonate there.
I know that it wont fit without any work on them, but i was wondering If anybody know If this is already been done.
Yesterday i recieved 2,5 head next week i will dismantle the 3.0 heads and make some measurements.

Tim
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Cool man it really seems your plan is well thought out - I am following this thread closely - I think you will be successful
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Also interested in the outcome - keep us updated....
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(Post Link) post #8 of 15 Old 09-09-12 Thread Starter
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Will do!
I did rough measurement on both the heads (3.0 compared to 2.5 head) and the ports on the 2.5 are lot smaller in diameter, maby 3mm! This is Great news because it is always better to remove material then to add to shape port.

Tim
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with smaller ports you will gain low down torque at the expense of top end power. Your power curve will be more compressed because you may not be flowing enough air at high revs to produce sufficient power. You could fit, as suggested, more aggressive cams that will help your engine swallow more air and more air equals higher inlet velocity. Also address the valve seats and valve heads to ensure there is lower restrictions to airflow into the engine, and raise your rev limit to 7500rpm. This will make more meaningful power at higher revs.

I've seen a 3.2 engine push out 206kW (280bhp) corrected to the flywheel with a good gasflow, valve job, porting job, remap, decat and exhaust and stock cams. This power was made close to 7000rpm.

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so you want 2.5 heads for small bore, with 3.0 valves that will then be restricted by the small input bore, which your going to machine out ?

2.8 have been tried in 12v engines but its a huge amount of work
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I talked to Jim Kartalamakis, and also a few others. The ports and valves of the 3.0 and 3.2 is big, very good for a high revving race car. Probably, a 2.5 head machined properly to fit the bore of the 3.0 block will yield a better road going car.
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(Post Link) post #12 of 15 Old 04-01-13 Thread Starter
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It is not the valves that are to big the problem is more in the Ports being to big, on the 2,5 head the Ports are a lot smaller.
I have decided to still go ahead with the 3,0 heads this coupled with bigger intake valves and epoxy filling the intake Ports to get a better shape and smaller csa.
This will flow alot better, i will do flowtests and velocity tests to back up the work in progress.

Regards,
Tim
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Hi Tim, I'm very interested in following this thread. would it be possible to post some pictures of the differences between the 2.5 and 3.0 heads?
This is a conversion i'm also thinking of doing, i see you're staying with the 3.0 heads, is there a particular reason?? Would the 3.0 valves fit in the 2.5 heads or isn't there enough room?
Looking forward to seeing how this works out for you, i'm sure you'll end up with a great engine!
Good luck from Australia
Regards,
Ben
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(Post Link) post #14 of 15 Old 19-01-13 Thread Starter
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Hi Ben,

I Will make some photos for you and post them here.
The 3,0 valves will fit the 2,5 heads fine maby also with a reworked 2,5 intake seat but not sure about this one.
The reason for staying with the 3,0 liter heads is, I want to use the exhaust valves of the 3,0 heads because they will fit in better with the 38mm intake valves.
If I want to use them in the 2,5 head this means another 12 valveseats needs to be replaced and reworked, also using the 2,5 L head the combustion chambers needs some reworking.
This will cost a lot more money compared to using the 3,0 heads where i can use the existing exhaust valve and leave the combustion chamber moreless alone.

Regards,
Tim
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Thanks Tim, it would be great to see what the differences really are... Much appreiciated
Ben
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