Help! Heads/Manifold Coolant ports

[Lloyd Barnes]

Have just received the cylinder heads last week for the 383 SBC I'm building. AFR 195's. Was planning on using these with a Performer RPM manifold which I also now have.

Here's the problem. The AFR heads have coolant ports at either end. In the centre is a small drilling which looks like it goes through to the exhaust port. The inlet manifold has coolant ports in the centre and at the front.

Have I ordered something wrong or am I just being daft and missing something? Can post pics if needed.

[ti]

Originally Posted by Lloyd Barnes

Have just received the cylinder heads last week for the 383 SBC I'm building. AFR 195's. Was planning on using these with a Performer RPM manifold which I also now have.

Here's the problem. The AFR heads have coolant ports at either end. In the centre is a small drilling which looks like it goes through to the exhaust port. The inlet manifold has coolant ports in the centre and at the front.

Have I ordered something wrong or am I just being daft and missing something? Can post pics if needed.

Can't help you with this one but i think it would be a good idea to put some pics on so that others in the know will be able to help you.
Maybe a bit longer than usual for a reply as every one is sunning themselves at Stoneleigh car show.

[Lloyd Barnes]

would have loved to have gone myself but no chance unfortunately.

I'll post some up later this evening. Wondering if the centre "coolant ports" are actually just a passage connecting the two exhaust ports, but can't figure out why you'd do that. Someone hopefully will know though

[Lloyd Barnes]

here's a pic of the head and the manifold. Does the centre port on the manifold simply connect the two drillings to the exhaust ports (and if so why??) or is it a coolant port and I've ordered something wrong?

Also the compression ratio is working out at 10.2-10.3, is this useable or should I be checking the dynamic ratio to make sure all is ok?

[craggle]

According to this page Edelbrock heads also have the hole.

Edelbrock

They call it an exhaust crossover passage for emissions purposes. Possibly the passage in the inlet just links the two heads together and some heat from the exhaust ports is used to warm the manifold?

Not sure really. Can you see if the channel on the inlet manifold goes anywhere else?

Craig.

[slogger]

Originally Posted by craggle

According to this page Edelbrock heads also have the hole.

Edelbrock

They call it an exhaust crossover passage for emissions purposes. Possibly the passage in the inlet just links the two heads together and some heat from the exhaust ports is used to warm the manifold?

Not sure really. Can you see if the channel on the inlet manifold goes anywhere else?

Craig.

Thats how my Chevy Big Block heads are arranged. The heat riser passage is for inlet heat and emission control. The Felpro gasket set provides a restricter and a blank so that you can do what you like. I have used the restricter as some exhaust heat would be a good thing in our winter.

[craggle]

This web page explains a bit more..

exhaust crossover

Seems it is simply a way of warming up the manifold to help with cold weather drivability. As Ian said, maybe some heat here is useful for our weather conditions.

Craig.

[Lloyd Barnes]

thats a relief, thought I'd ordered the wrong thing and the heads took almost two months to arrive!

what do you think about the compression ratio, anyone else running at 10.2/10.3:1?

[JamesP]

I've got the same heads, different manifold but running same CR.
Dynamic CR is key as CR is dependant on Cam profile.

I've posted an excel model somewhere that will calculate this for you.
Plus Ali heads run cooler so you can get away withy a slightly higher CR.

What are your cam specs?

James

[Lloyd Barnes]

Hi James

I've used a speciality grind cam from Comp cams. Have tried working out the dynamic ratio but all the calculators I've found need the intake closing point ABDC at .050". The cam card shows this at 0.06 and I'm not sure how to relate the two.

I've not gone mad with the duration (224/230) as I wanted to keep the motor strong throught the rev range, but tightened up the LCA to 108 degrees (can you tell I've been reading Vizards book!). Overlap won't be excessive I think with these specs so I'm a little worried that the dynamic ratio will be too high