3.2SS head porting etc
 

G`day gents and coming Merry Christmas to you.
Well it`s my turn to ask silly questions about porting. I have a build going on based on 82 SC, 11.5CR, 98mm bore (classic) with Triumph ITB`s. The ITB`s seat on PMO style manifolds. I don`t remember off the top of my head but seems like ITB`s are 42 (45?) or so mm lower diameter, manifolds lower diameter is 30.3 mm, small sized ports on the heads. Wouldn`t those 30.3 mm work as a restrictor?
So, I have a chance to port my heads, enlarge intake valves (51.5mm), match runners, what would you recommend to do with the manifolds? Keep them? Enlarge them?
I`m planning to have a rev happy up to 8k rpm street car (pretty hot street car), with cams built to specs based on ported head flows, so kinda custom or semi custom. Or whatever profile will mach those flow charts.
And what should I do about exhaust valves\ports.
Share you wisdom would you.
Cheers :)

Sounds like a fun build! Re: manifold sizing, conventional wisdom is to match the upper manifold to your throttle bodies and the low manifold to your intake ports (and blend in between). I don't have hp numbers, but if you are optimizing other aspects of your engine for performance, I'd think it would make sense to match the manifolds as well.

Scott

Why are the PMO manifolds so small, what were they made for. 3.2 heads are 42-43 mm and SC heads are 38-39mm at the intake port. Bob

I'm running Triumph ITBs with Clay's manifold. The bottom of Clay's manifold where it meets the head is about 38-39mm, so port your intakes at about the same. I went with 38mm exhaust ports. I run a twin plug 2.8 with earlier heads. Love the EFI/ITB setup

There is a chance to make new manifold\straight-to-the-head runners same size as ITB`s lower size. When to big is way to big?

Honestly I have no idea. Got them PMO style manifolds second hand since the build wasn`t this optimistic at start (first were ITBs, m a bit later engine rebuild with stuff) never paid enough attention to them, as long as they fit thing.
When I`ve started this conversion Clay wasn`t on the market yet so... And I`ve used different Triumph to start with, 675R instead of 955 as yours (I presume).
Anyway thank you gentlemen!

What is the intended use for the car? Street, autocross, track?

Street with a little bit of track. Once in a while

I would discuss the whole engine plan with the whiz doing the heads. If ya don’t have a whiz on the head work, it may be worth looking for one. The whole package has to be designed to work together to avoid disappointment. Been there, done that.

Whats the size difference between the 675R and the 955? Are there any Triumph ITBs that are 45/46mm?


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955 about 40 afaik.

I highly recommend you find someone that understands how to properly port heads. My engine guy was a guru on porting heads. He let me work on them for a couple of days with his guidance and then he worked on them for a couple of days. They were beautiful when completed like a polished vortex. Removed a zip lock sandwich bag full of aluminum shaving . I have a 3.2 SS twin plug with 46 PMO carbs. Also running 98 JE 10:5 Good luck building a rev happy beast.

Keep in mind the intended use. Intake velocity is important for a "driveable" car and going wild on port size can really kill low speed driveability. As has others have said-find a good head guy and match everything.

I am gonna talk to the guy who is doing my heads. Wanted to have a second opinion just in case.

macssc911 - what part of Charlotte are you in? I’m about 5 minutes from Forbes shop.

Todd

Todd, Think we know each other, I’m down in Marvin. I lived at Blackforest for a couple of years When we pulled engine last time and twin plugged I was out here ever week for about 6 months.

Ok, so far I have an opinion about making those intake runners 39mm, my TB bottom ends 42mm diameter, so if I`ll go with 51.5mm intake valves (which are pretty huge) there is some sense in making intake runners of 41mm. One of the builds on PP is 2.8 with 39mm intake runners. This gives me an idea of 41 for 3.2 kinda not bad...
Any ideas?

^^^
This. More than one engine has suffered from the bigger is better mentality.