LukeSportsman

I come from the world of Wedge heads and water cooled engines where we get huge cfm and cc ports. We have multiple aftermarket options and I rev my 9 liter engine to 7800 rpm.

I'm currently building a TT short stroke 3.2. I curently have a very nice rebuilt 81 SC heads on the engine. I'm looking at 930 heads that have been ported to 40mm and are twin plugged. They are for sale by well known engine builder and are said to be "nice" for $2200.

I'm running ITB's (that'll need intakes ported too) and EFI. Is this overkill? Is this worth it on a sub killer engine?

What will the 3.0 SC heads flow under boost? Are they equal, superior, inferior to 930 heads (other than thermal capacity)?

Thanks for all inputs....I need to decide on these and don't need to waste this level of investment on something I don't NEED.

PorschePhD

Personally I think with ITBs you will loose most of your low end. I saw that based on some other builds I have made. I guess the question is what are your goals. If a high revving motor is the goal with lots of high end power then this will be perfect. If not you may want to consider something else.

As far as the SC verses 930, you beat me to the thermal difference. As far as what can flow and what can't. That will be determined by your machinist. Any head can be made to flow and there is not enough difference between the 3.0 and the 3.3 flow wise to make a difference after the head work is complete. Personally I would use 3.3 heads or 3.0T heads. Either way the head work and a proper cam is the key. Not all head work is created the same. You could have the worlds best design and have it machined and loose all the gains.

What are you going to run for a cam? What type of ITBs?

m42racer

Best to have them flow tested and see how they flow. Have someone who knows what to look for do it. Someone who knows these heads and what makes them tick. Stock size Valves? These Heads can flow when they are ported big, but there are certain areas which need attention. I'm not exactly sure what these are, but I have seen large Port Heads out flow and have higher velocity than some smaller ones.

Then Cam choice as Stephen suggested will make them either work or not. Without flow numbers, Cam selection is a shot in the dark.

If you need suggestions as to where to send them for testing etc, PM me.

Geoffrey

I've done quite a bit of head analysis work on a flow bench and I don't think "bigger is better" necessarily. I believe the velocity is equally important and would give up CFM for velocity to a point. At 40mm, it sounds like these heads are not oversized, but you'd want to CC the port to check the volume and analyze the shape. If you figure core 930 heads are in the $600 range and a good porting job is in the $1200 range, then these heads may be more expensive than doing it yourself, or they may be fine. Your best bet is to get some factual information on the heads like a flow sheet and velocity map of the port. Also be sure to check the sealing surface and understand how much, if any, has been cut to true them.

The ITBs can be a great choice depending on the design, size, and brand. For the most part, the high butterfly ITBs don't work as well n the turbo application as they do in N/A, and if they are too large, you will lose low end throttle response compared to a 3.2 Carrera or 964 manifold. A properly sized ITB setup will give you excellent throttle response and power throughout the range. You will need an ECU that can use throttle position with manifold pressure compensation in order to properly tune the engine.

LukeSportsman

I've got 48mm tapered Jenvey's that are straight shot to the ports. I have the smaller "high velocity" SC ports and therefore my interest in the larger ports. I'm looking at moderate compression of say 7.5-8.0:1 compression to help throttle response. This is mostly a street application that will see DE, no serious race use. I'm guessing this might reduce the thermal load to the heads in respect to time in boost.

I'm certainly considering the GT2 Evo or 964 cams? recommendations?? I would like a engine with linear power curve with flexible powerband. I wouldn't mind softening the bottom end a little for street traction in a chance to gain a little rpm. I'd love to get a response similar to my 2.7MFI E cam but just added power. I don't think this is impossible with ITB's and 8:1 compression. Jeeze the RS only had 8.8:1 (might be tempted to blow it, but I'm afraid the Mag would blow too!)

The heads I'm looking at are with Paul Weir so I trust his opinion about the work. Just don't want to make huge mess with miss matched parts. A bunch of good parts doesn't make a good engine as you all know. And I realize that I'm not building what most of you have done regularly.

ngoldrich

I agree - bigger is not always better for port size. Many years ago on my old 935 type car I tried one set of heads with large dia exhaust ports and it killed the bottom end...

Norm

Geoffrey

ITBs are great, however, they do require an inventment in time to set them up properly and are a maintenance item. If this is a mainly street car, I would suggest using a 3.2 Carrera or 964 Manifold as they will give similar performance, certainly more than you need on the street, and will be less complicated for ECU tuning. The Jenvey's are great throttle bodies and 48mm is a nice size for N/A applications.

I believe the GT2 Evo cams are the smallest camshafts I'd use in an EFI engine and are great on the street. I also think 8.0:1 is the optimum compression ratio for an EFI engine running on 93 octane street fuel and .7-1.0bar of boost.