intake manifold differences

[shepherd]

I've been collecting parts for a turbo engine for about a year, and am finally going to order the heads. I would like to send a pair of manifolds to be port matched, but am unsure what if any difference the choice will make on a forced induction engine.
Engine will be 84Xthick wall 92, XR292 cam, cnc revmaster heads, 8.5 compression, maybe 8-10 psi through dual 40mm throttle bodies, in a 62 beetle, mostly street car.
I am looking at
http://www.cbperformance.com/ProductDet ... tCode=7366
or
http://www.cbperformance.com/ProductDet ... tCode=7359
Will the different styles make any noticeable difference one way or the other? I know what to expect with a normally aspirated engine, but this is my first time building a forced induction motor. The offset design fits my application better, but I could make the taller big beef fit if there was enough of a gain to be had.
SD

[Chip Birks]

I personally think that turbos are more forgiving when considering intake and head designs. That said I think there are huge benefits available to someone who takes the time to design a turbo combo like they would an NA combo. Remember, a turbo motor is only turbo'd 5% of the time you are driving it on the street, otherwise it's just an NA motor, might as well design it to run good that way too.

[Clonebug]

For what it's worth I really haven't noticed much difference between my stock heads and the new DRD 40X37.5mm valved heads I put on last winter.
I really haven't had the time to get the tune tightened up either but it certainly didn't make an obvious difference like I had hoped it would.

I have not been able to beat the one and only run at 22 lbs. on the stock heads verses 22 lbs. with the new heads.
I haven't gotten a good clean run either though.......maybe next year.

If you can get another 5-10 hp out of better heads and intakes when N/A.... then you will be able to multiply that hp with the turbo, so at lets say 10 lbs. you might gain another 60-65% of that possible 5-10 hp which could net another 5-6 hp.

[madmike]

Those intake are about linkage set ups,
Match port them yourself got a Dremil? use the gasket as a templet

[shepherd]

Those intake are about linkage set ups,
Match port them yourself got a Dremil? use the gasket as a templet

I've ported a few manifolds and heads myself, it's a ton of work and I have little experience. Mostly I just try to copy what I've been told works well. For this I have to purchase manifolds anyway, so it makes sense to have them sent to the guy with the cnc, who's doing the heads anyway. From what I have seen, he knows what he's doing

As for the style, I like the way carbs run with straight manifolds. It feels like I get better low and mid range. But with this, as I'm not drawing fuel through the auxiliary venturi (efi) and it will be boosted (some of the time), I wonder how much if any difference it will make. Both manifold designs have the injectors pointed at the intake ports, so the manifold is just about moving air. So I wonder..

[petew]

I'm no fluid dynamics engineer or racing engine expert, but I know this. The specific difference between a NA and turbo engine is the positive port pressure in a turbo/blown motor. So all the trouble we go to, to create a good vacuum and the like (for NA), just isn't an issue in a boosted engine.

What we need to chase is good port velocity and higher air density. On a boosted engine, that can mean small/stockish ports rather than big open ports like on a large HP NA motor. On a street motor, that provides boost just off idle. With cheap intercooling, lots of turbo choice and good ECUs, there's no need (or excuse) for laggy, 80's style turbo engines.

[Buggsy]

I added my first turbo to a 1915 with stock heads back in 2003. In 2006, I installed some "no name" generic ported heads with 42 by 37 valves. The gains from the heads felt almost as large as installing the turbo did in 2003. The more you increase the displacement, the more you need larger ports and valves whether you are turbocharged or not.
Match porting with a dremel is fine, but to do any real porting, your going to need something more capable than that. JMO

[Ol'fogasaurus]

When match porting is done the rule of thumb (or used to be) is about/no more than is an inch into the manifold or head before everything is flared back together. The distance depends on how much of a miss-match you are trying to get rid of.

Porting is an art in its self and really should be done with the help of a flow bench. One of the guys I know is a pretty good engine builder (now retired) and did his own heads. Just before he retired he thought he might save some time by buying already ported heads. When he got the first set in he put them on his bench and this set flowed less than stock.

When he called the company he found out that they were done by a CNC machine based using an older ported set of heads as a pattern. He did a set of heads for them (which, I understand they digitized) for a new pattern.

Caution should observed when doing it yourself as doing it wrong can make things worse. The valve pockets among other things can really make or break a port/head job.

[madmike]

I haven't done it yet
But I've seen Guy's make a few 'Door Stops'
or this WTF? I had to have them 'welded back up' and then I redone them
I don't use a Dremal,, I have these and a few bits

[miniman82]

Probably wouldn't make a lot of difference in a draw through setup, but you wouldn't want something like that for an EFI setup.