Ported plenum and I.H. increases-worth it?

[cuisinartvette]

On a 90. Or is it better to wait and do the heads also. I'll have (too much) time on my hands due to work the next few months so I was toying with the idea of pulling them off.

-What kind of rwhp on average should I see?
-What about the mismatch between the ported IH and the heads?
Can't do the whole motor til my other project is on the road, but want a little more power to passify me til I can..

[Aurora40]

I hear you on the mismatch. But I guess more flow up to the head matters more. I can see how that might be. It's like having the 1.75" pinch in our stock exhaust. It hurts, but not as bad as a full 1.75" system would. So the bigger TB bore, the bigger runners, etc, put more air at the port of the head.

Also, stock, that injector boss for the primary is really really intrusive. That thing is thick and sticks way into the path.

From reading around, it seems like 30-35whp is about the gain, putting a 1990 at ~415hp.

[crazyb1]

On my '90, I have P/P plenum and intake, plus headers and B&B. Last dyno was 386RWHP. Hope this helps.

[Locobob]

I put this up on the Corvette Forum also

1991 ZR-1 with cat back and DRM chip before and after intake porting: Heads were untouched, no additional tuning, stock size throttle body.




Just do some light clean-up on the bottom of the injector housings. The secondarys are plenty big already and the primarys should gradually neck down to the stock diameter at the head mating surface.

[Locobob]

Originally Posted by Aurora40

From reading around, it seems like 30-35whp is about the gain, putting a 1990 at ~415hp.

You'll only get this kind of gain on a 90-92 and then only in conjuction with tuning. If you look on Haibecks website you will find some dyno charts showing porting results on both 375 and 405hp ZR-1's, keep in mind these results include a 63mm throttle body and dyno tuning.

[Aurora40]

Originally Posted by Locobob

You'll only get this kind of gain on a 90-92 and then only in conjuction with tuning.

He was asking about a 1990 though.

I guess one other option, though one that seems kind of odd, would be to get the injector housings from 1993+ and put them on your 1990-92 if you didn't want to have porting done. Since the IH's are kind of cheap ~$150 per side, and less used. Seems like a lot of effort for not a lot of gain, but just tossing it out there. You'd need new primary injectors also, I'd imagine, since the old ones wouldn't fit right.

I sort of wish I'd dyno'd my car before. I'd be interested to see the gain from just a tune up and new vacuum parts, and then the gain from the porting. But I guess I'm a cheapo. Whatever power it make, it makes, regardless of what a dyno says or whether I can quantify that power. I mean, the car won't be any different after the dyno run than it was before it. And it's cheaper and more fun to just take it to the track...

[1990 quasar blue]

Originally Posted by Locobob

You'll only get this kind of gain on a 90-92 and then only in conjuction with tuning. If you look on Haibecks website you will find some dyno charts showing porting results on both 375 and 405hp ZR-1's, keep in mind these results include a 63mm throttle body and dyno tuning.

Robert, do you think the 63mm throttle body is worth anything on a stock CID?
Thanks,
Mike

[Locobob]

Originally Posted by Aurora40

He was asking about a 1990 though.

You typically need a custom dyno tuned chip to see 35rwhp in conjunction with intake porting on a 90-92. Around 20rwhp is more realistic without tuning.
The late style injector housings would be a HP improvement over the early style as is. The early style is slightly better for porting though because the primary injector seals high up in the boss allowing more of the boss to be removed.

[Locobob]

Originally Posted by 1990 quasar blue

Robert, do you think the 63mm throttle body is worth anything on a stock CID?
Thanks,
Mike

Hard to say, this topic was discussed on the listserve (If memory serves) some time ago. Seems like the consenus was it was a waste of money on a 350cid. On the other hand I know DRM, Mark Haibeck and others include this as part of their 350cid top end packages so you'd think there would be something to be had here.

[cuisinartvette]

That's a lot of work for 20-30 hp,. maybe I should wait til the heads can be done. Thanks for the input!