performance cam regrinding

I meant filter assembly, which would include the box...I should have been more clear.

 

What ever happened to the Elgin cams?

 

2 things I meant to post months ago. When I dyno'd my car the last time, I spend a couple hours tuning, then made a pull, 360hp. Let the car cool for an hour and it made 420hp. That was a 95 degree day, I'm pretty sure a re-do on a cool day would add another 30hp+, so I'm agreeing completely with James.

Second, old race bike was an 860cc twin, 430 per cylinder, redline at 9000, hp peak at 8200-8400, torque peak at 6500, so similar to your engine. Going from a 38 to a 40mm venturi added about 12hp (x4 for you). If I could have found a bigger carb, I'm sure a 42 would have been good for another 5+hp and 44 another 1 or 2 on top of that.

Now these were slide type carb, so increasing the venturi doesn't hurt the bottom end anywhere near as bad as on a butterfly carb, but it goes to your point about bigger is better.

That's is and always has been the fundimental problem with carbs, at the limits, they fail....what I mean is that your car runs great now and you love it, but you know going bigger will make more hp, but you also know it will harm the bottom end and drivablility. Going big enough to get the last couple hp will make it completely undrivable on the street. The general practice is to keep going bigger until you can't live with the result down low, then go back down 1 size to the one you could live with.

One possible solution (and I know it boarders on blasphamy) is to see if you can find a slide type carb. Yamaha used to put 38mm flat-slide down-draft carbs on there YZR1000. I fitted 6 of the to a 2.8 liter 911 that made over 360 hp. They can be had for about $100 for a bank of 4. A honda super hawk has a 48mm flatslide, but I'm not sure if it is a downdraft, or more like a 45 degree, I think it's a downdraft.

The last option is to just joy the cool toy you built!

 

So you found the tolerable limit of venturi size. Porting is goning to run about $2000 for a basic job plus install I'd guess. What about a set of 355 heads on that puppy?

 

I was just thinking cams again and looking over this thread and noticed this:

On the 348, the torque is almost dead flat from 4000 to 7500, it's really nice.

On Russ's carbed 328, a stock 328, an EFI 328 and every other 328 and 308QV graph I've every seen, the torque starts to drop at 5000-5500 and keeps dropping until redline. The drop in torque is about linear with rpm, that suggests that something ability to flow is reached at 5000-5500.

Anybody ever figure out what the hold up is? I thought is was probably the cams and the intake in particular, but the fact that changing the intake cam didn't help says it's not.

Anybody know what is different about the 348? Cams? Cam timing? head CFM?

The other thing that I've noticed on my supercharged engine is that I am pumping enough air and fuel into the engine to make about 800hp but only getting about 500, maybe 600 figuring it takes 100hp to turn the supercharger. The turbo QVs use about the same air/fuel as I do so it's something in the engine.

I'm thinking there are 2 problems. The exhaust port flow is just too high and there is too much valve overlap causing cylinder blow-down and accounting for the high air/fuel usage. And there is something wrong with the flow of the intake port that causes the torque to drop. I think it's got to be the head because CIS, EFI, Carbs all show the same symptom....and it's got to be a port not a valve problem because the 328 uses a bigger valve than the QV and it doesn't help

Any have any thoughts or data to share? I'm thinking my heads need to come off to correct it, but I'm not sure if the answer is to just buy a set of 348 or 355 heads and make then fit or some port/valve work will straighten out the QV heads. Anybody have a dyno curve for a QV/328 that's had the heads done by a professional?

 

You see, now I'm going to have to pull the heads off.

My bubby with the head shop was out for New Years. He looked at the dyno graphs and cam specs and thought that I already had plenty of cam, and your results with cam change basically confirmed that.

The funny thing is that when I rebuilt my engine I did it in his shop. We both looked at the heads (I had a flow bench before he did) and didn't see anything obviously wrong, in fact he had trouble believing they were factory....and we decided not to do anything to them since it was a blower motor anyway. So it will take some figuring to decide what they need. He's thinking the place to start is sinking the valve to extend the porting into the head, but that will drop the already low compression so I'll need pistons. If I need pistons anyway, I may go crazy and see if I can get 348 or better yet 355 heads on the engine. 355 heads should add about 200 hp.....that I don't need of course

 

Heck, while you're at it, see if the 348 or 355 block will mate up with your sump case. Then you'll pick up displacement as well as the flow to go with it.

Sorry for the belated response, was doing a bit of catching up on some of the performance threads & saw your question. Anyway, here it is:

 

I have a brand new thought tonight - reversion/resonator.

I was playing with my dynosim soft ware again tonight….I don’t really like it because I have a terrible time getting the number to match measured values, so I don’t consider it validated. Anyway, I noticed something and that is that when I put on the factory QV/328 type manifold, I get a torque curve that is the correct same with peaks in about the right places, with the torque falling after about 5500. When I put on carbs, I get about the same shape curve with the torque falling after about 5500. So that’s right.

But, when I put on a 348/355/360/456/550/575 type manifold, I get a torque curve that peaks in the same place, but then stays flat out to about 7000…it looks exactly like the 348 graph that’s posted.

So I have a brand new plan. I am going to pop the rear head off and get some flow number so I know and based on that I may or may not port them. But the main part of the plan is I’m going to build a new intake manifold (actually a pair of manifolds) that are a lot more like the 348 set-up. There has to be a reason that every ferrari engine built since 1989 uses that design and I’m guessing it’s the same reason the dynosim software wants it.….plus it’s way less work than the 355 plan

And Russ, I pretty sure adding the same kind of thing on top of your carbs should help your Carb engine too.

 

You might be able to fab something out of the dual airboxes on the 365 GT4 2+2
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Yep, with very long runners compared to the Ferrari version. Good luck finding one, though. I finally gave up.

 

That's pretty much exactly what I'm thinking....although I suspect there is probably a flow/tuning advantage to a tubular chamber over a sheetmetal box...in a thin wall box the walls will probably flex as pulses hit it, in the tube they won't, I don't know if it matters but ferrari seems to make them strong.

Something like a pair of these:
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Still curious about what happened to them Elgin Cams? Any updates?