Hello, I'm a first time poster, long time reader, and the following may seem like an odd set of words for this forum, but here goes.

I have been planning a 350 SBC build for a while. The project will center around a 1977 Caprice classic coupe with a 305. Although a B-body, this site is, hands down, one of the most informative for late model SBC info, and I have a few questions.

I will be removing the 2v carb, and installing a MegaSquirt II EFI system. I will probably get a stock TPI system for the initial conversion on the 305, but would like to put an HSR on the 350. This is a big, heavy car (3900 lbs curb weight) and it will be nothing more than a warmed up daily driver. I put the proposed 350 specs into my Desktop Dyno, and although the results were pleasing, peak HP was produced around 5500 RPM, which was my planned redline. Hoping to move the power curve a little lower in the rev range, I began looking for a upper/lower plenum spacer for the HSR. Does anyone sell these, or has fabbed one for their ride? What were the results? I don't know exactly what the optimum overall intake runner length should be (I plan on purchasing the Pipemax program to determine that). I was also hoping to install a ram air system utilizing a hood scoop (not yet sure about shaker or not), and if I'm lucky, the spacer would make the plumbing essentially a straight shot from atmosphere to upper plenum. I wanted to use MAF instead of speed density for the EFI, but I would like to retain a constant inlet cross-section from filter to throttle body, and I haven't been able to find an oval shaped MAF sensor housing to match the HSR throttle body. I would like the end result to resemble this, but protruding from the engine bay, and with a smaller, K&N X-Stream type filter. Does anyone sell an oval MAF sensor, or has anyone retrofitted an MAF sensor into an alternate housing successfully? Is this scheme just crazy enough to work? Any/all help is appreciated.

 

You could possibly cut out the stock MAF internals and put it in an oval housing. I have put the internals into a bigger tube for more air flow so an oval tube would be possible.

The amount of tuning to the MAF tables would be ALOT tho. You have to completely reconfigure the MAF tables to account for the new air flow. An oval tube will have alot of air moving in on both sides of the MAF reading sensors so it wont be as accurate as it was with the stock 3" tube.

Stock 3" tube however with no screens will support 400whp easily. Mine did just that. I actualy didnt gain much with the larger body.

The other option is buying a silicone reducer 4" to 3". The 4" side slips around the throttlebody and will give you the transition from oval to round. Then put a short section of 3" pipe to connect to the MAF then another section of pipe to the air filter.

Thats probly the best/easiest way to make an intake for these cars

 

Thanks for the reply. Here is the MAF sensor I was planning on using. Here are five (sort of) reasons I would like to figure out a way to maintain the same cross-section the length of the intake:

1. Since the car is carbureted, and the MegaSquirt system is extremely flexible, the sky is essentially the limit as to what make/model of MAF sensor I use. I have no existant ECU's or specialty connectors to worry about, and since the system supports use of either MAF, MAP, or a combination of both, the car could still run effectively until the MAF sensor is acurately tuned.

2. Since my hope is to have the intake contained in the hood scoop, the overall length of the system becomes a factor. Going from circular to oval might take a longer length than just straight oval.

3. The actual MAF sensor itself (hot wire) is contained in a plastic housing fully in the airstream. I'm not entirely sure, but I think it just reads a sample of the entire airflow. The range is from .5v to 5v, with a "pegged" 5v equalling about 988.24 cfm of flow, far more than even an oval housing will need to flow, so it just becomes a matter of tuning the MAF with the aid of a MAP sensor.

4. I would like to eliminate an unecessary choke point if I can help it. I would also like to maintain a screen for consistiency of MAF readings, an I think the larger cross section would compensate for the loss of flow due to having the screen installed.

5. I think it would look more intentional/cool if it was just one diameter on a straight run, instead of the science project aesthetic adapter(s) might lend.

 

Its actually the same length or so. The coupler is only about 5 inches long like most all couplings so the difference in straight oval or round is minimal.

yeah the hot wire reads a sample of air, just have to make sure the wire is in the middle of the intake tube for best sampling of air mass. If its not your fueling calculations will be off.

As far as megasquirt MAF's are concerned, if it can be adapted to just about any MAF, get a LS1 car's MAF since they read about twice as much as our thirdgen MAF's.

If your not looking to make power tho above 5500 rpm, then you wont need much more than the stocker MAF tho so I wouldnt get crazy with it. LS1 MAF can supply all the fueling you need, the stocker may need help with power enrichment tables if the MAF maxes out which can happen on a healthy motor. However it would have to be a fairly strong motor. My 383 maxed out the MAF around 4500 rpm and the rest of the fueling was done with PE mode.

For your build i think your getting abit too complicated with it. I dont think you need to worry about oval MAF's. It probly will be more trouble than its worth.

 

Thanks for the help, you're probably right, it would probably be easier to not mess with it, and looks ain't everything. How about the plenum spacer, anyone have any leads on that?

 

I'm not trying to stop you from doing your idea, its just a suggestion in my opinion. Plus, i dont think round setup will look bad at all.

No one makes a spacer that I know of but if you have any shops in your area that have laser cutters and can cut header flanges, they can also cut up a spacer flange for the intake plenum out of a piece of sheet steel. Just have to outline it and they should beable to cut it.

I wouldnt worry about that as well, since the HSR does make good torque. Keep the heads/cam somewhat smaller and it will be a very torquey car and move it well even tho it is a bigger car.

If you really want low end torque and power, stroke the 350 to a 383 and be done with it.