[Jim Robertson]

Don your cad design looks like the right direction for the engines we work with here as well as the 400 ci plenum. Offering Delrin or similar material spacers for additional volume/vibration/heat isolation is a very good idea.

For what it is worth/comparison: My junk (468 cid, iron D ports) has a plenum volume of 225 ci yes 225ci and that supports well over 850 hp on good fuel and runs 143 mph (7200 rpm) thru the mufflers at 3285lbs. Not big enough and probably why it runs so slow but it does have very civil street manners on the road and in traffic. :-)

I agree on the runner design offered above...get that right and save the customer a lot of time and money. Smaller plenum casting with optional spacers (1" and 2" thicknesses as an example) can cover many engine combinations.

For the carb guys I highly recommend you place the runner entrances "under the carbs" and do not abbreviate the end runner entrances by shortening the plenum box. Allow the full radius entry into the runner entrance the entire 360 degrees circumference. From my rough estimations using your manifold here, I believe you can cast a good runner entrance (with room to grow) and still run a MSD distributor. Hard core guys will run a belt drive front distributor

With the 500 cfm heads we have here, a single four top designed right could open a whole other market for your heads...people are asking me how can we get that done.

Also FYI...The NHRA legal pro stock engines we have had in the shop have had plenum volumes as much as 550 ci (HRE intake 2007 vintage.)

Good stuff...keep going

[dci]

Originally Posted by Jim Robertson

Don your cad design looks like the right direction for the engines we work with here as well as the 400 ci plenum. Offering Delrin or similar material spacers for additional volume/vibration/heat isolation is a very good idea.

For what it is worth/comparison: My junk (468 cid, iron D ports) has a plenum volume of 225 ci yes 225ci and that supports well over 850 hp on good fuel and runs 143 mph (7200 rpm) thru the mufflers at 3285lbs. Not big enough and probably why it runs so slow but it does have very civil street manners on the road and in traffic. :-)

I agree on the runner design offered above...get that right and save the customer a lot of time and money. Smaller plenum casting with optional spacers (1" and 2" thicknesses as an example) can cover many engine combinations.

For the carb guys I highly recommend you place the runner entrances "under the carbs" and do not abbreviate the end runner entrances by shortening the plenum box. Allow the full radius entry into the runner entrance the entire 360 degrees circumference. From my rough estimations using your manifold here, I believe you can cast a good runner entrance (with room to grow) and still run a MSD distributor. Hard core guys will run a belt drive front distributor

With the 500 cfm heads we have here, a single four top designed right could open a whole other market for your heads...people are asking me how can we get that done.

Also FYI...The NHRA legal pro stock engines we have had in the shop have had plenum volumes as much as 550 ci (HRE intake 2007 vintage.)

Good stuff...keep going

Thanks Jim for your insight. Intake manifolds are one of the pieces of an engine that if you get right can make a big difference in your HP. That's why I struggled with the cast intake I made. I just couldn't bring myself make a mediocre intake just to fit under a stock hood. Ironically enough all the guy's that were hounding me to make it fit under the stock hood haven't bought any heads yet LOL. I'm glad though that it happened the way it did. I like having a challenge and conquering it. My cast intake is very versatile and works extremely well. These drawings here are actually going to be for a sheet metal intake not a casting. So it can be built with any size runner that is needed for any situation. The plenum is the easy part of the design, because I can make it smaller and as you suggested just ad spacers to it. Or you could fabricate a top to suit as well. My biggest concern is the runner alignment in the plenum area. I want the runner opening directly under the carburetor throats like you suggested. So the best way to get that right is build a cad model and put carbs on it in the model. Then I can see exactly what it will look like before I even cut the first piece of aluminum. Kind of like that carpenter saying. Measure twice, cut once !!!!

Jim are you hinting that you have some 500 cfm DCI RA5 heads there???