bigger, but not too big

 

Ok well thats what I need to know I guess. What diameter (cc) intake runners.

I'll dyno the car next month for a baseline and then take pics of the fabrication process and do a final dyno in spring.

 

You DO NOT have a 6" runner in the head.
Ya need the CSA of the intake to figure the size.(H/W)

With that formula ya figure what RPM a given length works best at. Ya can't get the length to work best over a large RPM range but ya can give and take to make it spread over maybe 4000RPM's but closer to three would be about average.

 

Be careful with that "84000" formula. It doesn't work for all valve durations.There is some good discussion on this on "Speedtalk" forum. Search for it.

Are you sure that the port centerline length in a LT1 head is 6 inches? I think it's closer to 5-3/8.

If you change the runner length you also need to change the cam. I believe the LE2 was designed for the stock LT1 runner length. My guess is that you won't be happy with a 16 inch total runner length.

Just my $.02.

 

16" IS a bit long.
He needs more figuring to get there but he asked for a runner length formula.

 

Maybe I'm asking the wrong question.

With an LE2 cam and LE2 heads, is the stock LT1 intake perfect for it? Can you pick up more hp and torque in the midrange to get lower ETs with a better designed intake? If so, what would the new manifold look like, how long would the runners be, and what kind of improvement would I see?

Sorry for highjacking your thread grammerman.

 

The LE2 cam was designed to work well with the LE2 heads and the LT1 intake especially on a 350-355. Where you need more torque & power is probably dictated by your vehicle combination. As has been said many times before, getting the most torque in the rpm range you plan to operate the engine results in the best acceleration (assuming you can get it to the ground ) There are folks who don't need much below say 4000-4500 rpm because thay aren't drag racing, or they are using that much stall. That requires different valve timing, and perhaps intake runner lengths from a 2500-6500 rpm engine.

Look for information on the Super Victor single plane manifold LT1 conversions. A number have been done so some cam timing has already been worked out for 355, 383, and 396 displacements. I suspect it's different for each engine size.

Obviously displacement, head flow and vehicle matching will help determine a lot of the parameters. I think this has been addressed extensively in this forum.

FWIW, if I were considering building a manifold from scratch, I'd do a ton of simulation on a sophisticated sim program and I'd look closely at a program called "Pipemax" before I decided on length, CSA and taper as well as plenum volume. Doing all this well is a large task. An excellent knowledge of engine design would also be very helpful.

 

Which is probably why Wilson and Hogan charge so much for theirs.

The reason I'm so interested in doing this is because my welder is willing to do the intake very cheap because he's a friend of mine. My engine builder told me that the intake was the bottleneck in my buildup as well. So I'm wondering if there is anything out there that would not require a huge leap in research to build. Maybe improve on the LT4 design a bit but not so radical that you have to start from scratch.

 

Is it possible to grind a cam so it will make power to 6500 rpms with a 6" long intake manifold runner? I ran a hotcam before my current le2.2. I have a stealthram intake that I welded up and redrilled for lt1 use, Like Brett's exept it had stock length 6" runners. With the stock intake the car pulled to 6400rpms. When I put on the stealthram the car made more torque but power peaked at 5900-6000 rpms. I havent tried this intake with my le2, as I have been chasing lots of bugs. I now seem to have it running right. Will this cam pull any where near 6500 with the longer runners?
Thanks for the info, this is a great thread.
Kory

 

Ran a Stealth Ram on a 383 that would pull to 75/7800 with no problem. If ya got the head flow and the cam, it will go as high as ya want-- within reason. It had stock head castings flowing 300+CFM.

Bret can answer the cam question as I don't know the spects.

 

I just spoke with the guy that did Denny's manifold. He said I should look into modding the stocker. He said I would pick up some power and torque in the midrange with a sheet metal but I could pick up the same amount by reworking the stock LT1 intake by cutting it in half and welding, porting, etc. and it would be cheaper.

 

Cutting in half ware ?? Just above the runners??
There was someone on here that was doing that, they cut down the back of the TB mounting surface and across the top of the runners.
Now if you were to build your own and incresse your runners by an inch and give your self a nice plentum you would be golden IMO.

The other problem that you will have is thet cast alum. don't weld very good at all.

I also think I have an idea on how to do a LSx type manifold but for a LTx motor but I have to work that one out yet???
Lets just say there is going to be a lot of welding and machining involved

 

Cast aluminum welds fine if it's clean, and you have good rods. I've done alot of welding on my stealthram.
Kory

 

BTW does any one know what the runner size (dia) is on the LSx motors?

1 7/8 ??

 

Moderators, if inappropriate please delete. But since there is so much talk about longer intake runners and there benefit, I'd like to mention the one-off BRE ProRam has been listed in the for sale section today.