log manifold

[LEMHEAD16]

How much a of performance lose would the VH suffer from a log style manifold?

I plan on going FI in the future but I need to get it on the road before winter comes. A log manifold would be easy to make and get by until next summer.

[craigztoyz]

From a guy who drives his daily, ALOT.

Without forced induction, it'd be horrible. This thing needs to breath, and breath well, a log mani is a very poor flow design. It may work if you go large enough pipe, and can get it to flow BIGtime, but if there is anyway you can f with the headers to make them fit, I'd reccommend it, or use the ovals off it, to fab up something. Its more work, but in the end, making it work now, and then making things for FI later, is probably a wiser decission. And, to be honest, I have done most of my car at least a dozen times, and gone back and redid it, through trial error, and testing we find better ways to do things.

If your problem is the drop in height of the headers, they can be redone to fit. I ended up dropping in c channel I made to fit in recessess to get it low.

Pics of the space would be cool, if you have. Good for us to visualize, and for others in future who may want to drop a VH in same model.

[Q45tech]

The 16.5" tapered runners tune the 3rd harmonic of torque peak and 4th and 5th of HP peak rpm 5500 and 6,000 rpm.

The length from MAF to TB and the camber behind TB feeding the plenum are tuned to 1850 rpm to increase torque at 55 mph by 3-4%

I would guess that they provide ~~ 8.5-10% increases at these rpms.

The volume of the runners and cylinder ports should at least equal the volume of the cylinder [274/8= 34.25cubic inches]............oem volume is ~~ 38 cubic inches plus head port volume [~ 4 x 2 ~8 cubic inches] with valve in place. Providing 130% of air volume inrunner so that at peak torque VE can exceed 100%.

The new runner volume can tell you what the new VE will be..............plenum volume needs to be enough so that 4 cylinders cam fill or 137 cubic inches minimum.

Good Luck in maintaining near oem torque and HP.

[LEMHEAD16]

Wow! mighty fine technical post. Thanks

[craigztoyz]

2nd that.

this is helpful info, and as stated, Log on n/a will be very hard to achieve any real size, and tune.

I know that changing my tb-maf length and no precats, does adjust this flow, but for the better in some regards. Best it can be for what it is.

[LEMHEAD16]

I was looking closer at the factory manifolds there is no way to modify them to fit but they don't look much fancier than a log manifold.

Runner one tapers from 1.75 to 2 inch and all three other runners merge with the 2 inch section.

I am going to try and build something similar to that and make it fit.

[craigztoyz]

To do a home-made job as accurate as you can.

A few things, hope others will chime in.

Measure each pipe, and its diameter, get as accurate of a measurement as ou can of its volume, and try to keep each part of yours as close as you can. this thng breaths more then any n/a, stock cams LS1, i have ever seen. account for engine flex, movement, and ease to drop eng in car.

This is on the S car?

Hope any of this helps your designing

[LEMHEAD16]

Yes it is on a S13. All of this helps alot, thanks for the input guys. I am planning on using the oval part of the stock mani and fabricate from there. I have decent clearance on the driver side but passenger is going to be a lot tighter.

I need to make a post introducing my project but I am too lazy to take pictures.

[Carl H]

stock headers will not fit in an s chassis.the passenger one will BARELY squeeze between the frame rail but will need clearancing to keep it from banging the rail or manifold.the drivers will not fit without substantial modification and has severe steering column interference.