exhaust on a limited circle track class

[phantomfab]

Hey guys, the question of the day is whether the mandrel bent exhaust will work better than crush bent or the good 'ol flex pipe. 2 in being the limit and exhaust must extend past the driver. Rules mandate cast non center dump manifolds and lt1 manifolds are illegal at another track I run at. Exhaust must extend past drivers compartment and cannot exit out of the fender. The problem is it is hard to find a manifold that fits using a modified type engine mount. My thoughts at the moment are to use a vortec style truck manifolds and do a 180 with the exhaust to run it back around considering the exit ports would be facing up and I dont like the idea of running exhaust through the hood.

The engine is a standard bore 6cc flattop thats down 22 thousandths in the hole. Heads are a 77cc verified chamber 882. Camshaft is a 270hlhyd Iskendarian. Using a stock rochester four barrel intake.

RPM-Range: 2000-6000
Value Lift Int/Ext: .445/.445
Value Lash Hot Int/Ext: .000/.000
ADV Duration Int/Ext: 270/270
.050 Duration Int/Ext: 216/216
Lobe Center: 108

I'm just curios on what exhaust should be used and if you guys/gals think this thing will pull 16in at 1000 rpm.

I'm assuming the mandrel bent would be the best but any ideas on what kind of power differences it would be? Hopefully from someone that has seen it on a dyno. Thank you all.

[sjre]

I dont think you will see a diff between either tube.I dont think id use flex. I think the cam is farrrrrr out to lunch.What carb?

[phantomfab]

I dont think you will see a diff between either tube.I dont think id use flex. I think the cam is farrrrrr out to lunch.What carb?

I'm running an 1850 holley. Engine is still on the start stand. I haven't started it yet. Wondering why you say the cam is so far out?

[iadr]

You could combine that cam spec and that RPM range/duty if you had really good head- like unlimited.

But you don't. So it's a question of keeping the valve open longer to get the fill time you need.

You are correct in going with a single pattern tight lobe separation grind, but my guess is you are 10-12 deg short.

[barnym17]

look for 85-86 1 ton truck manifolds they are stock tube type if you can get away with it .

[barnym17]

if they try to say no tell em they are cast steel,lol

[mag2555]

Flex tube is a nightmare!!!
The internal ridges in the tube make for a great level of turbulence and hence restriction in much the same way that flex type radiator hose does!!

[sjre]

I dont think you will see a diff between either tube.I dont think id use flex. I think the cam is farrrrrr out to lunch.What carb?

I'm running an 1850 holley. Engine is still on the start stand. I haven't started it yet. Wondering why you say the cam is so far out?

I usually go with a single pattern and wider l/s with manifolds,seems to ok but in thinking, its about overlap with the overlap being restricted because of the manifolds.Not a cam expert at all, but im thinking 10 degrees less intake on a 112 in at 107

[sjre]

On second thought you could always use rhoades type lifters on the intake of your cam ,install the cam at 108 intake.But this all goes out the window depending on driver skills/ track surface.

[midnightbluS10]

look for 85-86 1 ton truck manifolds they are stock tube type if you can get away with it .

Something like these?

https://shop.advanceautoparts.com/p/dor ... t+manifold

[phantomfab]

I believe he was reffering to the tube type manifolds which I do in fact have a set of but they are illegal. The picture you shared though is a manifold i have in question. Because those manifolds would fit without horrible exhaust bends everywhere but i was wondering in terms of performance as I've heard they are quite limiting.

In regards to the flex pipe being limiting and horrible I would have assumed the same; however, has anyone dyno'd them to prove their lacking in performance? I've seen multiple front running cars with the "horrible" flex pipe. Most of the time it was 2 four foot pieces clamped on to a stub that were installed that day at the track and help up with wire....literally. Usually a quick fix for cars coming from tracks that didn't mandate exhaust.

[phantomfab]

Wouldn't the longer duration cam pull the vacuum down? And I've personally never had any luck with the rhoads lifters. They were always a pain to set to me but then again I was 15 the last time I even attempted to use them. I always set them too tight.

[Keith Morganstein]

In regards to the flex pipe being limiting and horrible I would have assumed the same; however, has anyone dyno'd them to prove their lacking in performance? I've seen multiple front running cars with the "horrible" flex pipe. Most of the time it was 2 four foot pieces clamped on to a stub that were installed that day at the track and help up with wire....literally. Usually a quick fix for cars coming from tracks that didn't mandate exhaust.

This has been tested and known for ages. A quick search for dyno test came up with this link. http://www.bobsmuffler.com/dyno.htm You can find plenty of info on flex pipe and crush or press bends if you look.

The difference may be small and there is a whole lot more to “running up front” in circle track than a few HP. However if you have a choice, it’s worth using mandrel bends.

[phantomfab]

You are correct on the fact that there is alot of people that have compared crush bent to mandrel bent but most everything i have found has compared a 2.5 crush bent to a 3 in mandrel bent. Which I am limited to 2 in OD duals. no crossovers allowed so I was wanting to see a comparison there.

[phantomfab]

And I've already read the article by Bob's but he never mentions anything for 2 in...If the difference is minimal I will most likely just take it to the located muffler shop and have it done. But the mandrel bent pre-manufactered pieces would only be around $34 for my pieces to do my exhaust.