cam guys....what do you see here?

[lorax]

I have read a lot of ideas in my time, and didn't necessarily agree with all of them. But I have never once heard anybody consider choking an engine to maintain a flame front. No matter what the fuel being used was.

[Warp Speed]

I'm not sure why he started this thread asking what people thought, as he already has is own views and isn't straying from them!?! LOL

[MtnMan]

OP,

Have you ever considered whether the inadequate exhaust and lack of overlap is preventing complete evacuation of burnt and burning mixture from the cylinder and that this contamination and possibly a residual flame source is responsible for the combustion issues that you are working so hard to correct?

BTW, I have personally beat a motor up with detonation running methanol and inadequate exhaust (423 SBF Cleveland 13.7 comp). Freeing up the exhaust and running less cam advance solved it and the car picked up over 2 tenths.

[Drag Chevette]

OP,

Have you ever considered whether the inadequate exhaust and lack of overlap is preventing complete evacuation of burnt and burning mixture from the cylinder and that this contamination and possibly a residual flame source is responsible for the combustion issues that you are working so hard to correct?

BTW, I have personally beat a motor up with detonation running methanol and inadequate exhaust (423 SBF Cleveland 13.7 comp). Freeing up the exhaust and running less cam advance solved it and the car picked up over 2 tenths.

Excellent and intelligent answer, thank you.

I can see where your thinking is coming from, and it makes sense to me.
BUT we have done several cam changes in the past with various degrees of overlap...and with each cam we added more duration and wider LSA, and the car picked up ET each time., and that's with the same heads and small exhaust.

yeah I don't understand it either.

I don't disagree I might need more pipe on it, and im willing to try it.

I have done over 700 E85 carburetors in the last 5 years, that's a lot of feedback from customers. Very few of which have had issues but when they have issues I start digging and exploring to find out why so that I can do my job better.
It strange how the few that are running into issues are also running camshafts that have a decent amount of overlap per their application. this is what led me to try the above grind....???

honestly im scared to death to go back to a 106* separation....

[Warp Speed]

What is happening to the events when you increased duration and widened the split?
What happened to the exhaust opening event?
How much did overlap change?

[CamKing]

I think the real issue is, the guy has no idea how to build an E85 carb, so he's blaming all the AFR issues on the cam, and trying to bandaid the crappy carb.
That's the only possible explanation for his backwards thinking.

[groberts101]

I think the real issue is, the guy has no idea how to build an E85 carb, so he's blaming all the AFR issues on the cam, and trying to bandaid the crappy carb.
That's the only possible explanation for his backwards thinking.

I'd be suspect of the ignition output and timing events as well. I think there are some unbeknownst band-aids being used here and the OP just doesn't realize what's actually taking place through all 5 cycles. Join the crowd buddy.. I'm still trying to figure it all out too. lol

I run e85 conversions on any vehicle I can these days.. including my 500 horse streeter(383/s10 Blazer) and moderately mod'd Vortec powered work vans. All I do know for sure is that they respond quite well to LARGER port volumes(intake and head) than typically used on my gas stuff. Which makes sense when we consider how much extra air displacement occurs when you introduce larger amounts of e85 into the mix. In my mind.. it's slightly the opposite requirements of an N2O setup aside from the fact that smaller exhausts do seem to help move in the extra.. and now heavier.. fuel mass a bit better.

Also worth commenting that with any performance stuff running higher CR's.. I see the tendency of greater need for atomization to occur in the combustion space through improved quench characteristics rather than using a smaller port to keep velocity up just for the sake of reducing dropout. e85 is obviously less than an ideal fuel but once the air and fuel mass are moving fast enough.. which seems to happen quicker and more often on racier stuff, right?.. fuel dropout is the last thing most will ever worry about. High compression is your friend there too.

[buddy rawls]

..... I was using as per example, I still don't think it makes sense. Using huge cam duration to pump through small exhaust, should we swap a cam when there needs to be exhaust? Sounds crazy to me.
Should I find the smallest valves on earth because I run a roller cam?

No, you dont run small valve because you have a roller cam. You run the roller cam because you have small valves or limited flow capability and the area under the curve cannot be compromised with wide seat events. This will dictate a lobe profile that is only obtainable as a roller.

there are lots of different conversation going on in this thread. This particular conversation is dealing engine combination constraints. As a cam designer, my job is to make the combo at-hand work to the best of my ability. Sure, I can say the motor needs exhaust help, or this or that. But I think things in this thread are heading towards motor combination based on camshaft design, this is backwards. The camshaft is reflective of the engine combination.

Lets say this is an engine swap. The 1 5/8 headers and 2 1/2 exhaust MUST stay with the combination. Given the 421cid, AFR 220 heads, 14:1 CR, 7500 rpm power capability, what does a roughed in camshaft look like? Make the combination work with only a camshaft change. when I ran the numbers, in my first post, I was surprised that my valve events (looking at .050 only) were darn close. At the time, E85, hadn't entered in to the conversation. Which really makes it even worse, because the terrifically restrictive exhaust, is now super-duper-terrfically restrictive.

[lorax]

But I got the idea from the OP that the engine, aside from the cam that he seeking advice on, was DESIGNED around E85, not some engine swap into a restrictive engine bay. The heads and exhaust were CHOSEN based on supposedly previous experience with e85. The restrictive exhaust was designed in to limit the scavenging, or as he called it, "supercharging" effect of the overlap.
This doesn't seem to be a case of "make it work" because its what I have to play with. More of a case of this is what I chose and why, and how do I cam it so it does what I think I need. Which appears to be, not over charge the cylinder with air/fuel.

Who does that?

[groberts101]

I got the idea from the OP that the engine, aside from the cam that he seeking advice on, was DESIGNED around E85, not some engine swap into a restrictive engine bay. The heads and exhaust were CHOSEN based on supposedly previous experience with e85. The restrictive exhaust was designed in to limit the scavenging, or as he called it, "supercharging" effect of the overlap.

What seems to be missing from this conversation is the fact that he's not necessarily reducing scavenging per se.. as much as he's MOVING the rpm range for which it's effect is strongest down below peak torque. Can't really see that being good unless it's a lower rpm stoplight racer.

There's a reason why most guys running e85 don't run tiny exhaust pipes on larger cam'd strokers designed to spin up a bit more than average. The scavenging falls off too quickly and the rest of the combo inevitably gets wrapped up in bandaids while trying to fix implications caused by the unnecessary restriction. The headers must work FOR the greater good of increasing mass through the motor at the desired rpm/flow. Not against it to prevent a combustion event from occurring. That's the camshaft and ignitions job.

[Drag Chevette]

Mike Jones, I don't know where you gather I'm having AFR issues....I'm not! I didn't get into personal attacks about you I would appreciate if you didn't get into personal attacks about me or the carburetors I build. I've been very successful in my business and what I have done. We have built about 700 carburetors in the last five years ,you don't do that many if you're not good at what you do. I'm asking nicely please stay off my post, I don't want or need your help! Thank You Mark Sullens

[Drag Chevette]

I got the idea from the OP that the engine, aside from the cam that he seeking advice on, was DESIGNED around E85, not some engine swap into a restrictive engine bay. The heads and exhaust were CHOSEN based on supposedly previous experience with e85. The restrictive exhaust was designed in to limit the scavenging, or as he called it, "supercharging" effect of the overlap.

What seems to be missing from this conversation is the fact that he's not necessarily reducing scavenging per se.. as much as he's MOVING the rpm range for which it's effect is strongest down below peak torque. Can't really see that being good unless it's a lower rpm stoplight racer.

There's a reason why most guys running e85 don't run tiny exhaust pipes on larger cam'd strokers designed to spin up a bit more than average. The scavenging falls off too quickly and the rest of the combo inevitably gets wrapped up in bandaids while trying to fix implications caused by the unnecessary restriction. The headers must work FOR the greater good of increasing mass through the motor at the desired rpm/flow. Not against it to prevent a combustion event from occurring. That's the camshaft and ignitions job.

Excellent answer....more of what I was looking for.

[lorax]

I got the idea from the OP that the engine, aside from the cam that he seeking advice on, was DESIGNED around E85, not some engine swap into a restrictive engine bay. The heads and exhaust were CHOSEN based on supposedly previous experience with e85. The restrictive exhaust was designed in to limit the scavenging, or as he called it, "supercharging" effect of the overlap.

What seems to be missing from this conversation is the fact that he's not necessarily reducing scavenging per se.. as much as he's MOVING the rpm range for which it's effect is strongest down below peak torque. Can't really see that being good unless it's a lower rpm stoplight racer.

There's a reason why most guys running e85 don't run tiny exhaust pipes on larger cam'd strokers designed to spin up a bit more than average. The scavenging falls off too quickly and the rest of the combo inevitably gets wrapped up in bandaids while trying to fix implications caused by the unnecessary restriction. The headers must work FOR the greater good of increasing mass through the motor at the desired rpm/flow. Not against it to prevent a combustion event from occurring. That's the camshaft and ignitions job.

Excellent answer....more of what I was looking for.

Just because what you are trying to do, doesn't mean I understand the why/
When I build an engine, I have three primary goals. Get it in, get it burnt, and get it out. Its pretty basic idea. Doing it better is challenging, but I never once tried to limit it. Not with a head, exhaust port, pipe or camshaft. The more I can get in the better. Then I deal with burning it and getting it out.

[CamKing]

We have built about 700 carburetors in the last five years ,you don't do that many if you're not good at what you do.

How many Big Mac's does McDonalds sell ?

Sorry, but there are many of us here that will step in, whenever we see someone making ignorant statments.
No one gets to throw around a bunch of false theories, without being called out on it. That's the way it works.

[groberts101]

Just because what you are trying to do, doesn't mean I understand the why/

When I build an engine, I have three primary goals. Get it in, get it burnt, and get it out. Its pretty basic idea. Doing it better is challenging, but I never once tried to limit it. Not with a head, exhaust port, pipe or camshaft. The more I can get in the better. Then I deal with burning it and getting it out.

Sure you do. You're simply not looking at it from that particular perspective.

Engine size, induction size, exhaust size, cam size, octane rating, etc. Just changing cam events and area's under the lift curve alone inevitably affect all the others as it affects DCR's. Then we're all forced to play knick knack paddy whack to get everything to play nice together. This is why dyno queens and "pretty numbered printouts" don't necessarily equate to best combos on the street or track. Just too many variables involved with all the various materials/gaseous masses, gravity, frictional losses, and drag being tossed into those perfect "on paper" builds. Just pick the compromises that best suit your wallet, is all.

Diving in even further.. the best built internal combustion engine in the world is just an endless series of huge compromises. Figuring out which ones to apply to your specific combo's monetary limitation is the tougher part for many. Personally speaking.. I didn't go to school long enough to garner myself a big enough salary to allow spending sufficient time to figure it all out. Luckily for all of us though.. many others are trying hard by spending huge amounts of time and cash. Looks like nothing but coat tails and major amounts of trial and error are in my future.