Ok, gave this some thought.
I think what your engine builder is thinking is that the engine needs more flow. More cubic feet per minute (CFM). More intake runner volume = more flow capability.
That is flawed thinking in this case IMO. At altitude in an NA engine you need velocity to compress the air to some degree. Velocity at low RPMS, not high RPMs. Low velocity=low torque due to lack of cylinder filling.
Your engine is suffering from lack of air density.
Velocity will recover some of that during and prior to cylinder filling if the air is moving fast enough.

Think of it this way. You have a cooling fan for your radiator that can produce, lets say, 2000 CFM for instance. That's great for moving air through a radiator.
However can that 2000 CFM do any good for airing up your tires?
Your air compressor only produces maybe 8 CFM. Yet it can put air into your tires and your 2000 CFM cooling fan cannot. Why? 2000 CFM should be a whole better than 8 CFM, shouldn't it?

Compression. That's what the engine needs too. So slow moving air at high volume is not doing it any good. Less volume at higher velocity, which will compress more, which is what is needed.

edit: forgot to add that velocity is of course needed to fill the cylinder as quickly as possible before the intake valve closes since you will need it to close early to conserve as much of the stroke of the piston up the bore for a greater volume of intake charge.

 

Thanks for the response, I did about the same when I did the top end on the l48 and also only did the chasis dyno, so was curious as to how you came up with that. The research i did pointed to about the same figures for automatic transmisions with the glide coming in lowest and the 700r4 coming in with the turbo 400 for the worst losses and of course manuals using less power. Motorhead is the only member that I know of that did both with his build and if I recall correctly he pulled the engine to settle a dispute. As far as the altitude build, I've no experience with that living at sea level. The only advice I could offer would be that if there was ever a chance of going lower in elevation maybe build to the happy medium in which at both end's performance would suffer.

 

That was my solution for the daily driver. Supercharged LS6. Gets up the mountain just fine I don't want to spend that for the Vette. Although this build is getting complicated enough......

I know that I am not going to get this kind of performance out of this engine.

Still working with the builder...... I will update when I know more.

Brad

 

The above gets an A+.


In the 90's with the restrictor engines Cup Engine Builders took the cast intake and built an inner runner system based on the inlet flow the engine could get through the restrictor plate. This system of inner tubes maintained the velocity numbers. One team when smaller CID and that engine set the MPH mark at Talladega that year. NASCAR then made a rule change, no smaller than 350CID and no larger than 358CID.

Cylinder pressure is your friend.

 

Thanks Straub! Means a lot coming from a professional builder.

 

I am no engine builder. Not my forte. Now figuring out the combination of parts to achieve a customers goals....that is my forte.....that camshaft thing also.

John Reed taught me many year ago with engine at high elevation that cylinder pressure was your friend. You don't get much air in so what air you do get you want to squeeze as hard as you can. Velocity and cylinder pressure is the name of the game here.

 

Ok.

 

Sorry this has taken a while to get back to. Thank you all so much for the help with this. I have spoken to the builder and they are building a new motor with 64 cc combustion 185cc runners, 1.6 rockers, and is looking at the cam now. He thinks that he will change it a little, but not a lot, to pull in some more torque down low. If on the dyno they think the intake is hurting it, we may change that out also.

He (the owner of the company) has been excellent to work with and is standing behind his product. It is great to see. He is going to dyno it for me this time and make sure all is right.

Somewhere in the original discussions there was a breakdown in communication and what I wanted was lost. As in most cases, communication is key.

I will post back up and let you know the final results!

Cheers
Brad

 

Great to hear. What you will be looking for on the dyno is low end torque and average HP and torque. Peak HP is going to be of lesser importance. A nice balance could be achieved with the correct combination of parts.
It will probably be likely that a higher stall converter will be in your best interest. When the engine is out is the time to do it.
At altitude you are going to loose bottom end torque in order to achieve some kind of high end power. The converter will allow the engine to come into it's power band and not lug up until it achieves it's power band.
Ask the builder about it. Get the cam specs and CR they will be using. Then call some torque converter companies to see what they recommend.
You can probably get a stall converter locally from a transmission shop that will work for less $$.

 

A stall converter is also under consideration. Thanks!!

 

I drive up over the the 8900 foot mountain pass on my way to Lake Tahoe and I drag race during the summer when the the ADA is well over 8000 feet. drive at Bonneville salt flats in august

Any body comparing a restricter plate motor from nascar!!!!!!!!!!!!!!!!


My first roller 383 was 11.2 with Dart factory ported 215 cc heads which were closer to 227 cc with 2.08 intakes and 1 .625 exhaust because i wanted to make some power out of my roller motor without going overboard. total CFM when you add up th flow at .100.200.300 all the way up to .700 or what ever your cam does. and how little time it spends at those low lift numbers when you are talking the steep ramps on a good roller cam



I think I only have .640/ 675 lift right now because I toned it down with lower lift rockers so i wouldn't have to replace my springs all the time for street driving

Never think small because you will always want more. i went up to a 427 then my spare motor is a 434with even bigger AFR heads

all I do like every smart person is change jets and timing for the ADA Talk to SMART people that go to the mile high drags

http://www.hotrod.com/how-to/engine/...ensity-tuning/

 

Good read gkull. Thanks.

 

There are those of us that do this for a living then there are those that don't. Our customers are our results, not just talk.

 

So I wanted to give an update on this build and let you all know how it went. We got it all sorted and essentially went with the same cam and heads but with 185 cc runners. I am happy with the results. The dyno sheet (elevation 2,000 ft) has 483 ftlb @ 3500 rpm(465 ftlb at 3000) and 456 hp at 5200 rpm. I am happy the way it performs. I still need gears to get the most out of it down low, but that is a little down the road.

Thanks to everyone who helped me on this. I am significantly smarter than I was 6 months ago.

Cheers
Brad

 

Very nice! Those numbers are corrected back to sea level so you still have a significant loss at your altitude and the carb may need to be leaned up for your altitude as well.

Do you have any information on the previous dyno for comparison to this dyno? It would be interesting to see how and when the smaller runners changed the torque.

 

I wish I had the Dyno sheet, but I dont. I did not get that with the first one. I am on to tweaking the tune, but generally runs strong.

I am going to ask a question on a new thread about a carb spacer I installed briefly. Thanks for all the help