Looking for thoughts on my 496's recent dyno session.

1. Did I leave power on the table with this particular combination? If so.... any suggestions to improve. I'm sure we could have squeezed a few more ponies out of it above 6k, but I didn't see the point in beating on it for such small gains.

2. Any ideas on the cause of the slight drop in torque between 3500 and 4000 rpm? We tried tuning it out of the curve with no success. He ran a static pull at 4k and the reading there would have fell in line with where it should be in the curve. He wasn't very concerned... just stumped. Maybe switching to a dual plane?


10.6:1
AFR 265's off the shelf with Ti retainer upgrade
Straub SR 260/268 .672/.648 109 lsa
Milodon 30951 with diamond stripper screen - ran with 6 qts
Vic JR as cast
950 hp
2" Lemons
Tested with 3" chambered mufflers


Engine will be going in a 66 Malibu 4 speed / 3.08's street car with possible strip time just for the hell of it.

I'm very happy with idle quality, throttle response. I was hoping for more TQ.... 600ish. Overall I'm pleased, just thought it would make a bit more power. Although it did meet my 600 hp goal. Thanks Chris!!

I'm just curious about what you guys think.


Tom

 

That's a stout cam for an otherwise moderate combination.

How was the oil pressure through the dyno pull?

What are the collector specs on the headers, and were collector extensions used on the dyno?

Chambered mufflers are often not the best choice for power.

IMO a dual plane would be a much better choice for this combination.

 

I didn't download the atmospheric conditions page, so I will just ask is that corrected hp and tq? It was still climbing when you stopped the test. I would guess it has another 500rpm in it and maybe 30-50 hp with no other changes

I also think you need a dual plane intake rpm air gap or similar with your rear gears

 

I didn't download the atmospheric conditions page, so I will just ask is that corrected hp and tq? It was still climbing when you stopped the test. I would guess it has another 500rpm in it and maybe 30-50 hp with no other changes

I also think you need a dual plane intake rpm air gap or similar

That is corrected hp and tq

 

Oil pressure was good 70-80 throughout the pull

3-1/2 collectors with extensions then mufflers

 

 

I was curious, as a snowmobiler I am aware of the thin air you have out there

 

Would a dual plane increase peak #'s or just move them down some?

 

Itd definitely move things down and probably give you more torque too .
Nice motor but I'd want a DP on it with those gears and application

 

That’s a heavy weight solid roller in my opinion.

1.2hp/ci, seems slightly low, 950 carb could be a resurrection. Did you try a large one?

 

No, just the 950. Didn't have enough time to swap parts. The operator felt like the 950 was on the large side for the combo since it was only pulling 694 scfm at 6000. But maybe the 950 was the restriction. I haven't heard particularly good things about the flow characteristics on the 950 hp.

 

Bigger carb on a Dp

 

Would have been good to test without the mufflers, it leaves you a lot of variables to work out.

I think you should consider more gear than the 3.08’s. What tranny - hopefully not a 2.2 low gear Muncie.

 

M23z 2.98 1st. I was on the fence with 3.08 but wanted to try it first then bump up to 3.31 if I'm not impressed. Here in MT we have a lot of open highway so it'll be run at 75 mph+ quite often.

We were trying to simulate the actual set up I'm planning in the car. You're right though, we should have uncorked it because I've been considering cutouts in the exhaust. Damn it.... should have thought of that.

 

Looks like it’s running a little lean
Hp still climbing at 6000 rpm’s
Was that cam picked for those heads? For street or drag use? Is that 260/268 @.05 or advertised

 

Straub designed the cam with the 265's in mind and 80/20% street/strip build. I wanted a 6000 rpm engine with gobs of TQ to pull the 3.08 rear gear.

Operator measured A/F two ways. Metered what went in, which I believe is what reads a little lean. Here is what I think is the wideband reading on the collector. It looks better

 

Somthins wrong. That's way not enough torque with those cubes and those heads .
Cam intake carb ignition or the combination thereof. 650 ft lbs out of 496 cubes is way not too much to ask . Almost seems like too much duration for the application to me .
For one .

 

The AFR is a good full point too lean. Did it make best power at that AFR? I would expect more torque also. Ten years ago my 427SBC made 640HP and 565 torque with a set of AFR210 head that I purchased in 2000. A 496 should make better torque than that. What fuel and how much timing? How well did the intake ports match up to the heads?

 

Yes after several runs he found that to make the best power. Fuel was 91 and 36 degrees. He played will timing but found no noticeable difference with more or less. It seemed to like 36 best. Port match was close, but I didn't want grind anything for a perfect match because of being unsure about using the vic jr.

 

The engine won't be running in the car til late summer and I have to pull the intake anyhow due to a pin hole leak in the rtv on the back wall. Given Kirk's and Vintage Musclecar's advice on the dual plane, I'm probably gonna bolt an air gap back on instead of the vic jr.

 

I'm a bit surprised as Straub has a cam specifically designed for the AFR 265 heads. To me the engine is overcammed and the dyno seems to prove that. Why run a solid roller if the plan was to only go to 6000 rpm in the first place? It's still climbing at 6000. A nice hyd roller seems like it'd be a better choice.

Even if the cam is too big, the AFR 265s are a mega efficient head and a small port for a 496 so I'd have expected a lot more torque. It feels like something isn't quite right.

If you put on a dual plane im sure that'd pick up a lot, but that may not solve a potential underlying problem.

 

I'm a bit surprised as Straub has a cam specifically designed for the AFR 265 heads. To me the engine is overcammed and the dyno seems to prove that. Why run a solid roller if the plan was to only go to 6000 rpm in the first place? It's still climbing at 6000. A nice hyd roller seems like it'd be a better choice.

Even if the cam is too big, the AFR 265s are a mega efficient head and a small port for a 496 so I'd have expected a lot more torque. It feels like something isn't quite right.

If you put on a dual plane im sure that'd pick up a lot, but that may not solve a potential underlying problem.

Not sure if it's specifically designed for the 265's I think he ground it according to my build. Solid roller was my choice, I realize hydraulic would work just fine. I just wanted solids.

I agree with the low TQ #'s I was expecting a fair bit more.

The operator said several times that he has a very conservative dyno (whatever that means) so maybe it's just that?

 

Mufflers are probably contributing some to the low numbers. Unfortunately you don't know much power or torque they killed. Did you have an air filter on it? Electric or mechanical water pump on the dyno?

 

Filter is in his air supply system in the ceiling. It's pulling room temperature air from main space of his shop. Electric water pump was used. Yeah I'm kicking myself for not doing a pull without mufflers just to see if there would be a difference.

 

I’d try a air gap dual plane and a 1” open spacer before you put it in the car, I realize no more dyno time, my 489 dyno sheet pic is in my media and that’s with a mild shelf hyd. roller 231/239 cam I picked for air cond., 1,000 HP and air gap & 1” spacer on 91 & 93 non eth gas, open 1 7/8” headers

 

That's more what I was expecting my curves to look like. ALL TORQUE. Very nice

 

I didn't get a print out of the observed #'s but they were lower than corrected so it's not likely the dyno. They fella that dynoed it, is my machinist who did all the machine work. I assembled the engine. I had to beg him to run it on the dyno because he only uses it for engines he assembles. He has some very good reasons for this and I feel lucky he did for me. So making adjustments and getting it on the dyno again is most likely out of the question.

 

I would be a little disappointed but I dont know what the mufflers did to it. This is a 496 I did a few years ago. 10 1/2 to 1 "No name" aluminum heads. Rectangular port manifold on oval port heads (dont ask) 1050 Dominator. The cam was a hydraulic roller that I am pretty sure was smaller than yours. I have the specs at the shop. I told them not to take it much over 6K and you can see it was still climbing there as far as HP.

 

Wow.... similar builds but night and day difference in peak#'s
Thanks for that info Bill.

 

So is there anyone out there that has done back to back testing with and without mufflers on a similar build?

. This has now got me really curious and hoping that my less than stellar numbers are due to the mufflers.

 

I don’t see mufflers being worth 50hp. Have you called Chris and gone over the results? I’m sure he’s camd dozens of 496s with those heads and similar compression…..what’s the normal expected result? Looks like a great cruiser but I agree that with the parts involved I would be expecting another 50 hp and more tq. The definite test would be mph at the track…. I tend to believe the mph out the back end over the Dyno hp numbers in many cases.

 

Yeah I didn't think so either on the mufflers.
We did the pulls on Thursday and I was off grid yesterday so I haven't had a chance to check Chris's thoughts. I plan on doing that Monday. Chris nailed my goal and then some on the hp. I asked for 600 and it would've likely pulled to the 620s if we had kept going.
From all the reading I've done here and other forums, mid 600's for both torque and hp is kinda the norm, haven't seen many TQ #'s below 600. I'm not questioning any of the parts specifically (other than the single plane) I just wanted check you guys for thoughts on the TQ. Just seemed like it should be closer to the hp.

It will make for nice street car and I shouldn't be too embarrassed at the strip. Overall I'm happy with the results, it's just my nature to question if anything was left on the table. I'm really anxious to get the car done and on the road this year!!

 

As for the mufflers, Engine Masters did an episode where they did a muffler shootout on a 1000hp motor. Here was the results of the straight thru and chambered Flowmaster. Not a whole lot of loss on this engine.

 

As for the mufflers, Engine Masters did an episode where they did a muffler shootout on a 1000hp motor. Here was the results of the straight thru and chambered Flowmaster. Not a whole lot of loss on this engine. View attachment 760588

As for the mufflers, Engine Masters did an episode where they did a muffler shootout on a 1000hp motor. Here was the results of the straight thru and chambered Flowmaster. Not a whole lot of loss on this engine. View attachment 760588

Well that's pretty damn negligible.
Thanks for posting that.

 

Ok......I looked at your conditions page, all that looks correct to me, did he inter your bore and stroke?

 

The correction factor and Barometer looked good to me. Air gap intake.