496 dyno
 

I had a 496 built and here are the details I know:

The block is a 455 from a 1974 Catalina. A stroker kit was installed to get to 496 along with a .30 overbore. The entire rotating assembly is forged. The heads are the real #16 super duty heads. They were worked on by previous people (comment on that later). The heads were benched flowed and the result was 260 CFM. The intake manifold is a Edelbrock performer rpm. The carb is a Quick Fuel 850 CFM. The cam is a Butler performance custom grind. Part number is CCA-BP8041SP. Specs-294/300,242/248,.594/619, 112 LSA. The lift is using 1.65 ratio roller rockers. This cam was my pick not the engine builder. He wanted to use a different cam. The builder checked with Butler and happened to talk to Jim Butler and he said go for it. Compression is 9.9 to 1. Total timing is 35 degrees. Doug’s long tube headers are used.

Before the dyno run, I saw a formula posted by someone a while ago. The formula is used to calculate CFM flow from the heads starting with horsepower. I worked it backwards from the 260 cfm and came up with 535 HP. I know that is with 100% usage of the head flow. I’m guessed 505 HP. My engine builder projected mid 500’s for HP and low 600’s for torque.

I want to state that the dyno used is known to throw off numbers on the low side. Many people have come back to the owner of the dyno and showed higher numbers on other dynos after being run on this one.

The dyno run took place last night. I don’t have a lot of information on it right now, but I will by the weekend. Here is the limited information I have: HP 519 @ 5200 RPM, TQ 578 @ 4200 RPM
TQ/HP RPM
544/311 3000
552.9/368 3500
529.4/519.4 5200
508/513 5300
497/511.6 5400
490/513.1 5500

This is after 10 pulls and the rings are not totally sealed yet.

My reaction is disappointed. Same thing with my engine builder. The builder mentioned he thought the previous porting that was done hurt the numbers. I seem to remember Cliiff R made such a comment on the SD 455 he did a while back.

The engine builder said he could have spent another day to get another 20 HP. I said no, it wouldn’t be worth another dyno charge.

I would like opinions.

Thanks,

Jim

Was the intake ported to match the heads?
First thought is the cam seems a little on the small side for the CID.

I would agree with Mike. The Performer intake may be holding it up also.

Maybe borrow a different intake for higher RPM/flow?

Post pics of the dyno sheet when you can, may tell something on it.

:confused:

I'll check, but I think it was port matched.

John,

It is a performer rpm.

Yes, I saw that and I edited it.
Maybe a Victor or Hurricane type?


I still think the engine has a lot more in it. Need to find the bottleneck.


:)

I would have went With a little larger cam, and a T2 manifold.

Forgot to mention...these are uncorrected numbers,

What size are the primary header tubes and did he run them open or through mufflers?

I don't think the intake is the issue. Maybe the cam is on the small side for the CI but not that terribly small. Probably has a nice mild idle and good vacuum.

I run a similar 242/248 in a 468 BBC, 30 CI smaller, and makes 600hp but has an excellent set of AFR's on it. The cam acts pretty big in this engine.

To give a Pontiac example, I just built a 455 (467) that has a 239/243 cam, a set of 7F6 heads that were ported, a stock 72 455HO intake on top and dyno'd through a set of untouched RA manifolds (no headers), that made 507/571 on a dyno that I'm told is a bit conservative.

I would expect better from a 496, especially the torque numbers. But can't race dyno's obviously.

How it runs in the car is what I'd like to see.

Primary tubes are 1'7/8th. They were run open.

Formula Jones,

I was told it has a nasty idle. Sounds really good. The builder took some video while it was broken in. If I can get them I hope I can post on youtube.

Jim

Horsepower numbers seem roughly in line with the head flow to me.

Interesting, I'd like to hear it.

The 242/248 I'm running is on a 110 LSA and in a smaller engine, so it's pretty rambunctious. Even with 10:1 compression it only makes about 9-10 inches of vacuum at 1,000 rpm and 5,000 feet elevation. But it rips pretty good and makes power beyond 6,000 rpm.

For SD heads to only go 260 they were not ported much. Get that RPM off that thing. SD heads, put a Warrior on it, period correct. A 496 will have plenty of low end with a single plane.
At any rate, for the cam had head flow the numbers don't seem too far off to me.

You need to post a dyno sheet. Why would someone dyno an engine and give you uncorrected numbers.?

Stan

"I don't think the intake is the issue. "

X2

My Performer RPM supported 580 hp at 5800 rpm in my previous 462 combo. On the same engine a Victor intake made 20 more hp at 6000 rpm. At 3500 rpm the RPM intake made 491 ft.lbs torque and at the same 3500 rpm the Victor intake made 487 ft.lbs torque. Both intakes port matched to the heads in use with the same HP950 carb.



.

Even with more cubic inches involved, on my 505 the Performer RPM intake supported 615 hp. This with higher flowing 320+ cfm Edelbrock heads and a 260 degree at .050 solid roller cam. It is in this level the single-plane intake is king and leaves the RPM intake way behind.



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Seems like very decent numbers given the combo....

I wouldn't sweat the numbers too much, although the peak seems low at 5200. Any idea of the spring pressures used?

To give you an idea how different these dynos can be. The last 455 I put together for my father, bored to 463, had a 254/262 @ .050 hydraulic roller with .628 lift, 330 cfm Edelbrock round port heads ported by Kauffman, 10:1 compression, and 2" hooker super Comps. Dyno'd with a 950hp and tried 3 different intakes and spacers, including a Victor, RPM air gap, and one other I don't remember.

It made best power with the RPM air gap and 1" open spacer. It only peaked at 500 hp but made 604 ft lbs. Odd power spread but this was another conservative dyno.

Didn't matter much, because the car was running at the track right along with some other 600hp engines we were either involved with or had knowledge of, and even spanked a couple of them. So dyno numbers can be misleading sometimes.