[adeeos]

Gents, I did not want to spoil 455rebels thread so hear goes with my own. I just got my 455 back from the machine work and was curious how much HP/TQ is may put out without spending 550 locally to find out on a real dyno.

Basic budget combo;

-TRW flat tops stock pistons
-Stock crank/rod combo
-6x 4 heads, non ported
-Q-Jet carb
-Rhodes lifters
-Crower 60919 cam .470/.470 lift, 304/316 advertised duration
-3 tube headers, 3 inch exhaust, 400 T with stockish converter
-3.73 gears
-Edelbrock RPM intake manifold

All of this is a heavy 70 GTO convert.

Any ideas?

Thanks!

[ponyakr]

400hp/500 torque

[Lee]

Those 3-tube headers are horrible. I had a car with a fairly similar motor on my chassis dyno a few years ago. It put about 260-265 to the wheels. With the compression and cam it had, it should have broken 300 at least, if it had a set of decent 4-tube headers or even R/A manifolds. I tried very hard to get him to change the headers, but he was totally happy with it as it was.

[adeeos]

Lee-how much HP could I expect from the 3 tubes to the something like the Hooker Headers, 4901HKR?

[Lee]

If you were local, I'd do before/after dyno tests for free, to verify! I recently gained 60rwhp @ 4500rpm (45rwhp at the peaks) by switching from stock log manifolds to a set of Tri-Y headers. Your gains will probably be a bit less, but I suspect you'd see at least a 35rwhp gain.

[tom s]

RA manifolds are as good as the 3 tubes IMO.400 HP.Tom

[PunchT37]

390 to 400 hp. The heads will probably start to choke at the same time as the 3 tubes. At least you`ll have a rev limiter for those stock rods.

[Lee]

Originally Posted by tom s

RA manifolds are as good as the 3 tubes IMO.400 HP.Tom

Tom, I'd LOVE to test, but I suspect the R/A manifolds are much better than the 3-tubes.

Maybe someday somebody will do a fair test.

[tom s]

I think it was done on a RA III engine by Dan Jensen some years ago in HPP.Tom

[steve25]

At .470" lift a stock 6X head Intake port flows 195 cfm@28" of depression, so with 4 tube headers the most hp you will have is 400, with 3 tube headers notch that down to 380 at best!

[SD455DJ]

Originally Posted by tom s

I think it was done on a RA III engine by Dan Jensen some years ago in HPP.Tom

tom s and Lee - Dan did an exhaust manifold test on a '69 RAIII 400 (+.030") from an TA w/ a TH 400 and AC, (62 heads) and an 068 cam. He dyno'd it with the long branch (original 2.4" outlets), A-body RA manifolds (2.25" outlets) and then regular exhaust logs with 2.06" outlets), all with kink/crush bent down pipes and 2.5" mandrel down pipes. The results were surprising in that the RA A-body manifolds only lost 5hp/5 lbft to the long branches and maybe 10 hp/15 lb.ft. with the logs (off of a 78 TA 400 motor) when tested with the mandrel downpipes. The moral of the story is the RA manifolds did surprisingly well and the logs were shocking! He didn't try any 3 or 4 tube headers unfortunately, so no comparisons there. This test told us that 2.5" mandrel bent downpipes are critical to making good power when using any cast iron exhaust manifold, especially the logs. I would think that you would get the same power as you would the RA manifolds.

My '70 YH 455 Bonneville engine (+.040" w/ #15 small valve heads @ 9.95:1 compression) with a Summit 2802 cam blowing through A-body exhaust logs pulled 390 hp/512 lb.ft. torque with the Pypes 2.5" mandrel downpipes. We ground the outlets out to 2.125" which is all we could do and still have enough meat on the flange for a good seal for the downpipe. This motor is in my '70 LeMans and it is all power down low and midrange... done at 5000 rpm. The #15 small valve heads flow 195/150 cfm at .450" untouched, so I would imagine the 6x-4's would flow 205-210 giving you 410 - 420 hp and 525 lb.ft. torque easily with the RAIV cam you are planning. My motor has cast pistons, but Eagle forged H-beam rods.

adeeos - Good luck with the build.

Dennis

["QUICK-SILVER"]

Originally Posted by steve25

At .470" lift a stock 6X head Intake port flows 195 cfm@28" of depression, so with 4 tube headers the most hp you will have is 400, with 3 tube headers notch that down to 380 at best!

500+ HP, nearly 20 years ago, with three tube headers. More cam and minor port work on heads. http://www.hotrod.com/articles/hrdp-...ngine-buildup/

Clay

[Cliff R]

440hp/530tq.

463cid
#46 heads from a 350 engine, 2.11/1.77 valves installed no porting.
Crower 60919 cam
Rhoads lifters
High ratio rockers
Stock intake
Q-jet (no spacer)
Factory HEI.
Hedman 4 tube headers (67-69 Firebird)

......Cliff

[73T/A]

Originally Posted by Cliff R

440hp/530tq.

463cid
#46 heads from a 350 engine, 2.11/1.77 valves installed no porting.
Crower 60919 cam
Rhoads lifters
High ratio rockers
Stock intake
Q-jet (no spacer)
Factory HEI.
Hedman 4 tube headers (67-69 Firebird)

......Cliff

Cliff,do you recall what compression ratio this engine has?

[steve25]

For the average first time around builder who will not fine tune such a combo on a chassis dyno , but in his driveway and then by the seat of his pants , 500 hp is a big stretch, get real here!

[Lee]

Originally Posted by "QUICK-SILVER"

500+ HP, nearly 20 years ago, with three tube headers. More cam and minor port work on heads. http://www.hotrod.com/articles/hrdp-...ngine-buildup/

Clay

If you've been around this hobby long enough, then you'll see some red flags that make that story a bit dubious.

Again, I'd love to see back-to-back testing involving 3-tubes, logs, R/A's, and quality 4-tube or tri-Y.

[Navy Horn 16]

That combo might see about 360 hp/ tq to the rear wheels. It'll still have a broad, flat torque curve and be a hell of a lot of fun.

[Navy Horn 16]

Originally Posted by Lee

Again, I'd love to see back-to-back testing involving 3-tubes, logs, R/A's, and quality 4-tube or tri-Y.

Obviously not that level of testing, but I recently put cutouts out my TA (3 inch header extension to the dump). I've got 1.75 inch primary headers and with tube past my dumps is 2.5 inch...so that's a pretty good exhaust. I've got a more aggressive combo than the OP, and I topped out at 389rwhp. Opened the cutouts and made 407/409.

Even a really good exhaust can be a choke point.

[Lee]

Originally Posted by Navy Horn 16

Obviously not that level of testing, but I recently put cutouts out my TA (3 inch header extension to the dump). I've got 1.75 inch primary headers and with tube past my dumps is 2.5 inch...so that's a pretty good exhaust. I've got a more aggressive combo than the OP, and I topped out at 389rwhp. Opened the cutouts and made 407/409.

Even a really good exhaust can be a choke point.

Back in the early 90's, my cousin had a '78 T/A, 400, automatic, 3.23's, and I had a '79 T/A with 455/6x, auto, and less gear. We both ran around 13.2-.3 in street trim. Both had about the same exhaust system - 4-tube Hookers, 2.5" pipes with Flowmasters, by the same shop.

He opened his headers one day, and ran 12.9's. Impressed with his results, I opened my headers, and ran 13.4's with the car bucking and sputtering. Turned out his carb was really rich in street trim, but was about perfect for open headers. I was about perfect on my carb to start with, and had lean-stumble when I opened the headers. I would have needed richer metering rods for the open headers, while my cousin needed to lean his out for street use.

Also note the thread I posted several weeks ago, where I detailed the metering rod changes required as I tested exhaust changes on my very mild 455. Just replacing the old exhaust (2.5" mid pipes, 3" Flowmasters, 2" tails) with the new (full 3" with Borlas) required a noticeable change in secondary metering rod size to correct the AFR.

[Navy Horn 16]

The AFR from my dyno session shows me pretty much where you cousin was. A little rich with the full exhaust, closer to the sweet spot with open headers.