What do you think a good HP/CI is for a street/strip engine?

Just curious: the last 2 engines that i’ve personally seen on the dyno were 1.31 and 1.21 hp/ci. These are both pump gas street motors that race a few times a year.

Eng 1: sb chevy 400 10.5:1 afr210 heads with single plane intake hp950 carb. Bullett hyd roller .612” and 240’s dur@.050”
495 lb ft. And 524 hp @6300


Eng 2: bb chry 505 10.6:1. Stealth std port hesds with indy dual plane Hp 950 carb. Comp solid roller 573” and 248-254 dur @.050”
630 lb ft @4500 and 609 hp @5900.


Being that peak tq of eng 1 was above 5250 rpm, is that why hp was greater than tq? And does this mean that the cyl head breathing was better comparing to the other engine, being the reason why hp wss greater than tq? What else can we surmise?

My last pump gas low deck stroker made 727 HP at 7000 RPM with around 675 Ft. lbs. around 5200 RPM on Oregon 91 octane pump swill with no Ethanol in Klamath Falls, OR which is right at 4300 Ft. above sea level on a DTS engine dyno.
The motor was a 400 block bored to 4.375 with a 4.300 stroke crankshaft which was 517 C.I. with right at 10.78 to 1 compression, it had a set of Indy SR heads with M.W. intake ports and a Indy 400-3 intake with a Holley List # 9375 non HP carb. with stock jetting The cam was a comp Cams solid roller lifter grind with 260@ .050 on the intake with .420 lobe lift and 266@.050 on the exhaust with .409 lobe lift , Harland Sharp 1.65 ratio single shaft roller rocker arms That makes it have 1.406 HP per C.I., not bad but not the best either
I had that motor in my old 1971 Duster that weighed 3450 Lbs. with me in it ready to race with full stock gas tank, it ran a best ever of 9.993 at 134.7 MPH at Woodburn, OR drag strip in August of 2008 or 2009, CRS, cork up full 3.0 inch diameter exhaust system to the rear bumper with the air cleaner on.
That motor and that car far exceeded my wildest dreams
I've thought of building another 1970/71 pump gas street Duster to see how much better I can make it run with what I learned from the last one
Probably not going to happen now though due to many other car projects in front of that desire

In the end, I think this still comes down to an individual's opinion on what "good" street is. I like my cars to be very mild mannered on the street, and I usually shoot for 1.10 to 1.15 on an engine dyno. You can build it with parts from Summit, and stuff it in a car with a stock-ish torque converter and a 3.23 gear.

my thought s on your question .
The SBC probably has effectively bigger head , bigger cam and better intake . This makes HP and higher RPM peak
The BBM has effectively smaller head , cam , carb and intake . Better TQ less HP and lower RPM peak .
The AFR head is probably a superior head also unless the Stealth is a CNC head or really well prepped .

Tex

From the limited information I know when the HP and TQ numbers are close it's typically because either the heads don't flow some big number, or its a lower RPM build. I built my wife a 408 (351W stroker). When we dyno'd it, it made like 510 TQ (I forget the RPM). and 535 HP at 5800. It's just a basic build, 10.7:1, AFR 185 heads, Victor Jr Intake, .571/.592 solid flat tappet cam. The engine builder said he'd really like to see the AFR 205 heads on it, but I compared the 185 vs 205 and even talked to AFR and the only way the 205 would be beneficial is if I got a bigger cam and twisted it more RPM. She shifts it at 6000, traps at 6200. The motor has ran in the 10.6-10.7s in a 3000 lb car. I built it to be a low maintenance, lower rpm build and not twist the guts out of it so it'll live a long time. It all really comes down to how hard you want to twist the engine. No sense in building a engine that peaks at 7-8K if your only going to run it to 6K.

Power per inch doesn't scale, small engines always have an advantage. This was known 100 years ago.
Just build a bigger motor and ignore power per inch.

The easy answer for these two examples is...... the cfm/ci is better for engine 1.

Take engine 2, install some TF270’s and a racy single plane and watch the hp/ci go up.

Engine 1 has about 5.5cfm/ci.
Engine 2 is closer to 4.6.

The TF270’s would put the 505 in the 5.5cfm/ci range.

The better heads should put the 505 in the 1.30-1.40 hp/ci range.

The current two combos have the bigger motor making more tq/ci.

Funny you say that........
446 just came off the dyno.......KB flat tops, prepped RPM heads, SD, 850DP, 1-7/8” headers, 230’s hyd roller.
535tq/515hp, pump gas.

Going in a 71 Charger with a 5 speed........ will have EFI in the car.
Owner wanted it pretty mild mannered.

A friend of mine has just bought a motor for his s/strip Roadrunner to step things up for next years racing and cruising, unusual spec for such a big motor>

589ci street wedge, 572-13's, 10:1, small solid roller .620", made 705hp/750ft lbs on the dyno with a single 850DP, his car will drive like a Cadillac and run mid>low 10's in the 1/4. Plenty of potential with head porting, a cam/carb upgrade when he gets fed up with the 10's.... has enough head to do it.

I am addicted to larger engines in a street car....Torque is what gets the car moving....Ever drive something on the street with 750ft/lbs on tap?

If I could afford a +650 Goodwin Hemi, I would have one in my street car....

Our little 400/512 is making 755hp, and I would drive that on the street anywhere if that car were street legal.

1.5

My 235 makes right at 1.06.

Boost is a wonderfull thing! Can do wonders on pump gas

gas ... lotsa boost ...

Looks like NOS with a cast piston!

Build the biggest motor you can and pick the cam to match the charactoristics you want for the street, depending on what you are willing to tolerate for street manners. The hp and torque will be what they will be.

Couldn't agree any more! A big mild motor will give you all the torque you can handle and live forever. The rest of the drivetrain will tell you where the weak link is.

in a build like this, would the trick flow 240 heads make much difference?

in a build like this, would the trick flow 240 heads make much difference?
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All depends on what level the Eddy's have been prepped to and the cam lift used. TF claim their 240 head flows 318cfm@.550", ootb Eddy's are around 271@.550 if your lucky, also 78cc for TF's and if 84cc eddy's were used on that build it could screw up the CR if already on the limit for p/gas......my 2c's.

I believe the intake type, single plane versus a dual plane, and the compression ratio have a lot to do on when the motor will make peak torque and HP.
The carb and cam size are a real player on that also of course
I've notice that most of the pump gas street motors I've built and dyno tested, stock stroke or stroked, will make more torque than HP if the compression ratio is under 10.5 to 1, above that they tend to make more HP than torque

basically, going with the philosophy of



low deck 451
M1 single plane intake (swap to performer RPM if the single plane is annoying)
cam like a mopar 528 solid ie. ~240@050" - 112LSA
1-7/8 headers
can make a piston choice to have the motor be roughly 10.4:1 with either heads

go with the smaller port heads and save some money, go with the trick flow with bigger ports and better flow...for a hot street motor, that will see the strip occasionally.

gain much torque down low with the RPM heads? gain much power up top with the PP240, maybe still have as much torque down low??

I’m sure there would be a difference....... how much? Only way to know is do the test.

When the TF 240’s came out, on their 600hp test mule I thought they said their heads were better than the RPM’s by 30hp.
That was ootb heads, on a motor that made 85hp more than the one we just ran.
This one had very mildly reworked heads, and less hp/ci....... so I’d expect the gap to be lower than 30hp....... but that’s pure speculation.

It wouldn’t surprise me if you did the test on a bigger cube motor with a bigger more aggressive cam that you could get the difference between ootb RPM’s and ootb TF240’s to be over 50hp.
Then, on an 8.5:1 383 with a stock replacement magnum cam and an old dp4b with a 600vs carb, there might not be any difference.

The motor that was on the dyno yesterday was something I originally built in 2004, that had a problem with one lifter bore.
The lifter bore was repaired, the heads freshened up, solid cam out, hyd roller in.

The heads on it flow 290/217@.600.

Had it been built from scratch today, it might have gotten different heads.

My pump gas small block dynoed 662 hp at 394 ci. That is 1.68 hp per ci. It was dynoed on super unleaded.
I have never ran anything but super unleaded in it. I have thought about running 110 in it and raising the timing to where Brett told me to put it. I don't trust the pump gas enough to raise it. It is raced with the Drag Radials and mufflers just like it is street driven.

Put some gas and timing in that thing and turn it loose!

Every SB I've mess with didn't like more than 33 total timing regardless of compression or fuel used
But if you don't test at the track you'll never learn what YOUR motors really wants and likes

The engine I built this year for my Coronet is probably the best street engine that I've tested so far. It is 496 inches with TF 240 heads, a small hyd roller cam, compression in the high 9's for pump gas and small tube headers. It made a little over 600 hp and 600 torque.

The cnc ported Stealth heads on my 505 flow almost identical to the TF 240's.

I'm really enjoying this combo with the mild hydraulic roller, 10.3:1 CR, 11" converter and 3.54 gears.

I drive it to work when the weather is nice, cruise it all over, run pump gas and it really requires very little maintenance.

I have well over 6,000 miles on it and it is super consistent! When I run it n/a at the nostalgia events, it runs within 2 hundredths all day long! I have two 1st and one 2nd place finishes this season racing. At one event we were running 104 mph in the 1/8th mile all day on a small shot of nitrous.