Inliners International Forums General Discussion Bench racing 'Guestimate' on horsepower... 292 v. 250

I'd like to get a ballpark idea of what I could expect for horsepower. This is what I'll be starting off with:

292, 30 over
Cam - 264-H ~ 264 duration 214 @ .050" .498" lift 110 lobe center
holley 390 cfm
offy intake
stovebolt cast iron headers
pertronix hei conversion
stock 292 head

Anyone have any guesses on what it will make for power?

How much would a 194 head and/or and 194 head with lump ports add?

How much would you expect a similarly built 250 to make?


What did the 194/230/250/292 make hp and torque wise in stock form?

Even though the engines are almost clones, the power per inch will always favor the smallest engine, and of these (if more than 1) that with the largest bore.
The peak power doesn't go up much with a 292 (despite Santucci's remarks) simply because the other parts are not and in some cases cannot be "scaled up" to match the displacement (valve lift, port area, venturi).
The longer stroke isn't the problem unless and until its maximum safe RPM is reached, at which point an engine of equal size but shorter stroke will have an advantage, but the higher specific power always comes at a higher speed.
The larger engine will always "feel better", since it develops a higher percentage of its torque lower in the RPM range (where you use it all the time), and the point where it "runs out of steam" is not used as frequently.
The larger engine is also more tolerant of cam timing - it both needs and accepts a hotter cam (sometimes it's one or the other).
The 292 is no more knock-sensitive since the bore diameter and exhaust valve position (the big limits) are the same.

All these engines have the same problem: the porting doesn't lend itself well to resonant tuning, which is the only way to get the VE over perhaps 95%. What you're left with is size and compression ratio to make torque, and head work and cam to extend the RPM at which this happens upstream to make HP.

As to your specific choices:
The cam is a bit mild for serious power, you could use another 10°. The cam reccos are way too generic - displacement is definitely a factor in cam choice (as are head efficiency, static CR, and exhaust backpressure). Elgin can make you something closer to what your engine wants than an off-the-shelf cam. In general - the more development you have in the motor the more targeted the cam should be. Stock and near stock engines are fine with the usual aftermarket cams since the engine's tune was already known - yours isn't.
You probably noticed that most of the street cams are 110 or 112° LSA - going down to 108° will produce more power but make the idle worse, and the transition to full power more "peaky". I prefer that, but it's annoying to drive in traffic.
The carb is a bit small, but this will only affect peak power.
The split exhaust of course isn't as effective as tube headers, but the other advantages make it (my opinion) a good choice for a street motor. I haven't examined a set, but I would guess that the interior surfaces could stand a bit of clean-up. Especially helpful is to make a template of the actual exhaust port outlines, and enlarge the manifolds to about 1/16-3/32" bigger all around (only where the casting permits, of course). No radius or blend - the sharp edge is important. This both prevents any minor mismatch from obstructing flow, but also makes a nice anti-reversion ledge to control back-flow on overlap (an engine with a stock cam won't get this benefit).
A big part of head efficiency is the bowl prep. Once your final valve choices are made (especially the intake) the throat should be enlarged to the usual 80-85% of the head OD (or as the casting permits - there's water around it) and blended into the curve. This is precision work - except to pay for it, but it's the most import area in the engine.

Thanks for the input. I've added some comments below, as well as added a few questions (numbered)


When I bought the cam for this engine, the engine was going into a daily driver, which isn't the case anymore. I would still like the car to do ok in traffic though... I'd like the wife to be able to drive it if she so desires.
The engine will be pulled out of the truck within the next month I believe. (1)Should I think about a cam swap, Or do you think this will be ok? (2)What do you consider serious power?


(3)What size would you recommend? I was told that the carb was working fine when it was pulled out of another nova. It has been sitting for 3+ years now. (4)Should I think about a rebuild?



With the nova being close to the ground, I was told I'd need to use either the stovebolt headers or the clifford shortys. I decided to go with stovebolt, partially based on the look.


I'll try to snap some detailed pics for you.

When I was putting everything together, I was told that I could expect 200hp & 300 ft/lbs torque. (5)Is this a bit optimistic with no head work?

The second 292 I had in my 66 was very similar to yours. 60 over with a 264H Clifford cam, Clifford intake, Edelbrock cam, 1.94 and 1.60 valves and flat top pistons. It had a 700R4 and 4:10 gears. Based on a horsepower vs et calculator it theoretically had 187 hp at the rear wheels. At sea level it like would pick up another 10 or 15.

Hi Bruce, Thanks for the input.

How did it run on the highway with 4:10 gears and the overdrive?

It was actually pretty nice. In od it is like running under 3:1. First gear was a little steep, but with the big gap between 1 and 2 it worked well with the low gears.

The engine speed is exactly the same as an axle with ratio = OD × current axle.
.70 OD × 4.10 = effective 2.87:1
However, it's not the same in other respects:
1. you have some additional fluid pumping loss in the transmission due to the extra gearset (minor)
2. the driveshaft is still turning the same speed as always with the 4.10 - very fast, and this is a safety issue for very high speed cruising. Your engine will like doing 100, your driveshaft and U-joints won't.

ok here are my guesses, I also have a 63 ssnova that might get a 292 so I am planning same.
As you described yours I will assume 8.2cr stock (mine just measured out to that) here is what my homebuilt computer says:
Torq 272 at 3100
Power 207 at 4600

Built as a 30-over 250 instead also at 8.2cr:
Torq 238 at 3300
Powr 196 at 4800

Back to the 292 build but with a 194 head.
Main diff is about 9.2cr instead of 8.2cr:
Torq 281 at 3100
Powr 216 at 4600

And with the lump port head:
Torq 309 at 3200
Powr 248 at 4800

At this level the 390 Holley would be a little small and in a 2860 lb nova you could use a bigger carb, 450 or 550 Holley or 500 Edel, etc.

Dyno tests are kinda rare on these, my computer lines up with the dyno tests I can find but beyond that I trust the computer, then the Gtech and the strip.

Thanks for the info!




Meaning, with the lump port head?

On thinking about it, the 390 Holley might be best for all those combos. With the lump port, a 550 Holley calculates to 6hp more at 254hp, but loses more down low (below 2500) so for the average streeter I'd still stay with the 390 Holley.

The 450 Holley gained 3hp to 251hp but did not give up any down low. Worth buying a carb for 3hp??? Probably not.

What does your program use as a factor for the number of cylinders?
For plenum volume?
For manifold type?

I thought about doing a lump port, but someone suggested that it may not be worth the money (I'd need to have someone do it for me), b/c it wouldn't make much difference on the bottom end.

i think a lump would help the bottom end. send the head to me, my machine shop does excellant work and i can put in the lumps. done a few for others too. port the head while you are at it, going to bigger valves requires unshrouding. tom

Thanks for the info Tom. How much do you think all of this would cost?

X2 ,lump port helps bottom end & everywhere else.


MBHD