Horsepower Estimates?
 

I pulled my engine this winter . I'll have the block back from the machine shop next week and I can start reassembly. I'm wondering what the forum wisdom will say for horsepower? It's a 1977 L48. The block has been tanked and magnafluxed, bored .30 over. Going to flat top pistons. Heads will be 906 Vortecs, with a Comp Cams 268 cam. I'm going with an Edelbrock Performer 2116 intake with rebuilt Quadrajet. Recurved distributor, 2.5" exhaust, no cats, stock manifolds for now. 2004r tranny, 3.70 rear gears, I'm looking for a nice, torquey cruiser...

Ted- see if there is a performance shop near you that has a dyno and you can get actual numbers when your engine is back in the car. Here in northern VA it cost me $75 to put the car on their dyno and do three full throttle pulls. You get a printout of the engine torque and rear wheel HP from start to the max rpm run. My shop will also do air/fuel ratio measurements and custom tuning for an additional charge.

I agree that the dyno would be the best. It can be humbling though. But it's a great way to fine tune it once it's in the car. I will estimate 375 hp/400 tq at the flywheel and should be very enjoyable to drive. Which is the most important in the big picture

Ted,

I am not guessing at all on this.

I truly hope you are not a 'numbers' kinda guy. When people 'feel' that the engine is going to be something spectacular...when it is put on a chassis dyno and they can see what the REAL horsepower and torque that is getting to the ground is not what they expect...it can be quite a hard pill to swallow.

But they also seem to forget...the horsepower and torque at the crank is NOT the same and the contact patch of the tire meeting up with the road.

DUB

The dyno not only tells you horsepower/torque; it also accurately tunes the engine for optimum drive ability. Go to the dyno.

I'm not interested in huge numbers, I just want a little more power off the line, and mid-range, say idle to 3k. Stock was around 200, so if I can get closer to 300, I think I'll be happy!

Just be aware ...like I wrote in POST # 4. If you do put your car on a chassis dyno. The 'numbers' at the wheel are not going to be the same as what would be if the engine was dyno'd at the crank.

DUB

I had cars and engines dyno tuned.

I can be depressing to see the numbers on both the engine or chassis dyno but it's the only way to know what you got. None of "the engine builder said" it should have ? horse power.

It's going to be a carbed steup so a good engine dyno tune will get you very close. I agree with above that your combo would engine dyno
around 360-370 hp. So at the rear wheels about 15%-18% less with auto trans. Also a engine dyno tune let's you break the engine in in a very controlled enviorment. No worries about coolant levels. Trans fliud levels. Getting the timing set.

Nice part about a chassis dyno tune is that they can also tune the trans shift points.

Let us know how it turns out.

I think you’ll make an honest 325-350hp at the crank with the vortec heads and XE268 cam...I’d probably put an RPM intake on it tho.

We just finished a 357” SB for my dad’s 70’ Nova. It’s a 9.8-1 comp, XE268, 2.02 Double hump heads, RPM intake, 750 vac sec, 1 5/8” headers and 2.5” exhaust. We just got it running and I haven’t even driven it yet. I was hoping for around 350 crank HP but....I’m not sure it will get there with the stock double humps. Your 906s will be a big improvement. Your intake and stock manifolds will kill 30-40hp tho...

What Dub said chassis dyno 's break hearts. C3's typically seem to lose a little more hp with their steel drive shafts and steel half shafts.

My 72 vette with the original 350, Isky 270 mega cam, blackjack headers, Q-jet, stock intake manifold made 175 whp on a Dyno jet. TH400 transmission and 3.08 gears. Stock rims.

I think your set up make about 275 hp crank and 225 whp with an automatic if the torque converter can be locked.

The stock manifolds probably cost 15-25hp depending on heads, cam and intake.

:thumbs::thumbs:

SUPER awesome 'real world' feedback!

Those customers of mine that did follow my advice and spend the time and $$$ on a chassis dyno do not regret it a bit.

Those that did not..still come by thinking that I have some magic wand that I wave over the engine and get all of there issues to magically go away. But yet they want to spend $$$ on chrome dress up parts and fancy hose covers.

When my exhaust analyzer broke about 6 years ago. I did not replace it. Because when I did have it, it greatly helped....but knowing that the chassis dyno is that and so much more I never bought a new one.

I guess it is truly...'to each his/her own' on what is important.

DUB

I agree completely. I had my NOM 454 dyno-ed before I started to mess with it to get a baseline. Each time I changed something I went back and checked again to see whether the $$$ and time spent gained any real advantage. The sales literature for cams, intakes, carbs, etc always forecast fantastic hp increases. Usually it is more conservative.

I have to get my 355 L-82 with AFR heads, 10.2 compression, Howards Roller Cam (.525/.525 Lift, duration 219/225, LSA110) with 1 3/4 inch LTH's on the dyno. My engine guy has a mustang dyno, not a dynojet, which will read much lower RWHP than the dynojet.

Your signature indicates:

100% Bone Stock... well, except the old 350 punched to 355 with 9.7 compression and a Howard's retro roller, Dart SHP heads, Weiand intake, Doug's headers and a McCloud super street clutch. Still running the original (rebuilt and tuned) Quadrajet and points. Dyno tuned at 391hp and 413tq.

What was your original Gross engine Dyno HP and the final RWHP figures? is 391/413 the gross engine stand dyno numbers?

Yes - my crank power on the engine dyno was actually 394 hp @ 5300rpm and 413lbft @ 4200. When I drove off the chassis dyno yesterday it made 326hp at 5350 rpm and 363lbft at 4050 rpm on the rear wheels, with a perfect A/F over the entire rpm range. I stand corrected. 17% hp delta and 12% tq delta in my case between engine and chassis dynos. It was on a Superflow engine dyno and a Dynocom 1500 series chassis dyno.

The A/F on the engine dyno looked a lot better than the A/F on the chassis dyno when I drove it in. What I thought was a stumble due to secondaries tipping in too soon actually ended up being a lean stumble - the motor wanted more fuel. I had "solved" it by tightening the secondary spring, which did fix the stumble on the street but the secondaries were only tipping 1/3 open. It was stifling the motor. You can't figure this stuff out by driving around.

We changed the secondary rod hanger to a higher hole position then to a thicker rod after the hanger change made it go a bit rich. I am also now running a pretty conservative 34 degrees total timing with 14 initial, and the car is snappy.

I know there are a lot of guys on here with 500/600/700+ hp which makes these numbers look small, but I'm pretty thrilled with this one. It's no slouch with the wide ratio and now 373 gears. Lots of fun on the street. I only have to wind it to 5500-5800 and it pulls hard all the way there. The Howard's roller (.500/.510 and 225/231 @ 50) has a solid and very flat torque curve, it revs fast, nice chop. I love it. 91 octane pump gas.

I wish I'd gone a bit more on the lift like you did. You should see some nice power with more lift and another 1/2 pt of compression. Good luck with the project! Let us know how it performs.

Joe Minnesota. I agree. I have a bullshit 355 sbc. 9.0-1 compression, reworked 882 truck heads with a dual pattern comp cam, not sure of specs, its my engine builders crate motor package he offers. Eddy intake and holley 670 avenger carb, and Headman headers. 25 degrees initial timing with 35 total, in by 3000 rpm. i make 350 HP and 390 TQ qt the flywheel. 3.55 gears and a 2000 stall converter, car is fun to drive.

Good luck with it..... I'm guessing 330 fwhp with around 265 rwhp through the auto.

Comp Cams website posts dummy dyno results for 350's, pretty close to your build:

http://www.compcams.com/v002/Pages/388/XE268H-10.aspx

Wow - that's pretty close. One difference is that I am running a Howard's roller, so probably picked up hp there, plus a stitch more lift. I am also running 9.8 on the compression.

For the O.P. I think you'll be happy with that 268 cam and it will meet your goals of torque and off-idle take-off power. Should be a noticeable lump on the idle and great torque.

I still won't guess on the numbers. Just be aware that a couple hrs on the dyno will get you the best tuneup possible, so spend the few bucks on that. You won't be disappointed. Good luck!

I know guys like to get HP numbers, but I prefer 1/4 mile MPH This shows how everything is working. Its also more fun for the driver.:thumbs:

I use Max MPH instead of 1/4mile time because time requires perfect launch as MPH is not as dependent to perfect launch. (no wheel spin to get similar MPH)


Did you every get your car to the track ?