Hot Rod Forum : Hotrodders Bulletin Board - Reply to Topic -- Hot Rod Forum

Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine> I need intellegent input concerning HP ratings.
User Name
lost password?   |   register now

Thread: I need intellegent input concerning HP ratings. Reply to Thread
Send Trackbacks to (Separate multiple URLs with spaces) :

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Additional Options
Miscellaneous Options

Topic Review (Newest First)
05-22-2008 06:56 PM
American Thunder I have $10.5k in my 332" 302 motor. Reliable HP doesnt come cheap. And making 500+ hp from a n/a small block requires a lot of cam. No way around it.

The twin of my motor made 530 hp on an engine dyno, so that's what I go by. I installed it in a Mustang II that I lightened, the car weighs in at 2550 lbs without me.
With 275/40ZR17 street radials, 3.10 gears with a detroit locker carrier,(9" housing I swapped in from a 1959 T-Bird donor) a custom built manually-shifted C4 "mighty mite" transmission from Dynamic with 5000 rpm converter, the car will hit 85 mph in about 6 seconds using half throttle. At 140 mph, it will pin me into the seat the same way it does at 60 mph, and I'm not sure where it would stop pulling, as I let off it long before the motor reaches its limit of 8500 rpm.

My recipe for 500 hp from 332 cubic inches is 10.95:1 compression, 260 deg dur @.050" solid lifter cam with .625" lift. Victor Jr intake, jetted 750 Race Demon, machined TFS Track-heat heads with o-rings, 5.5" eagle H-beam rods with floating pins, JE ultralight forged pistons, ARP fasteners, forged billet steel crankshaft, billet steel main stud girdle, Melling 85 psi oil pump, SVO race pump shaft, Cloyes double roller timing set, MSD ignition and distr. set at 20 degs initial advance, +18 deg more by 1500 rpm. I enlarged and smoothed the oil return holes in the block to avoid oil starvation at high rpm.
I run underdrive pullies and swapped to manual steering to save weight(about 35 lbs!) and wasted hp. I also have dual mr. gasket electric fans to save wasted hp.
Fine tuning of the fuel and ignition curves is critical for making maximum power. Even if you have the right parts, the wrong state of tune will prohibit you from reaching your hp goal.

I'm figuring on 400-425 hp at the wheels, I'll have it on the chassis dyno this summer, hopefully I'm not disappointed.

When I look over various uploaded videos on the internet, it seems that everyone's car is making 600 hp at the wheels, yet in the videos they post, at full throttle, the skinny street radials arent spinning. Hmm.
The import guys seem especially prone to claims of 600+ rwhp from .001 liter or whatever motors with hairdryers, and again, no tire smoke at all.

Anyway, here's a couple of my own videos.
Half throttle run up to 85:

And the gratuitous smoke show:
05-22-2008 01:48 PM
Originally Posted by glen242
Many people say they have a 400-500 HP SBC. Displacement from 327 to 400 CI.

Where these HP numbers come from is usually not quoted, but very rarely, an engine dyno is cited, numbers usually supplied by whoever sold the engine.

A chassis dyno reading, and I know these numbers can be massaged, is usually never supplied by the car owner, so that a comparison can be made between engine and chassis dyno numbers. Rule of thumb was, I believe, 15-18% manual and 20% and up automatic drive train loss. Does this "rule of thumb" still hold true?

My prior 350, stock 180HP, according to GM, with a cam, new heads, 9.2CR, long tube 1 5/8" headers, ST10 transmission, and Performer intake, measured 217 RWHP on a Mustang dyno. Using the 20% loss figure I came up with 271 Engine HP. Not too bad, I thought. Was my math correct?

I guess what I am asking is "how do you know what your engine specs are if it has never been on a reputable engine or chassis dyno"? Some say 1/4 mile speed will tell you, but how about driver error during the run, wheel spin, etc.? Computer sims can be manipulated, by what is input, to give different results.

I see people stating they have 450-500 HP on engines that are less built than my present 383 and wonder where the numbers came from, as they are usually never stated. Are we turning into ricers where we take each alleged HP increase from each separate aftermarket part and add them together and then add the total of them to our factory HP?

Maybe I'm just an old fart, but I find it hard to believe that 1.3 HP/CI, in a 383, is easy to get on a NA STREET CAR.

I once told someone on a Corvette Forum that there were more 400+ HP SBC cars on the internet than on the street, and I stick by this statement.

You might want to consider this post just an old man/hotrodders vent.

Comments welcome.
What do you expect; we live in an age where an Indiana cop claims he radar-ed a kid driving his old man's Subaru at a 147 miles an hour and that fake performance magazine Road and Track prints it.

We've know forever that the cops fake radar data and the courts swear to it. But anybody that's really gone a 147 miles an hour knows it takes a crap pile more rocket science everywhere in the vehicle than simply having big horsepower numbers to go that fast and not experience free flight.

Combat story; Many years ago I was at the San Diego County fair where there was an Ambulance company with a display claiming to get 450 horse out of a 390 Caddie engine. At the time I had a highly modified 390cid/401 HP Ford and getting 450 hp out of it, on the dyno, I was sweating blood. How they did it with a mild street cam, single Rochester WCFB four barrel carb, cast iron exhaust manifolds, etc. and an automatic transmission is apparently way beyond my abilities. Apparently you need a degree in advertising instead of engineering to do stuff like that.

05-22-2008 09:39 AM
opelitis5 This was the way it was explained to me... As I said one has to figure out why the numbers are over 1320... Looks like traction on the 383... Reaction times and dial-ins are non existent.. Maybe a shorter tire on the 305 would bring up the revs and bring down the 1358 to the 1320 magical number... Maybe if the 383 was "walked off the line" things would change... I don't know. This is a brand new type of competition if you'd want to call it that.
The money is great at 2G per Sund. and you can get as many runs as you want. How one would go about getting the 1320 is going to be interesting.
Slamming the brakes on or having the proper gearing would certainly help if the numbers are somewhat near or below 1320.
05-22-2008 09:09 AM
upstand2 "If over 1320 you are leaving power on the table and under 1320 which not many people are, your engine is overly-efficient.."
This sounds like traction , not HP.
Because my car with a 305 running 15.8@86mph =1358.8
and the same car with a 383 runs 12.9@105=1354.5
Pretty close. But the 383 is making way more HP!
05-22-2008 08:07 AM
opelitis5 On your next trip down the 1/4 mile, multiply your E.T. times your speed and see what you come up with... Should be 1320 if you are close to the ultimate setup... If over 1320 you are leaving power on the table and under 1320 which not many people are, your engine is overly-efficient.. Check it out!!!
There is / was a dyno book published that if you knew the weight of your car and the trap speed there was a certain HP level that you had... Witten by a Dr. Dean Hill entitled "Pocket Dyno"... There are other computative features in this neat booklet...
Starting this weekend at a track near Mtl. called Sanair, they are trying out a Speed times ET system of racing in which reaction times and dial-in times do not even come into play.... The closest one to 1320 as in the first paragraph wins a pretty big purse. Believe it to be $2G. Can run as many times as you want, and again reaction times and dial in times are not important in the least... Supposed to be some sort of European racing system and much safer for the competitors... Will be interesting to see how many cars show up as many racers with big $$$ cars have stated they want nothing to do with this in any way... Still 2G is a lot of scratch... We will see...
05-22-2008 06:14 AM
barnym17 Real funny thing the Ford popped at the end of last year owner threw in a 350 with mild hyd cam no comp. and was almost as fast proving once again in dirt racing setup and driver is where it is at.
05-22-2008 06:12 AM
barnym17 I think a lot of it is computer dynos and optomistic parts selection.I.E "there ain't no way my engine is that weak I better use the max ported flow numbers" I use ea pro but anything it tells me I knock abou a hundo off the top to be realistic. Altho around here the dirt hobbystock motors have been turning between 550 to 690 on a real pump.The 690 version was a real Bad a** 427 stroker Ford with N351 heads a lot of work.
05-22-2008 01:52 AM
Originally Posted by hardhatz
Well, I have a .030 over 350 with a cam, headers, manifold, MSD ignition, and pocket-ported heads. According to my fanny-dyno, it makes 223.75 HP @ 4750 RPM, with enough torque to spill 2.4 ounces for Pepsi from the cup in the drink holder, or spin a tire on sharp right-hand turns. Deduct 5% for each 1000 ft elevation above sea level. Your mileage may vary. Not valid in Rhode Island, or if you are left-handed.
Thanks for your VALUABLE INTELLEGENT input.
05-20-2008 07:19 PM
hardhatz Well, I have a .030 over 350 with a cam, headers, manifold, MSD ignition, and pocket-ported heads. According to my fanny-dyno, it makes 223.75 HP @ 4750 RPM, with enough torque to spill 2.4 ounces for Pepsi from the cup in the drink holder, or spin a tire on sharp right-hand turns. Deduct 5% for each 1000 ft elevation above sea level. Your mileage may vary. Not valid in Rhode Island, or if you are left-handed.
05-20-2008 01:35 AM
curtis73 I think with common engines, its just the proliferation of experience. If I post a question that goes something like, "how much hp will I get with X heads, this compression, this cam, these exhaust manifolds, etc..." chances are there are four guys on this board who have done a nearly identical assembly and had it dynoed.

Its also just good old fashioned guessing. You can get really close just knowing about how much cam and compression it takes to get a 350 to make X hp.

The other phrase I HAAATTTE is "balanced and blueprinted." Bulls#!t. You slapped new bearings and pistons in an untouched 30-over shortblock. That does NOT mean B&B.
05-20-2008 12:16 AM
carsavvycook I understand what you say! I cringe every time I here the kid in the shop next to mine says "all of my motors have 650HP they cost me 5K". I know better having tuned them for his engine builder who states the rated HP off of a desk top dyno program. His builder tells me they should be 420HP realistically because of the early camel hump heads the kid wants to run. They are lucky if they have 380HP in chassis with my built in dyno our Lord gave us after tuning.

I know how much you have to spend to get real horse power having spent 22K total for 560HP out of a Boss 302 Ford (twin turbo-ed in the early 70's, 65K total to get 981HP out of a 481CID BBC(dual stage nitrous injection) in the late 80's. Both were engine dyno tested. This Corvette (in my pictures)was 405.5HP in chassis 4 years ago, and it is much faster now(he now calls it his Screaming Yellow Zonker). It is going back for a re-dyno later this summer
after suspension replacement changes to the 35 year old parts.
05-19-2008 11:27 PM
Originally Posted by sam-missle
yep, lot of head porters out there too, but without the bench.


That is a gross understatement in my neck o' the woods.

I have a huge pile of junk heads, that were once useful, because of these hacks. I've also had these a-holes buy heads from me and have their names carved into the accessory pads, or put their valve cover stickers on an engine that I built.

Ehhh, this kinda junk is a real sore spot with me.

05-19-2008 08:52 PM
Guy Hiltz I can give you a real life comparison.A friend of mine did a dyno sim program on my big block for me,with all the right parts & specs.His program came up with 637 HP.On a real dyno,with no "fudging",it showed a best of 554 HP.This is a huge difference.
05-19-2008 08:41 PM
F-BIRD'88 I've found that if you run the car down the quarter mile if its making MPH, its making horsepower. No two ways about it.
Driver error, traction, shift points, gearing all effect the ET but will only effect the MPH a bit and always to the milder side. Never makes it MPH higher.
3 or 4 good passes tell the story. All you need is an accurate car weight w/driver. If you make an engine tuning change and the car responds with more MPH, you're makin more power.

I've found that with Desk top dyno if you enter the estimated real airflow consumption in CFM of the motor in question instead of carb cfm its much more accurate. Most people over estimate on the choices in the cylinder head choice menu.
eg Stock head stock ports and valves refers to the best stock unported SBC heads, (like a set of 461X or untouched 034 bowties with 2.02's) not any stock junk head. all others are "low perf" Once you know what each menu choice actually flows, its suprisingly accurate, expecialy if you can determine the actual valve "running duration" (cam doctor and a bit of math)

A "400hp motor" will consume around 550-575 CFM if real airflow on the dyno.
05-19-2008 07:19 PM
Originally Posted by techinspector1
The worst thing anyone can say to me is "ported and polished" AAAARRRRGGGGHHHH

Well, that and "how will this cam sound?" DOUBLE AAAARRRRGGGGHHHH

yep, lot of head porters out there too, but without the bench.

This thread has more than 15 replies. Click here to review the whole thread.

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

All times are GMT -6. The time now is 01:20 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright 1999 - 2012. All Rights Reserved.