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Old 09-13-2016, 07:45 PM
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Horsepower & Torque/good combination?

I know I've posted a similar thread in the past, but a lot has changed with this motor since then. If anyone would be able to provide an estimate of the horsepower and torque this engine will produce that would be awesome! This is going into a 1978 GMC truck with a TH350 w/ shift kit and 3.08 gears that weighs about 5,000 lbs. Here are the (pretty much) full specs:

Block: 1990 L05 350 (#10054727) bored 4.030" and decked to .015" piston/deck clearance

Crank: Stock ground .010 .010 under

Rods: Eagle forged steel 5.7 inch 5700BPLW

Pistons: Speed Pro H345DCP30 4.030" 6.9 cc valve relief

Head Gaskets: Clevite Nitroseal 5746 4.125" bore .026" thick

Rockers: Summit 1.5:1 roller tip poly-lock steel

Heads: Summit Racing SUM-152123 72cc Chamber 165cc int. runner and 2.02 1.60 valves. Same casting as Dart Iron Eagle s/s 165. Flow numbers for Iron Eagle heads w/ 1.94 1.50 valves (thinking the 2.02/1.60 will flow a little better):
-------Intake Exhaust
.200" 116 95
.300" 161 126
.400" 195 135
.500" 210 138
.600" 208 139
.700" 210 139

Compression ratio: 9.29:1

Camshaft: Comp Cams XS256S solid flat tappet 218/224 @.050 and .465/.477" lift

Intake: Edelbrock Performer 2101 dual plane

Carb: Edelbrock Thunder AVS #1805 650 CFM manual choke

Exhaust: Hooker Competition 2452HKR full length headers w/ hooker full 2.25 inch dual exhaust and 2.25 inch magnaflow straight through mufflers.

I'm looking for around 350 hp and 425-440 lb/ft torque and I hope this motor is capable of that. Please let me know. Thanks for all the help I've had in building this motor and it's getting close to being finished and started for the first time. I really appreciate your advice on this engine although parts changes probably can't happen at this point as I have most of them already installed.

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Old 09-13-2016, 09:41 PM
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Three things I see, 1 5/8 primaries for a cam and heads that are going to give up by 5000-5500 might cost you some low end, gears are too high if your tires are normal 28-30" tires, and no mention of TC stall. With those gears it would need a 3000 dead stall and 3500-3800 flash stall. BUT, it should be really snotty below 3500 with the solid lifter cam and the smallish heads. I think that it would be REALLY snotty with a set of 4.10 gears with 28-30" tires but a screamer at 70 mph. Maybe a compromise of 3.73 gears if you intend to be doing much 60+ mph driving.

I'm assuming the tire size is the tires in avatar?

Looks like a pretty decent build that'll be fun to drive. Hopefully TechInspector will run your info though his dynosim and hit you with some clse numbers, but my guess is 325HP/360-380TQ.
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Old 09-13-2016, 09:52 PM
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Quote:
Originally Posted by 64nailhead View Post
Three things I see, 1 5/8 primaries for a cam and heads that are going to give up by 5000-5500 might cost you some low end, gears are too high if your tires are normal 28-30" tires, and no mention of TC stall. With those gears it would need a 3000 dead stall and 3500-3800 flash stall. BUT, it should be really snotty below 3500 with the solid lifter cam and the smallish heads. I think that it would be REALLY snotty with a set of 4.10 gears with 28-30" tires but a screamer at 70 mph. Maybe a compromise of 3.73 gears if you intend to be doing much 60+ mph driving.

I'm assuming the tire size is the tires in avatar?

Looks like a pretty decent build that'll be fun to drive. Hopefully TechInspector will run your info though his dynosim and hit you with some clse numbers, but my guess is 325HP/360-380TQ.
I ran the numbers through Desktop Dyno 2000 and I got 353hp and 432 lb/ft torque. I will be using stock torque converter and I might change to 3.42 or 3.73 gears with 31/10.50r15 tires. The tires in the avatar are 30/9.50r15 which are actually smaller than 30 in. dia. It will be a daily driver/stored in the garage for long periods of time while I'm away at school.
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Old 09-14-2016, 08:28 AM
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3.55 or 3.73 rear gear would be a great compromise.

Using a measured 29" tall tire at ride height as an example; your 3.08 rear is turning approximately 2500rpm at 70mph. The same tire, and 70mph with a set of 3.73s is going to get you 3,016rpm.

The extra 500rpms, to me...no big deal. If you back your cruise RPM with the 3.73s down to 65mph (I know its hard for you midwest guys to do that in some places) - you'd only be turning 2800rpm. If your tire is a measured 30" tall; you'll drop approx. 100rpm from the numbers I posted earlier.

You have a 5,000LB truck; if you're doing 70 down the interstate....PLEASE put good brakes on this thing.
When you decide what rear axle gears to swap in there (Id go 3.73s); then get a quality torque converter from a manufacturer who asks about your engine, vehicle weight and tire height.
In a couple years, I'd go get me a nicely built 700r4 and custom converter. But thats after the brakes, stereo, seat covers, paint, etc.
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Old 09-14-2016, 11:28 AM
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Those pistons,IIRC,have a 1.54" pin hgt.That is gonna put your quench at approx. .061".That's a bad thing.You will not have any benefits of a proper quench & no detonation resistance.This will also effect your tuning,efforts,power output.You want to shoot for a quench distance of .035" to .045" for best results.You really need to use a taller 1.56" piston.Even cutting the decks to a 9" deck will only get you to .046".
IIRC,that 9.6:1 compression is calculated using a 64cc head & .041" gasket,& @ stock .025" deck.
Using the above specs as planned,your compression will only be approx. 8.9:1. Way too low for that cam.This is gonna be a pretty soggy build,if,you don't make some changes.You won't make 350 HP.

Last edited by jokerZ71; 09-14-2016 at 11:53 AM.
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Old 09-14-2016, 02:42 PM
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Quote:
Originally Posted by jokerZ71 View Post
Those pistons,IIRC,have a 1.54" pin hgt.That is gonna put your quench at approx. .061".That's a bad thing.
According to NorthernAutoParts.com:
DDP Pistons feature:
DDP™ Technology: Digital actuated diamond turning process produces precision skirt profiles.
Barrel profile: Creates an oil wedge between the skirt and cylinder wall.
Thermal Arching Compensation™ (TAC) Ring Groove Geometry: Machined uptilt offsets thermal “arching” distortion; squares the ring face to the cylinder.
Next generation DUROSHIELD® coating: Reduces friction and wear.
Precision-machined pin bores: Accommodate fixed or floating wrist pin installation.

Ring dimensions 5/64, 5/64, 3/16
Flat Top; 4 valve reliefs
Compression dist 1.548"
Deck Clearance .025
Skirt Clearance .0010


If they cut the block, and you're using iron heads; you can used a coated shim gasket most likely. That would get you a quench of approx .051" I do believe. Not horrible; but not great. Ideally you want stock wrist pin height (compression distance).
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Old 09-14-2016, 03:03 PM
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The more recent pistons do have 1.548", but, there is still some older 1.54" being sold.I would definitely measure them.A .015" shim will get him to .042" which will work & have compression in the 9.2:1 range.Still a little weak for that cam, but, it wouldn't be terribly bad.I haven't ran the #'s.If his current deck hgt is 9.015",those pistons will sit approx. .027" with a 1.548" pin hgt,so,a .015 will put him at .042".He basically had .010" cut from the decks to arrive still just above stock .025" deck.

Last edited by jokerZ71; 09-14-2016 at 03:09 PM.
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Old 09-14-2016, 04:38 PM
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That cam will need a higher stall converter than stock. 3000 - 3500 is a good place to start. the cam won't allow an idle below 800-900 rpm and your stock converter will pull the engine down enough to stall out.
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Old 09-14-2016, 06:57 PM
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Quote:
Originally Posted by jokerZ71 View Post
Those pistons,IIRC,have a 1.54" pin hgt.That is gonna put your quench at approx. .061".That's a bad thing.You will not have any benefits of a proper quench & no detonation resistance.This will also effect your tuning,efforts,power output.You want to shoot for a quench distance of .035" to .045" for best results.You really need to use a taller 1.56" piston.Even cutting the decks to a 9" deck will only get you to .046".
IIRC,that 9.6:1 compression is calculated using a 64cc head & .041" gasket,& @ stock .025" deck.
Using the above specs as planned,your compression will only be approx. 8.9:1. Way too low for that cam.This is gonna be a pretty soggy build,if,you don't make some changes.You won't make 350 HP.
I don't mean this sarcastically, but maybe you misread. The block was decked so that the pistons measured .015 in the hole. And they were measured. I knew full well going into this that that would have to be done and as it sits it has a quench of .041"
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Old 09-14-2016, 07:00 PM
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Quote:
Originally Posted by 64nailhead View Post
Three things I see, 1 5/8 primaries for a cam and heads that are going to give up by 5000-5500 might cost you some low end, gears are too high if your tires are normal 28-30" tires, and no mention of TC stall. With those gears it would need a 3000 dead stall and 3500-3800 flash stall. BUT, it should be really snotty below 3500 with the solid lifter cam and the smallish heads. I think that it would be REALLY snotty with a set of 4.10 gears with 28-30" tires but a screamer at 70 mph. Maybe a compromise of 3.73 gears if you intend to be doing much 60+ mph driving.

I'm assuming the tire size is the tires in avatar?

Looks like a pretty decent build that'll be fun to drive. Hopefully TechInspector will run your info though his dynosim and hit you with some clse numbers, but my guess is 325HP/360-380TQ.
Alright so I ran the numbers through Desktop Dyno 2000 and got 353 hp and 432 lb/ft torque

Then I ran them through a more advanced program Engine Analyzer Pro and got 333 hp and 403 lb/ft torque.

My guess is that it would be somewhere in between those two
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Old 09-14-2016, 07:26 PM
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Peak number have never meant very much to me. I look for average HP and Torque between 1500 and the peak HP rpm plus 10%. That average is more important than peak numbers because it tells you what you have when driving and not what you have at peak power that you stay at for a second before you shift.
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Old 09-14-2016, 08:55 PM
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Quote:
Originally Posted by EragonSuperH View Post
Then I ran them through a more advanced program Engine Analyzer Pro and got 333 hp and 403 lb/ft torque.

My guess is that it would be somewhere in between those two
That's pretty close to my guess 325/380. But keep in mind desktop dyno's are just that. I truly expect I'm a little low, but getting that last 10-15 out of the tune AND getting it to daily drive is a demanding task.

If it makes 400 ft/lbs, give or take a little, then it'll be no slouch IMHO. Best of luck - Jim
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Old 09-15-2016, 05:19 AM
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Quote:
Originally Posted by EragonSuperH View Post
I don't mean this sarcastically, but maybe you misread. The block was decked so that the pistons measured .015 in the hole. And they were measured. I knew full well going into this that that would have to be done and as it sits it has a quench of .041"

I did misunderstand. I thought you meant that the block had been decked to .9.015".
With proper tuning & exhaust, I would think you should be close to your goals.

Last edited by jokerZ71; 09-15-2016 at 05:24 AM.
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Old 09-15-2016, 12:16 PM
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In a Vortec headed 350 with 10:1 compression & a 750 carb,GM's Hot cam can knock on the door of 400 HP.It has similar specs @ .050" lift,but,it's wider LSA,& ICL moves it's power band on up the rpm range,along with added lift.Whereas your cam's specs are geared more for low & mid range power.The Hot cam is also a roller.Your heads are decent heads & very comparable to the Vortec L31.The 2.02/1.6 valves are not gonna help your setup that much.They will only help on the very topend & I am guessing your motor is gonna be done by 5200 to 5500 rpm.Set up & tuned properly,I don't see why you shouldn't be able to hit the 350 HP 400 ft/lb mark with what you have.
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Old 09-15-2016, 01:18 PM
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If the Summit heads are Iron Eagle SS castings, the flow may be a little better than EragonSuperH has. From the Dart catalog the flow figures given shown are a little better:
.200” 126 108
.300” 185 128
.400” 221 136
.500” 232 138

The exhaust/intake ratio is .615 at .400 lift and .595 at .500 lift, so the heads could use a cam with more split between the intake and exhaust durations.
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