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Old 04-26-2011, 04:34 PM
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low end torque and low compression

I'm building a new engine for my airboat and need some help, I'm building a 389ci, 350, 60 over flat tops, 5.7 rods, 400 crank all ballanced 4 bolt main. My question is I need a good set of heads for the most low end torque at 3200 rpm what stock heads will produce massive low end and not alot of compression, i have a set of 462624 cast heads and need some advice , please help.

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Old 04-26-2011, 04:56 PM
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The tbi heads are good for torque at low rpm, I would not even think about using those 624 heads. You can keep them to practice porting on or scrap them. Vortec heads would be another good option.
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Old 04-26-2011, 05:36 PM
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Quote:
Originally Posted by blowboatjunky
I'm building a new engine for my airboat and need some help, I'm building a 389ci, 350, 60 over flat tops, 5.7 rods, 400 crank all ballanced 4 bolt main. My question is I need a good set of heads for the most low end torque at 3200 rpm what stock heads will produce massive low end and not alot of compression, i have a set of 462624 cast heads and need some advice , please help.
191 or 193 TBI Swirl Ports.

Bogie
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Old 04-26-2011, 06:48 PM
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A 389 with RHS 170 heads, 1.94"/1.50" valves, 10.0:1 static compression ratio, 1 3/4" headers with no mufflers, RPM intake, 600 CFM carb, CompCams solid flat tappet cam 12-607-5 will make 465 ft/lbs @3200. With stepped-tube race headers and cam advanced 2 degrees, she'll make 485 @3200.

Last edited by techinspector1; 04-26-2011 at 06:59 PM.
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Old 04-26-2011, 06:49 PM
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low end torque and low compression

are these heads easy to come by or are they scarce, what did they come on stock. I guess i need to explain what i need, I'm running a direct drive boat no gear box, so i need to produce the most torque i can up to 3200 RPM, i think i have a great bottom end structure so far. I talked to Scott at Comp Cams and give him the run down on my setup and he wanted to know what heads i was using and i realy couldn't give him an answer, so he told me to call him back when i find out what heads i'm using and he can grind me a custom cam to fit the application to make a high torque machine. I have a Edlbrock performer dual plane intake and a 600 holley carb. all i need is a good set of heads. Where could i find some heads without breaking the bank.
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Old 04-26-2011, 07:02 PM
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The 191/193 TBI swirl port heads are common- and the good part is, most guys wouldn't run them if they were free- so cost will be minimal. Check craigs or ebay or your local machine shop/cylinder head exchange. These heads have the '87-up 72º center intake flange bolt angle so the intake will need modified to fit them if you have the early style '86-back 90º bolt angle intake.
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Old 04-26-2011, 07:29 PM
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Quote:
Originally Posted by blowboatjunky
are these heads easy to come by or are they scarce, what did they come on stock. I guess i need to explain what i need, I'm running a direct drive boat no gear box, so i need to produce the most torque i can up to 3200 RPM, i think i have a great bottom end structure so far. I talked to Scott at Comp Cams and give him the run down on my setup and he wanted to know what heads i was using and i realy couldn't give him an answer, so he told me to call him back when i find out what heads i'm using and he can grind me a custom cam to fit the application to make a high torque machine. I have a Edlbrock performer dual plane intake and a 600 holley carb. all i need is a good set of heads. Where could i find some heads without breaking the bank.
They're not OEM heads.
CompCams makes the DynoSim software that I use to put combinations together. They also make the low-buck cast iron RHS heads.
Chevy 383
Bore 4.060"
Stroke 3.750"
Rod length 5.703"
RHS GM Vortec Pro Torker 170/?? (chamber depends on your piston configuration), 1.940"/1.500" valves.
Flow numbers factored as follows:
0.100 67 56
0.200 136 108
0.300 198 138
0.400 245 151
0.500 254 156
28" water
10.0:1 static compression ratio
600 CFM @1.50" Hg
Dual-plane max flow (Edelbrock RPM)
Large, stepped-tube race headers (1 3/4")
12-607-5 Comp solid flat tappet cam, advanced 2 degrees
RPM HP TQ
1000 39 204
1500 99 345
2000 160 419
2500 216 454
3000 275 481
3200 295 485
3500 328 492
4000 376 494
4500 420 490
5000 452 475
5500 455 435
6000 404 354
Peak volumetric efficiency 92.1% @5000
Peak BMEP 191.6 @4000
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Old 04-26-2011, 08:00 PM
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Quote:
Originally Posted by techinspector1
They're not OEM heads.
Tech, I believe he was asking about the TBI heads, note the post times between #4 and #5.

EDIT- In any event, the "191" or "193" heads are factory production heads used on 5.7L TBI truck engines, ca. '87-'95.

The "RHS 170" heads referred to above are aftermarket heads sold by Summit, Jegs, etc.

Last edited by cobalt327; 04-26-2011 at 08:11 PM.
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Old 04-26-2011, 08:17 PM
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Quote:
Originally Posted by techinspector1
A 389 with RHS 170 heads, 1.94"/1.50" valves, 10.0:1 static compression ratio, 1 3/4" headers with no mufflers, RPM intake, 600 CFM carb, CompCams solid flat tappet cam 12-607-5 will make 465 ft/lbs @3200. With stepped-tube race headers and cam advanced 2 degrees, she'll make 485 @3200.
That's an impressive low rpm torque # from a small block ! I run a direct drive caddy 500 on my boat. .030 over 10:1 comp cam custom grind , awesome torque !
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Old 04-26-2011, 08:46 PM
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Quote:
Originally Posted by sidejobs
That's an impressive low rpm torque # from a small block ! I run a direct drive caddy 500 on my boat. .030 over 10:1 comp cam custom grind , awesome torque !
You think THAT is good- check out the 0.060" over 283 500+ HP 292 CID “build”- 283 performance engine build post #21. One HP per ci and 385 ft/lb torque @ 4000 RPM. Peak 525 HP at 7500 RPM.
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Old 04-26-2011, 09:15 PM
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Quote:
Originally Posted by cobalt327
Tech, I believe he was asking about the TBI heads, note the post times between #4 and #5.
Thanks Cobalt, I understood that, but he's not gonna make the kind of torque he's looking for with production heads. That's why I moved on to aftermarket heads to show what could be done. They're cast iron and they're relatively cheap.
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Old 04-27-2011, 08:23 AM
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low end torque and low compression

Thanks guys for all the help, you have helped me more than you know, I have the information i need to start my search, I will let ya'll know how it turns out.
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Old 04-27-2011, 08:55 AM
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Quote:
Originally Posted by techinspector1
A 389 with RHS 170 heads, 1.94"/1.50" valves, 10.0:1 static compression ratio, 1 3/4" headers with no mufflers, RPM intake, 600 CFM carb, CompCams solid flat tappet cam 12-607-5 will make 465 ft/lbs @3200. With stepped-tube race headers and cam advanced 2 degrees, she'll make 485 @3200.
As impressive as that is, he needs a torque peak at about 1800-2000 for an airboat. His top RPM will be about 3500 unless he's running a reduction gear, and even then he'll top out at 4500.

I think a production TBI type setup might work well. He'll get better power and torque if he does something like vortec heads or s/r torquers, and I would suggest a cam with a little less LSA than the factory cam, but I think 250-275 hp at 4500 is a good target.
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Old 04-27-2011, 09:10 AM
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air boats are just like water boats in the respect that the prop pitch determines your rpm range more so in air/water boats that use a 1:1 drive ratio.

the more hp you run the more prop you can effectively run at any given rpm.

air boats are a bit more complex when it comes to prop selection but follow the same theory.

so in short make sure your prop if you currently have one, matches your engine build or buy a prop after the fact as 460ish hp may over-speed the hull if your not careful with your selection.
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