Off Road 383 Stroker Buildup!

[Sandytheman]

Hey there everyone, I am gathering parts for a 383 project 4X4.
I am looking to generate approx 450 ft of torque off idle and as much hp as possible at around the high 3000 to mid 4000 prm range.

Currently I am using a 4 bolt main block
Decked 0.005 and bored 30 over.
Custom internally balanced Scat Crank
6" Scat 4043 Rods
KB Hypeuratic Pistons with offset pins
Edelbrock Performer intake
Holley 650 Truck Avenger Carb
Total Seal Gapless Rings

I am curious what Heads and Cam you guys would sugggest I try. I have my own ideas but would just like some input. First engine I have built specifically for an offraod 4X4,

I am considering the AFR 190 cc street/strip head and a extremelly mild cam with a tight lobe center angle, about 106 or 108 degrees.

The truck still has to be streetable everday.

Thanks

[ou812]

For off idle torque you will need a smaller runner head. afr has a 180 head that would work good, and yes tight lobe center will work good too. I suggest Comp cams exteme engergy 262 cam on a 108 or the 268 cam on a 106. Will idle rough though!!
Brian

[Sandytheman]

I will check out those 180cc heads for sure. And I was on the right track with the cam to I guess. I'm pretty new to this engine building thing. I havn't built anything for low rpm power yet. So any more info anybody has would really rock.

thanks

[OldSStroker]

Hey there everyone, I am gathering parts for a 383 project 4X4.
I am looking to generate approx 450 ft of torque off idle and as much hp as possible at around the high 3000 to mid 4000 prm range.

Currently I am using a 4 bolt main block
Decked 0.005 and bored 30 over.
Custom internally balanced Scat Crank
6" Scat 4043 Rods
KB Hypeuratic Pistons with offset pins
Edelbrock Performer intake
Holley 650 Truck Avenger Carb
Total Seal Gapless Rings

I am curious what Heads and Cam you guys would sugggest I try. I have my own ideas but would just like some input. First engine I have built specifically for an offraod 4X4,

I am considering the AFR 190 cc street/strip head and a extremelly mild cam with a tight lobe center angle, about 106 or 108 degrees.

The truck still has to be streetable everday.

Thanks

450 torque off idle? No chance. 450 @4000 good chance, but max hp will be higher than 4500. GM's HT (High Torque) 383 crate engine gets 435 lb ft @ the flywheel at 4000, but needs to get to 2500 before it gets 400. It gets 340 hp @ 4500. This is with Vortec heads and a 196/206 @ 109 cam with .431 and .451 lift.

On the other hand. The ZZ383 gets 449 lb-ft @ 4500 and 425 hp @ 5400. It uses Fast Burn heads and an 846 cam and a 750 Demon.

What do you have against a nice flat torque curve from say 2400 to 5500? That's about the same rpm spread as off-idle to high 3s mid 4's and it gives you about 20-25% more torque multiplication thru gearing.

Depending on your cost, Fast Burns and a custom cam might get you pretty close to where you want to be if you forget the 450 off-idle. If you have a self-imposed (and chipped) rpm limit of say low-mid 5s, the cam could be SHORT but quite aggressive, idle like a sleeping baby and pull from under a 1000 rpm. Would that, along with appropriate gears, be ok?



My $.02.

[Sandytheman]

I want alot of low end torque (off idle) because I am turning 46" tires under a 79 chev half ton. I am mostly building the truck for mud, deep mud. In deep mud its real hard to keep the revs high enough with a engine, especially a small block to keep going. I don't want a big block which would solve most of my problems because in the mud they just get to heavy and don't cool very well in my experience.

I have built a few decent 383 strokers before. All for high revs, 6500, 8000 rpm. On the dyno I have recoreded real high numbers in the high end range and low end range, none of which has been quite what I want in my new 4X4. A 383 put together like a strock 350 with a 400 crank produces around 360 fooot pounds of torque off idle. Assuming idle is in the 700 rpm range, Different from a drag car I don't need the torque at launch I need it at idle. A race car launches at 3000 rpm or more. In mud you are not, your just moving along at a steady speed.

I have seen the numbers that I want in a 350 before so I know that I can produce them with a 383. So its not that I am against a nice flat torque curve or anything it is that I want to be able to produce a truck capable of going through, or over anything in my way. an i need the torque to do it.

[OldSStroker]

I want alot of low end torque (off idle) because I am turning 46" tires under a 79 chev half ton. I am mostly building the truck for mud, deep mud. In deep mud its real hard to keep the revs high enough with a engine, especially a small block to keep going. I don't want a big block which would solve most of my problems because in the mud they just get to heavy and don't cool very well in my experience.

I have built a few decent 383 strokers before. All for high revs, 6500, 8000 rpm. On the dyno I have recoreded real high numbers in the high end range and low end range, none of which has been quite what I want in my new 4X4. A 383 put together like a strock 350 with a 400 crank produces around 360 fooot pounds of torque off idle. Assuming idle is in the 700 rpm range, Different from a drag car I don't need the torque at launch I need it at idle. A race car launches at 3000 rpm or more. In mud you are not, your just moving along at a steady speed.

I have seen the numbers that I want in a 350 before so I know that I can produce them with a 383. So its not that I am against a nice flat torque curve or anything it is that I want to be able to produce a truck capable of going through, or over anything in my way. an i need the torque to do it.

What you need is torque at the tires. There are a couple of ways to get that. Gobs of engine torque at low rpm. Think CAT diesel. Otherwise, a decent amount of engine torque at a moderate rpm and throw gear and/or torque converter at it. The dumb tires don't know how the torque got there. Also, a flat torque curve from 2400 or so up gives you nice control of wheelspin.

This must be a manual trans because no automotive torque converter that I know of stalls at 700-800 rpm. What would be the problem with an auto? It seems that a torquey 383 with a 2200-2500 stall and 2.0+ multiplication ratio would be just what you need, or maybe too much! As the tires bog down the torque multiplication factor goes up. Again, just what you need, right?

I don't understand why you are running the engine so slowly if it's a manual trans. Just doubling the overall gear ratio would get you to 1400+ rpm and double the torque to the tires plus. Shoot, if you are using 700 and up to crawl along in your lowest gear, you might need to triple the gear ratio.

At 5 mph and 800 rpm, your overall gear ratio is about 22:1. If you actually get 350 lb ft at 800 engine rpm, you have 7700 lb-ft at the tires. If you triple the overall to 66:1, the rpm goes to 2400, the engine torque might be 450 and the torque at the tires would be 29,700 lb-ft., or almost 4 times as much. That's about 15,000 lbs of thrust at the tires, BTW.

If you are talking 10 mph at 800, cut those numbers in half.

FWIW, most non-diesel transmissions are not rated for their max torque at very low (off idle) rpms. 450 lb-ft at 800 would be tough on any GM manual (non-diesel) truck trans I'm familiar with.

Good luck.

[Sandytheman]

I am using a custom rebuilt chev 400 transmision built by a personal friend of mine and he has never let me down. I told him what I wanted and he said he could do it. I am not a slight bit worried about the tranny.

I am using a dual transfer case setup with an Np203 and an Np205 with some internal work done by Pats Driveline to achieve a very low 6:1 gear ratio or a 4:1 or a 1:1.96 ratio.

In my experience the math that one uses to figure out torque to the wheels is not often acurate. I have been told time and time again on different projects that I don't need that much torque at the flywheelat that Rpm. I don't have an engine dyno in the town that I live in, I have a roller dyno and have never seen any accuracy in the math. The drive line in my 4X4 is not a car driveline, it is all custom for strenght and it is heavy. This means more loss along the way and I have seen numbers cut in half on the dyno in comparison to what the figures actually say they should be when you do it on paper. I think I will lose alot of torque through the dual transfercase setup, I have never used one before so I guess I cannot be sure.

If I cannot keep the tires doing what I want them to do then I can do an intake and cam change and change the torque range in a couple hours I guess.

I guess I am being pretty stubborn on this issue but I feel that all of the other offroad vehicles I have built or been in have never had enough torque to keep going. This truck is never going to go over 65 Mph so I want everything I can get out of it at the bottom end.

[OldSStroker]

I am using a custom rebuilt chev 400 transmision built by a personal friend of mine and he has never let me down. I told him what I wanted and he said he could do it. I am not a slight bit worried about the tranny.

I am using a dual transfer case setup with an Np203 and an Np205 with some internal work done by Pats Driveline to achieve a very low 6:1 gear ratio or a 4:1 or a 1:1.96 ratio.

In my experience the math that one uses to figure out torque to the wheels is not often acurate. I have been told time and time again on different projects that I don't need that much torque at the flywheelat that Rpm. I don't have an engine dyno in the town that I live in, I have a roller dyno and have never seen any accuracy in the math. The drive line in my 4X4 is not a car driveline, it is all custom for strenght and it is heavy. This means more loss along the way and I have seen numbers cut in half on the dyno in comparison to what the figures actually say they should be when you do it on paper. I think I will lose alot of torque through the dual transfercase setup, I have never used one before so I guess I cannot be sure.

If I cannot keep the tires doing what I want them to do then I can do an intake and cam change and change the torque range in a couple hours I guess.

I guess I am being pretty stubborn on this issue but I feel that all of the other offroad vehicles I have built or been in have never had enough torque to keep going. This truck is never going to go over 65 Mph so I want everything I can get out of it at the bottom end.

OK, the THM 400 has a 2.48 first gear. With your 6:1 "granny" 4.56 final drive gears would give you about 66:1 overall or 2400 engine rpm with NO Converter slippage @ a 5 mph crawl. Even with a "tight" 12 or 13 inch conveter, and a 383 built for low end torque, there will be some slippage and torque multiplication at full throttle. Lets say 400 rpm so you are up to about 2800 rpm. That's possible for 450 lb-ft.

With no converter multiplication, and 50% losses in the trans, transfer case and final drive, you still have about 15000 lb-ft at the tires. That's over 7500 lbs. of force at the tire contact patches.

If that isn't enough, throw in a converter that stalls above 2400. Now there is still more engine torque multiplied by the TC ratio, say 1.33 to be conservative. You are geting closer to 10,000 lbs of force at the tires still figuring 50% losses.

Now if that isn't enough, go to 5.13 gears and you have twice as much force at the wheels as the truck weighs and a speed range up to about 10 mph in the lowest gear, and 25 mph without shifting the transfer case.

Lots of numbers, but it all assumes you run the 383 at rpms above 2400 where it's possible to get a decent amount of torque. 500 lb-ft at the flywheel isn't diffcult at a reasonable rpm, say 4000.

I've beat this horse until it's nearly dead. Sorry.

Good luck.

[Sandytheman]

ok, i'll let you know when I get it done then.

thanks