383 sbc, LT4 HotCam cheap gas question.

[Monzsta]

The back story is I picked up an '89 C1500 truck for a song and the tpi 350 engine is shot. So I'm throwing together a lot of stuff I've had laying about over the years to go in it.

The block is a 70's 4 bolt bored .060 over and has a cheapo Eagle 383 rotator with 5.7 rods, and dished hypers.
The heads are Canfield 195-500-65's which are a 195cc runner with a 65cc chamber. My compression ratio should be in the 9.6 to 9.8:1 territory, it seems to vary depending on the calculator you use.
I've chosen an LT4 GM Hot cam for good durability and torque, and will start out with 1.5 rockers which will give me .492 lift.

Duration @ .050" Lift( Deg): Intake: 218 / Exhaust: 228
Maximum Lift (in) W/ 1.5 Rocker: Intake: .492 / Exhaust: .492
Maximum Lift (in) W/ 1.6 Rocker: Intake: .525 / Exhaust: .525
Lobe Centerline ( deg): 112
IVO 0.5 deg BTDC IVC 38.5 ABDC
EVO 49 deg BBDC and EVC -1.0 ATDC

I'm scrapping the tbi set up and putting on an Edelbrock Pro Flow 3500 manifold running on megasquirt and using 35 lb injectors. The throttlebody is rated at 1,000 cfm and the manifold is a single plane Victor Jr style. Ignition timing will also be megasquirt controlled.

Now I'm worried about pump gas and detonation. This truck will be an all purpose machine for towing and playing as needs arise. I'm at the point of the build where I need to consider how to set the cam. My timing set allows 0, +4 degrees and -4 degrees. Playing with the DCR calculators if I install it straight 0 my DCR is 9.03, but if I retard it 4 degrees that drops to 8.89.

Would you put the chain at -4 degrees and pray to the 87 octane gods, or am I already too far past that and put it at 0 or +4 and go for the 93?

[F-BIRD'88]

Put the cam in as designed and use spark timing judicially to allow running on 87 octane gas. Use better gas if/when hard towing. There is no free lunch.
The cam from the 350 Ramjet motor will be more efficient for towing. 196 ish @ .050". For towing you want torque and efficientcy. Idle to 5000 rpm.

You Re trying to chase horsepower. You want more torque at low mid rpm.

The Long runner 80's Camaro /Corvette Tuned Port Injection EFI system would be good for this purpose.
Big big mid range torque.

Balanced dialed in EGR flow, Afr tuning at steady hyway tow running allows your high cr on 87-91 gas and decent timing.
EGR does what water injection can do at part throttle without the water tank and maintanence.

[dannobee]

Agreed on the egr. Reduced detonation and better fuel economy in cruise.

Doesn't the megasquirt have provisions for knock sensor(s)? They should be on the TPI engine, at the block coolant drain plugs, IIRC.

[dfarr67]

TBI can make power- use the DynamicEFi ecu and you can retain knock and tune with it, also has lean cruise to save a little on the hwy.

[cardo0]

I agree that LT4 cam is not the best choice for a truck used for towing. I use the RamJet 350 cam (#14097395) in my '94 Z28 and it's got plenty of low end torque which burns rubber as much as I care to and more.

You could also use the RamJet 350 intake manifold for torque as the RamJet 350 combination on a stock crate motor 350 makes over 400ft-lbs. I really like that ProFlow intake but it compliments the LT4 Hot Cam more than the RamJet 350 cam. Now the Edel PFT 4 XT looks pretty bad azz.

Even with aluminum heads I think you would need a lower c.r. to use low octane gas. The best way find out is measure the compression pressure. 160psi or less should allow low octane fuel but no guarantee as so many variables at work here. Smooth cylinder head chambers with good swirl and quench will tolerate much more compression than not. Coolant temps have a effect as does intake air temps. What I want to say is there are some thumb rules and guidelines for using low octane fuel but you won't know what you got until you build it and test it. You can look at the GMPP catalog crate motors and read what their truck motors and sporting motors use for compression (and cams). BTW the RamJet 350 cam (#14097395) is used in the GMPP 383 crate motor.
Retarding the cam advance is leaving torque and power on the table. Myself I don't see enough reason to buy good parts and then de-tune them.

[Orr89rocz]

That cam seems to act pretty mild in my experience

I did a 350 tpi car with afr180’s and that cam. It had over 350 lb ft at the tire from 3000 to 4000 rpm and over 300 lb ft from 2500 to 4700

Idles great with efi.

Also did one on a 95 lt1 camaro with tfs 195’s. Very strong to 6500.

Intake makes a big difference the long runner stuff better for trucks and i think it would run fine on 87-89 oct but these cars ran on 93 just cuz.

In a 383 that will help keep that cam acting even more tame. It should work. I have no experience in truck towing but efi will help save you. You got better fuel and timing control available so just work at it

[Monzsta]

The Megasquirt (actually Microsquirt, same same) does have knock sensor provisions, and I'll be retaining the factory distributor and ESC module with it's knock sensor output wired to the Microsquirt. I've had my eye on a J&S Safeguard module for some time and I don't mind getting one if necessary. We'll see how the tbi knock sensor likes the roller cam with link bar lifters.

I was hedging my bets a bit with the hot cam, as I had seen a few 500 ft/lb 383 builds and figured it would be ideal as a truck cam in a 383. Dyno graphs of the hot cam show an impressive torque table with a lot of meat under the curve, and just a tickle of a cam at idle but with good vacuum.

I plan on gearing this truck fairly aggressively with a 4.56 and a truetrack, That deep a gear is the only hope for the 700R4, besides the best build I can put in it. I'm also a fan of the characteristics of using V6 torque converters behind V8's. They're inexpensive and you retain the good low end pull and the same diameter lock up clutch. They just stall a tad higher than the factory. Lock up will also be mapped to the Microsquirt.

I should be able to get the heads on and wire up a starter for some cranking compression numbers as soon as my valve springs show up. Lost one, now I had to buy another 16. Gah.

[dfarr67]

I cannot give you part numbers but there is a ESC module that is a little more forgiving- computer carb model I think for noisey engines and I also have the hotter GM small cap HEI module for a bit more zip.
What does the V6 converter stall at? I am just ordering a owm reman at 2400.

[Monzsta]

I cannot give you part numbers but there is a ESC module that is a little more forgiving- computer carb model I think for noisey engines and I also have the hotter GM small cap HEI module for a bit more zip.
What does the V6 converter stall at? I am just ordering a owm reman at 2400.

Depending on the torque of the new engine you can see 600-1,000 rpm increase over the oem converter. I have a relatively stock '98 Trans Am LS1 and with a trailblazer L6 converter it was stalling around 2400-2600. I tried the same with a Chevy Lumina I put a 3400 V6 in place of the 3.1 v6. I went for a 1.8 Pontiac Sunbird torque converter which stalls at 2,000+ behind the 4 banger, The 3400 ran that up to 3700 rpm stall and scared me the first time I stepped in it. I thought the transmission was slipping. The OEM's were wise to this trick and did it too. The first SRT-8 Jeep used a torque converter straight from the either the 3.5 or the 3.7 v6 behind the 6.1. Didn't even bother to change the part number.

Looking across the truck and 3rd gen boards the 4.3 "S10" converter generally will put a stock tpi/vortec motor in the 2300-2600 stall range. You just need to make sure what you're borrowing from has the same spline count.

[CamKing]

Because you're going with a 383ci, that cam will be a good choice.
The seat duration on the GM HotCam, is 273/281. In a 383ci, this 273/281 duration cam will have the same power band as a 264/272 seat duration cam in a 350ci engine. It'll peak HP around 5,300, and be great for towing.

As for fuel requirements, with the HotCam degreed in on a 110 ICL, and your aluminum heads, you should be fine running 87 octane with 9.6- 9.8:1

[dfarr67]

Well, my application isn't competition, I simply cannot justify spending big $$ on a name brand and I just get the feeling the value for me isn't there, some industry segments offer a $1000 part that really is worth $300. Regardless the us$ kills me in the end. I'm putting my faith in a builder who can combine oem parts to get where I want in a sbc LT 700R/4L60E application. I tend to over think things.

[Monzsta]

Just an update, got this thing together and in the truck. Finishing up some wiring before it runs, spun it over checking the microsquirt signals and stuck the compression gauge in it.

With a half dead battery this hit 195 psi in about 5 slugs before the battery gave up. I am worried about my 87 octane ambitions. It hasn't even ran yet to seat the rings.

[1980RS]

The LT4 Hot cam is a very good versatile cam. Has good street manners and will pull very easy to 6500. I had one in my street car and with a T-56 I thought it was bucking because of the cam having too much duration, it turned out to be a bad Eddy 600 that was too lean at part throttle. My 750 Holley street HP VS carb took care of that problem.

[Monzsta]

So I got stymied by my angle plug heads and the Hedman headers I nabbed for this truck. The tube on the passenger side for #2 cylinder is all over the #4 and #6 plugs. Tons of room topside So I'm going to haul it out of there and cut and remake that tube to go over the bundle instead of under and save myself grief in the future.

Just on a whim, I had the plug wires laced for the driver's side, and really wanted to hear it run. "It'll never start," I thought as I turned the key. A couple of revolutions and it lit off and settled into an even idle! On four cylinders! I was amazed, and it sounded wicked the few seconds I let it run. I did a leak check and fired it again, this time touching the throttle a few times. The throttle response is amazing, considering only half the engine is running, I haven't even set the timing yet or even hooked up a wideband. Just running off Tunerstudio's default settings for CId and injector size.

This thing is going to be nuts on all 8.

[Monzsta]

Okay, I've got the truck running decent. Have to chase the old owner down to get the title notarized and get my tags so I can drive it legally on the street, so I've just been pootering around the property. With the stock converter this thing just rocks this truck. It idles at 700 easily with a very slight lope and throttle response is immediate. It'll even sit happily in drive, with the lights and a/c on. The vacuum brakes are pretty good, probably would be a bit better with the idle at 750 or 800. Can't wait to get some road miles on it.

Now I put 1.5 rockers on this, and I'm wondering if putting 1.6's on later on will compromise my near OEM idle and throttle response. I still have some tuning to do. I