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Discussion Starter · #1 · (Edited)
Ok, after 3 or 4 years I'm back with more camshaft questions.

Vehicle:
1992 Chevy SWB standard cab
The truck has 3.42 or 3.46 differential...not sure which but one of those.
It's running a 700R4 transmission

Here's my engine in a nutshell:

It's a 1998 Vortec 350 that I've converted from fuel injection to Carburetor.
650 Edelbrock AVS2 carb
Edelbrock Performer Intake
Stock vortec heads with valve guides machined to allow for a higher lift cam
Long tube headers with dual flowmaster exhaust
Flat top pistons with 2 valve reliefs for a compression ratio of approx 9.4:1

The Cam:
Erson E119703
Grind: RH-272-320-1
LSA: 112+4

Figures at .050"
Overlap -2
Duration Int/Exh: 218 / 226
Lift: Int / Exh: .480 / .480

The crank timing gear is one that'll allow for -4, +4, and 0 degrees of cam advance. It is set on the "0" keyway

Now, this thing doesn't perform anywhere near how I expected it to. It idles with a slight lope that disappears as soon as you touch the throttle. That was expected when I had someone spec the cam for me. It simply does not make much in the way of power. It'll turn hard and will move the vehicle easily but is doesn't even seem to have the power of a stock 305, much less a 350. I was hoping to get about 350 crank HP from it but I know it's not making that kind of power. I had a Q-Jet on it and it ran out pretty good but the thing was worn out to the point of a vacuum leak around the throttle shaft so, after speaking with many people, and a few at summit and jegs, I landed on the edelbrock 650. I was going to get a holley 750 but caved to people I thought might know better than myself.

So, can someone tell me which direction to take to wake this thing up? New cam with different grind, bigger carb, what??

Thanks for any advice.
 

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Discussion Starter · #3 ·
What’s your timing curve like?
Initial?
Mechanical?
Not sure. There is mechanical in the distributor and I've tried the vacuum advance on full intake vacuum and the "metered" vacuum port. Neither really make much difference in overall power. I've got it set to 12 degrees at 600 RPM with no vacuum advance.
 

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That cam should make 300 horsepower all day at a minimum. Something is wrong with your tune.

Base timing + mechanical advance = total timing. Answer RWE nuts question with those 3 numbers. Do you know how to determine these 3 numbers?
 

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Discussion Starter · #6 ·
And what do you have for a fuel pump?
Hopefully not the stock in - tank one!
Do you have a fuel regulator set at 5 psi?
It has the original fuel pump in the tank that drove fuel for the TBI unit that used to be on the truck. I've installed a pressure regulator with a return line and it's set to 6 PSI. I'm pretty sure that a fuel pump capable of 12-16 PSI can feed a barely more than stock 350.

The engine doesn't seem to be starving for fuel. If you stay in the throttle, it will climb past 100 mph. It just doesn't have anywhere near the power I expected it to have. If you're doing 35 and stomp it, it'll downshift but not really set you back in the seat much at all but it does get going. It did seem to buck and pull harder with the Q-Jet carb than with the edelbrock.

As to your timing curve question earlier, I set it to 12 degrees at 600 rpm without vacuum advance. With a timing light, I can gradually increase the throttle and see the timing mark move way up past the end of the degree plate next to the balancer. My neighbor, who has built and driven race cars for almost 40 years, used his timing light to check total timing and said it's about 35 or 36 degrees when maxed out. I don't remember what RPM that occurred but he didn't seem to think there was anything wrong with the way the timing was acting.

I'm at a loss. The engine, when in the 98 Suburban had great torque and would accelerate that huge vehicle like it was a car. I understand that it was computer controlled then but it also had over 200,000 miles on it. I went through it with new pistons, rings and other rebuild necessities. It has great compression and runs great. It just doesn't make the kind of power that I think it should make. I've driven 325 HP trucks many times and this one definitely is NOT in that league.

thanks for your respons
 

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The cam you selected is really intended to run with EFI rather than a carburetor. The lack of much overlap in the timing combined with a lot of ramp between .050 and zero lift makes the cam react at low speeds like it has a late to close intake which bleeds cylinder pressure while the lack of overlap provides high idle vacuum but poor top end. But all that said this is a near relative to the LT4HOT in timing and ought to do better if it is a cam issue.

Your build specs certainly say this should be 370 to 400 horse with similar numbers at peak torque. which leads into knowing exact specs of the build including piston part numbers, head gasket used and actual squish/quench distance from piston crown to head deck.

I’m somewhat surprised this idles at only 600 RPM, is that hot and in gear or in neutral/park.

You can’t discount that if this is an old 700R4 that it is going out and loosing input power internally. A frisky fresh engine can tear up an old automatic pretty easily.

I run a HOT cammed 350 and have built quite a few, they all liked about 18 to 22 degrees of advance at idle at sea level, you can split that up with base and vacuum. I mostly do that with 12 to 16 degrees in static base and 10 to 6 in adjustable full time vacuum. This is with aluminum heads. I also run the Edlebrock AVS which is richened up one jet size front and rear with this combination, everything else being as Edlebrock built it.

Bogie
 

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Discussion Starter · #10 ·
The cam you selected is really intended to run with EFI rather than a carburetor. The lack of much overlap in the timing combined with a lot of ramp between .050 and zero lift makes the cam react at low speeds like it has a late to close intake which bleeds cylinder pressure while the lack of overlap provides high idle vacuum but poor top end. But all that said this is a near relative to the LT4HOT in timing and ought to do better if it is a cam issue.

Your build specs certainly say this should be 370 to 400 horse with similar numbers at peak torque. which leads into knowing exact specs of the build including piston part numbers, head gasket used and actual squish/quench distance from piston crown to head deck.

I’m somewhat surprised this idles at only 600 RPM, is that hot and in gear or in neutral/park.

You can’t discount that if this is an old 700R4 that it is going out and loosing input power internally. A frisky fresh engine can tear up an old automatic pretty easily.

I run a HOT cammed 350 and have built quite a few, they all liked about 18 to 22 degrees of advance at idle at sea level, you can split that up with base and vacuum. I mostly do that with 12 to 16 degrees in static base and 10 to 6 in adjustable full time vacuum. This is with aluminum heads. I also run the Edlebrock AVS which is richened up one jet size front and rear with this combination, everything else being as Edlebrock built it.

Bogie
I didn't realize it was for EFI. The person who balanced this engine is the same one who ordered my cam. He knew everything he needed to know to order the cam. He knew I was putting a carb on the engine. He's built race motors for many different drivers for 35 years so I trusted his "know how".

The engine idles fine at 600 - 650 and doesn't stumble or stutter when you put it in gear, but it will lope a bit more as the RPM is pulled down a bit. As far as the tranny, It was just completely rebuilt and upgraded internally to corvette parts where applicable. I guess the first thing for me to try would be to advance the timing a bit. I did try a little more advance and it started kicking back when you try to start it hot.

Thank you for your input
 

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Interesting that it kicks back on a little more advance, compression way higher than you think it is or the cam not as aggressive as it’s thought to be. Bigger cam lopes till it gets some RPM built up, the cam you have should have an authoritive idle not stagger drunk rough but barky. Don’t get me started on “built“ transmissions, there‘s more cheating in that industry than voter fraud in American elections.

On paper nothing about your build jumps out, it should have good torque and power even rationed against the weight in a full size pickup. One thing not discussed is tire size. Large diameter tires remove gear ratio.

Bogie
 

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Does the engine seem to pull better the higher the rpms go? That cam should be starting its power band around 2000 rpm. Did you degree the cam when you installed it? Is the torque converter stock stall speed?
 

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Discussion Starter · #14 ·
Interesting that it kicks back on a little more advance, compression way higher than you think it is or the cam not as aggressive as it’s thought to be. Bigger cam lopes till it gets some RPM built up, the cam you have should have an authoritive idle not stagger drunk rough but barky. Don’t get me started on “built“ transmissions, there‘s more cheating in that industry than voter fraud in American elections.

On paper nothing about your build jumps out, it should have good torque and power even rationed against the weight in a full size pickup. One thing not discussed is tire size. Large diameter tires remove gear ratio.

Bogie
Well, as for the compresssion, I figured it all up when buying pistons and I kept it as close to 9.4:1 because with iron heads that's about as high as you'll want to go and still be able to run 87 octane gas.

The cam was purchased from a company in Louisville, KY that specializes in custom ground cams. The fellow that balanced my rotating assembly ordered it for me based on everything I told him we had and wanted to do. It's not an agressive cam as far as loping. It barely lopes at idle when warm and the lope disappears as soon as you touch the throttle.

The transmission was rebuilt by someone I trust. They've been doing it for almost 40 years and he basically took me on a tour of my transmission after he got it took apart pointing out where things failed and where upgrades would benefit. He's pretty good at what he does. It shifts very firmly and holds great. I think it's the real deal

As for the tires, they're actually smaller than original. They're a bit on the low profile side.

Again, I'm at a loss as to why it's sucky. Probably the weak side of "if you built two identically you'd have one that'd run like a scalded dog and one that'd run like ****". I think this one runs like ****. lol

Thanks
 

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Does the engine seem to pull better the higher the rpms go? That cam should be starting its power band around 2000 rpm. Did you degree the cam when you installed it? Is the torque converter stock stall speed?
My thought went to cam degree'd position as well....symptoms point in the direction of retarded installation.

Wouldn't be the first time a mismarked or mismachined timing set showed up. It's gotten to the point you better degree the cam with a degree wheel even on stone stock rebuilds.
 

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Perhaps you've done all of these items, but when I've been at your point I start at the beginning so as to not overlook anything stupid that costs me alot of time and money.
  • verify TDC, base timing and all in timing degree and rpm - safe all in is 34 degrees at 3K rpm
  • compression test hot - should be well over 165psi with that cam and shouldn't be over 185psi
  • verify full throttle and proper secondary operation - I know nothing of your carb - good luck there, others here will know
  • verify correct vacuum readings with a gauge inside the car while driving
  • verify transmission line pressure with a 250+ psi gauge - if you don't know what they're supposed to be, then ask and you'll receive answers
  • degree the cam

If you find any issues along the way, then of course correct them. And no matter what, I would verify trans line pressures only for the reason of making your 700 live a long time.

Good luck - I've felt your pain before - it drives me nuts until I figure it out lol.
Jim
 

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As a point of comparison, my old pickup's engine uses a 97 block and new GM Vortec heads with a RamJet 350 cam (196/206, 109 lSA). It has 1.6 rockers on the intake side (for .460"/.451" lift), and LS6 valve springs with Comp retainers and locks installed at 1.750" . Compression is around 9.3:1. It has a 600 cfm VC Holley and 1-5/8" long tube headers with 2-1/4" exhaust pipes. So. I'm thinking around 350 flywheel HP based on GM specs for the Ramjet engine. Mufflers are 20" Dynomax. No cat converter. Ignition timing is around 14 initial, 34 total, 10 degrees vacuum. Trans is a TH350 with a TransGo 1&2 kit using the Tow & Go parts (firmer, but not harsh shifts).

Not exactly a high performance build, but even with the tall axle I am pleased with the performance. Lots of torque at low-mid RPM, and the truck moves really well when stomping on the gas and downshifting to 2nd. It will spin the tires in 1st gear, and I expect it would do the same on the 1-2 shift if it had a 3.23-3.42 axle. The truck will surprise drivers who may be thinking, "Oh crap, now I've got to get around this old truck that just pulled out from a side street."
 

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me also needs to consider that the cam that was delivered may not math the specs that were ordered. It happens , actually often enough that if you build performance engines much you find yourself setting up V blocks, a degree wheel, and dial indicator to check out the actual timing and lifts against your specs before even sliding the cam into a block.

In your case of multiple ways to set up the timing set there is always a risk of getting these things off or of the parts being machined off. That’s the next cam check to be done which is to repeat the V block inspection in the block with the timing set attached. You will find that as the inclusion of performance parts goes up (this especially points to the timing set, cam shaft, valve train, and ignition timing) the engine’s sensitivity to small inaccuracies greatly increases. Errors with a cam designed for 300 horses from a 350 are hardly noticeable, the same error when shooting for 350, 400 and more creates big to way bigger problems. This being a reason I ask for specific specs that fall out of these assembly inspections because the accidental inclusion of small errors each by themselves cause unexpected problems or performance results but when a few combine it all can go crazy.

Frankly I stay away from custom cam grinders for engines not being built for specific competitions. There are so many mainstream cam makers and so many combinations have been tried and tested that for the average guy building a street performance engine this is just time and money wasted and has great potential for unnecessary problems both technical and financial. The cam you bought is basically somebodies copy of the GM LT4HOT cam to and for which there besides GM is a zillion big name cam grinders cranking these things out by the thousands. It’s popular cam that works very well for a street performance engine, even I run one from GM, my personal motor is most similar to yours and a recipe I used a lot back in my “professional” days, that just flat works. I run nothing super special the timing set is an SA Gear double row roller for the factory roller block, the cam came from Scoggin Dickey, the lifters are stock GM, pushrods are for an LS 3 as a cheap way to get the length I needed without spending the money on custom length pushrods, the rockers are Ebay cheap aluminum 1.6 rollers, the heads are coolant modified LT1 with 53 cc chambers, the pistons are Keith Black. I run an SCR of 10.7 a DCR of 9.8 which is a calculated average of closing between point oh-fifty and zero, with a .045 inch squish/quench. The intake is the GMPP, LT1/4 spread bore 4 bbl, high rise with an Edelbock AVS, ignition is a dog house ProComp small cap HEI and their external coil. There is nothing magic going on except for the external coolant returns; it really is a pretty basic set up that works alarmingly well and has required little maintenance. Except for the heads and intake this is basically my Gen I, SBC go to for moderate street performance builds. Lots of torque and power, great reliability, minimum continuing maintenance, decent fuel mileage, a lot of fun to drive for the cost.

But as always the devil is in the details.

Bogie
 

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Discussion Starter · #19 ·
Perhaps you've done all of these items, but when I've been at your point I start at the beginning so as to not overlook anything stupid that costs me alot of time and money.
  • verify TDC, base timing and all in timing degree and rpm - safe all in is 34 degrees at 3K rpm
  • compression test hot - should be well over 165psi with that cam and shouldn't be over 185psi
  • verify full throttle and proper secondary operation - I know nothing of your carb - good luck there, others here will know
  • verify correct vacuum readings with a gauge inside the car while driving
  • verify transmission line pressure with a 250+ psi gauge - if you don't know what they're supposed to be, then ask and you'll receive answers
  • degree the cam

If you find any issues along the way, then of course correct them. And no matter what, I would verify trans line pressures only for the reason of making your 700 live a long time.

Good luck - I've felt your pain before - it drives me nuts until I figure it out lol.
Jim
Well, I performed a compression test with the engine hot and all my pressures were over 185. They ranged from 190 to 200. Would this be a sign of the cam timing being wrong? When I was installing the crank timing gear, I struggled with determining which keyway was the one for zero. I remember thinking that I had definitively figured it out but maybe I was wrong.
525649
 

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I would agree with cam timing. You can not rely on the timing marks to be correct and the mark on the balancer for top dead center. All cams should be degreed when installed.
Carb should be fine. Yes reducer the pressure to 4.5 to Max 5 psi.
Ignition could be advanced some if the timing mark on the balancer is correct?????
For a 9.4 CR and that cam 200 psi cranking pressure seems to be slightly high but someone may know better than me.
 
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