Bad Combo?

[MadOgre]

Which reminds me something I forgot about.... Torque converter. While upping the cam a bit will the stock(scratches head not sure if I have a stock converter still) converter be okay or is this something else I will need to replace.

I should be okay as long as the cam is idle-4500 instead of 2200-6400 right?

Ya you will be fine for quite a while with an off idle(750-4500) cam. I doubt if you would ever need to change it. But could definitely be something to address if you ever upgrade your transmission.

By the way what do you have for a tranny? LOL

Im not saying that you shouldn't explore the realm of roller cams especially if you have a roller block. Which Im curious whether you do or not. Because that would stop any roller talk if you don't have a roller block lol But this Comp cams 12-300-4 Is a very proven and reliable and peppy cam with huge power gains in the very real world usable realm of driving a truck! If you drive a Camaro then you need something else for sure, but for a heavy truck you cant beat this cam!

And no 1500 is not off idle and yes you connect your vacuum advance on the dizzy to FULL vacuum at the front of the carburetor. @RichWeyand

Heck 1500 is 35 mph in 3rd gear its also nearly 13 mph in first gear 1500 rpm is what you match with a performer RPM intake and you will have a significant delay waiting for the power curve to kick in. This is fine if you have an F body with a 5 or 6spd manual tranny, but not for a heavy truck!

 

[MadOgre]

Another option would be to verify if you do indeed have a roller bloc, and if you do phone Comp Cams themselves and ask what they have that would work well in a roller form for your application.

I myself am curious to see if they would recommend something else or not?

It is curious too that this 12-300-4 cam is made for 57-98 not 57-86 So Im guessing from what I have researched that even if you had a roller block these guys would redirect you to this cam anyways ???

 

[RangRayy]

Ya you will be fine for quite a while with an off idle(750-4500) cam. I doubt if you would ever need to change it. But could definitely be something to address if you ever upgrade your transmission.

By the way what do you have for a tranny? LOL

Im not saying that you shouldn't explore the realm of roller cams especially if you have a roller block. Which Im curious whether you do or not. Because that would stop any roller talk if you don't have a roller block lol But this Comp cams 12-300-4 Is a very proven and reliable and peppy cam with huge power gains in the very real world usable realm of driving a truck! If you drive a Camaro then you need something else for sure, but for a heavy truck you cant beat this cam!

And no 1500 is not off idle and yes you connect your vacuum advance on the dizzy to FULL vacuum at the front of the carburetor. @RichWeyand

Heck 1500 is 35 mph in 3rd gear its also nearly 13 mph in first gear 1500 rpm is what you match with a performer RPM intake and you will have a significant delay waiting for the power curve to kick in. This is fine if you have an F body with a 5 or 6spd manual tranny, but not for a heavy truck!

I have a TH350 non lock up so '60-'70 TH350.
I called Comp yesterday and while on hold they prompted me to have my current setup ready to give to the tech but he never asked what the cam was to be going in. Just gave me a round about cfm of carb needed for the cam.

I will hopefully find out what block I have this weekend if I can finally get the motor pulled out of the truck.

 

[MadOgre]

I have a TH350 non lock up so '60-'70 TH350.
I called Comp yesterday and while on hold they prompted me to have my current setup ready to give to the tech but he never asked what the cam was to be going in. Just gave me a round about cfm of carb needed for the cam.

I will hopefully find out what block I have this weekend if I can finally get the motor pulled out of the truck.

OK well best of luck on your adventures this weekend and I guess we will have to wait to find out a bit more info about things.

With that 3spd tranny you definitely don't want to be waiting for your power curve to ramp up. Especially not with a heavy truck!

 

[RangRayy]

Anyone know yet if the ecm can be removed completely? I read on another forum that was a step they said at the end to do. Just reach over and rip the sucker out. Not quite in that manner but that's the jist of it.

I dug around and saw that the speedo is mechanically done.

Not sure about oil pressure and temp gauge. I mean how are those sensors ran on pre ecm controlled motors?

 

[MadOgre]

@RetroC10Sport @chengny @HotRodPC

 

[HotRodPC]

Anyone know yet if the ecm can be removed completely? I read on another forum that was a step they said at the end to do. Just reach over and rip the sucker out. Not quite in that manner but that's the jist of it.

I dug around and saw that the speedo is mechanically done.

Not sure about oil pressure and temp gauge. I mean how are those sensors ran on pre ecm controlled motors?

Really, most of us in this day and age would say LEAVE the ECM and keep the electronics. But, to each his own. While most of us are wanting to and upgrading to ECM injection systems, some do take them out.

Yes you can remove the ECM if you're willing to remove the TBI injection system and go to Carb, don't forget to regulate your fuel pressure form the fuel pump, convert to standard HEI ignition distributor. If you want to do away all electronics, swap to an older speedo and pull the reluctor wheel off the trans tailshaft and replace with a drive gear and driven gear.

 

[MadOgre]

They had VSS in 87' ?

 

[rich weyand]

...
According to my holley HP book and the instructions that came with my 670 street avenger, the metering block is the correct spot. You don't want vacuum at idle with the throttle blades closed. The Q-jet, edelbrock and street demon might be different but for the holley it is the metering block. If the Q jet, edelbrock and street demon have a low port for the vacuum advance than that port is gong to a source above the throttle blades when they are fully closed. Its just slightly lower than the sight plug on the Holley. The port is called the timed spark vacuum source. The lowest 1/4" port is full manifold vacuum at which point you might as well pull vacuum from the port on the intake it self.

This is NOT correct. Ported vacuum -- dropping the advance at idle -- is pollution nonsense. It fires the spark too late for the thin mixture and dumps the burning charge through the exhaust valves, out the exhaust runners in the head, and into the manifold. The AIR pump then adds air to encourage combustion of pollution gasses in the manifold. The result is a hotter running engine, poorer idle, worse gas mileage, and a potential balk off idle.

Ported vacuum was introduced in 1968 with AIR pumps. From the first vacuum advance in 1938 through 1967, there was no such thing as ported vacuum. It all comes down to combustion chemistry -- thinner mixtures burn more slowly and need more time, so the spark is fired sooner. The manifold vacuum measures how thin the mixture is right at the engine.

http://www.hotrodders.com/forum/distributor-tuning-theory-part-1-a-59033.html

 

[HotRodPC]

They had VSS in 87' ?

As a matter of fact, NO. I think it was 89 that started. A converter off of the speedo sent signal to the ECM, so that means in this case, he can keep the same speedo and no changes to the trans tailshaft.

 

[rich weyand]

For the record, 1500 rpm is not off-idle. The 12-300-4 cam has 300+ lbft of torque at 1000 rpm. I can pop the throttle at a stop -- no brake torquing, no dropping the transmission into drive, just take my foot off the brake and punch it -- and spin both BFG 31x10.5s with a G80 and 3.73:1 ratio. Judicious throttle application is the rule when pulling out of a driveway or driving on loose or wet pavement when the beef of your torque curve extends down into true off-idle territory.

A normally aspirated 350 will pump 10cfm for every 100rpm if it had an ideal 1.0 volumetric efficiency. So an engine with a redline of 5500 will not pump more than 550 cfm. If you have a cam with a higher redline -- say 6500 -- then more cfm is necessary. With a 600-4600 rpm range on the 12-300-4, 500 cfm is probably even enough.

I think the Edelbrock intake manifolds are listed as compatible only through 1986 because they won't fit under the 1987 TBI. The blocks and heads, though, are the same, so the manifolds would work with a carb setup on an 87 block/heads. It's just the TBI that makes those manifolds unsuitable for an otherwise unmodified 87. Ask Edelbrock to be sure.

 

[RangRayy]

As a matter of fact, NO. I think it was 89 that started. A converter off of the speedo sent signal to the ECM, so that means in this case, he can keep the same speedo and no changes to the trans tailshaft.

Does the ECM control the oil pressure? Knock sensor and the temp gauge? I have a majority if not all the wiring unhooked on the motor right now just wondering what wires I can eliminate if at all.

 

[HotRodPC]

The Oil Pressure and Temp gauges are read just like the earlier model trucks with electronic sending units. You've got me stumped on the knock sensor, I know the ESC system uses knock sensor, don't recall know for positive, but almost positive, TBI did away with the knock sensor, or was that Vortec SFI system that did away it? Getting old brother. Someone else chime in on that. But I will say for certain, if TBI does use a knock sensor, for cetain, yes it does feed into the ECM. Even on the ESC, it fed into the ECM. That's how the system knew to retard the timing. Once a knock was detected by the sensor, it immeditialey tattled to the ECM and the ECM then told the ICM (Ignition Control Module) to retard timing. You know how it is when **** rolls down hill. Same SAME.

 

[rich weyand]

Yep, no knock sensor on pre-ECM engines (through 1978). So if you are losing the ECM and going HEI, you can lose that.

If water temp sensor is on the side of the head between #1 and #3 plugs, with a green wire attached, that feeds to the temp gauge, so you need that.

 

[HotRodPC]

There is also a way to use the TBI dizzy if it's similar to the ESC dizzy. There will be a couple of wires you snip and twist together. Once you do this, then it operates just like a standard 1974 HEI ingition where the ICM doesn't do any timing adjustments. So you'd then set your initial timing and that's what you got other then centrifical or vacuum advance.

And someone may want to confirm for me that can be done with a TBI dizzy too. I know it can ESC, but not 100% positive on TBI. I'm forgetting to much. Getting rusty.