Cam Swap

[Aidan Kesler]

I know the stock tuning can handle the marine cam no problem. Although it won't sound lopey at all. It's still a relatively small cam. Same one that comes in the ht383 and ramjet 350.

I actually have a marine cam I just pulled out of my truck. Idk exactly how many miles I put on it. Around 5k if I had to guess. Still in perfect condition. If you're interested I can sell it for $75 + shipping.

I also have a computer that's tuned for it from black bear performance. But it's out of a 98 so it won't work with your 95.

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This guy claims to have cammed tbi 350 with 1.6 roller rockers, modified throttle body and upgraded injectors with stock computer and it runs fine? People all around youtube and the internet claim to cam their TBI's with no modification of the TBI's or computer as well. I actually don't have a tbi, its an MPFI which i feel like i could confidently say would be equivalent to 600-650 cfm carb. Is there anything else that would stop me from doing this cam swap with no mods? Or are these guys just bluffing?

EDIT:

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This guy also claims to have cammed his stock TBI and computer with no issues. He claims that he daily drove it and the computer adjusted itself and broke in and drove fine.

 

[Awest623]

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This guy claims to have cammed tbi 350 with 1.6 roller rockers, modified throttle body and upgraded injectors with stock computer and it runs fine? People all around youtube and the internet claim to cam their TBI's with no modification of the TBI's or computer as well. I actually don't have a tbi, its an MPFI which i feel like i could confidently say would be equivalent to 600-650 cfm carb. Is there anything else that would stop me from doing this cam swap with no mods? Or are these guys just bluffing?

I'm not saying you "can't" do it. But you won't gain any performance from it with the stock tune

 

[Aidan Kesler]

I'm not saying you "can't" do it. But you won't gain any performance from it with the stock tune

I understand that, I don't think tuning would be a huge issue. I'm just not familiar with how to tune a computer controlled fuel delivery system. I'm old school and know how to work carbs lol so if I understand correctly, I could swap a cam like for example a Comp Magnum or a Comp xtreme energy cam and have the computer tuned to the cams specs and get performance out of it?

 

[Awest623]

I understand that, I don't think tuning would be a huge issue. I'm just not familiar with how to tune a computer controlled fuel delivery system. I'm old school and know how to work carbs lol so if I understand correctly, I could swap a cam like for example a Comp Magnum or a Comp xtreme energy cam and have the computer tuned to the cams specs and get performance out of it?

Yes. But good luck finding anyone that can tune a 95 black box. You'll probably have to upgrade to an 0411 computer. Black bear does good work.

Also, don't go too crazy with the lift. Stock vortec heads can only support about .48", and even that is pushing it. You can upgrade to beehive springs for more lift. Personally I went with some AFR 190cc heads.

The LT4 hot cam is popular for stuff like you're wanting to do. It will start and run with the stock tune, but you really do need a different tune to get it running best. Most people end up swapping to s10 converters for higher stall with that cam.

The problem with just swapping a cam and going is that the computer uses two different forms of airflow metering. The mass airflow sensor and the manifold absolute pressure sensor.

The maf directly measures airflow and commands the amount of fuel for the airflow, similar to a carb. But it isn't fast enough to recognize quick changes in airflow. So it usually doesn't take over till 4000 rpm on the stock calibration.

The MAP and RPM are used to determine volumetric efficiency below 4000 RPM and during throttle transients. This is where the problems with changing the cam come in. Basically any change in the engine, intake, and exhaust will change the volumetric efficiency at different points on the table. The computer can correct for some of this using fuel trims, but it's not very refined can only do so much.

The spark values will change too. A "larger" cam will have longer duration. Decreasing the dynamic compression of the engine. This will decrease power some but will allow you to increase spark timing to compensate. The computer can't advance timing further than the programmed amounts. So you'll lose power there too without a tune.

Sorry if you already knew some of this. Just trying to explain why I'm saying what I'm saying.

 

[LC2NLS6]

So it is a vortec? Are all the intake bolts vertical or angled? If vertical = vortec and have the best stock 350 heads you can get. A cam should help, anything under 220 at 050 would be ok. Tune would help. If you go too big, you'll need springs that can handle it, and then you can eject the press in studs on the rockers. Get a milde cam, 218 ish at 050, headers and a tune, see what she does.

 

[Awest623]

So it is a vortec? Are all the intake bolts vertical or angled? If vertical = vortec and have the best stock 350 heads you can get. A cam should help, anything under 220 at 050 would be ok. Tune would help. If you go too big, you'll need springs that can handle it, and then you can eject the press in studs on the rockers. Get a milde cam, 218 ish at 050, headers and a tune, see what she does.

I'm kinda wondering if it's a vortec too. I thought they didn't start using l31s until 96.

 

[Aidan Kesler]

Yes. But good luck finding anyone that can tune a 95 black box. You'll probably have to upgrade to an 0411 computer. Black bear does good work.

Also, don't go too crazy with the lift. Stock vortec heads can only support about .48", and even that is pushing it. You can upgrade to beehive springs for more lift. Personally I went with some AFR 190cc heads.

The LT4 hot cam is popular for stuff like you're wanting to do. It will start and run with the stock tune, but you really do need a different tune to get it running best. Most people end up swapping to s10 converters for higher stall with that cam.

The problem with just swapping a cam and going is that the computer uses two different forms of airflow metering. The mass airflow sensor and the manifold absolute pressure sensor.

The maf directly measures airflow and commands the amount of fuel for the airflow, similar to a carb. But it isn't fast enough to recognize quick changes in airflow. So it usually doesn't take over till 4000 rpm on the stock calibration.

The MAP and RPM are used to determine volumetric efficiency below 4000 RPM and during throttle transients. This is where the problems with changing the cam come in. Basically any change in the engine, intake, and exhaust will change the volumetric efficiency at different points on the table. The computer can correct for some of this using fuel trims, but it's not very refined can only do so much.

The spark values will change too. A "larger" cam will have longer duration. Decreasing the dynamic compression of the engine. This will decrease power some but will allow you to increase spark timing to compensate. The computer can't advance timing further than the programmed amounts. So you'll lose power there too without a tune.

Sorry if you already knew some of this. Just trying to explain why I'm saying what I'm saying.

So it is a vortec? Are all the intake bolts vertical or angled? If vertical = vortec and have the best stock 350 heads you can get. A cam should help, anything under 220 at 050 would be ok. Tune would help. If you go too big, you'll need springs that can handle it, and then you can eject the press in studs on the rockers. Get a milde cam, 218 ish at 050, headers and a tune, see what she does.

Not sure if it is vortec heads or not, will check but pretty sure its stock tbi heads. Also I already have the aftermarket MPFi fuel delivery system and medium length headers. The only thing i'm considering now is a cam swap to the Comp 12-242-2 Xtreme Energy cam, which i just called comp and they said stock torque converter will work, its just a matter of a tune. So i will figure out the heads and report back and see what yall think. Pretty sure i dont have MAF as well, I have the following sensors: MAP sensor, IAC, TPS, EGR valve, Coolant Temp Sensor and O2 sensor. (may be forgetting some but im pretty sure that's all)

Also i really didn't know much about all that you said, so it's really good info to know. I have built and tuned quite a few carbed engines with big cams, aftermarket heads, this and that lol but never messed with fuel injection and automatic transmissions that much.

 

[Awest623]

Ahh. You have a standalone system. That's completely different than working with an oem computer. Sorry for the confusion.

Same principles apply but it's so much easier with a standalone. I think most of the modern standalone will tune themselves to boot.

 

[Aidan Kesler]

Ahh. You have a standalone system. That's completely different than working with an oem computer. Sorry for the confusion.

Same principles apply but it's so much easier with a standalone. I think most of the modern standalone will tune themselves to boot.

Standalone? You are referring to the MPFI right? I have had some troubles with it running smoothly when altering the smallest thing lol for example, the TPS and IAC and pulling air cleaner off are such small changes but make it run very differently each time, and it seems to smooth itself out each time. We are now replacing the whole ignition system, EGR valve and headers along with O2 sensor to sort out a hard start issue. (plus it needed it anyways lol)

 

[PlayingWithTBI]

This guy claims to have cammed tbi 350 with 1.6 roller rockers, modified throttle body and upgraded injectors with stock computer and it runs fine? People all around youtube and the internet claim to cam their TBI's with no modification of the TBI's or computer as well

Yes you can, as mentioned before, and it may run fine BUT, I can tell you a little story;
In my 88 350 TBI I put in a bunch of go fast parts including bored out Throttle Body with higher pressure spring, aluminum heads, mild cam (.464/.484), headers, high flow Cat, etc. When it was stock it ran 0-60 in 11.2 secs. With the go fast parts and a mail order tune it was ~8.2, with 4.11 gears from 3.42, 7.9 secs, got down to 7.6 with data logging and custom tunes from a guy @Gearhead-EFI.com then I got the EBL Flash-II and data logged/tuned repeat and logged some more. Now with a 2500 stall TC and the EBL I'm at 7.3 seconds mainly because I can't get off the line with my 1 tire fryer open diff. Otherwise I'd be in the mid to high 6's.

Yes, IMHO, tuning will give you better performance than just hard parts. YMMV