dannyidp

I have a 305 with a flat tappet cam compressions very low it's in a 95 K 1500. I am looking to get a 305 roller motor 2 replace the dying 305. do I need a different knock sensor? I was also wondering would there need to be any tuning on the prom chip?

6998poncho

Over five years ago I replaced the 350 flat tappet cam engine in my '89 K1500 EC with a spare I had in the garage I was saving for another project. Same exact engine block number, low miles with a roller cam. I've never gotten as good of mileage in 200K miles with the flat tappet cam engine that I have with the roller cammed one. I took a trip east through Texas and I consistently got 20 mpg with my truck on many tankfuls of gas. 17 mpg in Calif. is about the best I get because of all the hills and grades I travel on. I'd say swap the engine and all the parts provided everything is in good condition and drive on!

dannyidp

Thank you that is awesome!! I was wondering if a rv roller cam would work without any mods to the pcm? should I just stick with the stock 88-95 roller cam? I'm looking for low end torque for pulling?

Street Lethal

iTrader: (16)

Danny, all the ECM does is look at that data being sent. It essentially tunes a range. Some 305's made more or less power over the years, but not as much where chip tuning would really be needed. Re-use your original sensors, including your current injector size, and the swap will be fine. Older ECM's usually have a six percent threshold when it comes to O2 correction, and if by chance your replacement 305 takes in a tad more air due to it's more modern design, then it is only a matter of upping your fuel pressure a tad until 128-BLM is maintained with no correction needed. Of course, without upping the fuel pressure the ECM would correct for a tad more air on its' own anyway, but it's better to try and keep your air/fuel stoich with 0% correction by upping pressure (if needed), this way the VE table stays on the money throughout...

- Rob

dannyidp

Thanks guys I do have a couple more questions. I have not got the engine yet but I'm wondering about the roller cam will a RV cam work without modifying the pcm?if so what is a good roller cam for torque that does not require tuning?

Street Lethal

iTrader: (16)

Danny, you weren't listening. The ECM doesn't care what cam you are running, all it cares about is if it has enough fuel to compensate for the incoming air. Example, eight 19# injectors will cover up to 300 horsepower at 80% Duty Cycle, this includes upping fuel pressure a tad. Doesn't matter what engine, it's just the matter of enough air and fuel calculating 300 horsepower. If your 305 is making less than 300 horsepower, which I am sure it is, then no ECM tuning is necessary.

Just up your fuel pressure just enough to compensate for the additional air to keep 02 correction at its' minimum, and retard the timing some to make the cam happy. Yes, you can maximize your tune by burning a new chip and getting a tad deeper into the tune, but at that level it's not even necessary. So again, to answer your question, any cam will work without a tune so long as it falls in between your ECM's current horsepower range.

- Rob

Fast355

iTrader: (2)

It depends on what heads are on that roller engine. If it has TPI heads or Vortec heads it will not run right under a TBI system regardless of how much you tweak on the timing and fuel pressure without digging into the chip. The OEM 305 roller cam in a TBI engine has the same exact grind as the flat tappet. 179/194 @ .050, .350/.385" lift, 109 LSA, 106 ICL. Off-idle to 2,500 rpm, you will not find a better low rpm cam for a small block Chevy than the peanut roller cam.

Street Lethal

iTrader: (16)

.... if someone has trouble getting an engine to run right based on the information given, then I would tend to look at the individual's ability, not the need for additional tuning in the bin. To maximize a tune, as said earlier, additional tuning would be needed to maximize air/fuel. But to consider an engine, regardless of heads, with a mere difference of fifty horsepower at best, then imply it will not run right, is not correct. Unless he is exceeding injector limitation, and the cam has a tremendous amount of overlap like mine does, averaging 10" of vacuum at idle, then I may consider additional bin work being needed. But for his goals, and what he is suggesting, he has nothing to worry about.

- Rob

dannyidp

thanks again guys I'm not looking for any conflict. I have been Building engines for 20 years but I have never got into roller cams and computers or chip burning.I bought the truck like new with the 305 it never was a Powerhouse I purchased a aftermarket prom chip which helped also put a spacer under the TBI which also helpedI do lots of Towing the 305 is now dead compression is down to 80 psi.I am going to build a set of 114101081heads I was going to Port them and put some 194 intakes and put them on a roller motor I'm hoping for some horsepower increase that's why I was asking about a good roller cam for torque I totally understand open the fuel pressure and getting the timing right. just have not made my mind up yet if this is what I want to do or do I want to jump on a Vortec 350 with an aftermarket TBI. Adapter.

Fast355

iTrader: (2)

081 heads are counter productive to your torque goals, compared to the swirl ports they will lose torque under 4,000 rpm. If anything build a flat top piston 305 with 1.56" compression height pistons, get the quench as close to .040" as you can and use a set of 193 or 810 350 swirl ports with 1.94/1.50 valves. Use the GM 395' Marine cam with some 1.6 roller rockers. You will end up right at 9:1 compression and about 7.8:1 DCR which is perfect for iron heads on 87 octane with towing. The 395' cam performs very well in a 305.

Fast355

iTrader: (2)

I AM GLAD YOU FEEL THAT WAY!!!!

Timing and Fuel Pressure changes are global adjustments that for lack of a better way to explain it offset every value in the tune. You cannot adjust the slope of the fuel map or timing map without going into the chip.

For example stock TBI head engine TBI tuning.

Timing Advance
Idle = 20-25* BTDC
WOT 1,000 rpm -6* BTDC
WOT 2,500 rpm 10* BTDC
WOT 4,000 rpm 20* BTDC
Cruising at 2,000 rpm 34* BTDC
Cruising at 4,000 rpm 42* BTDC

Those TPI heads are going to want 32-34* total advance at higher rpm. If you simply advance the timing 14* to get there you will be at 56* of timing at cruise speed and 34-39* of idle timing, both of which are way too much. The TPI heads are also going to want 8-12* of timing at WOT by 1,000 rpm.

No on to fuel pressure....Factory spec is 9-13 psi for a TBI. A TBI engine running at less that 13 psi fuel pressure is actually running marginally lean even with zero changes. Injector duty cycle runs very high and typically all the available pulse width is used by 4,500 rpm. This means that the ECM cannot get more WOT fuel by increasing the pulse width at higher rpm open loop even if it wanted to. The ECM will increase fuel delivery at WOT if the BLMs are higher than 128 but only up until the injectors are maxed out.

In the case of a 305, the TPI roller cam engines with the good L98 cam were a solid 50 HP over a peanut cammed TBI. That same L98 cammed TPI 350 was 20 HP over the highest rated 350 TBI. I built a 0.040" over flat top piston 305 with 081 TPI heads and a GM HO 305 cam. I can tell you from first hand experience it was not even driveable on the factory chip and 305 injectors. Even at 18 psi of fuel pressure it would go so lean on the slightest throttle opening it would spit fire. The only way I got it running half way right in a time before I could tune chips (2003ish time frame) was to use 350 injectors at 14 psi and the matching 350 ECM. The timing ended up being about 8* BTDC, but that was a comprimise at best. Total timing was only running at 28*BTDC and the advance curve was very lazy. The accelerator pump shot was also very weak and it often had a lean hesitation. Chipped a 7747 ECM, bought a Moates Burn1, started datalogging with WinALDL, created an excel spread sheet to correct the VE tables and started datalogging on weekend trips out of town. Within a month I had it running as well as if GM had built it.

6998poncho

I think my original answer was valid. Once you start throwing in variables it's hard to say how you're going to end up. My truck was originally a 305 truck and I installed a 350. Some have said they didn't need to change the PROM on a swap like that. I HAD to. It wouldn't run, take it back, it wouldn't pull right. Engines in trucks do a different job than they do in a car. More weight, for one thing, so coming off a stop is going to use more throttle than a car comparatively speaking. There's a lot of good info here, but remember it's still a truck and that makes a difference.

Fast355

iTrader: (2)

Your experience was like mine then! I used aftermarket GM equivalent parts to build that TBI HO 305 clone for the old 1983 G20 van and it would not run well enough to move itself up the driveway much less down the road with a stock 305 TBI and Prom Chip.

dannyidp

Thank you guys for all this great information because my main goal was and is torque. I do have a set of 14102187 I heard these heads were boat anchors that's why I was not going to build them so basically you're saying this is what I need for torque? so should I do some undercutting of the valves and put 194 intakes and a little bit of porting or not?I was also wondering do you have the specs on the Marine cam?with this setup if I'm going to need 350 injectors then I might as well build a 350 and put in there the whole point here for me use to keep it simple by keeping my computer injectors and keeping fuel mileage down. hard to believe but I have been getting 24-26 hwy mpg.

dannyidp

​​​​​​​poncho in your original post you stated you swamped a 350 for a 350 roller in your last post you stated you swamped a 305 to a 350 was that a typo which was it 305 350 or 350 350 thank you

6998poncho

I probably confused you leaving out history. My truck was originally a 305 which had a defective engine at 30K. Cracks in the lifter valley and created jello in the oil pan. Took my truck to the dealer for warranty work and it was poor quality. They replaced the short block and then bolted all the original parts like heads back on the block. I worked graveyard shift at the time and when I came out in the morning and started up the truck a bunch of white smoke came out the tailpipe and I was smoking out all the people walking by at shift change. I put up with it for about a year and then went to my local Pontiac dealer (different dealer this time) and bought a 350 crate engine and installed it myself at the curb next to my apt. It wasn't a problem back in the '90's. Best thing I could've done. I put about 190k on that engine. I retired and was working on my car projects. I decided to use my spare roller-cammed 350 in my truck. That was five years ago. My truck doesn't look pretty on the outside but it looks good under the hood. And I did have to change the PROM going from the 305 to 350 like I stated above.

Fast355

iTrader: (2)

The 395' cam
256/264 @ .006
196/206 @ .050
.431/.451" LIFT WITH A 1.5 ROCKER
109* LSA
106* ICL

dannyidp

Thanks again guys I'm almost ready to pull the trigger. I do have another question it's hard to find any info on 305 as you probably know would I gain anyting going to a L30 Vortec 305 head versus the 187 swirl port?

Fast355

iTrader: (2)

The trade off would be low-end torque for higher rpm HP. The L30 305 heads flow very well, even better with 1.94/1.60 valves but you will end up costing a good bit of torque off-idle and under 3,000 rpm.

dmccain

iTrader: (2)

Id find an L98 cam and throw in there. 049 GM. 207 213 .415 .431 lift.