1MeanZ

iTrader: (9)

Title says it all, I've built a TPI 305 with stock LT1 cam and TBI heads. I'm sure these heads have different timing requirements than the 081s did, so I'm just looking for suggestions if anyone has done any TBI tuning and knows about what they like timing wise. I may just dump the timing values from a TBI tune in to the stock TPI 5spd .bin and start from there. Thanks guys.

thomas1976

This is SA im running right now with premium gas, with regular its a little knock sensitive.

1MeanZ

iTrader: (9)

Thanks Tomas, I'll use your info.

rockit

iTrader: (3)

whats the idea using those heads? been a couple years since i was a tbi'er but nobody liked em then.

Prickly

OK take this with a grain of salt since Im not a pro, but Ive owned and drove 3 TBI motors. Small cam, small rockers, small valves- from what Ive read the valves dont stay open very long due to the bore size. Edelbrock and GMPP make replacements that are better than stock by far and with a "lot" of work can be good. Im gonna say those L03 heads are the first things to throw away on any TBI motor, theres some '305 build' articles out there that explain the head condition-Keep digging. GL

Fast355

iTrader: (2)

The stock timing table on a TBI engine is THE reason it will not run with a Peanut cammed, single cat TPI engine. Its terrible. I was able to crank in a substantial amount of additional timing in my 305 TPI running in my van. Never even pecked the knock sensor.


And those who say throw away the TBI heads on an engine that is setup to run below 5,000 rpm are in the WRONG.

I had almost the same exact engine in my fullsize chevy van (LT4 Production cam). The TPI intake is resonance bound by 5,000 rpm or so and the TBI heads make a perfect companion. They build more torque EVERYWHERE under 4,500 rpm than the TPI heads. Combine that with a short duration, high lift roller cam, 1.6:1 rockers, and exhaust modifications and things start to run. I left my stock torque converter in my 4L60E and stock 3.08 gears. 0-100 mph run in a 5,500 lbs G-van. 0-44 mph in 1st gear and 44-86 mph in 2nd. 0-85 in roughly 14 seconds and it was only 310 CID.



and just because its 5,500 lbs with brick like aerodynamics, has a 5,000 rpm WOT upshift, and 3.08 gears, doesn't mean it cannot get gone on the highway. I don't condone it but thats ~ 120.

1MeanZ

iTrader: (9)

Every thing in your post is total BS so I'll need the whole salt shaker. Do a search for my screen name and you'll find that I've been a member here for a very long time. I also had a 300+ HP TPI 305 in my IROC before I built the 383. This is far from the first engine I've built I don't need to keep digging for info about TBI heads. I installed them on this new engine on purpose.

Fast, thanks for the info. This has been very helpful. I'm going to start it tomorrow night. I'll report how it runs, if it runs LOL

Prickly

Ive never read in any CHP or HPP or Car Craft or Hot Rod mag about ever using those heads. It seems to be very conventional wisdom to replace them with Vortechs or pre 86 heads. Im glad someone found a use for them. Thanks for sharing your comment.

As far as tuning, I want to hear if you can actually get it to run. I have to spend more time learning the ECU end of things so some word of mouth detail on your build here would be good, as thats how we learn from the questions we ask.

1MeanZ

iTrader: (9)

There is more to life than what is in HOTROD magazine.

Why would it not run? If I assembled it correctly it should run perfectly. Judging by the 6 engines I've built previously, it will be just fine. I will have to mess with the timing in the tune a little, but I've hardly built a combination that wont run.

You have to remember, this engine build was for cheap mileage and torque. Going fast is not the point here. The car is heavy and has 2.73 gears. It will never see above 5000rpm, and rarely see above 3000. It needs to be efficient at low rpm. So it has to fill the cylinders full at low rpm. This is where the high velocity of the swirl port heads and the intertial supercharging of TPI will be a benefit to me.

This build is contrary to what everyone else builds. It is for low rpm torque and mileage. Everyone else is building for power and higher RPM operation. GM isn't stupid, someone spent a lot of time developing the swirl port heads. They are good when used for the purpose they were designed for. People give parts like this a bad name that is undeserving. The fact is that they have changed the way they want to use the car and the heads no longer meet their design requirements, but that does not make them junk.

Prickly

Thanks for the clarification. I wasnt aware of your total intentions regarding the build.

1MeanZ

iTrader: (9)

Got the car running this weekend. It runs fantastic overall. Not being one to blindly copy other's work, I made my own spark map using Fast355, Thomas, stock TBI and stock TPI maps as refrence. basially my first map was more aggressive than Thomas', and more mild than Fast's. The car ran well but felt a little lazy so I added some timing and it certainly made a difference. It looks like Fast355s timing map may be ideal, but I'm verifying it on my own and will continue to post results. this is what I have right now. I've not made any WOT pulls to redline, but I have waded in 75% or so and backed out at 4000. It starts pulling and runs good above 2800 or so. it will still spin the tires (2.73 posi) in 1st gear, but I think there is more left in it below 2500rpm under 25%-75% load. My fuel BLMs appear to be fairly close at this point.

thomas1976

Wery interesting results, I would not have tought TBI vs TPI intake requires such different SA.

Mine really starts pulling @2500rpm, below that its bit like stock tbi. My SA table is kinda the result of a 0 knock hunt.

Fast355

iTrader: (2)

I ran a very similar timing advance table on my TBI setup. The TPI setup only required a slight timing retard from around 60-100 KPA from 2,400-3,600 rpm. That coincedently is where the TPI runners are doing their thing.

1MeanZ

iTrader: (9)

Fast355, I believe you are correct. I added more timing today at lunch and drove the car home from work and noticed another very large difference. It now has the punch it had when it was stock, maybe a tad more actually. Again, this engine has 300 miles on it, so I've not done any WOT pulls on it, I'm just trying to improve responsiveness. But it is really waking up from where I started. My timing map is starting to have the same curve and shape as the stock TPI map. I'll keep cranking it in and see what happens. Here is where I am now.

Fast355

iTrader: (2)

I honestly cannot read the numbers in your timing map because of how it was distorted, but I have found the TBI heads like a substatial chunk of timing immediately and a very conservative total advance all in fairly early. Basically your 60+ KPA spark advance will taper off to a lower value than the TPI heads. I had to delay the timing advance ramp on the van because of its weight, aerodynamics, tight torque converter, 3.08 gears, and dynamic compression ratio. Running 93 octane instead of 87, I could bring in full advance by 2,800 rpm. It liked 28* BTDC all in by 2,800 rpm. If I remember cruise timing was capped around 40-42* BTDC @ 50 KPA and 3,200 ish rpm. At higher loading and lower engine speeds, the advance is obviously less. I think at 1,800 rpm doing 70 mph, 60 kpa map, I was running around 32-34*BTDC. The 305 pulling around a Van gets pretty sensitive to knock as it cruises on the freeway.

tony_cogliandro

iTrader: (3)

ok i have read and read this site and i still dont know what the outcome was.
are the swirl port stock heads good or not?
will they handle a cam that pushes them to .510?
i have read this over and over and i still dont know, but then again im not too bright.
are we talking about those 187 tbi swirlport heads with tpi?
im confused, my head hurts.

thomas1976

Thanks Fast for posting your SA table and sharing all this good information guiding us in the right direction.

I finally had some time again to play with the tune and tried the SA table you posted, way better then what I was using.
I had little knocks in the 95kpa @ 4000rpm, I took out 1° and will see what comes out next session. Will definally add in the 60-100 KPA from 2,400-3,600 rpm like u pointed out.

Made me wonder what cam u are using.

1MeanZ

iTrader: (9)

Yes we are talking about the swirl port heads with a TPI intake. If you want power and torque below 4500rpm, the swirl ports are better than the TPI heads by a moderate amount. I would not tell someone to yank their TPI heads and put TBI heads on if they are looking for max power. I wanted an engine with sharp response and strong power and torque at low rpm, this is ideal for the TBI heads.

I do not know what the max lift these heads will tolerate, I'm using a stock LT1 cam and it works fine.

He said he was using the LT4 cam above.


I also wanted to post up more info about how this tune has shaped up. I think this is a good combination for the intended purpose and would like to supplement more info here for those interested.

I have spent a LOT of time on my timing map getting the engine to respond smoothly at all rpms and engine loads. In some areas I am running slightly more timing than Fast355 is, but it is interesting to compare our timing maps as they do seem similar from what little bit I've looked at them. I was not able to run as much timing at 100kpa as he is, but I may have a different PE spark curve than he does.

I have not touched any of the VE tables and at this point don't really plan to. My lowest BLM is 122 and thats close enough for me at this point.

So far this combo has produced 23mpg repeatably, which is not as good as I would have liked. I expected 25mpg, but I'm not there yet. I have messed with highway mode a tad, but i'm only leaning out to 15.5 right now in an effort to sneak up on the ideal setting. If anyone has any insight here post up, I'd appreciate it.

As far as performance goes, I am happy with the car. It still has the little TBI manifolds and TBI single 2.25" exhaust with stock converter and muffler. I also did not port any of the intake parts. Depending on the ambient temp and surface, it will spin the tires hard from a roll in 1st gear. Not bad for 2.73 gears, amazingly the posi is still good and tight too. In warm air, the car just squats and goes squealing the tires but not ripping them loose. I've not dumped the clutch but if you slip it hard at 2000rpm and get on it, it will boil the tires so hard I have to back out to not over-rev it. I was suprised, but this car will melt the rear tires if necissary. If it had an open diff it would be a useless smoke machine in 1st gear. For other uses such as passing, or just normal driving, the engine feels very strong, especially as it breaks in more. I'd guess the car would go a very low 15 right now. Not setting the world on fire, but the car certainly does not feel slow or sluggish. If I get the opportunity to measure its power output some how I'll certainly post here. I realize all my bragging is useless without any data to back it up, but at this point a description of how the car acts is all I can give. Here is the .bin I have pretty much settled on.

Fast355

iTrader: (2)

I was running a LT4 cam in mine.

This could have ALOT to do with the lower than expected fuel mileage.

1MeanZ

iTrader: (9)

Interesting.... I have a set of edelbrock shorties, a set of stock 350TPI manifolds and y-pipe, and a stock LS1 cat back at my disposal. I haven't decided whether I want to just bolt stuff on that I have, or make a dual exhaust setup in the factory location for a beautiful sound. Maybe I should move that up in the priority list...

thomas1976

What xdf file for tunerpro do I need to look at your bin?

1MeanZ

iTrader: (9)

this one.

JamesLLeary

Hey Fast,
What would you recommend as a base timing setting for a tpi...193 heads, 12-388-4 compucam, in an 86 suburban, until I can afford to get it tuned properly?
I have it set a 6btdc right now, it is a speed density system, using the large HEI distributor.
BTW-Did you get my PM on FSC?
Thanks,
Jim