rickpilgrim

Hello everyone! I'm a newbie to turbo engines that are not diesels and in the quest for making our worktrucks more mpg I set up a small chevy V-8 with a single turbo last year and it was a failure in some respects. I'm going to try it again but first here's what I did.
Last year we set up a sbc with turbo in one of our work trucks for towing. It was a 1972 chevy 307 V-8, 1987 chev 305 HO v-8 heads 58cc chamber with port and larger valve work, Melling MT1 cam and Moly Plasma rings, 8qt oil pan and Edelbrock performer manifold. Distributor was recurved HEI with early Buick turbo vac adv/boost retard can, med adv springs.
Turbo kit was a $600 single turbo kit(china) set up as a draw through system. Holley 700cfm carb w/boost referenced enrichment. I made a water/methonal injection system with a surflow pump a couple of hobs switches and 2 nozzles that injected after the turbo. Wastegate set at 8 psi and run 91RON minimum fuel Kept it simple as this was my first turbo system.
With the draw thru throttle response was ok but not ideal, however after 2000 rpm it was better than our 460 ford powered truck for towing ability and all around fuel economy in this 1982 GMC C25 Crew Cab long box truck while towing and is geared 4.10 was 11 mpg on average and 14 max.
We tore the ring lands off a few pistons one day going up a hill and starved the methonal inj pump, by the time I heard the detonation it was too late.

Now I am going to try this again. This time using cng(propane) as fuel to !-get 106 octane at $2.56 a gallon and 2-I found a system that I can use a throttle plate at the manifold and the mixer at the turbo inlet and vent the bypass back to the mixer air tract. I also will be adding a "sump" to the methonal tank to prevent starvation.
Now here's the question- I'm using a forged piston Chevy 350 this time, as with the "small" turbo boost should rise faster, around 8/1 compression. Which way is better, large chamber heads with flat/slightly domed pistons or small chamber heads with dished pistons. I have all the parts to go either way.
And whats a better low rpm turbo torque cam than I'm running? We never exceed 5200 rpm and most of the time 2200-2500 rpm is where we are running.
Thanks in advance!

busa4

save yourself the time and headache. convert the sbc to fuel injection. a late 80's corvette, camaro, transam tpi assembly can be found fairly cheap and can be tuned. its a bolt on assembly. all you would have to do is run a fuel supply line, fuel return line, and install a fuel pump. it is very difficult to make a turbo carbd application reliable. they are very difficult to tune. as you already know from running lean on your last attempt the biggest disaster in the automotive field was teh 80's maserati biturbo. it was a carb'd turbo and it was very unreliable. my buddy was a tech and he loved the money they made him....

lowering the compression would be ideal but if your running low boost then its not neccessary. if your running more than 6 psi then an intercooler is recommended. water/meth/propane injection is great for race applications but for a daily driver or work vehicle it is not a good idea as it can fail and/or require top ups. intercoolers are efficient and require no maintenece.

running one small turbo to make low rpm boost will over rev the turbo, reducing its lifespan and creating more heat. my advise would be a twin turbo setup.

a turbo'd sbc can make a ridiculous amount of power reliably if done right. its all in the tune...
gl with build. post pics....

rickpilgrim

I have a 305 TPI with a 350 prom on the 327 powering our 1978 chevy van. It did increase torque but is no where near the power needed to tow 8500 lbs of equipment in a 5800lb truck around town here.
Most of our trucks are 454 /460/488V-10 powered vehicles and 10mpg is more than we get with them. 8.5 to 9 is all the compression we can get away with our non ecm N/A trucks that have cast iron heads without detonation problems on warm summer days.
The 307 was not really running lean, the plugs were dark tan.
The water/methonal injection was not for power, it was for decreasing the detonation you get when towing a heavy load in city and hilly terrain at 2500-3000 rpm. Even with 28 degrees total timing@ 3200 rpm starting at 8 degrees at 650 rpm idle was the most timing I would run towing, with the truck unloaded 36 degrees total and 12 at idle produced the best power and mpg.
Biturbo and even the original Lotus Espri were blow thro webber carbed for less lag but required constant tuning I'm told. I went carb first, turbo second, intake manifold third to avoid that headache but that still put the carb 10" from the intake manifold which degrades throttle response. The CNG should cure that as the throttle plate is right at the engine, it has a 106 octane rating, has similiar btu contant to gasoline, is only $2.48 per gallon today here and mixes with air so well and burns so clean I can't see the downside. I have the complete system including the 85 gallon pickup bed tank, and there are 5 places to fillup within 15 miles, and I can run a BBQ tank in an emergency.
I'm just trying to figure out the best combustion chamber and cam to work with this.

busa4

theres has to be a crane or crowler cam for turbo applications. all it is is a regrind that removes the valve overlap. you dont want overlap when boosting. as far as cam, i wouldnt go too far beyond stock cam grind. get a little more lift and remove the overlap and you should be good. im a firm believer in roller cams so if you want to invest even more on that upgrade is is well worth it.

cast iron heads maybe be your biggest limit. i would bring the compression down to at least 8.0-8.5:1. if aluminum heads are in your budget that would be your best bet. if you can find a used set on ebay, jump on it.

good luck. post up some pics when your ready to go.

rickpilgrim

Thanks for the cam advice busa4!
We do so much stop/shut off/restart/go (repeat) in the growing season that I sold the aluminum heads I had on our 98 Vortec truck as 1st set of head gaskets(Fel Pro) went 38K mi, tried Trick Flo for blower motor and got another 43K mi and those went out so I sold the aluminum heads and went back to cast iron and it's 81K mi later with plain fel pro with no problems. Machinest said it's to many warm/cold/warm/cold cycles for aluminum heads on cast iron block engines doing the yard care thing.
I'm trying to figure if with wedge heads is there any advantage to running a small chamber (58cc) deep dish (30cc) piston which puts the mixture closer to the center of the spark plugand creates alot of turbulance or go with the 76cc heads and a flatter top piston which puts the spark plug on the small edge of the chamber and has less tumbeling of the mixture. I can only wish we had a dyno and resorces to test this out.

busa4

i would go with the smaller wedge head and dish forged pistons to lower the compression. i think your going to want the turbulence and the mixture closer to the spark plug. this should create a lot more power.

turbobob68

FIRST real with turbocharging is that you MUST have an air/fuel wideband meter. The only way to know whats going on inside the combustion chamber. In my opinion most turbos sold as kits do not have a carbon seal on the compressor side, needed for a suck thru turbo set up. They don't call them SUCK thru for nothing! They do Suck, poor throttle response and the need for coolant heating of the carb for cold start up. Ad the fact that you are adding propane to the mix it makes for poor idle and low speed driveability. When we add propane injection to our diesel injection setups they must have heated water to keep the propane from freezing things up when outside air is cold.
Whatever you do don't usr ordinary hose for propane. Propane hose is specially designed to not let the propane leak thru the hose itself. Leaking propane in a hot engine compartment is a ticking time bomb. Contrary to pobular belief a blow thru carb can be vert dependable and create great power and reliability. Just go to TURBOMUSTANGSFORUMS.com and check out what can be done with a blow thru set up. Also in my opinion fast burn vortec heads may cause problems as turbocharging increases rate of burn in itself. Add faster burn chambers to that and in a turbocharged world octane and or water/meth injection with an intercooler made be needed to control detonation. Thats what broke the top of those pistons! If ya want to go blow thru I can let ya know an easy DIY method to convert a Holly carb to dependable blow thru without a BIG BUCKS "SPECIAL" carb. Good luck!

rickpilgrim

Thanks for the reply turbobob68.............
however- what I am saying is that I will NOT be running any carb/fuel pump/fuel tank or gasoline of any kind. This time a dedicated propane system with no other fuel will be used. I have the COMPLETE system for a 454 GM truck that includes all the hoses and small parts and yes, the regulator has fittings for coolant and a temp comtrol valve to keep the regulator at around 70 degrees or so, according to the operator/installer manual.
For heads I have a set of 76cc World products with 2.02/1.60 valves and 170cc ports and also the 305 HO GM heads, updated to 1.94/1.60 valves, milled to 53cc chambers that are moderately ported and polished. With the 350, a
30cc D dish piston and the 53cc heads around 8.6/1 compression. With th 76cc heads a flat top piston goes about 8.7/1. Using 106 octane propane I can go either way BUT.....
With the 30cc dish and small chamber heads the fuel mix is right under the spark plug and with the 76cc and flat top it is all the way across the chamber in a wedge shape,large end by spark plug.
On the 307 in NA trim(hot cam/intake/650 holley/headers) those reworked 305 heads made everyone think I had a hot 350 or mild 383 in that 78 Nova soo....
Will that also work on a turbo engine or will that pack to much in a small space and invite detonation problems?

turbobob68

My opinion is that I would go with the larger cc heads with a wedge piston/head
combo.The reason being I love boost and I got greedy once and kept turning up the boost. I was a neewbe to boost and found it addicting. It wasn't long until I had surpassed my octane requirements. The thing with boost, is the more octane, lowered compression ratio, the room for more boost!
Sounds to me like your on the right track. Just gotta feel it out, and pay attention to your A/F ratio for your specific type of fuel. Lean fuel mixes with
any type of fuel is a Baaaaaaaaddddddddddddd thing with boost.

Good luck

Deputy Diesel

I know its an old thread im bringing up here. But just wanted to see how this is going or if it happened.

I definitely can offer some propane input. As well as turbo/propane input.