Don Terrill’s Speed-Talk

I got a fuel economy run out of the engine I built for my 79 El Camino. On a 250 mile freeway drive running 70+ mph I got 19.778 mpg. This build cleared a bunch of junk from the shelves. I had a low mile block that only need a hone. I used rods and pistons from a low mile Vortec 350. I used a pair of 305 boat motor screw port heads with 1.84 valves and 58 cc chambers. Static CR came out to 9.27:1. The cam is the 204/214 rv grind I have had for over 10 years. As this is a low rpm application, (2.73 gears), I used the SP-2P manifold I have no other use for. The out of pocket cost was the set of 1.5 mm piston rings, a rear main seal, an intake gasket, and a $5 swap meet Quadrajet. I had an exhaust built using stock iron manifolds and a Y connector into a 2 1/2" single tail pipe The engine made all the power I need, and will spin the tires forever. Thanks to Tuner for letting me know about the timing needs of a screw port head. I have the black bushing and heavy silver springs in my ready to run MSD distributor, with 4 degrees of initial it comes out to 22 total. It is on the ragged edge of pinging on long hills but some vacuum advance tuning may solve this.

That is awesome, especially for the $$$ spent!

I’d bet a set of 1.5” long tube headers and some small 2” or 2 1/4” duals would add another 1-2 mpg to that.

I actually have the headers, but the system I used was like new from another vehicle. The goal was always fuel economy, It wouldn't make sense to add power to a car that struggles for traction.

What are boat motor screw port heads?

Some people call them swirl port. If you look down the throat under the valve, there is a half helix cast into the port to induce swirl in the chamber. They were the precursor to Vortec heads. Very low rpm usage, not ever considered a performance head. Because they were on a boat motor, they were a heavy casting with 3/8" stem exhaust valves. These have the 1.84" intake valve instead of the 1.72" intake common to most 305 engines. The 58 cc chamber gives the compression a serious boost, even with dished pistons.

NICE JOB, NICE WORK AND AND GREAT RESULTS!!

gmrocket wrote: ↑Sun Nov 04, 2018 2:07 pm What are boat motor screw port heads?

187 TBI heads, I'm guessing. Found on the L03 305 TBI.

The engine was the easy part, the car needed everything. Interior trim , floor pan and carpet, rear springs, shocks on all 4 corners, steering center link and idler arm, alternator, power steering pump, motor and trans mounts, heater core , radiator, all of the dash lights, and on and on. It took most of the summer. After a month I started thinking another $1000 over my purchase price would have saved me some grief, but a quick search on cragislist showed me that $2500 would get me the same crispy vehicle. These vehicles are popular and expensive. I'm pretty satisfied with the results, these are nice driving and practical vehicles.

midnightbluS10 wrote: ↑Sun Nov 04, 2018 4:35 pm

gmrocket wrote: ↑Sun Nov 04, 2018 2:07 pm What are boat motor screw port heads?

187 TBI heads, I'm guessing. Found on the L03 305 TBI.

You would be correct. Most people throw them away. I had a set of Vortec heads on the shelf it they didn't work out.

Nice build and nice car. Might get a few more mpg with a new carb and a new coil.

I've seen those heads at a machine shop. Interesting intake bowls. Always wondered what they were from. Although I thought they should have had the screw in the other direction like some of the AFR heads.

Looks good. I like reading about these practical street engine builds. It's more of an area of interest for me that all-out race effort stuff. Is this a TH350 (no OD)?

There is likely more in it. My distributor is the ready to run model and I haven't tried an MSD 6A box yet. I have yet to put the AFR meter on it to look at the mixture, but when I get around to it I might find some more playing with the apt on the Quadrajet. The trans is a dual bolt pattern 350C, so if I can get the lockup converter wired up it should make a difference. The car had a Buick V6 in it and the converter is pretty loose. I have the impression these heads were common in the late 80s and early 90s. I talked to several people with large GM vehicles from that era that got phenomenal fuel economy. My assumption was the combination of overdrive and fuel injection produced the results, but the heads may have played a significant part. Certainly better than the heads from the mid 70s. When the government agencies started requiring better fuel economy and emissions, the manufacturers had to scramble to keep up. When I lived in the Portland metro area, I had to make all of my cars pass emissions testing. The quick way to reduce hydrocarbons was to retard initial timing. These heads require much reduced timing and produce good economy, so they likely met the goal.

rfoll wrote: ↑Mon Nov 05, 2018 10:14 am I talked to several people with large GM vehicles from that era that got phenomenal fuel economy. My assumption was the combination of overdrive and fuel injection produced the results, but the heads may have played a significant part.

My Dad has owned two 1989-1990 TBI 305 Caprices over the years. They really do get great MPG for a large car with poor aerodynamics. Great throttle response too for a little 305 in a big car. These both had 2004R transmissions and ~2.9x gears IIRC. The 1990 he had was still running like new after 200k+ miles.

novadude wrote: ↑Mon Nov 05, 2018 9:39 am Looks good. I like reading about these practical street engine builds. It's more of an area of interest for me that all-out race effort stuff. Is this a TH350 (no OD)?

Me too!

I am sorry but those here who think a late 80's -early 90's 305 Caprice has good throttle response you need to go drive a new Dodge Hellcat or new Copo Camaro and get your perceptions realigned!! Now those have f** kin throttle response! Sorry but I refuse to get in my rocking chair just yet!