Vortec or Summit heads for high MPG?

[Surveyor75]

Hi.  I'm an old visiter, but new member.  Great site!  So, I have a 1975 Chevy G20 camper van with the original 165hp LS9 350 (the 70's LS9) with stock heads (GM #14034811).  I'm trying to decide between Summit heads (SUM-152123) and the Chevy Performance Vortec heads (12558060).  I know the Vortec is hard to beat, but I won’t be racing or towing.  I almost always stay out of the Thermoquad secondaries and drive smoothly for high MPG (low highway speeds, too).  I'd be happy with 20 more HP over my stock motor, just to help maintain speed on steep mountain highways.  Otherwise, it's all about improving MPG’s, keeping my highway RPM’s low, and having nice starting and idling, with no warm-up needed before driving.  I am now leaning towards these Summit heads over the Vortecs because they have a heat passage for a nicer-running cold engine, and I have a heat riser choke as well (so, less mods needed).  They are also cheap, like the Vortecs, and built VERY nicely by Dart, according to the rave reviews.  Do these heads make more sense for me?  What compression should I be targeting?  These Summit heads are 72cc chamber, the Vortecs are 64cc, my stock head chamber volume is unknown.  Will the style of stock piston I have (GM #3991488, see photos)  match one head much better than the other, or is it not much of a factor for a daily driver?  Is quench an issue with either head?  My stock piston # matches to a 1476H or 1470 in this catalog:  http://www.uempistons.com/catalogs/uem_catalog_web.pdf.  I’ll be replacing the stock cam with a suitable high-MPG cam from Summit, Crane, Comp, or Lunati.  Crane suggested their #10003 for the Vortec heads.  I’ll also replace the stock intake manifold with a Edelbrock Performer Vortec, if I go with that head.  Intake suggestions, if I go with the Summit heads?  My motor has GM H.E.I., EVAP, and AIR, but no EGR.  My trans is a TH350 with a 3.08 rear end.  I have AC and power steering. FYI - I am paying a mechanic to do this work, so budget is a concern.  I DON'T want to spend extra money to tear apart the block, port, stroke, add EFI, swap to an OD trans, etc.  Trying to keep this relatively simple.  My original block has low miles and almost perfect compression, so I’m leaving it alone.  I’m pretty set on using one of these two sets of heads, so looking for advice on that specifically, and then matching cams and intake to my mission, which is:  High MPG's, lowest possible highway RPM's (at 60mph, with my TH350), and smooth drivability.  Very little extra HP needed, and I drive very miserly (I know, boring).  Thanks in advance!

[Stewart G Griffin]

This is making my head spin-----and i just woke up from a nap.

1) Are you sure the Summit heads are made by Dart?

2) If you want MPG, then i would go with the Vortecs.  Because they will raise compression, which helps with mpg.  i think the stock ls9 has 8:5 to1 compression?

3) Low cruise RPM is mostly a function of gearing.  Although that RV cam will probably put the power band lower.

4) Fast/no warm up is mostly a function of how the choke is set up, not heads.  Although yes, those lumpy cams don't help with idling, but you're not getting one of those.

5) Take all my opinions lightly, as again, this is making my head spin.  i do however, have extensive logs concerning MPG (see my threads entitled MPG PT.1 and MPG PT.2 if you haven't already)

If you're not towing, then it may be more cost effective to just get a tonneau cover to increase mpg.  Also what size rear tires do you have?

[Stewart G Griffin]

P.S.,
If you haven't already read this, then read:
http://www.oldsmobility.com/old/carlife_apr67.htm

i think you are on the right track for mpg as far as lowering rpm.

[Surveyor75]

Thanks for the feedback, Stewart.  I forgot I posted here, so it's been a while.  I've pretty much decided I'm either going to do the Summit (Dart) heads on my old block, OR get the 195-260hp GM crate engine (#12681429) and either leave it as is, or sell the heads off of it and put on the Summit heads.  I just can't stand the idea of having all this work done and ending up with an outdated head that is essentially similar to the crappy '75 head I'm replacing, but maybe the difference isn't worth the swap?  The Summit head is a very nicely-finished head with a fast-burn (Vortec-style) chamber.  I would think it would be at least a little smoother, more responsive, and get a bit better MPG's.  The compression would go from 8.5:1 to about 8.95:1, which will help to that end.  Anyway, here's some answers to your questions:

This is making my head spin-----and i just woke up from a nap.

1) Are you sure the Summit heads are made by Dart?Yes.  They are essentially the Dart S/S heads. 

2) If you want MPG, then i would go with the Vortecs.  Because they will raise compression, which helps with mpg.  i think the stock ls9 has 8:5 to1 compression?  I've decided to abandon the Vortec for simplicity sake, but point taken.

3) Low cruise RPM is mostly a function of gearing.  Although that RV cam will probably put the power band lower.  Roger that.  I think the idea is to be near peak power during highway passing / climbing hills (midrange), so I'd be able to use the least amount of gas to get the power I need.  Stock cams like my 929 or something close seem nearly ideal.

4) Fast/no warm up is mostly a function of how the choke is set up, not heads.  Although yes, those lumpy cams don't help with idling, but you're not getting one of those.  Yes, but I've read that since the Vortec has no heat crossover, warm up and smooth running when cool can still be an issue.  I don't want to keep coming back to my mechanic and paying him to sort out issues.  I want an engine that's not tempermental. 

5) Take all my opinions lightly, as again, this is making my head spin.  i do however, have extensive logs concerning MPG (see my threads entitled MPG PT.1 and MPG PT.2 if you haven't already).  I'll check those out.  Thanks!

If you're not towing, then it may be more cost effective to just get a tonneau cover to increase mpg.  Also what size rear tires do you have?  My tires are 27.44" touring 225/75R15. 

[Captain Swampy]

http://www.jegs.com/p/Chevrolet-Performance/Chevrolet-Performance-1996-2000-Truck-350ci-L31-R-Long-Block-Crate-Engines-Install-Kits/1532025/10002/-1

I would recommend this. It has vortec heads and a roller camshaft. The vortecs are the best flowing factory head offered. The roller cam can be much more efficient. They can open and close the valves much quicker than a flat tappet cam. You also won't have to worry about using a high zinc oil to protect the flat tappet cam. Zinc was removed from oil because it contaminated catalytic converters. I think if you added an RV cam you would love this engine. Even stock it should be much more efficient than the other engine.