Thread: SBC mileage

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Hi,
I am recently retired and trying to realize a dream of a Model A street roadster. So far I have a title, a repro frame, a Magnum 4" drop front end with econo brake kit, a 74 Maverick 8" rear and a 76 Corvette 2-bolt 350 V8 (80K miles) along with a recently rebuilt TH350 (no lockup) with a B&M shift kit and new clutches. I have searched the Internet for anything I can find on the 350 V8 and I am disappointed to find that power requires high compression and that requires 92 octane fuel! I do not want to spend more than about $1600 on the engine but I want a low rpm torque cam for mileage and able to use 87 or 89 octane fuel and as near a 300 HP as possible. I really like the Comp Cam XE250 cam, but the best deal from Manufacturers Wharehouse only offers Melling cams and the MTC-1 seems to have too long a total duration for economy. The question is can I find a way for under $1600 to get an engine with low rpm torque (2.79 rear gear!). I have a set of good, bare 461 heads but with 62 cc chamber, I can't find a short block that will yield something near 9:1 C.R. What kind of mileage can I expect with a 9.1 CR, Melling MTC-1 cam and cheap rams-horn exhaust manifold; I have a cast iron intake and a useable Q-jet carb. The Magoo 29 claims 18 mpg with a 3.08 rear and a hi-po 327, can I find a way to get 20 mpg? I look forward to expert communication.

Don Shillady

I have a 383 stroker with t-5, and 3.42 gears in my 34 Ford 3 window, Weighs 2150 lbs, gets 17 driving easy, which I did once, just to check the mileage. 300 hp on regular gas, turbo 350 trans, and good mileage seems like a reach. Maybe a 4x4 high torque cam will make it feel like 300?

Well thanks for some replies. It looks like I can expect 16 mpg so I will have to opt for lower compression to favor 87/89 octane fuel. One other idea/question is about Rhoads lifters. What is the collective experience on variable lifters? Can I use say a Comp Cam XE270 for high rpm HP and then have a 258 degree cam at low speed? Japanese high tech engines now use variable lifters even though U.S. street rodders have had Rhoads and Crane variable lifters for years. Are variable lifters noisy? Does use of a high volume oil pump spoil the effect so that one should use a stock oil pump with variable lifters? Why don't more rodders use variable lifters? The bottom line is: can variable lifters help mileage AND keep high rpm HP?

Don Shillady

Well thanks for the welcome. I apologize for some long posts, but I tend to be a motor-mouth and after lecturing for 33 years I am able talk about any subject for 75 minutes! Today has been a beautiful day! Yesterday I received my TCI 4-bar kit for my 2.79 Maverick rear and today I found a friendly welder who did a great job for a very reasonable fee. Mr. Gary Dye of "Best Welding" is a bit remote but a friendly "Harley Man" with a neat MIG welder. He is down on Route 460 just off of I-295, east of Petersburg VA and asked that I advertise him a bit for rodders in the mid-Atlantic region. He is right next to the Mid-Atlantic VW Garage with an impressive number of junk VWs to choose from. Anyway, I guess I am a bit over my head in discussions with Brickman and Richard/TechInspector1 regarding squish. Briefly I have learned that probably I can increase the mileage of my roadster (SBC350/TH350/2.79:1 Maverick rear) with a short duration cam AND I CAN RUN HIGH COMPRESSION IF THE SQUISH SPACE IS SMALL. Richard's suggested 0.035" clearance seems tight to me but the good news is that by using a Felpro head gasket with 0.015" compressed thickness and a standard deck height of 0.025" the squish space should be 0.040". I am reluctant to go all the way to 11:1 C.R. but I can now hope that with tight squish space I might even be able to run 89 octane with a 9.1 C.R.???? With my "Copper Parachute" retirement package I probably will choose a low end crate motor from Automotive Warehouse in Charlotte and trade in my '76 Corvette two-bolt 350 for a 4-bolt 9.1 CR engine. The only problem is that they only sell Melling cams and so I will have to choose from their standard cams. Well I note that the original Model-A engine made 42 HP at 2200 rpm and used a 3.78:1 rear with 21"/19" tires and achieved 20 mpg. While a 260 HP 350 with a short duration cam might not deserve "He He He", at about five times the original HP it ought to deserve a "He He" and maybe I can crack the 20 mpg barrier and still cruise at 70 mph running only about 2200 rpm. I am amazed to find this forum when I had so many questions. It is really a GREAT FORUM with a lot of collected expertise and I am glad to have found it. If I can keep up the fast pace of construction I might be on the road by next summer and realize a life long dream of owning a Model A roadster? I hope to become just an assembler but running the brake lines look like the next challenge. This is progress report rather than a question, but I might ask other roadster owners with coil-spring rear suspension how to choose among the three holes in the shock mount. The obvious answer is probably to use the middle hole first and see how it sits? I like the "down hill" stance so I may end up jacking it up in the top hole but I guess it depends on tire size.

Best Wishes,
Don Shillady
Retired Scientist/teenage rodder

Streets,

Thanks for your reply. Well so far no pictures. All there is a is a Brookville frame, Magnum 4" drop front end with sping and disk brakes and as of yesterday the 8" Maverick rear with TCI brackets welded, sanded and painted black (according to Henry Ford). I still have to bolt in the Vega steering box and the cross-steering setup. Walking around the VW junkyard during the welding yesterday I noted how much smaller almost every part is; expecially the main drive spline. Still I am reminded that on quite a few occasions I was able to pull a VW engine by removing just four bolts and using a floor jack to lower the engine. Since there was almost no sheet metal on my 1600 cc Dune Buggy I only had to disconnect the electrical wires and fuel line to drop the engine! Well I guess I will have to buy a "cherry picker" to install the combined SBC350/TH350. I don't know yet if I will buy a Heritage or a Bebops body but both use the combined fenders and floor all in one piece and both fit the Brookville frame that I have with the rear arch behind the rear instead of over the rear. I don't see any sense buying the body until I get a rolling chassis. On my budget and taste from '50s memories, my goal can be seen on the Heritage body website showing plain steel wheels with baby moon caps and an Ididit steering column. For some reason steel wheels and baby moon caps on a '29 really "sends me"; maybe something in my brain from age 17 is still in there! I am willing to accept the razzing from this group because I have already learned a lot and I finally found a place to get expert answers. There are going to be a lot more questions, but maybe other readers can learn along with me. Back to the main issue, if the Magoo '29 reported 18 mpg with a 3.08 rear and a hi-po 327 should I not expect 18-19 mpg on the highway with a 9.1 CR 350 and a MTC-1 cam (similar to Edelbrock Performer-plus cam; NOT exactly a short duration cam!) with a 2.79 rear gear? Well there may a lot of compromises along the way to getting a roadster that runs, but let's not forget the main goal of having a roadster that runs! I will try to get this forum an end-of-summer picture of the chassis, but I doubt if I can get the body on this year? Maybe I will just buff the fiberglass and run it black for a while???

Best Wishes,
Don Shillady

Techinspector1,

Thanks for the Elgin Cam address and the other site on lobe separation. The cam you cite has less lift and duration than the stock 350 cam, but I guess 3-5 mpg has to come from somewhere. From the tight lobe separation it might be a mistake to add 1.6 rockers on the intake valves? I am still digesting your claim regarding the squish and 11:1 CR. I have played with the automatic C.R. calculator from Cambellenterprise.com and the PAW catalog and there are several possibilities ranging from flat top pistons to 22 cc dish pistons to use my old 461 double-hump heads and various gaskets to achieve C.R. from 8.8 to 10.7. Then again I could buy a low end crate motor with 9.1 C.R. and replace the cam. I still like the Comp Cams XE-250 which is also marketed by Elgin. However, my first choice would be a Holley-Lunati "Avenger Truck Cam", 253/265 adv. dur., 204/216 @0.050", 112/107 lobe sep. with 0.427"/0.454" at the valve because it has higher lift and the claim is that it will operate with stock springs. You bring up a deep issue in "hot rod philosophy" as to what are we trying to do? I had hoped that I could use a medium range cam with Rhoads lifters to get BOTH mileage at low rpm and occasional "performance" at higher rpm. So far no one says the Rhoads lifters are worth anything but clicking noise, so I am back to the choice of MPG OR PERFORMANCE, not both. Thus I would prefer the Avenger Truck cam or the Elgin 5870 (their second cam). How sure are you that if I were to use 0.025" deck and 0.015" gasket (0.040" squish) with 10.7:1 I would be able to use 92 octane pump gas without detonation? If so I may build up my present block rather than trade it in, otherwise I will just order a crate engine with 9.1 CR and swap in the Holley Avenger Truck cam. You are the expert!

Don Shillady

Richard,

Thanks for your prompt reply. I get the message about small squish for high C.R. but as a former/retired scientist HOW/WHY does it work? Maybe the small squish volume prevents buildup of carbon deposits which form hot spots? What is your explanation as to why the small squish prevents detonation?

Don Shillady

Richard/All:

Well "magic" is not a good answer for me but there is a pretty good answer from Speed-O-Motive at:

http://www.speedomotive.com/Building%20Tips.htm

Apparently for squish between 0.035" and 0.060" the gas is squeezed sideways to create TURBULENCE that reduces detonation. In addition, if the piston comes close to the underside of the slightly cooler head, some cooling of the piston occurs, again reducing detonation. Also no benefit seems to show up if the squish is more than 0.080" but 0.060" might be needed to allow for rod stretching at high rpm (>6000). This answers my question that 0.025" deck + 0.015" gasket = 0.040" squish would work and be a little safer than 0.035". In addition I have learned from Richard that he thinks any cam with more than 200 degrees duration at 0.050" lift will degrade mpg. Thus my search for the ultimate cam now looks like GM part No. 3896929, the original 300 HP cam for the SBC 327. The duration of this cam at 0.050" is listed as 195/202 with lifts of 0.390/0.410 I/X. This cam fits Richard's formula for mileage and if I can get 300 HP with this cam in a 350, that is enough for me just cruising and telling myself I am getting 300 HP, although I think I will add an Edelbrock Performer intake and ceramic-coated short tubular headers. Well Richard is the expert with a little help from Speed-O-Motive and I have learned a lot. What a Forum!!!!!

Best Wishes,
Don Shillady
Retired Scientist/teenage rodder

Street/Tech1:

No offense intended. It does make one ask what is the intended purpose of the car. I recall I did annoy some of my science colleagues by asking Why, Why, Why? I have little or no intention of bracket racing, although many on this Forum are interested in some form of racing. Thus I am just interested in "brisk performance" with reasonable mpg. Richard was the only one to respond about how to improve mileage, but I do not want to go to extreme measures like high pressure tires and keeping my eye on a vacuum gauge or other measures which can lead to extreme high mpg in an impractical way. Thus I am glad for the information Richard has provided and the additional info from Speed-O-Motive cited above. My "worst nightmare" is the first Tech Inspection of my car at a Street Rod event, which I recognize is necessary but there are so many parts in a complete buildup that I will have to go through Virginia State Inspection just to get on the road and then a Street Rod Tech Inspection so maybe they will find flaws that need fixing right away. Well again I know now how to plan for good quench/squish to achieve higher C.R. which leads to higher power and better fuel efficiency and Richard's 200 degree duration limit for mileage. The 300 HP 327 cam does indeed look good now for cruising. I hope that when I get the car on the road I will be able to travel and meet some of the folks on this forum. Thanks again.

Don Shillady
Retired Scientist/teen rodder

Richard/Tech1,

Thank you VERY MUCH! You read my mind regarding lock washers. All the stuff from TCI has NyLok nuts and I wondered about them. Actually on the four-bar bolts I would rather have cotter pins, but clearly lock washers on anything that rotates will not work very long. Back to my cam obsession. I take it that your recommendation of the VERY short duration cam with 184/194 @0.050" ASSUMES the small squish/quench volume we have been discussing. I checked the Melling catalog again and they have the same cam as well as a replica of the 327 300 HP cam. I don't know the C.R. of the 300 HP 327 but I assume it was pretty high, maybe 10.5:1; I know the 327 350 HP SBC had 11:1 C.R. Since I am mainly flirting with the Automotive Warehouse people in Charlotte and they sell only Melling cams, I now can specify several of the cams we have discussed. Getting back to "what am I trying to do?", I want a little more performance than the stock cam (260/268 @0.006", 194/202 @0.050", 0.383/0.401 w 1.5 rockers), so what about trying to recreate the 327 300HP with the 350 block? If I can't see potential for more performance than stock, I will probably go with the 327 300 HP cam. If I use the 184/194 cam will I get better mpg AND more low rpm torque? The description of "poor" performance above 4000 rpm does not sit well with me and I guess if I have to wimp out and take the well worn path to performance at 16 mpg I may do that. Are you saying that the very short cam improves torque up to 4000 rpm? Thanks again, it is great to be able to chat with experts on this Forum.

Best Wishes,
Don Shillady
Retired Scientist/teen rodder

Richard/Tech1,

Well I have indeed learned a lot about high compression related to the SBC and I do not want to annoy you. Within the limit of your patience, I will ask one last question. According to the Speedway catalog, Rhoads lifters reduce duration by 10-15 degrees and lift at the valve by 0.020-0.030". You have hinted that they do work while others have responded on another thread that they just make clicking noise. Therefore my (last and also first) is what cam specifications would be within range of the variability of Rhoads lifters to achieve BOTH fuel economy below 2500 rpm but still allow performancement in the 4500 rpm range. Thinking over what rodders want it is to be "slick" beyond the average family sedan,and yes I do want BOTH mileage and performance. Since I now realize the Melling MTC-1 cam is almost the same as the Edelbrock performer with specifications: (I/E)

278/288 @0.006", 204/214 @0.050" lift and 0.420"/0.443" at the valve

Or should a shorter duration cam be used? I would expect the Rhoads lifters would effect the 0.006" duration more than the 0.050" duration. Assuming I can put up with the clicking noise, does that hurt the longevity of the lifters?

Thanks a lot for your previous helpful comments.

Don Shillady
Retired Scientist/teen rodder

Techinspector1,

Putting aside the discussion of the optimum mpg/performance cam, let's get back to the question of lockwashers. I have assembled the TCI four bar assemblies with the bolts just finger tight. The bolts came with nylon locks instead of lockwashers. My question is which side of the nut goes to the outside? Is the nylon supposed to be on the inside and be crushed to a lock? Or is the nylon supposed to be on the outside? IT is much easier to start the nut and put the nylon on the outside. This is a simple question, but I want to get it right.

Don Shillady

Street is Neat!
Thanks for the quick reply, I should have waited for your reply but I paid for the call to Calif. and got the same answer from the TCI Customer Service. Next time I'll just sit here and save the cost of the phone call (NOT an 800 No.!). For interested listeners, there is another point about the rear four bar. There is a heavy 1/4" oval plate that fits over the two bolts on each side as a reinforcement to maintain the spacing between the upper and lower bolt. I did not know how to phrase a question about that here and that is why I called TCI. I suppose on a 9" rear with a 400 HP setup there might be a chance of bending or wrinkling the rear mount brackets, but on my 8" rear and only a 250-300 HP motor those plates placed on the outer part of the rear brackets should be more than adequate to keep the rear aligned without "drag twist". Streets I am pleased that you take an interest in my roadster, I guess there is a responsibility with a classic roadster to do it right so I'll probably have more questions as I build.

Best Wishes,
Don Shillady
Retired Scientist/teen rodder

SBC Mileage?????

Today I spent some money on brief phone (non-800) chats with Tech people at Crane Cams and at Speedway Motors, the main two sources of variable hydraulic lifters. The guy at Crane was really sharp on their many products, but had never heard of using their "Fast Bleed Lifters" or "High Intensity Lifters" for low rpm torque or for added mileage. The Tech guy at Speedway Motors was more open to the idea that the Rhoads lifters add low rpm torque and that it could lead to more mileage, but said that with a SBC350 it would be tough to get above 18 mpg. Well, I know I have already disagreed with some experts on this forum but for my money I am probably going to try the Rhoads lifters with a Melling MTC-1 cam which is a very close approximation of an Edelbrock Performer plus cam. If (??) the Rhoads lifters take about 12 degrees off the 0.006" lift of the MTC-1 it should be a very good torque cam in the low rpm range (nobody seems to know at what rpm the lifters will pump up fully, it depends on the oil used and the condition of the oil pump) and at higher rpm (4000 ?) I should get the full benefit of the longer duration just like a Performer Plus cam. My wife says that she will not mind the clicking of the lifters if it means more mpg so I guess I am working toward "doing the experiment" with:

SBC 350, medium valves 1.95/1.55 in 76 cc heads but with 0.015" steel shim gasket and decked block for squish/quench of about 0.035"-0.040". The cam will be a MTC-1 with Rhoads lifters. The car will be about 2500 lb. (Model-A roadster + us) with a TH350 and 2.79:1 rear from a '74 Maverick (8"). The engine will have short tubular headers and turbo mufflers.

With no intention of offending anyone here I have had to thrash out what I want, namely performance AND mileage! The Tech guy at Speedway said circle track racers use Rhoads lifters to gain low rpm torque while using long duration cams for speed on the straightaways so I think I am on the right track except that I am looking at a lower rpm range where the lifters pump up for a smaller cam. Unfortunately I probably will not know if this works until next summer since I am just assembling the chassis, but if anyone tries this before then I would like to know the results. Who knows, maybe gas will be over $3.00/gallon by then?

Best Wishes,
Don Shillady
Retired Scientist/teen rodder

Well I guess I am talking to myself because hot rods are by nature performance machines, usually without regard for mpg. Anyway TechInspector1/Richard suggested a short duration cam and I guess I "ticked" him off discussing Rhoads lifters. Anyway, I have continued to study the situation as the time approaches to purchase a crate engine this Summer. Here is a comparison of some similar cams mainly so Tech1 knows I am still thinking.

Cam Adv Dur. I/E 0.050 Dur. I/E Valve Lift I/E LCL I/E

Elgin 5911, recommended by TechInspector1
260/270 184/194 0.368/0.398 104/104

GM-Crane Part No. 12353914, Lo Speed, Hi Torque
180/194 0.378/0.401

Mellling 22108 (Probable Choice) *****
260/270 184/194 0.368/0.398 104/104

Holley Truck Avenger, Lunati 90350LUN
253/265 204/216 0.427/0.454 107/112?

Corvette 327 300 HP
195/202 0.390/0.410

Melling MTC-1 ( the same as Edelbrock Performer Plus)
278/288 204/214 0.420/0.443 107/117

CompCams XE250
250/260 206/212 0.432/0.444 106/110


It is clear that small changes in the cam can make large differences in performance and mpg. The claim of the Elgin 5911 is an increase of 3-5 mpg. In addition, it is my understanding that if I purchase a crate engine fom Automotive Maufacturers in Charlotte I must use a Melling cam and the 22108 appears to be identical to the Elgin 5911 and maybe that is the way to get 20 mpg with a SBC 350 and still have fast 0-60 mph acceleration, by sacrificing higher mph needed for short 1/4 mile times. As TechInspector1 says, for light-to-light acceleration one needs high torque and maybe the Melling 22108 is the way to get BOTH
traffic light performance and highway mileage. Anyway, if I think I need more torque I can add 1.6 ratio rockers later without changing the cam! Sorry about another long post, but as the price of gas goes up this topic may become more relevant!

Best Wishes,
Don Shillady
Retired Scientist/teen rodder