Techin’ In With Fletch - November 2013

Technical editor Dan Fletcher discovered that there are a few more oddball deals out there that confuse things even further, and apparently a 1968 307 Nova, specifically, is one of them.

Dan Fletcher Dec 18, 2013 0 Comment(s)
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Mount It Properly

I have a 1968 Chevy II that was an original 307 car with an automatic transmission. I bought it with a 350 and an M-21. The 350 became unhappy, so I am putting in a 408 SBC. I bought some Moroso solid engine mounts, and am using the stock frame mounts. The driver’s side installed properly, but the passenger side is off about a full bolt width. The Summit website shows three different Moroso engine mounts with SBC applications, and I suspect I did not choose wisely.

I have had all sorts of advice, ie: use rubber mounts and chain the engine, just elongate the frame mount holes, unbolt the frame mounts attach to engine mounts and weld to sub frame, etc. I’m in need of some good ideas. Should I go with a front motor plate with a rubber transmission mount? The car is a driver, setup for autocross and the odd dragstrip session. Thanks for your time, and I hope to see you at Bandimere soon.

Kasey Renken
Fort Collins, CO

I have a somewhat decent level of experience here, as it’s a similar set up as my ’69 Camaros. You don’t mention which part number you bought, but I only really see two choices for a small-block in your car, part numbers 62500 and 62510, and I believe you are going to ultimately want part number 62510. Here is a link to the Moroso website and corresponding information regarding your configuration: www.moroso.com/catalog/pdf/Motor_And_Transmission_Mounts_191.pdf

The whole big-block vs. small-block frame mount thing can get confusing; this I know from personal experience. But after researching your question, I’ve discovered that there are a few more oddball deals out there that confuse things even further, and apparently a 1968 307 Nova, specifically, is one of them. To that point, I’m guessing the motor mounts that were on the 350 you removed were modified to facilitate the install.

I called my friends at Camaro Specialties in East Aurora, New York, for some help after I started to uncover some irregularities in the scenario. Saving you all the gory details, I think the root cause of your problem very well may be the frame mounts, which I’m guessing are the ones that the car was born with as a 307. There is something “off” with that particular configuration. I would order and install new small-block frame mounts. These are readily available, and a ’67-’69 Camaro mount should work as well.

With all that said, look at the Moroso chart closely, and evaluate your situation. Again, I don’t know which of the two part numbers I’ve mentioned above is the one that you’re using, but maybe the other one gets you lined up without a frame mount swap. I don’t think so, but stranger things have happened. And no matter how confusing things may seem right now, I certainly don’t see a need for cutting, welding, etc.


This Doesn’t Suck Much

I have incredibly low vacuum on the 454 in my 1970 Camaro. It is at 9.5 both at idle and in gear. I have fixed some really bad vacuum leaks, yet the vacuum remains low. The engine has probably 20k on it, but was rebuilt way back in 1986. The cam I chose at that time was a Comps Cam 282H, which I have very little information on regarding the specs. It recommended a higher stall converter, and I chose to go with a used B&M Hole Shot. The throttle shafts are a bit worn in the Holley 750 cfm 4160, and I plan on having it re-bushed, but when I manipulate the shaft the vacuum or idle doesn’t change. Is this low vacuum a problem? Is the cam a culprit? I like the way the engine runs even though I know it could use some modernization in the cam and cylinder head department. Any input would be greatly appreciated. Thanks.

Jim Erskine
Vacaville, CA

First off, I guess one can call 9.5-inches of vacuum at idle “low”, but frankly, I wouldn’t be the least bit concerned about it, especially if the car otherwise runs and drives in an acceptable fashion. Secondly, it appears as though the cam probably is in fact the “culprit”, as your combo is producing virtually identical vacuum numbers as compared to the Comp Cams dyno test. Check it out here www.compcams.com/v002/Pages/397/XR282HR-10.aspx.

Again, if you’re happy with the car’s performance, and any and all vacuum aided features work well, then I say disregard any concerns you may have and mash onward…


Block Number Crunching

I have a 350 block that I intend to rebuild. The number 3970010 is stamped on the block behind the driver’s side head. Can you give some info on this block?

Bow Tie Iron Guy
Via email

That particular engine block was produced over quite a long period of time. The first year of production was 1968, in which case it was a 327. In 1969-1979, that engine block casting number was strictly for a 350, and it was produced in horsepower ranges varying between a low of 185 and a high of 370. It could be either a two- or four-bolt main, and it was used in a wide array of vehicles, from cars to trucks, and even in Chevy’s two-seater, the Corvette.

If you can still read the engine ID code (as in it hasn’t been obliterated by a decking process), you can learn a great deal more about the history and original application of your motor. The engine ID code is located on a pad in front of the passenger side cylinder head, and it will contain the assembly plant code, production date, and a suffix code that will speak to the application. Additionally, the VIN code will add to the story. In ’68 and ’69, this would be stamped in close proximity to the ID code. In later years, it may be found on the block pad, above the oil filter, or somewhere on the transmission flange. The combination of these two inputs, along with the engine block casting number, tells a pretty complete story of what you have and the history behind it.


Rim Size Query

I have subscribed to Super Chevy since 1984, and I am the proud owner of a 1983 Z28 with four-wheel OEM disc brakes. The original factory rims were 15x7-inches. My question is, will a 1991 or 1992 IROC style 16x8-inch wheel fit my car? I know there is a front and rear rim difference. I appreciate any help that you may provide.

Keith Franklin
West Bloomfield, Mi

Keith, as I often do for this type of question, I consulted my tire and wheel expert, Don Raiser, at Tread City Tire in Buffalo, New York. The late-model IROC wheel will in fact fit your car, however, there does exist an issue with the hub diameter, both in the front and rear. The application dictates hub centric fitment, and the late model wheels have a larger diameter hub than your ’83 model. With that said, Raiser tells me that all you need to do is have the balancing operation performed by the Hunter Road Force process. This will balance to the bolt-holes and should result in a dead on scenario with no vibration issues.

Your original 15x7 wheels came with a 215/65/15 tire, so obviously you’re going to need some new 16-inch rubber to complement your late-model wheel choice. You can go with either a 245/50/16, 255/50/16, or a 235/55/16 tire for your application, but Raiser recommends the 235/55, in part due to ease of procurement.


Got a restoration question that’s been puzzling you? Send it to: [ m ] Super Chevy, Fletch, 9036 Brittany Way, Tampa, FL 33619. [ e ] questions4fletch@yahoo.com [ f ] 813/675-3559

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