The Stovebolt Site Forums The Shop Area The HiPo Shop My approach to V8 conversion (Long)

I recently converted my 1952 GMC 3/4 ton long-bed 3-window pick up truck to a 355 Chevy small block V8. It runs very well and is strong, strong, strong. But I still have one task left before it's road-worthy. So for the benefit of others wanting to make this conversion, I am posting my approach. The reason for this is because I wouldn't consider this a straight-out swap. Absolutely everything seems to require custom-work and modification. Everyone will have a different approach to this, but here are mine.

Mounting the engine:
Speedway Motors has a few different kits for custom mount applications. The one I chose was a solid-type mount on a metal bar that acts as a crossmember, that can be either bolted or welded onto the frame. I chose to bolt onto the frame because I discovered that this bar REALLY needs to be able to swing and move in order to move the engine rearward to mate with the bellhousing. This is a very narrow engine bay, and I think if I welded it, it would have been disasterous.

Transmission mounting:
I chose to use the stock Muncie 4-speed SM420 because it's such a rugged transmission and I really like the supergranny gear. You can move a mountain off its foundation with that 7.06 first gear ratio. There are bellhousings that mate to this transmission, which are cast iron, and are common in salvage yards. I believe they were used on 292 applications well into the 70's. They have a standard Chevy bellhouse bolt pattern except without the top 12:00 bolt, so they work. I had a 1968 Corvette flywheel for a 10.5" clutch sitting around, from when my Vette was a 327. I had a new ring gear put on and had it resurfaced. I bought a brand new stock '68 Vette clutch and a '68 Vette starter motor, and this works well. I took measurements from the engine to the transmission and found it to be exactly the same as it was for the 235 motor. So I reused the cast iron clutch fork and stock-style throw-out bearing. The stock clutch pedal works fine.

Steering & Exhaust:
Basically what I did was to keep the stock steering for now. I didn't want to get a brand new steering set up until I've completed my 4WD conversion, which will change everything anyway. I just wanted to make the stock steering work for now. Actually, someone here on this forum gave me the idea.

If you unbolt the steering box and do some minor sheetmetal clearancing at the firewall, you can move the box about an inch to inch and a quarter outboard. But to hold it there, you have to use longer bolts and shim it over. I "shimmed" it using brass pipe connectors that I had, but you can use anything.

Keep in mind that it's still very tight. I took out each of the 3 bolts on the engine-bay side of the steering box and replaced them with grade 8 bolts that I had shaved down the heads on with a grinding wheel. Even with that and the shimming, I could not really fit anything in there except stock exhaust manifolds. And because I am using a single-pattern Iskendarian cam that requires a good exhaust system, I really wanted headers. So I picked up a set of 1986 Corvette shorty headers and turned them upside down like you would for a twin turbo application, with the collectors turned up. Then I made my own pipes using 2.5" J-bends, mandrel bent and aluminized. To address the heat issues, I wrapped everything in fiberglass header wrap. That is how I avoid burning everything from wires and hoses to the back of my hands. The J-bends go back down in the rear corners of the engine bay.

Underneath the truck, I used all mandrel-bent 2.5" aluminized pipe. I bought a Summit Racing X-pipe crossover kit for about $85 bucks and have 12" leg 90 degree bends going directly into the X-pipe. The kit comes with four 45 degree bends. I used two exiting the X-pipe and going into 24" long Autozone-brand aluminized 2.5" extensions, and then into a pair of Thrush Super-Turbo aluminized mufflers. Exiting the mufflers, I used two 90 degree 6"-leg aluminized 2.5" mandrel bends pointed outwards, and then used the other two 45 degree bends that came with the X-pipe kit to point it back. Then I bought two Heart-throb brand chome slash-cut tail pipes, 18" x 4" and they exit just in front of the rear tires and stick out about 2" beyond the side-steps. They look nice.

Brakes:
This is the last part of the conversion that I'm still working on. The stock brakes won't work because the brake pedal pushes on a lever arm that hits the exhaust on the V8. For this, I am turning back to Speedway Motors for a solution. They sell a swing-arm racing pedal that mounts to the firewall. On the other side of the firewall, you can use either a power brake booster, or just a manual master cylinder. But it has to be a twin, tandem master cylinder to develop enough pressure for the stock drum brakes. You can use a Chrysler-style master cylinder. I am using a manual master cylinder, but I may change my mind later. The pedal has a 7:1 ratio and the master cylinder has a 1-inch bore, which is what Speedway recommends for manual brakes.

Other Considerations:
Firewall: If you use the stock SM420 transmission, it sets the V8 very close to the firewall. You will have to modify the firewall in 3 locations. Where the valve covers go, and where the distributor goes. It might be better to use a non-HEI distributor because you won't have to do so much modification. I used an HEI, which works, but you only if you push the firewall back a good inch.

Alternator: I used my old IROC alternator and bracket, because it's a big, 93 amp alternator and it uses a 3/4" wide ribbed belt which is harder to roll or throw. The alternator is on the passenger side. I plan to reuse my IROC tuned port injection once I buy the $400 stand-alone wiring harness. Why? Because these trucks LOVE torque, and nothing makes better torque than the TPI. But for now, I'm using a Holley carb and dual plane manifold. In the future, I plan to twin-turbocharge, since the headers are already in the right location, there is loads of vertical space under the hood, and the TPI responds well to forced induction.

Radiator: Not wanting to spend $600 bucks on a stock-style radiator, I went with a modern 3-core truck radiator and mounted it right behind the stock truck grill. I had to fabricate the fan shroud using galvanized sheetmetal. I'm using a stock mechanical fan with a fan clutch and a 2.5" spacer, but I will probably eventually convert to twin electric fans, also off the IROC, which were aftermarket and expensive! The radiator is copper/brass, painted black, and that was chosen because you can't see it through the grill, and so the truck looks stock...if you ignore the sewer pipe exhaust sticking out in front of the rear wheels.

Gauges: I'm switching over to Autometer 5" Antique Beige gauges, which fit the holes and are beautiful. So contact me if you want my old gauges for a good deal.

Wheels: I wanted more of a modern ride, so I got rid of the split-rims in favor of stock chrome year-2000 GMC wheels. They're 16" and have Uniroyal 265/75R-16 steel belted all-season truck tires on them. Look great and ride a thousand percent better than the stock "school bus tires".

Rear Diff: I have the stock 4.56 diff, but since I don't want to cruise at 75 mph at 3800 rpm for the rest of my life, I will be switching over to a Ford-style Dana-60 rear diff with 8-bolt lugs that still fit the GMC wheels and has 3.73 limited-slip. That will lower my 75 mph rpm to about 3100, which is doable.

Gas Pedal: The stock one won't work at all. So some kind of a cable-type aftermarket pedal is needed. I bolted the stock pedal to the floor and used it to mount my aftermarket pedal to. The position is much more comfortable for long drives without fatiguing my ankle so much.


This truck looks TOTALLY stock, so it loses none of its appearance to the V8 conversion. Probably not the smartest choice with $4 a gallon gas, but I figure the 16 mpg I was getting with the weak 235 motor was no worse than the 16 mpg I could be getting with a far-stronger V8. And that will improve once I put the TPI fuel injection back on.
This 350 is not a stock IROC motor. It is a 4-bolt main truck 350 from the 70's. It has 10:1 compression, ported and polished heads with 1.94/1.55 valves, and an Isky 270-Megacam with 221/221 degree @ 0.050" lift. In the TPI IROC, it pulled strong to 5000 rpm, so the combo works.

...Bring on the Porsche Cayennes.

You mention several things I want to ask about, and one that worries me a little.

I'll start with the worry. In my experience brass isn't a structural metal, and is both soft and maybe a bit brittle. I'd worry that as you use the truck the brass is going to allow some movement, and as time goes by slop in the steering will develop, and perhaps those pipe connectors would crack and break.

I might be overly cautious, but steering and brakes are too important to take chances. Maybe I've got the wrong picture. If these pipe connectors are huge blocks of metal it may be fine, but what I picture is much thinner material.


Regarding the rear you plan to switch to, you call it a Ford type Dana 60. Is there a reason for choosing a Ford type? The Dana rears were used under GM and Dodge trucks too, and I'm just wondering why you would specify the Ford.


If you've mentioned your plan to go four wheel drive in other posts about this truck I've failed to notice. I'm curious how you intend to aproach that conversion. What transfer case you'll use, how you'll connect it to the transmission, and what front axle you'll use.


I have a set of 265/75-16 tires I've though about putting on my 1-ton. From your description the stock GMC wheels from a later truck may be a good choice in doing that. Can you email me some pictures, or tell me where they are posted? I'd love to see how yours looks with those wheels and tires.

Your concern may be well-founded. I only used brass because that's what I had. It is, however, a soft metal and would sooner bend than to crack. However, perhaps a nice, thick, steel pipe, cut to the length I need, would work better. I'll put that on my to-do list.

The reason for the Ford Dana 60 is because that is what I found. The width seemed compatible and the 8-lug GMC wheels fit. The price was right, it only cost me $200. I bought it from a friend of mine.

The way I plan to convert to 4WD is this:
I have a Muncie SM465 transmission out of a tow truck. I intend to mate it with a married transfer case. I found a company that does this service when they rebuild it, but I don't remember the exact type of transfer case. I'll have to look at the old e-mail from them to tell you. The front driveshaft I plan to use is on the passenger side.
Then I plan to use a Dana 44 front axle with the same gears of course, 3.73. This will require rebuilding of the front suspension. Speedway Motors does sell components to convert to a wishbone suspension. This is probably the method I'll use.

Yes, I do have a picture online. I will send it to you from my cell phone. It's not a high quality picture, but it gives you a general picture. As you will see, my truck looks stock from the outside.

Steve, did you get my e-mail okay? If not, let me know. I sent it from my phone, but being a T-Mobile Shadow, it is not very user friendly, and I don't get a confirmation message.

Got it!

It does look very stock except the wheels. I was mostly interested in how the wheels fit under the fenders, and they look right, and it does not appear the tires would rub the fenders at all.

In actuality, the tires are much smaller in diameter than the ones it came with on the split-rims. I wondered if they would rub when I saw the new ones, but they don't. I have an error in the speedometer that is somewhat profound, but the new Autometer gauges have a programmable speedometer, so I can correct the error.

One thing I personally don't like are trucks converted to low riders. I really like my truck remaining high-riding. I think they look better that way. Although I would love to modernize the front suspension so that it's not so dangerous with the bump-steer and stiff leaf springs, it is hard to find a conversion kit that doesn't assume you want the low-rider stance. So whatever I come up with will probably have to be customized to some extent...typical. What hasn't had to be custom?

Hey Hot Rod Dad here is a thought for making your steering shims if you have a hole saw kit cut some pucks out of the appropriate thickness steel plate. This works well for spacers for most anything and the round puck from the center of the hole saw will have a pilot hole in the center that can be redrilled to desired size.

Hot Rod Dad

How about sharing some pictures Buddy?

Did it have a bump steer problem before you moved the steering box? If you read my thread about power steering bump steer is something I'm working hard to avoid as I convert my 1-ton to power steering.

Yes, it always had bump steer. The most treacherous is when you encounter a bad rut in the road or hit a bad expansion joint while making a turn on the highway. It's very stiff, so it would prefer just to jump over bumps like that than to keep the turn you need to make. A cross steer system is supposed to reduce bump steer, but a rack and pinion works better.

My digital camara is on my cell phone and it's horrible. I need to take conventional flash photos. Don't know how I'll put them on the internet though.

Here's a deal on a digital camera, $32.00 includes shipping.

Hey Hot Rod Dad I know that Wal-Mart will give you a digital disk of your standard type when they process your film if you ask.

Yeah but the photo size (bits) is ENORMOUS. If they can cut it down to something more easily e-mailed, that would be possible.

You can shrink the size of photos using tools that come with Windows XP and I assume with Vista. I don't know what you use, but I'm sure something similar is possible with a Mac.

Or you can mail that CD to me, and I'll shrink them and put them where the rest of the gang can see them too.

Sounds like a great idea. Okay, I'll load up some film and photograph everything pertinant. I'll let you know.

Great news. I took a closer look and the brake lever arm just barely touches the headers. So I cut a quarter inch off the corner and adjusted the brakes as far as I could, and it was enough. I've got brakes!

I'm still going to upgrade the brakes though, because the originals aren't that powerful.

Took it out for a drive last night and it was sweet. The 350 pulls so much better than the 235 did. It's got plenty of strength. Feels like I've got to adjust my vacuum secondaries so they open sooner. But it's nice. I'll get plates on it this week and it'll be on the road.