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PostPosted: Sat Apr 20, 2019 2:43 pm 
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Today I ran a 373 Cleveland on my dyno. This engine was a freshen up build for a Pantera. It was built long ago probably in the 1980's using an offset ground stock crank with a 3.660 stroke. That along with a 4.030 bore makes a 373 cubic inch engine. It came in messed up from old gas, a broken valve spring and a solid roller cam that had several lifters which were coming apart. The pistons were fine after a short soak in some lacquer thinner to remove the sticky stuff from the old gas. Same for the block and heads which needed only a trip to the hot tank, a little honing and a valve job to get back in shape.

It has a set of 5.7 length Oliver rods and a set of Venolia pistons. All of these parts were good and were reused along with a fresh set of rings and bearings. Clearances are approximately .002 rods and mains. It has a new Avaid Pantera oil pan and a stock Melling oil pump pumping Valvoline 10W-30 oil.

It has a set of what look like Isky 1.73 rocker arms, chrome moly retainers. I used a PBM double spring and a set of Morel hydraulic roller lifters. The engine was set up to use a 3/8 pushrod. The cam is from Demos' Cams and it has one of the new DM lobes that I had designed late last year. It has a .310 lobe for .536 lift with a 1.73 rocker and 214 duration at .050. on a 107 lobe sep in on 105 intake centerline.

Heads are Boss 302 heads fitted with stainless steel valves. They may have had a very small amount of porting done to them a long time ago.

The intake is a stock Ford Boss 351 factory intake that somebody ground on a little bit to make a regular Holley carburetor fit. No carburetor spacer was used. I ran the engine with a set of headers and exhaust system for a Pantera. The headers are 1 3/4 primaries with 2.5 inch collectors into a 2.5 inch pipe which feeds a muffler with two outlets. Not the greatest but its what fits on a Pantera.

For a carburetor I used my 4777 650 Holley that I had built by Competition Carburetion. Its nothing fancy but it does have the choke horn removed and it is fitted with down leg stepped boosters. It is a really great running little carburetor.

Distributor is an MSD that came in the engine . I ran several pulls to find what it liked for timing and 35 degrees total was best with Mobil 93 octane gas and an engine temperature of 185 degrees.

The engine made peak torque of 435lbs/ft at about 3500rpm and 424 horsepower at 5900rpm. I was amazed that the engine managed to power peak that high with such a short duration camshaft. The customer wanted a very mild engine that will run well at low speeds using as many of the old parts as possible.


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PostPosted: Wed Apr 24, 2019 3:14 pm 
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Thanks Dave for posting that build! Were those a flat top piston?We run a similar cam in wifes cougar only with 2v heads. Never dynoed engine but i estimated 350ish hp. That combo you have has nice power with mild mannered cam. I've been debating adding the 4v head might be a nice boost.I looked up cam. It was Elgin grind 924p. 510-536 214-224 @.050.


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PostPosted: Thu Apr 25, 2019 2:03 pm 
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This engine has a flat topped piston yes.


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PostPosted: Fri Apr 26, 2019 9:06 am 
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DaveMcLain wrote:
This engine has a flat topped piston yes.

So likely 10.5-10.8 compression? The peak tq at 3500 is what surprised me. I didn't think be that low in rpm range. Actually that engine work decent in that heavy car thread.


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PostPosted: Fri Apr 26, 2019 1:58 pm 
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Initially I was concerned that the compression ratio would be a little too high so I checked the chamber volume of the heads and it was 68cc which was bigger than I thought it would be. The piston has a single valve relief of about 3cc so I figure that even if the piston gets to a zero deck(it was pretty close) that it would be just a little over 10.5:1 which should be ok.

The testing was done with an aftermarket set of Pantera headers, pipes and mufflers which are probably somewhat better than stock but they are still a shorty header with a 2.5 inch outlet and pipe. The mufflers are a square box with two resonator tips sticking out and up at the back.

I just looked at my notes from a 410 build that I did last year also running through this exhaust system, 476lbs at 4000 and 470Hp at 5900. That engine had the TFS heads, Edelbrock Perf RPM air gap intake, a slightly different cam and a 750 carburetor. Running through a set of Hooker competition headers it made 528lbs/ft torque and 508HP. If you extrapolate the numbers just for fun this engine would make about 10% more torque and HP with a better header.

If I was building one of these engines with these gigantic ports for a heavy car I don't think I could make the torque peak happen much lower without making the engine larger. 408-427 or more would probably work great.


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PostPosted: Sat Apr 27, 2019 5:03 pm 
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I like that big tq you get with that 410!Dave i seen similar results with the 1 3/4 tube header. Last two engines i did really liked the small header( mind you we kept rpm under 6500) We tried the hooker super comp 1 7/8 only to see power drop sustantially. Im doing a 357 now with 10.8 flat tops set of 4v closed and with this we are trying small solid roller. 588 lift and 236-240@.050. The lobe cut on 112 and set on 110! Should be interesting to see how it works. The truck has the small 2v 1 3/4 header so we machined a .750 adapter to fit the 4v to 2v header. Ive dynoed with 2v headers on 4v before and they always made more power except prone to leaking. This cures the leaking and is inexpensive for truck guys. The bores were a little rough on this one with just a mild cleanup but for most part cleaned up, owner did not want expense of doing another block. So we'll see!


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PostPosted: Sat Apr 27, 2019 7:41 pm 
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Steve.k wrote:
I like that big tq you get with that 410!Dave i seen similar results with the 1 3/4 tube header. Last two engines i did really liked the small header( mind you we kept rpm under 6500) We tried the hooker super comp 1 7/8 only to see power drop sustantially. Im doing a 357 now with 10.8 flat tops set of 4v closed and with this we are trying small solid roller. 588 lift and 236-240@.050. The lobe cut on 112 and set on 110! Should be interesting to see how it works. The truck has the small 2v 1 3/4 header so we machined a .750 adapter to fit the 4v to 2v header. Ive dynoed with 2v headers on 4v before and they always made more power except prone to leaking. This cures the leaking and is inexpensive for truck guys. The bores were a little rough on this one with just a mild cleanup but for most part cleaned up, owner did not want expense of doing another block. So we'll see!


I think that one of the big problems with the 4V Cleveland design's exhaust port is that it just gets too big too quickly and the opening at the flange is way too large for a header that's appropriate for most applications that use the engine. With exhaust once you get big you should NEVER get smaller in the primary pipe. If the bowl, port and exit were sized so that a 1-5/8-1-3/4 inch pipe could be used off of the flange without causing a reduction in area it would be MUCH better. You always hear that crap that Cleveland engines like big header tubes and that's why.


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PostPosted: Sat Apr 27, 2019 11:22 pm 
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I'll test this flange and get back to you. See how it works. Im going to take a bigger set of 4v hooker super comps and see how it goes.


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PostPosted: Sun Apr 28, 2019 10:01 am 
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Steve.k wrote:
I'll test this flange and get back to you. See how it works. Im going to take a bigger set of 4v hooker super comps and see how it goes.


That sounds good it'll be interesting to hear the results. Better, worse, or no difference at all..


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PostPosted: Fri May 10, 2019 10:13 am 
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Well just off dyno with 358. It never hit the 500 hp mark but did make a respectable 430hp @5900 and 430ftlb @ 4500. Very mild mannered and offered over 10" vacuum at idle. Even with air cleaner on and snaller (1 5/8 header tube for truck) it still made 425 hp and 421 ft lb. The higher numbers were with my 1 3/4 dyno headers. We tested a rpm airgap and a torker and the air gap won by offering over 36ftlb in the 4000-4500 rpm range. Huge difference! The carb used was a 3310 and a 830 holley. The 3310 worked very well only giving up 4peak hp at top to 830 not worth the change. The dyno operator said he was impressed by 3310 as in most cases his dyno carb (830)usually gains substantially on most engines. The motor had over 400 ft lb from 3500-4500 and at peak hp only drops to 378 ft lb @5900! The 1 7/8 header dropped over 10 ftlb through mid with only minimal gains at top. Also not worth changing to a custom fabbed set.


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