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Pros / Cons of early / later engine

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Wirewheels Avatar
Wirewheels Gold Member Brian Induni
Oregon City, Oreogn, USA   USA
1963 MG MGB
1963 MG MGB "Casper"
1966 Austin-Healey Sprite "~ Sold ~"
1973 Triumph Stag    & more
I know this is going to sound like a first world problem, but I need your collective input on this dilemma. When I bought my '74 TR6 a few months ago, it came with 2 engines (car was apart of course). Doing some research, it turns out the totally dissembled engine is the original (CF25767UE) and the other seemingly ready to go engine is about a 1970 (CC60437E).

My question is: what are the advantages/disadvantages of each? I'm planning on keeping the correct numbered block to stay numbers matching, but are there advantages of internals, head, etc? Planning out the rebuild and want to keep the "good stuff"!



Brian
CEO, Classic Automotive Innovations
http://www.classicautoinnovations.com

(too many classic come and go, so I've given up listing them...)


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titanic Berry P
Albany, OR, USA   USA
Brian-The later block with the recesses around the cylinders are less prone to blow head gaskets (although I have never had a problem with the earlier blocks). Also, the later head uses a better flowing intake manifold. PM me, I may have been the previous owner of the 70 engine.
Berry

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Darth V8R Avatar
Darth V8R Vance Navarrette
Beaverton, OR, USA   USA
1980 Triumph TR8 "Wedgie"
In reply to # 1503109 by Wirewheels I know this is going to sound like a first world problem, but I need your collective input on this dilemma. When I bought my '74 TR6 a few months ago, it came with 2 engines (car was apart of course). Doing some research, it turns out the totally dissembled engine is the original (CF25767UE) and the other seemingly ready to go engine is about a 1970 (CC60437E).

My question is: what are the advantages/disadvantages of each? I'm planning on keeping the correct numbered block to stay numbers matching, but are there advantages of internals, head, etc? Planning out the rebuild and want to keep the "good stuff"!

This topic runs pretty hot, so I will offer what I have learned and others may disagree.

The later head is the preferred one. It has better ports, a superior intake manifold, and despite a slightly smaller exhaust valve it actually flows quite a bit better than the earlier head due to reduced valve shrouding. The downside is the miserable compression ratio. This is easily fixed by skimming the head by 0.125", which will raise the compression to a very respectable 9.5:1.

I would use the cam from the later motor, as it was the so called 125HP cam and offers more power than the earlier cam - this was done to offset the lower compression ratio of the later head. Skimming the head may require the earlier shorter pushrods, but they are inexpensive. On my engine I skimmed it and did not find it necessary to use shorter pushrods, but depending on your camshaft and whatnot, your mileage may vary.

The later exhaust manifold is a twin pipe design, and flows well, but the real advantage is that it uses the later muffler by virtue of the twin pipes. The pipes themselves are not the issue, rather it is the pathetic muffler that offers the restriction. By going to the twin inlet design, the restriction is reduced and you pick up a pony or two. The early manifold also flows well,and offers a lighter single pipe design, but suffers when it reaches the muffler with its single inlet.

The bottom end is not as clear. The earlier engines had a different crank design and required a different spigot bearing. I would keep the original bottom end to avoid any fitment issues with the transmission, although I believe that I may have read that with the appropriate bits this can be circumvented as a concern.

Whatever combination you end up using,be certain to check your mixture carefully as it will be affected by any alterations you make.

Lastly, the later head has EGR which has no effect on performance if it is operating correctly. It will however reduce your highway fuel economy by roughly 1MPG if you remove it as many will suggest. And remember - the vacuum capsule on the distributor is a RETARD, not an ADVANCE and it must be connected to the correct port on the carburetors or you will have all kinds of weird problems.

Vance



1980 Platinum Metallic TR8, navy blue interior
Bare metal respray, Crower cam, raised compression
ported heads, modified Zenith carbs, 0.060" overbore



Edited 1 time(s). Last edit at 2017-12-17 11:07 AM by Darth V8R.

tapkaJohnD Avatar
tapkaJohnD John Davies
Lancaster, Lancashire, UK   GBR
Brian,
If the first engine is the disassembled one, then fit the one "ready to go" and start on the rebuild.
For a man who is "CEO, Classic Automotive Innovations" swapping it back later will be no problem, and you will have a running car to sell on, with perhaps a special offer to the customer of the original engine when it's ready.
JOhn

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dsixnero Avatar
dsixnero Dan Colanero
Westville, NJ, USA   USA
Brian, first,I would wonder if the 70 engine was bought because the 74 had a serious problem. Of coarse the right engine is best but these cars sell best when they run and drive good and are not full of rust. It also makes them fun to own.The later low compression engines,if left stock, have a sweet idle, the earlier engines did not but felt stronger.I modified my 75 and wish I would have left it stock. You get alittle more HP and you just keep wanting more.

gozto11 Avatar
gozto11 Todd Bermudez
Cincinnati, OH, USA   USA
In reply to # 1503118 by Darth V8R
In reply to # 1503109 by Wirewheels I know this is going to sound like a first world problem, but I need your collective input on this dilemma. When I bought my '74 TR6 a few months ago, it came with 2 engines (car was apart of course). Doing some research, it turns out the totally dissembled engine is the original (CF25767UE) and the other seemingly ready to go engine is about a 1970 (CC60437E).

My question is: what are the advantages/disadvantages of each? I'm planning on keeping the correct numbered block to stay numbers matching, but are there advantages of internals, head, etc? Planning out the rebuild and want to keep the "good stuff"!

This topic runs pretty hot, so I will offer what I have learned and others may disagree.

The later head is the preferred one. It has better ports, a superior intake manifold, and despite a slightly smaller exhaust valve it actually flows quite a bit better than the earlier head due to reduced valve shrouding. The downside is the miserable compression ratio. This is easily fixed by skimming the head by 0.125", which will raise the compression to a very respectable 9.5:1.

I would use the cam from the later motor, as it was the so called 125HP cam and offers more power than the earlier cam - this was done to offset the lower compression ratio of the later head. Skimming the head may require the earlier shorter pushrods, but they are inexpensive. On my engine I skimmed it and did not find it necessary to use shorter pushrods, but depending on your camshaft and whatnot, your mileage may vary.

The later exhaust manifold is a twin pipe design, and flows well, but the real advantage is that it uses the later muffler by virtue of the twin pipes. The pipes themselves are not the issue, rather it is the pathetic muffler that offers the restriction. By going to the twin inlet design, the restriction is reduced and you pick up a pony or two. The early manifold also flows well,and offers a lighter single pipe design, but suffers when it reaches the muffler with its single inlet.

The bottom end is not as clear. The earlier engines had a different crank design and required a different spigot bearing. I would keep the original bottom end to avoid any fitment issues with the transmission, although I believe that I may have read that with the appropriate bits this can be circumvented as a concern.

Whatever combination you end up using,be certain to check your mixture carefully as it will be affected by any alterations you make.

Lastly, the later head has EGR which has no effect on performance if it is operating correctly. It will however reduce your highway fuel economy by roughly 1MPG if you remove it as many will suggest. And remember - the vacuum capsule on the distributor is a RETARD, not an ADVANCE and it must be connected to the correct port on the carburetors or you will have all kinds of weird problems.

Vance

To be clear, the earlier engines (68-69) have the long back crank.

You can use a either exhaust manifold on either head or a header of course

Wirewheels Avatar
Wirewheels Gold Member Brian Induni
Oregon City, Oreogn, USA   USA
1963 MG MGB
1963 MG MGB "Casper"
1966 Austin-Healey Sprite "~ Sold ~"
1973 Triumph Stag    & more
Thanks to all for the replies!

I appreciate the input... now I need to go restore a TR6.... :-)



Brian
CEO, Classic Automotive Innovations
http://www.classicautoinnovations.com

(too many classic come and go, so I've given up listing them...)


Member Services:
Inventors of Classic Speed™. At last, your mechanical speedometer will always read accurately!
. Hide banner ads & support this website by becoming a > Gold Supporting Member <

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