Couple of rookie questions....

[Cliff Beer]

Hi and thanks for any help on this one. I'm looking to modestly increase the hp and torque in my GT40 and I'm looking at a couple of different options. The present front runner option is basically to just install a new stroker engine - something like a T&L 347/webers - rather than monkey with the current 302/Holley. A couple of basic rookie SBF questions here:

1. As I understand it, the 347 has a higher deck height to accommodate the longer stroke (same bore as the stock 302 I believe) - does this mean that the exhaust ports are moved up and outwards such that the stock 302 bundle of snakes exhaust probably will not fit?

2. I'm guessing that a spacer of some sort has to be used for the inlet manifold to accommodate inlet ports that are higher and farther outboard as compared to the stock 302, is that correct?

Thanks in advance for any help here.

 

[Ron Earp]

The 347 is built on a standard deck height motor like you have. You won't have any issues there. Now if you go to a 351W you'll experience the exact problems you describe since the deck height is taller.

R

 

[Rich A]

1. As I understand it, the 347 has a higher deck height to accommodate the longer stroke (same bore as the stock 302 I believe) - does this mean that the exhaust ports are moved up and outwards such that the stock 302 bundle of snakes exhaust probably will not fit?

A 347/331/306 is built on a 289/302 block so your 302 bundle of snakes will still work.
A 392/408/418/427 is built on a 351 block which has a higher deck height, so your 302 bundle of snakes will NOT work because the exhaust ports are moved up. Some other things you have to change because of the higher deck height of a 351 block would be your intake manifold and distributor.

2. I'm guessing that a spacer of some sort has to be used for the inlet manifold to accommodate inlet ports that are higher and farther outboard as compared to the stock 302, is that correct?

There is no spacer. If you are using a 351 block you will need a new inlet manifold(intake manifold).




*302/306/331/347 are not the only CID possible for the 289/302 block.
*351/392/408/418/427 are not the only CID possible for the 351 block.

 

[Jac Mac]

Many aftermarket cylinder heads have the exhaust port 'raised' toward the rocker cover, as this exh face is not vertical but tilted outboard slightly at the top, simply fitting any of these heads to any cyl block will require a rework to the existing bundle of snakes exhaust system ( assuming of course that the first set of heads are of std port configuration).

Similar situation on the intake side if the intakes are raised ( not as common, & some manufacturers have added material here so that thicker end corks or spacers are all that is reqd.)

 

[Ian K]

Hi and thanks for any help on this one. I'm looking to modestly increase the hp and torque in my GT40 and I'm looking at a couple of different options. The present front runner option is basically to just install a new stroker engine - something like a T&L 347/webers - rather than monkey with the current 302/Holley. A couple of basic rookie SBF questions here:

1. As I understand it, the 347 has a higher deck height to accommodate the longer stroke (same bore as the stock 302 I believe) - does this mean that the exhaust ports are moved up and outwards such that the stock 302 bundle of snakes exhaust probably will not fit?

2. I'm guessing that a spacer of some sort has to be used for the inlet manifold to accommodate inlet ports that are higher and farther outboard as compared to the stock 302, is that correct?

Thanks in advance for any help here.

As others have already said, the typical 347 uses a stock deck height. However, it is
overbored .030. The 342 is the same stroke as a 347, but without the overbore. Now,
I imagine some 347s might utilize a taller deck, but that would be that particular builder/
manufacturer's choice.

The increased stroke clearance is achieved by relocating the piston wristpin closer to the
piston head (and there may be some shortening of the skirt for clearance) to accommodate
the longer rods. Also, the block will need some clearancing near the journals as well to avoid
the longer rods hitting the sides. And you will need to check the piston/valve clearance.

Ian

 

[Cliff Beer]

Super, thank you gents, that is very helpful. Thanks for setting me straight on the deck height question with regard to the 302/331/347 configuration (same height) v. the 351 based blocks. It shouldn't be too painful of a conversion with at least the exhaust remaining as-is. I'm guessing a turkey pan for the webers, fuel pressure regulators and some vacuum work for the brake booster might just about do it.

Think I'll be calling T&L now, and praying for luck with a good engine from them....

 

[Dutton]

Cliff,

Ian's point about piston pin location was the reason I opted for fewer cubic inches. That and, even with the horepower loss due to Webers, my 331 came in at 435 hp / 450 torque.

Think I'll be calling T&L now, and praying for luck with a good engine from them....

Two words: Keith Craft.
Two (more) words: no diasppointments.

Give me a call sometime.

T.

 

[Ian K]

Cliff,

Ian's point about piston pin location was the reason I opted for fewer cubic inches. That and, even with the horepower loss due to Webers, my 331 came in at 435 hp / 450 torque.



Two words: Keith Craft.
Two (more) words: no diasppointments.

Give me a call sometime.

T.

OK, to explain what Tim is talking about -

The original 342/347 strokers had an issue where the piston wristpin was relocated
intersected the oil ring groove. There was always concern that this was a "bad
thing". Some 342/347 strokers are still machined this way, but there are others
that do not. YMMV, so do a little research. Also, the jury is out on whether the
pin/oil ring intersect is a problem. IMHO, it's better to be safe than sorry, and
either find a 342/347 that doesn't intersect, or go with a 327/331 where the wrist
pin is isolated. I also prefer the slightly shorter rod/stroke for higher RPMs.

Also, there is a 355 stroker using a 5.5 inch rod and 3.5 inch stroke (the 342/347 uses a
5.315 inch rod with 3.4 inch stroke).

Ian