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I found out today from the original owner of my new coupe that he thinks the guys who did his engine put 302 con rods on the 351 clevo thats in it for some reason to increase something...what would this be?
 

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Young Angus said:
I found out today from the original owner of my new coupe that he thinks the guys who did his engine put 302 con rods on the 351 clevo thats in it for some reason to increase something...what would this be?
this combo works well and increases the dwell time of the piston at TDC.
it also gives your motor the so-called best conrod to stroke ratio, 1.71:1.
it improves mid-topend performance and will help your heads flow better than shorter rods. i did this combo to a mild 351 and picked up 24hp and 2 tenths down the quarter mile.
 

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Young Angus said:
I found out today from the original owner of my new coupe that he thinks the guys who did his engine put 302 con rods on the 351 clevo thats in it for some reason to increase something...what would this be?

It increases the length of the connecting rod from 5.780" to 6.02".

It increases the nearness of the piston pin to the top of the piston.

It increases the reduction in dynamic compression ratio of engines with camshafts with a good bit of valve overlap.

It increases the piston dwell time at/near TDC.

It increases the reduction of dwell time at/near BDC.

It increases the weight of the connecting rod used in the rotating assembly.

It (probably) increases the reduction of weight in the piston used in the rotating assembly.

It likely increases the controversy in discussing rod lengths and what is better/worse/best/good enough.


:davis:
 

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The reason my motor runs 302C rods, is because the appropriate piston was lighter. This reduces the load on the rods.
 

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Yep, as above.

Just so you know, the pistons to match are called "short deck" pistons. If you keep a stock 351 piston on a longer rod, you'll obviously have issues with them trying to escape out the top of your heads :hy:
 

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xbgs351 said:
This reduces the load on the rods.
Yeah? By how much?

What was your "before" piston weight and "after" piston weight? Also, what of the differences in weight of the rods themselves?


:davis:
 

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davis said:
Yeah? By how much?

What was your "before" piston weight and "after" piston weight? Also, what of the differences in weight of the rods themselves?


:davis:
According to ACL, 302C rods are 12 grams heavier than the 351C rods.

The long rod ACL pistons are 72 grams lighter than their 5.778" rod pistons. The 6" Rod Ross pistons are 30 grams lighter than their 5.778" Rod Piston.
 

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As Davis suggested, i think this may open up the old debate of long vs. short rods.

I use 6.250 rods and Ross custom pistons, not because of weight, but because they give the engine characteristics i want.

I drive a car with a wheelbase 16 inches shorter than a Hyundai Excel and wanted more mid range and top end power than stump pulling torque at 1500rpm.

cheers
gus351
 

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hey xw383,
My weekender is an AC Cobra replica. Nearly 5 yr project. Just got to do paint and have the interior trimmed. Should be ready to register in February. It had better be as i have been asked to drive one of my mates to his wedding in it! Engine/trans specs are as follows, from a previous thread.

http://www.fordforums.com/showthread.php?t=113866

Tell me about the XW, i had an XY a few years years ago and love those two models most.

Cheers
gus351
 

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gus351 said:
hey xw383,
My weekender is an AC Cobra replica. Nearly 5 yr project. Just got to do paint and have the interior trimmed. Should be ready to register in February. It had better be as i have been asked to drive one of my mates to his wedding in it! Engine/trans specs are as follows, from a previous thread.

http://www.fordforums.com/showthread.php?t=113866

Tell me about the XW, i had an XY a few years years ago and love those two models most.

Cheers
gus351
I can just see it now! The minister says to the groom "You may kiss the bride" and he leans forward to give her a big pash but all his teeth fall out after the ride to the service in your teeth chattering Cobra replica. Man that cam is big enough to rattle anyones teeth!
 

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From my experience of 302 rods vs 351 there was a noticable improvement in the spread of torque from a 351 with ported 2v heads.
As far as Im concerned all the dwell time etc etc is BS. if you do the calculations the diference is so slight that you wouldnt see it with the naked eye.
Overall I cant say why theres a difference, but there is!
A7m
 

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gus351 said:
As Davis suggested, i think this may open up the old debate of long vs. short rods.

I use 6.250 rods and Ross custom pistons, not because of weight, but because they give the engine characteristics i want.

I drive a car with a wheelbase 16 inches shorter than a Hyundai Excel and wanted more mid range and top end power than stump pulling torque at 1500rpm.
cheers
gus351
I USED 6" 302 RODS IN A 351C WITH CROW 212 +224 @50" CAM AND 750 VAC HOLLEY, EDELBROCK PERFORMER MANIFOLD, BACK YARD PORTED HEADS,IN A XE FALCON WITH 2500 STALL AND 3.5 GEARS THAT RAN [email protected] REVED TO 5200rpm AND I SHIFTED AT 5000rpm. THEN I PUT IT IN A 1800kg F100 WITH SAME GEARS AND STALL AND TOOK IT IN NARROGIN BURNOUT COMP WITH THE CROWD ASKING FOR MORE.
IN THE CASE OF THE 351C THIS ROD COMBO WORKS.
I DID HAVE THE XE IN NARROGIN 2 YEARS BEFORE WITH STD RODS BUT IT DID NOT SOUND OR PERFORM AS GOOD.
PEOPLE WHO HAVE NOT TRIED AND DONT WANT TO TRY THIS COMBO WILL ALWAYS BE LEFT IN THE DARK.
AS A BUILDER OF 351Cs I HAVE ALSO NOTICED LESS WEAR DUE TO LESS SIDE LOADING OF THE PISTON TO WALL.
IV ALSO USED THIS COMBO ON SOLID MOTORS PULLING 7000+RPM.
THE CAMS USED ARE ALL OUT OF THE BOOK CAMS WITH NO MODS OR ALTERED ROCKER RATIOS.
AT THE END OF THE DAY I SAY THIS COMBO INCREASES POWER AND TORQUE EVERYWHERE IN 351Cs.
TRY AND YOU WILL SEE. JUST BALANCE THE MOTOR.
 

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aussie7mains said:
From my experience of 302 rods vs 351 there was a noticable improvement in the spread of torque from a 351 with ported 2v heads. As far as I'm concerned all the dwell time etc etc is BS. If you do the calculations the difference is so slight that you wouldn't see it with the naked eye. Overall I cant say why there's a difference, but there is! A7m
I dont understand which way you are voting.

Are you saying that the long rod setup gave you more torque?

Have you or anybody else done a test were everything in the 351 remained the same, except that the rods and pistons were changed over?

I wonder if the time slip would change at all. I doubt it, but I am open minded.
 

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Oh, im in favour of the long rods for any type of 351c use. They seem to work particularly well with the 2v head ports, I could notice the difference in the Spread of torque, not the quantity, which made the car easier to get allow with.
However i wouldnt bother doing it UNLESS I was doing a rebuild and it wasnt going to cost much to do. I dont think the difference warrants a tear down just for that.
A7M
 

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aussie7mains said:
Oh, im in favour of the long rods for any type of 351c use. They seem to work particularly well with the 2v head ports, I could notice the difference in the Spread of torque, not the quantity, which made the car easier to get allow with.
However i wouldnt bother doing it UNLESS I was doing a rebuild and it wasnt going to cost much to do. I dont think the difference warrants a tear down just for that.
A7M
How does the 302 rod improve torque? If its not the dwell thingy, what give the improvement?
 

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Personally i think its more to do with the pistons acceleration away from TDC being able to get the flow of those heads going sooner. ive set up an XL sheet to calculate the piston position by crank angle, and when you change rod ratios with the 302 rods the difference is very small. As i said though it does seem to make a feelable difference and to do that I feeel theres about 5% difference in performance, anything less than that isnt perceptable.
A7m
 

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According to my Dynamic CR calculator the longer rod does reduce cylinder pressures by .04 points of compression ratio... Still does not expain improvement if any.
 

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When i had my clevo built i bought a kit which had a 351 crank...302 rods...and hypertech pistons with adjusted gudgen pin height...the pistons were very short in the skirt area compared to the normal pistons, but this set up also strokes it out to a 387.
 
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