10.4 vs 10.25 CR and Piston to Head Clearance

General engine tech -- Drag Racing to Circle Track

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F-BIRD'88
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by F-BIRD'88 »

Everybody thinks because yhat trans has a 3.06:1 first gear ratio that it will launch "like its got 4.56's,"
Unfortunay withthat th700 trans it is not realized.
These tranys absorb a lot of power they weight a ton.
(Rotating mass inertia)
The big gear drop 1 to 2 is a power/ acceleration. thief.
The torque converter is not as "torky" as a th350-400 TC is. "Stall torque ratio" is not as good..
When I swapped out my Th700r4 for my trusty old th350 trans (I've owned since 1975. The car dropped 4/10th ET.
It was like night and day.. My th350 has no special or low friction parts at all. Its stock wiyh a shift kit and good clutches.

Re: cruising in OD you may find that to cruise in OD at low rpm you may prefer to keep the intake manifold Fully Divided. 180° split plenum VS a reduced plenum divider.
won't know till you drive the car.
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by Bill Chase »

F-BIRD'88 wrote: Wed May 31, 2023 2:51 pm Your 108 lsa. am is not that hairy.
What you may want to do is control tC lock up manualy or have a override switch... or...
You'd want to avoid driving in OD at low engine rpm reguardless.. The OD only really benefits you at steady long highway speeds... Otherwise its a toy.
Cammed engines by nature want to run at high(er) cruise rpm.
You'll know as soon as you get to driving it axjust as needed..
With overdrive you can gear the hell out of it for drag launch ET. Don't be shy.
I don't see big issues with your combo in that reguard.
friend with a c3 vette, 700r4 stock converter and crappy 3.08 gears was getting some pinging at cruise rpm high load when going to wot, the corvette servo allowing almost full throttle without downshift made it worse. knows he needs a better rear gear ratio. talked him into putting a manual switch to unlock the converter when cruising and the pinging stopped. good advice, and observation dude.
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by skinny z »

Bill Chase wrote: Sun Jun 04, 2023 2:37 pm
F-BIRD'88 wrote: Wed May 31, 2023 2:51 pm Your 108 lsa. am is not that hairy.
What you may want to do is control tC lock up manualy or have a override switch... or...
You'd want to avoid driving in OD at low engine rpm reguardless.. The OD only really benefits you at steady long highway speeds... Otherwise its a toy.
Cammed engines by nature want to run at high(er) cruise rpm.
You'll know as soon as you get to driving it axjust as needed..
With overdrive you can gear the hell out of it for drag launch ET. Don't be shy.
I don't see big issues with your combo in that reguard.
friend with a c3 vette, 700r4 stock converter and crappy 3.08 gears was getting some pinging at cruise rpm high load when going to wot, the corvette servo allowing almost full throttle without downshift made it worse. knows he needs a better rear gear ratio. talked him into putting a manual switch to unlock the converter when cruising and the pinging stopped. good advice, and observation dude.
Yep.
skinny z wrote: Wed May 31, 2023 3:51 pm I've got the converter lockup dialed in. It's activated in OD only plus a manual switch to disengage should I want to. Very much like driving a 5 speed.
I've had a manual switch for the lockup since day one.
And since the new transmission went in (another TH700 built by an old friend and racing transmission tech), the shifting sequences are extraordinary. I like to shift manually but the way this new unit is setup, it's truly automatic.
That was on the street though. With the new engine and a shift in priorities to more track specific, it'll be interesting to learn how it behaves at the dragstrip.
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by Chris_Hamilton »

Completely OT but since the 700R4 was mentioned.....Speaking of heavy....I was a kid (17) and fixing my parents '90 Blazer that the transmission went bad. It was a 700R4 and we had gotten a reman. I was alone, didn't have a transmission jack and wanted to get the job done that day cause I was going to take a girl out that night in the Blazer. I thought I don't need a tranny jack, I'm a man, I can get it out without one. Well long story short, I got it loose, when I caught the full weight it pinned me to the ground and I was wedged in with the tranny fully on my chest. Couldn't move. It was actually hard to breathe. Waited two hours until my Dad came home and was able to wrestle it off me. I decided that it would be a good idea to use a jack to install it.:) Was actually able to borrow one that day, got the tranny in and got cleaned up in time to take the girl out.:)
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by skinny z »

Chris_Hamilton wrote: Sun Jun 04, 2023 5:13 pm Completely OT but since the 700R4 was mentioned.....Speaking of heavy....I was a kid (17) and fixing my parents '90 Blazer that the transmission went bad. It was a 700R4 and we had gotten a reman. I was alone, didn't have a transmission jack and wanted to get the job done that day cause I was going to take a girl out that night in the Blazer. I thought I don't need a tranny jack, I'm a man, I can get it out without one. Well long story short, I got it loose, when I caught the full weight it pinned me to the ground and I was wedged in with the tranny fully on my chest. Couldn't move. It was actually hard to breathe. Waited two hours until my Dad came home and was able to wrestle it off me. I decided that it would be a good idea to use a jack to install it.:) Was actually able to borrow one that day, got the tranny in and got cleaned up in time to take the girl out.:)
Yikes!
The pinned part freaks me out.
I fashioned a "transmission jack" out of floor jack and some rigging made out of plywood. That said, I much prefer the engine/transmission install/removal as a unit. But I understand the situation when it's a transmission swap on it's own. I've been there many times.
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by Tom68 »

Chris_Hamilton wrote: Sun Jun 04, 2023 5:13 pm Completely OT but since the 700R4 was mentioned.....Speaking of heavy....I was a kid (17) and fixing my parents '90 Blazer that the transmission went bad. It was a 700R4 and we had gotten a reman. I was alone, didn't have a transmission jack and wanted to get the job done that day cause I was going to take a girl out that night in the Blazer. I thought I don't need a tranny jack, I'm a man, I can get it out without one. Well long story short, I got it loose, when I caught the full weight it pinned me to the ground and I was wedged in with the tranny fully on my chest. Couldn't move. It was actually hard to breathe. Waited two hours until my Dad came home and was able to wrestle it off me. I decided that it would be a good idea to use a jack to install it.:) Was actually able to borrow one that day, got the tranny in and got cleaned up in time to take the girl out.:)
Used to do it with Powerglides, last time at around age 50, decided then no more.

Was never strong enough to do it with anything heavier.

By the time you have the car high enough to get the trans under it, it's borderline too high to bench press it up to height to get on the dowels.

700r4 ratios are good for low power to weight vehicles with stock cams.
Ignorance leads to confidence more often than knowledge does.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by skinny z »

Tom68 wrote: Sun Jun 04, 2023 7:54 pm ... to bench press it up to height to get on the dowels.
The operative phrase there.

I've done all manner of heavy lifting under a car.
I much prefer operator assist when I can get it.

What's a TH350 weigh? And add a Gear Vendors OD on the back.
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Re: 10.4 vs 10.25 CR and Piston to Head Clearance

Post by skinny z »

The internet says:
TH350; 120 lbs.
TH700; 155 lbs (some accounts are 135).
No converter is each case.
Can't speak for the parasitic losses described earlier though.
Kevin
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