Team Chevelle banner
  • Hey everyone! Enter your ride HERE to be a part May's Ride of the Month Challenge!

21 - 27 of 27 Posts

·
Registered
Joined
·
3,582 Posts
I would use the th350 with a 3:08 rear end. Use a street friendly cam that idles smoothly and has a lot of bottom end. You'll have a blast with that car. For some unknown reason people use cams that hold the valves open far too long then it slams them shut creating instability.. You want nice smooth ramps opening and closing the valves.. You want to have 20" of vacuum at idle..
 

·
Registered
Joined
·
1,158 Posts
Discussion Starter · #22 ·
Well lets see if I can convey my line of thinking here in a somewhat orderly manner without writing a book.

Having had the Lemans for almost 4 decades now its seen a few different setups. I've learned that what works at one level doesn't always work at another and just because something worked on someone else's car doesn't mean it will work the same on yours.

I started out putting the car back together taking a combination of parts laying around and built a 781 headed 468 shooting for 10.90's. Made it to 11.43 @ 118 before an oil filter failure wiped out the bearings.

That got me to the 9.90's N/A street idea.
So I started doing some math to figure out what power do I need to achieve the goal.
Then comes street ability and durability. ( what RPM range is that power made )
After tons of engine research, countless computer combination tests, and many e-mails ( 3 yrs) .
I picked out my 532 combination with some assistance.

Once I had power figures, more math and computer simulations followed.
The simulation trends showed that while not being optimal for 1/4 mile ET, an engine with a nice flat torque curve won't be giving up much using a lower stall and a taller gear letting the motor work rather than being at peak power and running on the converter short gears. ( think trebuchet -vs- catapult )

Here's an example of two different lines of thinking.
My buddies 55 I've been doing fab work on, is a 423 cid SBC ( 700hp @ 8000 rpm ), Powerglide w/trans brake and 6500 stall, 4.86 gears and 31.5" tall tires. ( back halved w/ladder bars )

View attachment 710736 View attachment 710737 View attachment 710738

-- VS --

My 65' Lemans 532 BBC ( 840hp @ 6700rpm ) T400 foot brake and 4500 stall, and 3.50 gears and a 275/60-15.
( modified stock rear suspension configuration ) View attachment 710740

Two different paths with a similar destination.
His is optimized for the track where mine is not.
Mine is street legal where his is not.
Mine is somewhat freeway friendly and his is not real road friendly at all.
It depends on what your after.

I'm not an expert on cams, I left that to Mike and Bullet cams.
I just told them where I'd like power peaks if possible to coincide with the projected gearing/tire.
I don't see where 1.6's would help that much, the heads don't really flow anything more after .550 lift and your at .589 with 1.5's.

As for the GV ?
Never played with one.
In my opinion if you want to play that game, shit can the hole works and just go LS with a 6 speed.

Dyno numbers would help you to narrow thinks down, as then you'd know what your working with.
After I got numbers, I set the stall about the beginning of the torque curve flattening and geared for slightly below peak power and converter slippage.
I went about mine knowing what I was after, and figured out what I needed and tailored it to do it.
It hasn't run 9.90's yet as I'm still finishing the transformation, but fuzzy math says it should with some cushion room.
Man those are some baddass rides . Both of them ! What year is the lemans ?
What is the 55 ? It's not a chevy .

Yeah I guess I'm in Somewhat of a backwards situation regarding the cam/ gear selection . You had told the cam guy about gearing first and had him design a cam for that end . I on the other hand already have the cam so I'll just have to play the hand the best I can now regarding the gearing .

When you say you set the converter for the beginning of the torque curve flattening are you referring to peak torque or some point under peak ? And yes I do understand that what works on one car and combo may not work on the other but I really do want to work this program around a 355 gear and hence won't be seeing max hp at the end of a quarter unless my final transmission gear is shorter that 1:1 .

I'm just speculating here now without a dyno but I anticipate this engine being at about 6700 peak power given the cam I've already selected . I'm now wishing I'd have held that back down about 400 rpm less now but oh well . But if my peak power does end up 6700 ish and I want a 355 gear then there is only one variable left . Converter . If I could get a shorter 3rd gear in this 350 tranny I'd do that but they dont make one as far as I know so far . Its 1:1
 

·
Registered
Joined
·
565 Posts
The Lemans is the 65' in my signature getting new running gear.
It's on the hoist behind the 55' in the one pic. you can kind of see the rear bumper.
The 55' is a F word Fairlane Club Sedan.

No, I had no say in the cam other than solid roller and approximate peak power rpm.

I started out figuring out how much power was needed to move my car 130+ mph to attain a 9.90.
Then took intended gear and tire size to figure RPM needed.
Then went about figuring out how to make the needed power within the desired range.
Resulting in the 532.

With this torque curve I'll be using no more than 4000ish, maybe 4500 rpm stall.
Shifting 6700-6900 rpm and 6000ish trap rpm @ 130ish mph. ( according to fuzzy math )
With a T400, 3.50's and a 28' tall tire.
2300ish @ 55 mph and 2800ish @ 65
No weird trans gears or overdrives.
With the loose converter and 4.10's in it, 2300 is more like 40mph and 2800 nearing 50 mph

710846
 

·
Registered
Joined
·
1,158 Posts
Discussion Starter · #24 ·
The Lemans is the 65' in my signature getting new running gear.
It's on the hoist behind the 55' in the one pic. you can kind of see the rear bumper.
The 55' is a F word Fairlane Club Sedan.

No, I had no say in the cam other than solid roller and approximate peak power rpm.

I started out figuring out how much power was needed to move my car 130+ mph to attain a 9.90.
Then took intended gear and tire size to figure RPM needed.
Then went about figuring out how to make the needed power within the desired range.
Resulting in the 532.

With this torque curve I'll be using no more than 4000ish, maybe 4500 rpm stall.
Shifting 6700-6900 rpm and 6000ish trap rpm @ 130ish mph. ( according to fuzzy math )
With a T400, 3.50's and a 28' tall tire.
2300ish @ 55 mph and 2800ish @ 65
No weird trans gears or overdrives.
With the loose converter and 4.10's in it, 2300 is more like 40mph and 2800 nearing 50 mph

View attachment 710846
Yep kinda thought it was a Ford. Ford with a sbc lol cant knock fords though . They have a stack full of Daytona races in the 60's.
I think 6. Pontiac had 2 very early 60's .Plymouth had 3 I think it was

Man that's a nice flat torque there and it looks like you have 600 @ 3 grand from the looks of that graph yet the taller gear is gonna help with hook . Love it . It's an inspiration . I think this sb I'm doin now is gonna be nasty but my next build is gonna be a bb brother to what you've got going here. Its different and its badass and cool. Can seriously hurt some feelings on the street with a get up like that lol and if they want to race farther than a quarter it might only get worse for them Haha. 900 rpm left over
 

·
Registered
Joined
·
11,730 Posts
The Lemans is the 65' in my signature getting new running gear.
It's on the hoist behind the 55' in the one pic. you can kind of see the rear bumper.
The 55' is a F word Fairlane Club Sedan.

No, I had no say in the cam other than solid roller and approximate peak power rpm.

I started out figuring out how much power was needed to move my car 130+ mph to attain a 9.90.
Then took intended gear and tire size to figure RPM needed.
Then went about figuring out how to make the needed power within the desired range.
Resulting in the 532.

With this torque curve I'll be using no more than 4000ish, maybe 4500 rpm stall.
Shifting 6700-6900 rpm and 6000ish trap rpm @ 130ish mph. ( according to fuzzy math )
With a T400, 3.50's and a 28' tall tire.
2300ish @ 55 mph and 2800ish @ 65
No weird trans gears or overdrives.
With the loose converter and 4.10's in it, 2300 is more like 40mph and 2800 nearing 50 mph

View attachment 710846
You're most likely going to need another 5 mph for 9.90's.
 

·
Registered
Joined
·
565 Posts
You're most likely going to need another 5 mph for 9.90's.
I did say 130ish.
But ya probably 3-5 more mph.
Fuzzy math and computer sims are spitting out numbers close to 9.70 @ 140 mph when I'm done with changes. ( provided I can get it to hook)
 

·
Registered
Joined
·
11,730 Posts
I
I did say 130ish.
But ya probably 3-5 more mph.
Fuzzy math and computer sims are spitting out numbers close to 9.70 @ 140 mph when I'm done with changes. ( provided I can get it to hook)
And that’s another thing, looking at your combo and your plan, a simulator will be hard to figure. They’re kinda set to figure numbers based on average “race” car et’s. I think in your case the 60’ will be soft based on the gear and converter, and have more mph upstairs. So you’re probably going to have more mph for a given et but less 60’. I think my car was 9.50 at 140 but it was 1.30 in 60’. You definitely have the hp to pull 9.90’s.
 
21 - 27 of 27 Posts
Top