I'm going to be changing my rear gear ratio shortly and am having a hard time finding the optimum ratio for my application. Here are my specs...

'90 S-10 2dr 2wd Blazer
probably 3600# race weight

'97 L29 454 big block 9:1CR
cleaned up stock heads
ZZ502 roller cam 224/234@.050 .527/.544 lift
RPM Air Gap intake
3310 750 vac sec carb
1 3/4" long tube headers
3" exhaust thru Dynomax Ultraflows
alternator,waterpump,powersteering

TH350 with shift kit and a few other tricks
Hughes GM25 converter supposed to stall around 2800-3000 behind the BBC
ProStick shifter

Currie 9+ rear curently has 4.11 gears from when it had a SBC
leaf springs and lakewood slapper bars

I will probably run 28"+ radial tires on the street and could switch to a 26" slick at the track. This a mild street cruiser I hope will run a decent number at the track. I am in the process of preparing for PowerTour and would like to make the long haul. I've been tossing around going with anywhere from a 3.00:1 all the way up to staying with the 4.11's

I don't think the engine will like being buzzed at high RPM for thousands of miles from my home here in WI all the way to FL and back. I also think that the torque of the 454 will be forgiving at the track if I err on the safe/low side for gear ratio. What ratio sciences out best for my torque curve?

DD2000 says I'll have 550lb-ft all the way up to 3500rpm and 450hp@5000 that should make for some tire shredding fun no matter what ratio is in the rearend. As you guys can probably tell I'm getting excited to get this thing on the road soon. The BBC swap took WAY longer than I had anticipated, but I'm in the home stretch.

PLEASE HELP!!!!

In my opinion, based on my car and a buddies car...is that 454's really don't care what gear ratio they have to push.
I'll give you two real world examples.
My Nova made 565hp on the dyno. 540 torque @ 4600. It had a fairly long cam, and 3.73 gears to start with a 10" B&M converter. It went 11.03 @ 122 best. Slicks were 29" Hoosierdaddys. Ok, I wanted that 10, so I swapped in 4.10's. Got my 10, but it was a 10.98....under similar conditions. Eventually I ran a 10.9, but that was in mineshaft conditions. The 3.73's probably would have been damn close.
So my buddies car. Also a 454, but a 70 Chevelle. Stripped for sure, but still as heavy as my Nova. Again, a 468, 10:1, rectangle port heads, Comp Cams XR roller (not the biggest they make) a 10" B&M superholeshot converter, 950 Holley and 3.31 gears. This car has run a best of 10.95! At 123! And by all counts, the heads are wrong as are the gears.
On the bottle, 175 shot or so he says, 10.4 @ 132.

So in my opinion, gear the S10 for the cruise, within reason, and be happy. At the drags, the rat won't really care.
The torque converter just makes up for gear swaps......

Ron

I'm leaning towards a 3.50 gear set and some P285/70R15's for the street if they fit. Then switch to my old 26X9 Hoosier slicks at the track for a little fun and games. I am REALLY hoping to get into the 12's, but low 13's will be ok. The previous best was a 13.24@106 with the small block and no interior(3100# race weight).

I finally got some reliable flow data for my cylinder heads and I am seriously screwed. The engine is going to give up completely by 4500RPM with a peak HP of about 350@4000 and boatloads(550++) of torque down low. I'm thinking I need like a 3.00 gear just to get all the way down the track now. I ran a simulation using my current gears and it got to 450ft and was out of revs. All this work and I will still be in the 13's!!!!!

Find a set of large oval ports and your worries are over, I think you could/should still get 12's with those PP heads and 3.55's

I got a similar set up but with a powerglide. Going from a 456 to a 373 helped out as far as highway goes, but it still winds higher than I like with a 275-60-15 tire. With a lower first gear than what I got, I think a 320 something would work great. Mark

Find a set of large oval ports and your worries are over, I think you could/should still get 12's with those PP heads and 3.55's

I thought these are large ovals??? They are the same size as the RPM AirGap intake and gaskets. They didn't require any grinding to gasket match. I just had the machine shop clean up the area behind the valve a little. I wish I had just bought a SBC shortblock and kept on racing...

I finally got some reliable flow data for my cylinder heads and I am seriously screwed. The engine is going to give up completely by 4500RPM with a peak HP of about 350@4000 and boatloads(550++) of torque down low. I'm thinking I need like a 3.00 gear just to get all the way down the track now. I ran a simulation using my current gears and it got to 450ft and was out of revs. All this work and I will still be in the 13's!!!!!

What casting head do you have? Who is the source for the flow data? Without seeing the data ourselves we can't necessarily agree that your engine is going to give up so early.

Rod

IF they are large ovals, then they will have no problem going to 6k even in stock form, whats the number on them? Darn computers :D

These are the sites:

http://users.erols.com/srweiss/tablehdc.htm#BBChevy

http://www.strokerengine.com/GMBBC.html

just scroll to the L29 cylinder head data.

"The large oval port design flows better than any factory oval port head." - If that's true then you need not worry but without knowing the casting # we cannot verify that statement from the website.

Rod

I pulled the passenger side valve cover

These are the numbers I have...

10141279 on #4 cylinder intake runner

208 on rear coolant passage

and a GM3 also

First. don't go by DD2000. There is so much fluctuation in the way numbers are loaded, that who can make heads or tails of it sometimes. Your 454 will be a solid 400HP at 5000 RPM motor as a minimum. Run it and forget it. Key hwre is to gear the car so that you are running the desired RPM at the stripe with the tire size selected. Check out anr speed/power calculator and you will get the info. My own personal choice would be 3.73's w/ 28" tall tire. If you go to 285-70/15's, they will knock your effective gear down quite a bit. I am considering stepping up to those myself to knock my 3.73 down for highway use with the 502 motor.

try www.tciauto.com (think that's the link) for the MPH/ET calculators.

I pulled the passenger side valve cover

These are the numbers I have...

10141279 on #4 cylinder intake runner

208 on rear coolant passage

and a GM3 alsoI've never run across that head in my wheelin' and dealin' so I'm not sure what to make of it. If the flow numbers on that webpage are any good you really are not that far off from the "known" good ovals on the page. ... and then the other webpage claims they are "the best kept secret".

I wouldn't be too concerned until you run it and see. If you are unhappy with it then start making some changes. JMHO

Rod

L-29 heads are only like 230 cc's or so EVEN if GM calls them large ovals!!

They were made as upgrades for the old peanut port -236 heads that are right at 200 cc's or so AND in their truck applications do great!

BUT not any sort of hi-po application..

Pick up a set of real large ovals, open or closed and rework them accordingly and you will go great, imho!! Look over at the Mortec site for a list of BB heads to pick from....

OR buy a set of Merlin cast-iron large ovals and then make sure the pistons and headgaskets used will create the CR. you want....

pdq67

I was looking at the Edelbrock Performer High Compression Oval port heads, they seem to be pretty decent and have standard exhaust ports so I can use my headers. I'm just sick of throwing money at the damn thing and still being rediculously slow.

I guess this is just a learning experience to not trust anyone and not try to use factory parts to go fast. Hopefully my next engine will be better and I can come up with the $10-12K to build a real engine like some of the quicker guys around.

I thought these are large ovals??? They are the same size as the RPM AirGap intake and gaskets. They didn't require any grinding to gasket match. I just had the machine shop clean up the area behind the valve a little.

If they are the same size as the ports on that intake then you have large oval heads. There is a VERY obvious visual difference between large ovals and the small port 230cc heads.

Rod

The L29 heads lose some CC's due to the swirl inducer built into the intake tract. For all effective purposes, you could grind this out of each intake port in about 2 hours if max power was the utimate goal. But this swirl vane is what makes the broad torque curve that Vortec's are famous for. I would run it as it sits, do some tuning to maixmize where you are and make changes based on real world data - not computer programs or hypothesis.

PS, the correct link is www.tciauto.com

FYI - a 12.50 @ 108MPH will come out as
26" tire, 3.42 gear, 5000RPM at stripe w/ 5% conv slip. Step up to 28"tire and the gear goes to a 3.67. I would go with a 3.73.

The key here is to always try to get to peak HP at the stripe. That way the car is still accelerating through the traps. If the motor wouldn't hit peak power until 1500', that sure as heck doesn't serve any purpose and you also don't want to hit peak at 1000'.

OK

I got my first time slips.

First pass ever with P235/60R15 regular BFG's
air temp 76 degrees track temp 101 degrees low humidity sunny
60' - 1.964
1/8 - 8.228@85.935
1/4 - 12.808@106.219

I was having some shifter problems so I'm not sure of the exact shift points

The rest of the runs for the night were a bit slower(low 13's) since the sun went down and I couldn't hook up at all, but all were just over 106MPH. Smokie burnouts out of the water box all the way to the 1/8 mile marker are lots of fun though.

now here is the million dollar question...
How much will I slow down if I change rear gears? It was turning about 5700 through the traps and pulling good so it seems as though the 4.11's are the right gear for the track, but I really want to drive my toy more than around town. I am on a budget so a gear vendors is probably out of the question and a 700R4 just seems questionable with a BBC making grunt down low.

Is there any way of guestimating the change in ET and MPH if I were to change to a 3.XX gear and run 26 X 9 Hoosier slicks and then 28" street tires?

well I'm taking the 9" center section in for gears tomorrow. I've decided on 3.25's with a 29" tire they are about the same as the 700R4,4.11's and 26"tires

Well the gears are in and I love it. I can actually drive on the highway!!!!

Approximately how much ET/MPH does a car pick up going from street radials to a slick? I have a few buddies talking **** now one of which runs 12.20's on a 150 shot. Do you think 6 tenths is too much to ask out of a tire change?

I ran a best of 12.69 on Cooper Cobras, then 12.0's/teens with slicks, but I'm thinking that gear ratio is gonna hurt you a little, going from 4.11's to 3.25's. You gotta hook it to go anywhere, higher gears will spin more once they start spinning too.

I'm reading and I;m reading and I;m thinkin' 9" , man, somewhere between 3.08 and no more than 3.31s. You have so many ratios to choose from . GOOD CHOICE! Very curious about ET now.

So I have read all the posts...my first question is...you have a 3600# vehicle with a 454 and it is backed by a TH350, and you are going to drag it with slicks?! How well is that TH350 going to last? Also, you say you are having a hard time picking gears for street, strip, and highway and that you have a Currie 9". Now I know that you have already selected a new set of gears and installed them, but why not just get a second center section and swap gears at the track? It is so easy with a 9". That way you could have the best of both worlds without spending the money on a overdrive tranny. Keep the 4.10s if they fit the vehicle right for the track and set-up a new center section with street gears.
Just a thought...

So I have read all the posts...my first question is...you have a 3600# vehicle with a 454 and it is backed by a TH350, and you are going to drag it with slicks?! How well is that TH350 going to last? Also, you say you are having a hard time picking gears for street, strip, and highway and that you have a Currie 9". Now I know that you have already selected a new set of gears and installed them, but why not just get a second center section and swap gears at the track? It is so easy with a 9". That way you could have the best of both worlds without spending the money on a overdrive tranny. Keep the 4.10s if they fit the vehicle right for the track and set-up a new center section with street gears.
Just a thought...
Having two centers sounds like a good idea, but have you ever changed one when you get to the track, then changed back to drive home? Way too much work for one trip to the track in my opinion. What you have here is the age old problem of having to compromise between street driving and racing. Anything you do will be a compromise one way or the other. You have to decide which you want the most, street driving or drag racing. I would keep the 3.25 gears and consider a small nitrous shot to keep up with your buddies at the track. Just my two cents.

I love my 12 bolt's 3.31's!!

pdq67

The th350 will hold up if its a good one, I had one for 4.5 yrs with a B&M converter and B&M shift kit,,,,made plenty of low 12, high 11 passes. I swapped to a th400 and have had nothing but trouble since, even went back to a th350,but the 505 ate it for lunch :) Just got the 400 back tonight, I just hope it lasts this time :confused:

i wouldn't be worried about the th350 at all. i ran one for 3 years in a mid 11 sec 3900lbs ride, and mine was nothing trick. i don't think your motor will even notice the gear change at the track. it might even run faster with the 3.25's if you can hook it.

The TH350 is built up a little. It has a hardened sprag, but not a hardened drum. It has a ATI valve body and good clutches. I added a deep finned aluminum pan and a HUGE tranny cooler as well. I met my first goal of going 12's, but you know how it is? I'm not delusional though, I don't think I'll get into the 11's with this engine.

Well I got the answer to how much ET and MPH would change with the 3.25's w/slicks vs 4.11's w/radials. I slowed down by 2 tenths and 2 mph. I did pick up a tenth in 60' though.

Here are my 3 good passes I got after figuring out my new shifter.

2.033 - 60'
8.492@84.221
13.163@104.947
too much air pressure in the slicks 15psi

1.872 - 60'
8.343@84.043
13.040@104.180
12psi and a HUGE burnout

1.883 - 60'
8.301@84.089
13.011@103.769
11.5psi and another HUGE burnout

I think I went with too little gear. When I shift into 3rd it drags the engine down too much. I need more TORQUE!!!!

Thanks for the up date.

When I changed from 4.56s to 3.73s it knocked .3 off my ET and gained 5 mph. But I was over geared with the 4.56s and was running into valve float on the top end. But, my 1/8 mile ET and mph were also better with the 3.73s.

You want more torque, eh??

Install a 177 Mini-Blower on it!

Then, I figure you will have all the torque you will want, imho.

pdq67

I'd love to put a blower on it,but the all cast engine would blow up in no time at all. I think I need to build a stout 540 to get solidly into the 12's.

I'd love to put a blower on it,but the all cast engine would blow up in no time at all. I think I need to build a stout 540 to get solidly into the 12's. A stout 540 will most likely put you into the Tens.

you should be able to get into the 12's no problem with a 454. if your blazer does weigh 3600lbs i don't think 15psi was too high for tire pressure, if anything maybe too low. i run about 18psi and my car weighs 3700lbs. gauges might be different, i guess. the more air you can run and still hook is the best, imo.

Well I got the answer to how much ET and MPH would change with the 3.25's w/slicks vs 4.11's w/radials. I slowed down by 2 tenths and 2 mph. I did pick up a tenth in 60' though.

Here are my 3 good passes I got after figuring out my new shifter.

2.033 - 60'
8.492@84.221
13.163@104.947
too much air pressure in the slicks 15psi

1.872 - 60'
8.343@84.043
13.040@104.180
12psi and a HUGE burnout

1.883 - 60'
8.301@84.089
13.011@103.769
11.5psi and another HUGE burnout

I think I went with too little gear. When I shift into 3rd it drags the engine down too much. I need more TORQUE!!!!nah, the gear is ok, you just have way too tall of a tire. put a sticky 26" tire on it and i'll bet it runs faster than it did with the 4.10's in it before.

I am running a 26 x 9 Hoosier slick

I am running a 26 x 9 Hoosier slick
my bad. i saw in this thread earlier where you said you decided to go with a 3.25 gear and a 29" tire, just assumed that was what you were using when you raced it. i think you would need a little wider slick under it though. a 26x9 is pretty tiny.

Knudsonm, although you could indeed "need" more torque to pull third gear, a classic cause of lack of pull in third gear is a weak fuel delivery. Any of the following: float level too low, fuel line too small, fuel pump too small or damaged, actual restriction in the fuel tank pickup sock.

By the way, you have a strange homepage - twisted humor?

Thomas

Knudsonm, although you could indeed "need" more torque to pull third gear, a classic cause of lack of pull in third gear is a weak fuel delivery. Any of the following: float level too low, fuel line too small, fuel pump too small or damaged, actual restriction in the fuel tank pickup sock.

By the way, you have a strange homepage - twisted humor?

Thomas

I don't know where that homepage came from

The fuel system might be too small... The floats are set to the bottoms of the sight plugs. I have the fuel pressure set to 5psi flowing. The fuel line is AN-10 from the tank to the regulator at the carb and then a pair of AN-8 to the carb. I have a Holley blue and a BG -10 filter and -10 bulkhead in the sumped fuel cell. The tank was 3/4 full. I could use a larger capacity fuel pump, but with under 400 crank HP, I don't think so.

you should be able to get into the 12's no problem with a 454. if your blazer does weigh 3600lbs i don't think 15psi was too high for tire pressure, if anything maybe too low. i run about 18psi and my car weighs 3700lbs. gauges might be different, i guess. the more air you can run and still hook is the best, imo.


The best 60' I've ever had with the Blazer was a mid 1.7 and I was running 9psi, but it got kind of scary at the big end.

do you have any traction aids? cal-trac bars would probably be a good investment. with 9psi i would think that if you had enough torque it would just buckle the middle of the slick and therefore hurt traction by having LESS total contact with the pavement.

I have new leafsprings and Lakewood slapper bars with a little preload.

Is my fuel system adequate?

I can't afford a 540 build up, so I might just fix up the 454 a little.