MajD

I'm upgrading the engine in my 79 and it will probably put out about 400 - 450 ft-lbs of torque when I'm finished. I will not be drag racing, but may occasionally autocross. Most driving will be either touring or commuting. I will not baby the car and want it to stand up to occasional abuse and spirited driving.

I plan on installing either the TKO 500 Quick Launch (3.27 first gear) or the TKO 600 Street and Strip (2.87 first gear). The car originally had the Super T-10 and I plan on keeping the 3:38 differential gear. I plan to install 275 / 60 R15 tires on the rear.

I am installing Spicer 1350 u-joints. I don't think safety loops are necessary, but wanted to hear from others to check my thinking.

I'm also interested in opinions on which transmission would be better with the stock rear gear. Thanks.

Maj D

Ibanez540r

I think loops are an easy safety item / insurance. But it seems not many are running them on street cars. I'm doing so much work on my ground up resto-mod, it was an easy decision. When I'm all done and possibly blow a joint, I don't want to have to worry about replacing/fixing a destroyed fiberglass underside.

Your next question is going to get widely varying opinions as there are many past posts with no agreement. The old "General Rule of Thumb" was a 10:1 first gear ratio. By the way, you have a 3.36 rear, not a 3.38..

So, with the TKO 500
3.36 rear x 3.27 first = 10.98

TKO 600
3.36 x 2.87 = 9.64

Do you know what ratio T10 you have for comparison?

You will probably here as low as 9 being great, up to others having 12+ first gear ratios and loving it. Personal opinion.

Also, having an "in between" 3.36 rear, the debate between .64 vs .82 OD gear with the TKO 600 will also need discussed (your area, engines cam, driving style, and goals). I would likely be a vote for the .82

chevymans 77

I'm running the Dragvette 6 link rear suspension on mine and one of the main reasons I went with the Dragvette is the half shaft and main drive shaft loops. When half shaft comes loose its not pretty.

I'm an auto man so not much input on the tranny, sorry

Neal

wzschirnt

Hi,

One question would be whether you are going to run 'sticky' tires? The stickier, the more likely you will bust stuff. Manual transmission and 'rev it up and dropping the clutch' won't help! Usually, the half-shaft u-joints are the weakest link. On my 74, I ran a driveshaft safety loop ever since I got serious about racing - auto-x and drag, but always broke the HS u-joints. I did figure out what caused most of those failures and fixed the problem.

Most loops will need some fabrication to make them fit and work. Bolting to the fiberglass floor is NOT the way to do it!

Anyway, good luck.
walt z.

REELAV8R

Did this job last year. Not too hard and worth it if a u-joint lets go.

https://www.corvetteforum.com/forums...p-install.html

MajD

Ibanez540,

I'm doing a resto mod myself and putting in a mildly build 400, so 450 ft-lbs is probably an little inflated. The car came with an L-42 so I believe the first gear was 2.85, which is close to the TKO 600 Street and Strip. I am looking at the American Powertrain website and they show an OD of 0.68 for the Quick Launch and 0.64 for the Street and Strip version. The Road Race model has the 0.82 OD, but i hadn't considered that one.

I'll be running a mostly stock 400 with a compression ratio of 9.0 - 9.3, a mild cam (probably a Lunati Voodoo 1000 - 5500 rpm), Profiler 195 heads, a Holley TBI set up on a Perfomer Air Gap, and 1.625" long tube headers. Except for some weekend touring and an occasional trip to the autocross track, most of my driving is a 35 mile commute on interstate and secondary roads, so the lower gear ratio is attractive. I will occasionally flog the car, but most of my driving is "sensible", whatever that means. Since the combination is aimed at a low - mid RPM power range, I think the 0.68 OD should work, would you agree?

Since you are using the loops, how much horsepower are you planning for on your resto mod? Thanks for the info.

Maj D

Ibanez540r

The TKO500 has the .68 OD along with the 3.27 first gear.

The two variations of the TKO600 have the exact same 1st through 4th gears (2.87, 1.89, 1.28, 1.00) only difference is a .64 vs .82 OD.

The obvious is the 500 is rated at 500 ft lbs of torque and the 600, well, 600 ft. lbs.


There are so many variables that go into the equation, and there are a ton of previous multiple page threads discussing other's decisions / opinions. Be sure to check those out.

The downside to the .64 (similar to .68 but most here have the TKO600) is that it is a pretty large drop from 4th to 5th. I have heard it described as a highway only gear as you really have to get up to a good speed before dropping it into 5th and just cruise. (Which may be good for your description?) The .82 is a more fluent drop from 4th to 5th and can be used daily driving at lower speeds. So all in what you want.

Based on your 3.36 rear, 28" tall tire, here is an example:

.82 OD @ 70 MPH = 2314 RPM.
.64 OD @ 70 MPH = 1806 RPM.

That's why cam plays a role too. Can yours handle cruising at 1800 rpm?



My car will be 550+, and after quite some looking I chose the .82 OD. I will use the car much more on city streets and back country roads. I wanted the more shift/RPM/daily friendly OD. For times on the interstate, it will still be OK.

MajD

Thanks again for the thoughts. You're quite a bit higher in the hp range than I will be, so the safety loops might not be necessary. They are pretty cheap insurance though, I have to admit.

The cam I'm looking at makes power from 1000 - 5500, so it should be OK in that range. You've definitely given me something to think about. Thanks.

MajD

keithinspace

I was just discussing "insurance items" with my Engine Builder and the subject of hoops came up.

This is one of those things that you never think you need UNTIL YOU NEED IT. You could go 40 years without having anything happen. Then one day, out of the blue sky, you lose a universal and it takes half your car with it. Or worse.

He even brought up the idea of a scatter-shield bellhousing. I'm running a ~500 hp 350 and have it capped off at 6,000 RPM...somewhat tame by some standards, but still pretty angry compared to 'regular' cars. Spending the $400 to have a shattered clutch disk or flywheel be a $300 "oh well" instead of a freaking chainsaw ripping through your ankles seems like a pretty good deal.

Horsepower is no joke. It takes some effort to keep all the stuff contained.

So whats the deal with the hoops? Brand? Price?

Metalhead140

Interesting, I'm doing something pretty similar with my '79. Just ordered my tko, and I went for the .82 ratio, as I figured my ~500hp 383 that I am going to drop in at the same time wouldn't be too happy cruising under 2000rpm at our 110km/h (66mph) speed limits. I also have the 3.36 rear end, and factory size 27.05" tyres (though 255/50r17s in my case, in place of the 255/60r15s my car had previously). The 275/60r15s you are talking about are larger and will lower rpms at a given speed more. Have a look at some online calcs and consider what rpms you want to be sitting around.

Hadn't considered safety loops yet to be honest. What are you looking at?

MajD

I'm not for or against the safety hoops at this point. I'm just collecting information to try and make a decision. The cars didn't come with the hoops from the factory for obvious reasons, but it begs the question as to when they become necessary. They weren't even on the 435 hp '67s that I'm aware of. But those cars were running street tires also.

I understand driving intentions are relevant and a drag racer probably has more use for them than I do. Most of my driving will be commuter stuff with occasional touring and autocross. But I will also burn out occasionally for the fun of it, and that's when they would be likely to break.

A set of hoops is around $130. Four Spicer 1350 u-joints are about the same price. So together they are around $250. While not heinously expensive, who wants to spend $250 when $130 will do? I am going to buy the Spicer u-joints and I'll be running a 275/60 R15 street tire on the back. I tend to think that the tires will be the weak link and break traction before the u-joint comes close to snapping. I was hoping to hear from someone that has experience with this application.

If I'm way below the threshold, then I can use that $130 somewhere else. I understand that $130 buys some insurance against possible damage, and that's worth something too. But u-joints can break on a stock car and I've not heard anyone recommend the hoops for that application. Thanks for the info.

MajD

Metalhead,

I thought about that and checked the difference in tire size and here's what I came up with:

The difference in tire height between a stock 225 / 70 and a 275 / 60 is a little more than half an inch. The 225 is 27.4" tall and the 275 is 28". This makes the difference in their circumference 2" (86" and 88").

At 2,000 rpm engine speed, a 0.64 overdrive gives a drive shaft speed of 3,125 rpm, and a 3.36 gear translates that to a 930 rpm tire speed. At 930 rpm, the 86" tire covers 6,665 ft/min, or 75.6 mph and the 88" tire covers 6,820 ft/min, or 78 mph. So at 2,000 rpm, my speedometer will show a little over 75.5 mph but my ground speed will be 2.5 mph faster. As you go lower down the rpm scale, the difference decreases.

At an RPM of 1,000 in fourth gear (1:1), the tire speed would be 298 rpm, and the ground speed would be 24.8 mph for the 275 and 24.3 mph for the 225, a difference of 0.5 mph.

Since these differences represent such small amounts, even at high speeds, I do not plan on regearing the speedometer. So I will always be going slightly faster than the speedometer shows, and my rpms will remain as if the tires were stock. I'm targeting my engine to generate power in the 1,000 - 5,500 rpm range, so I think this will be ok, but I'm always open to suggestions, corrections, and feedback...that's how we learn.

Regarding the safety hoops, I looked at the ones on the dragvette website, but I'm sure others offer them as well. Maybe some other folks can chime in on that. Thanks.

Maj D

Metalhead140

I used the bottom calc on this page: http://www.csgnetwork.com/multirpmcalc.html

Running a 28" tyre and 3.36 ratio, shows ~1800 rpm at 70mph with the 0.64 ratio, or ~2300rpm with the 0.82. All depends what speeds you expect to be cruising at, and how well you expect the engine to run at different rpms. Cheers!

MajD

Thanks, I'll check it out. I usually cruise down the highway at 70 - 75 mph, so either ratio would work OK for my application, but I agree the 0.64 gear would be pretty useless except on the interstate. I think the 0.82 would have a little more passing power since it's deeper in my target rpm band, and that's something to consider as well. The taller first gear on the TKO 500 Quick launch is attractive and sounds fun as hell if I decide to get on it a little. Obviously I haven't made up my mind yet. I'm a ways off from the decision, so you'll have to let me know how you like the 0.82. Thats a close ratio transmission, right?

BKbroiler

I have the Drag Vette half shaft loops on my car and Spicer solid u-joints. I also have billet caps on the inner u-joints. I put about 40 1/4 mile runs per year on my car, using drag radials. I've run 1.69 60 ft times and 12.15 ET. I haven't broken anything yet. This is with a TH350 trans. I run 275/60/15 tires on the street and believe me the difference in traction between a street tire on the street and a heated drag radial on a prepped track is like night and day. I don't think you'll need the loops based on your intended use.

larrywalk

To the OP...
The tires are the "fuse" in the drivetrain. With normal tires, they will breakaway far quicker than it takes to break a solid Spicer 1350 u-joint. If you were using slicks or drag radials on a prepared drag strip and dropping the clutch at high rpm - watch out! On the other hand, I've never seen an autocross course with a prepared starting line that could prevent tire spin even with sticky autocross tires. So, you will probably safe with a healthy driveline in your intended usage. However, since I'm always for safety, use your best judgement.

gg521

Safety is the most important thing you can do. You can never be too safe. If the front u-joint lets go, it not only the car but your hip and upper leg that could be mangled. Same thing goes for the scattershield and your right leg. If you are going to push the car, anything can happen. Take it from a vintage racer.