I want more hp or something what to do??

[johnd]

I have an 81 vette it has a 300hp engine/auto trans...then thing is I get ripped BAD out of the hole I mean it could be against my cavi that is a 4 cyl/3spd and will jump me for about 200 feet then as soon as my rpms start to climb I am good I can hang with a friends 96 vette with no problem. What I am thinking is it is in total smog trim...I do not need any of this I don't have smog regulations in WI I bought it from cali...that has to be robbing me of some HP, I was wondering if maybe getting the tranny rebuilt with a shift kit and getting a new torque converter would help my jump off of the line. Is there any easy hp to get everyting is stock except the enigine having 300hp and a free flowing exhaust but it has the cat there still. I mean no headers or nothing. I also bought a k&n but those are only like 2 or 3 hp so I need some help tell me what you think.

 

[AKRAY4PLAY]

John,
do you know what rear gear you have?? a stall converter is always a way to improve ETs. tall rear gears like 3.08's are not drag friendly unless you making serious torque, like 500ft/lbs. dropping some smog stuff could help boost power a little. headers and 2.5 inch dual exhaust with no cats will make a huge difference. putting some "power brake" rpms into your launch will shave some time off your ET as well. do the exhaust and get a converter if you can afford to, they will be money well spent, Brian

 

[Tom73]

I have an 81 vette it has a 300hp engine/auto trans...

Stock they were 190hp. What mods have been made to add the 110hp?

tom...

 

[Stallion]

John,
do you know what rear gear you have?? a stall converter is always a way to improve ETs. tall rear gears like 3.08's are not drag friendly unless you making serious torque, like 500ft/lbs. dropping some smog stuff could help boost power a little. headers and 2.5 inch dual exhaust with no cats will make a huge difference. putting some "power brake" rpms into your launch will shave some time off your ET as well. do the exhaust and get a converter if you can afford to, they will be money well spent, Brian

I agree. If you are only going to use it mostly for racing, and not much highways or daily driving, put on a 4.11 in the rear. That way it'll shoot right off the starting line with great acceleration. That's a good rear, too. Still drivable on the road, though fuel will run low quicker, and the engine will be at higher RPMs because of the ratio. But it is worth it, in your case, I think.

Good luck!!

TR

 

[cmegga]

CAM will play a role here too. But definitly the gear is going to make the night and day diffrence off the line.

Keep in mind if you do go with a taller gear, like 3:55 or up your also going to want to consider upgrading the 3 speed transmission.

I have a 3:55 with the 3 speed TH350 right now and she dosnet like cruzen much over 65 - 70 MPH( about 3300 RPM in this range) down the highway. I could really imagine and taller gear with out goint to a 4 speed.

However a 3:55 does really rip nice out of the hole for me !! I started with a stock 2:81 . So I gained allot .

 

[WhalePirot]

Hi John, fellow cheeser!

You should know that Federal EPA rules hold a huge fine if you remove the cat for on-highway use. I found no difference in trying a 'test pipe' vs a factory cat on my modded 350, w/ headers, cam, etc. Don't blame the smog stuff so easily. The air pump takes virtually no HP and I doubt the factory cat restricts flow any more than the rest of that plumbing. 'HiFlow' cats are available should yours be restrictive.

I'll add this about what has been said about rear ratios. I would ask/think about your engine characteristics, too. My L-83 quickly ran out of revs and I did not like the 3.73 gears. I had looked or and could not find a reasonably prices set of 3.36 or 3.54s.

It all depends on finding the balance which is right for how you drive. Headers, wrapped to keep the heat in the pipes and a good exhaust system, with the cat, will help noticeable and keep you legal, smog testing or not.

Enjoy!
mike

 

[Tom Bryant]

If you are considering rebuilding the transmission anyway why not convert to a 700R4? With a THM 350 or a 4 speed stick you still have a top gear ratio of 1:1. With the 700R4 auto you get a top overdrive ratio of .70:1 and a much deeper 1st gear for off the line launches. You can then go to a 3.73 rear gear, keep your highway cruising rpms low and amaze your friends all at the same time.

Tom

 

[Stallion]

If you are considering rebuilding the transmission anyway why not convert to a 700R4? With a THM 350 or a 4 speed stick you still have a top gear ratio of 1:1. With the 700R4 auto you get a top overdrive ratio of .70:1 and a much deeper 1st gear for off the line launches. You can then go to a 3.73 rear gear, keep your highway cruising rpms low and amaze your friends all at the same time.

Tom

I agree with you. This would be a good combination.

 

[johnd]

The engine is a replacement gm engine rated at 300hp I do not believe the trans is upgraded...for those of you talking about a 700-r4 how hard is that swap?? I have stock rear gears I belive they are like 3.40-3.50 something I am not sure and the car is not here right now. Anyone have any advice on the headers like what type? Also how long/hard is it, I know it is cramped under there seems like it could take a while I guess the bright side is the car has no idea what rust is...I am kind of on a budget but not that much of one the army pays for my college and then some.

Thanks,
John Dykstra

 

[Tom Bryant]

All '81 automatics came with a 2.87 rear gear. Now you can see why the trans and rear end would make such a big improvement. Do a search of this C3 forum for 700R4. I know several members are running them and it has been discussed before. Maybe one of them will see this.

Tom

 

[johnd]

ok...so if I were to change to a say 3.53-3.73 that is a fairly streetable gear and it would certainly give me a better jump, then I either put a shift kit and new stall converter in, or did a 700r4 swap that would work together nicely, then I am looking at gettting some hooker super comp ceramic headers that would atleast be a few more pony's...I am not looking for a brawler I just would like a chance to hang with cars if they wanna drag, but I need it for driving to.

Also I have never done a rear gear swap how hard is it? I have the assembly manual I could look at that and see.

Thanks,
John Dykstra

 

[MaineShark]

I've been doing a bit of reasearch on this.

Be advised, 3.55 rear gears will put you at approximately 3000rpm at 65mph. That drinks a lot of fuel, and can't be good for the engine. And the performance increase isn't all that incredible. If you're going to do it, 3.73's would be nicer, and will put about at around 3150rpm at 65mph.

I've been looking into this, and I think the best way to swap rear gears is to buy a rebuilt rear end, with the ratio you want already installed and the tolerances set. That should run you about $800-900 through Eckler's, http://www.madvet.com, or Ikerd's.

I'm not sure what would be involved, but it might be possible to replace your rear with the stronger unit that came in the '79 and earlier 'Vettes. Maybe someone else who's done the swap will chime in (I know there are a few here on CAC who've switched).

Switching to an overdrive transmission will require about $1500, roughly. You'll need to modify your shifter to have four positions (there are kits), install a TV cable between the shifter and the carb (again, there are kits), replace the torque converter, and some other assorted items.

If you go with a 700-R4, you'll need to replace your crossmember and have your driveshaft cut (the 700-R4 is longer than the stock transmission). With a 200-4R, the driveshaft can stay the same, but I think that they changed the crossmember mounting in '80, so you'd still need a new crossmember (maybe someone can confirm this?).

The 200-4R will be a bit cheaper, since it doesn't need the driveshaft cut, and might not need a new crossmember.

Contact Bowtie Overdrives for more information on overdrive tranny swaps and prices. They'll be able to recommend what sort of tranny you need, to suit your engine's power level.

Aside from the price difference, the 700-R4 and the 200-4R have different gearing. The best description of the difference that I've heard, is that the 200-R4 is a close ratio version of the 700-R4. It also has a better overdrive gear, allowing you to run more aggressive rear gearing, without driving the rpm's too high. I'm eventually going to install a 200-R4 with either 3.73 or 3.90 rear gears. The 200-R4 with 3.90 rear gears, will have approximately the same rpms as the 700-R4 with 3.73 rear gears.

With the 3.90 rear gears, the 200-4R will not have as aggressive a first gear as the 700-R4 would, even with 3.55 rear gears. But it will have a much more aggressive second and third, and that's where most driving is done. If you like doing burnouts, the 700-R4 will be great. But that aggressive gearing can be a problem, if you upgrade the torque output of your engine - you may have trouble keeping the wheels from spinning. The 200-4R, IMO, should be a much better match for the Corvette. Especially one that's a fun driver, not a full-time racer.

Plus, the 200-4R is equipped to make full-throttle upshifts, while the 700-R4 isn't. I'm not sure if there is a way to modify the 700-R4 to do this - Bowtie would know.

So, hope that covers some of your options.

And, if those prices are more than you'd like to spend right now, the headers certainly won't hurt. Replacing the heads, themselves, if you can find a good deal, would also be a way to get a power boost.

P.S., you might want to track down a dyno and get some actual numbers for your car, before you make changes, so you can get a general idea of what changes are most helpful. Plus, the shape of the curves can help estimate what parts will work best with your engine, since it sounds like you aren't certain exactly what the internals of the engine are, and a lot of parts need to be matched to the engine to get best results. Before you freak at the power difference from what you expect, remember that the rear wheels see 15-20% less power than the crankshaft hp numbers, due to losses in the transmission and drivetrain.

Joe

 

[cmegga]

$1500 for the tranie swap in not so accurate.

I looked into this about 5 weeks ago. I called bowtie for a price on the 200rR with the necessary components to make the swap. The quote they sent me was $2200, without the stall converter !!

Then top it off with labor !! OWWWCh.

Needless to say i rebult my th350 for $900 and can do it twice more if i need to before I reach the price.

 

[Tom Bryant]

I put 700-R4 and 200-4R in the search and come up with 15 threads dealing with this subject. As I said above several CAC members have been there and done that and can clue you in to exactly what they had to do. Just reading one thread it says a 200-4R uses the stock crossmember and yoke.

Also you may want to check Hot Rod magazine www.hotrod.com and search the tech articles index. They put a 200-4R in something a while back but I can't remember what issue right now. They have also done several stories on retrofitting the 700-R4.

Here's a couple other suppliers to contact for info. They advertise the 700 but I'd ask them about the 200 also.


Phoenix Transmission Products
1304 Mineral Wells Hwy
Weatherford TX 76086
817-599-7680
www.phoenixtrans.com

"TH-700-R4 from $1395. includes torque converter, dipstick and tube, TV cable, mount and transmission cooler, 2yr/24,000 mile warranty. Custom built to your cars specs and dyno tested."



Street Rod Overdrives
2836 Lent Rd.
Apopka FL 32712
407-880-2882
no web listed

"Ready to install $1145. No core required. Includes converter, dipstick, TV cable and mount. Doesn't say what the warranty is."

Heres the thread I spoke of above. Has some good links for further research.

200-4R/700-R4 Thread

I've been kicking this around for my '69 C10 project but I haven't contacted anyone directly yet. I may just run the THM 400 for a while while the budget replentishes. :L

Tom

 

[jsimpson]

My guess is that your GM replacement engine, though rated at 300hp, is putting out WAY less than 300hp as set up in your Vette. But I'm also of the opinion that what you're looking for is not hp, but torque. Swap a TPI onto that 350 and you'll have more out-of-the-hole power than you can stand. Use an aftermarket manifold and a massaged plenum and TPIS cam, and you'll be performing out of the hole like a big block and producing power to the rev limit!

 

[MaineShark]

$1500 for the tranie swap in not so accurate.

I looked into this about 5 weeks ago. I called bowtie for a price on the 200rR with the necessary components to make the swap. The quote they sent me was $2200, without the stall converter !!

Then top it off with labor !! OWWWCh.

What were they listing as necessary parts? The quote they gave me was around $1500. Were you looking at one of the extremely radical racing trannies, or what?

Joe

 

[jsimpson]

...so who can afford to buy new? If I could afford to buy new, I'd probably be driving a C5! Then again, maybe not...

 

[gooney0]

the right amount of slip

Well.. I think the torque converter is a good idea. I had a 2500 stall TQ in my 72 Monte Carlo.

It worked pretty well. You could kind of skip past the first 1500-2000 rpms. It wasn't too bad in parking lots either. The only downside is traffic. You can't just let off the brake and roll forward. Perhaps in WI this isn't an issue?

Same idea with the shift kit. I'd recomend the "mild" B&M kit. It really only shifts hard when you floor it. I had the race version in the Monte Carlo. It was too hard. Scary in the rain, when your wheels spin from 1st to 2nd in a corner. (while you are driving normally) I also got tired of the "clunk" all day. It did bark like mad when you floored it though.


-Gooney0

 

[gooney0]

the right amount of slip part 2

On my car (4 speed manual) I have the same problem.

Its a ZZ4 (355hp)

Its hard to get the right launch. If you rev past 3 and pop the clutch the back of the car dances around, and sometimes it won't straighten out. You have to back off.

If you don't rev past 3 you get great traction, but everyone passes you. :-( Now you have to catch them.

The problem is :

If you are racing cars with similar 1/4 mile times. (within a second) I could spend a whole second burning out and backing off! Which means I probably won't catch them soon enough.

Same problem if i take off too easy. I lose almost a second due to the bogg.

So what do I do? I don't race people! Instead I impress them with 25mph - 75mph blasts. (its works like a charm btw) That way the engine is past 3,000 when I romp it.


-Gooney0

 

[KANE]

Geez....

I spent $1500 on the tranny swap to a 700R4. And that covers a really reputable tranny, installed, plus crossmember and TV cable.