I had posted in another thread about my new crate motor cam being to big. It it a hydraulic roller
248/254
562/580
110*
With this cam I can't even spin the tires
My setup is is a 355, 9.8-1 cr, flat top pistons, aftermarket aluminum heads, 68cc, 2.02-1.6 valves, 1.5 rockers, full hydraulic roller, aftermarket dual plane intake, 650DP carb.
tranny is a rebuilt TH350 that has been toughened up a little and shift kit added. A 2200-2800 stall converter was added to try and help the bug cam but no go. Rear end is still stock, I believe 2.87? Rear is going to be changed eventually

I am changing the cam now and looking for a good fit for my setup. I want to have a good choppy sound and still idle around 800 with more low end power. I'm not racing and not a daily driver but want to have fun when I do drive it.
I found this cam with a range of 1900-5600 and thought it might be what I'm looking for without having to change the stall again.
https://www.summitracing.com/parts/cca-08-423-8

I appreciate any input

Thanks

 

That new cam choice is pretty much what I have in my 355. However, 3,000 stall & 4:11s.

Your present cam has a lot of lift. A lot of lift. I assume the engine builder took a "clay" measurement between the valve & piston.
I believe the minimum is 0.080 but I went .090ish for safety margin.

The next cam you selected looks milder and will still have a lope sound.
You already have the roller lifters. Current pushrod length should be alright, but for $20 you can check it with the tool.
I would not run any 1.6 rockers because, one not needed. And two, you don't know your piston to valve clearance.

The biggest factor here is the rear axle ratio. Its killing anything you want in street performance.

 

A performance car consists of various "matching" components. You've identified the problem, but you don't realise it, and it is not the cam. Change your rear gears and make sure they will work in conjunction with the transmission ratios as well as the engine rpm range. Have the rear diff rebuilt while you are in there if it needs it, or, if you plan to beat on it regularly. BTW spinning tires is not how you achieve performance results, all you are doing is wasting money.

IMHO the engine is just fine.

 

I spent a few hours on the phone with several Cam companies before choosing the cam I am using. Comp Cams had some wonderful techs who would walk you through the various options available and make an educated suggestion for your engine based on your intentions.

They would not sell me the Cam I wanted because of my rear end ratio (3.36) in my 4 speed Corvette. They said I would need to go with a 3.70 at the minimum and better yet with a 4.11. Having a 427 built up like a L88 engine I wanted to get something close to the L88 cam. They finally sold me a kit that had the Cam, lifters and valve springs which worked out okay. Some experts have suggested that my cam is "too small" for my BB engine which may be true.

I can get from 0-60 in just over 3 seconds with dry traction, I have no idea why they told me to get a 4.11 rear end as it would spin all day long. At a drag strip I would spin the tirespast the 1/8th mile mark with a fast takeoff. The Dyno software and my GTechPro both predict a 10 second quarter mile with over 560 hp for my C3. I love Compression and the power it can make!!

Desktop Dyno is another useful tool as it allowed me to try different combinations before building the engine. Back when I used Desktop Dyno I had to enter the cam details manually, today they have them on file so you can try different cams easily. A very useful product for those getting ready to build an engine.

 

Yes, I understand that's spinning the tires is not how I achieve performance. I was just stating that it would not. But it would on the older motor before I put the new crate motor in. Also this new crate motor will only idle at 1200
I want my power range to start well below 3200, Will changing my rear gears achieve this?

 

With that rear gear ratio no matter how much HP.it will remain a dog off the line Thats your problem

 

I guess you missed the part where I stated that it did spin the tires with the stock motor before I put the crate motor in

 

Yes i know my rear gears are stock, and are going to be changed soon, but changing my gears now is not going to help my new motor idle at 800, instead of 1200+
I apologize for upsetting everyone one with this thread, I was just looking for cam suggestions with my current setup.

 

Thanks for the input, I am buying a Differential after I get my motor finished.

 

Same as you, we want your Corvette running at peak performance. We think obtaining an official diagnosis from one of our GM-certified dealerships would be the next best step towards a resolution. If you'd like support connecting with one, you can reach us via email at socialmedia@gm.com.

 

https://spicerparts.com/calculators/...rpm-calculator

Use the gear ratio calculator on this site. The stock TH350 transmission gear ratios are 2.52.....1.52.....1-1........first, second, and third gear. You said your transmission has been modified, so, for the purpose of this post I am assuming your internal gears are still the same as stock. Changing the rear end gears will not move your power band down, it will allow the vehicle to get into power band faster. I used a 27.00 " tall tire, you need to confirm your spec first for accuracy, but, you will get the point with my example anyways.

Using a 2.87 rear end and shifting out of first at 5,500 rpm puts you at 61.1 mph...........slow.........

Using a 3.70 rear end and shifting out of first at 5,500 rpm puts you at 47.4 mph...........smoking.......

Getting into the power band earlier, and hitting the red line quicker, is how you accelerate faster. You can also use a 1.00 transmission gear ratio to calculate your third gear highway speed with different rear gears. If this was my car I'd put 3.55 or 3.70 gears in the rear end with a useable 6,000 rpm redline. Don't worry about where the engine idles once it is properly tuned.......800-1,200 is not out of the norm depending on the cam specs, and how well it has been set up with timing and carb.

 

Right.. thats because your stock motor had more torque at launch because its powerband rpms were better matched fit for the stock gear ratio you have.

This is the issue some dont seem to get, there is no free lunch. Everything is a bit of a tradeoff when you are working with trying to make more HP with the same displacement. You end up moving the rpm band way up requiring other mods like a new rear gears and a higher stall torque converter and all this makes the car less enjoyable as a street cruiser. If its going to see the drag strip thats one thing but otherwise I suggest to avoid going with too big a cam to chase more HP.

IMO torque is what you want for breaking them tires loose and fast acceleration on the streets thats what throws you back in the seat not HP.

 

Guys, i am not trying to get more HP, in fact i will probably be losing some by getting the right cam for my setup. I didn't choose this cam and it is not the cam that was supposed to be in the motor, it is too big for my purpose. I am just trying to get it running right, idle around 800 and not die at idle with the AC on. This car will never see a drag strip and probably never hit 5500rpm's. It wil be around town only, maybe on the interstate but no more than 10 miles. 3200-6200, lol, I will be at the next red light before 3200. I am trying to drop the power band for more torque in lower rpm's.

this was a cam suggestion thread and somehow it turned into a "keep the big cam and change rear gears" with not one cam suggestion. I have tried calling comp but am on hold too long, I have an email request into a couple places since last Friday with no response yet, so I came to this forum for suggestions.
The cam is the bigger problem right now, not the gears. A rebuilt Differential will be put in once the car is running correctly.
i don't mean to rant, I'm just frustrated, putting a lot of $$ in this car. Interior is perfect, all guages work, all power options work including the driver seat antenna and rear defrost. It's just not fun to drive yet, but sounds awesome.

 

LotVenture,

Going back to post #1 and going over your crate engine specs:
Even with the 2.87 gears it should be a bad-*** once the road speed and RPMs come up a bit.
In other words, it should easily do "rolling burnouts" (above 20 mph) all day long.

You also stated a high idle. You have a double pumper. This issue could be something as simple as the secondary throttle not closing enough.
Or high idle choke sticking.
Are you sure the secondaries pump is delivering a "shot"?
Are the accelerator pump arm "gaps" set perfect?
What is your Initial Timing?
Are you using Full Manifold Vac to the dizzy?

 

5 of us have here all said the same thing.
I've posted the link to the tool you heed to use to chose what gears are right for you.
Swapping rear end gears is the easiest and cheapest fix for immediate performance gains on any muscle car.
Back in the day GM marketed 3.70 and 4.11 rear gear ratios as "peformance gear ratios". They never sold an LT1 (370 hp), LS6 (425 hp), or L88 (560 hp) engine with a 2.87 rear gear ratio AFAIK.

"Once the road speed and rpms come up".......and it's the correct rear end gears that will get you there.

It's your money.....good luck.

 

I haven't tried the rolling burnouts yet, the motor is not even broken in yet. It has about 115 miles on it since install. I am not doing the work. I have a very reputable restomod garage doing the work. My car has been in this garage for 4 months while they have repaired or replaced what I wanted. They have tried tuning everything. The high idle is to keep it from surging at a stop because the recommended stall converter for this cam is 3500. A 3500 stall is not for my purpose. So a 2200-2800 was put in maybe temporarily or maybe not. Depending on the cam. It has even been on the Dyno. 50 at low end and 270 at 3500. Did not go over 3500 due to motor not being broken in.
The garage said this cam would probably work and not have to change the converter. It is supposed to have a good choppy sound and will lower my power range
https://www.summitracing.com/parts/cca-08-423-8

 

Maybe I'm missing something, will changing the rear gears kepp the car from surging when in gear at a red light ?

 

No! This issue is carb and / or IGN issue.

You show me a shop that has a car for four months,
and I will safely say, they don't know what the "H" they are doing.
Good Grief.

Surging is not from a cam or torque converter. See above ^^^^^

 

well it's also being stored there since I work out of state and only come home every 2 months or so. They don't work on it every day, lol
and yes the surge is from the lope of the cam, it doesn't surge when idled up, it doesn't have the 3500 stall converter in it.
wow, I only asked for a cam suggestion, I guess nobody has one and I don't won't to argue. I guess this forum is not for me
Yes they know exactly what they are doing, it's all they do

 

Asking for a cam suggestion on a Vette forum, Stang Forum, Mopar or any other forum is a crap shoot.
You could get dozens of suggestions, but how many are spot on?

In other words, no one is likely to have your exact engine build. Your exact trans & convertor. And your exact rear ratio.
So, seldom to never are you comparing apples to apples.

That is why all cam companies have tech helpers and about 20 questions to ask you about what parts you have and what you want out of them.
Keep at it with Comp Cams research. They get hundreds of request a day. Better to get it perfect the first time than . . . . . .