700r4 and 4L60E are both too weak for a 5,500 lbs vehicle, much less one weighing in at 6,500. Just asking and begging for problems. 80E is a much stronger transmission even stock than the best 700r4 or 4L60E.Originally Posted by Xenon
700r4 and 4L60E are both too weak for a 5,500 lbs vehicle, much less one weighing in at 6,500. Just asking and begging for problems. 80E is a much stronger transmission even stock than the best 700r4 or 4L60E.
Wrote to comp cams for a recommendation and this was their reply:
A cam that best fit your mods is our xtreme energy cam (12-262-4)specs are below. The cam will have to be on a small base circle to clear the stroked out engine.
The cam will help increase power and torque, excellent throttle response, also will have a nice lumpy idle
The cam will be 218/224 @ .050 and the lift is .464/.470 on a 110 LSA
If not done so I always do recommend in upgrading valve-train to protect your investment. The upgrade helps in getting the most power from the engine/cam and keeps its safe. We do offer a cam kit which includes(cam,lifters,springs,retainers,locks,seals ,timing set)
What do you guys think of that?
-Frank
1987 GMC Suburban K2500 400SBC, TH400 Trans, 3.73 Gears
1995 GMC Suburban K2500 454BBC, 4L80E Trans, 3.73 Gears
Too much cam for a vehicle as heavy as yours with a stock converter and only 3.73s. I would look into something more like this. It may have to be ground on a small base circle depending on connecting rod clearance.
http://www.summitracing.com/parts/cc...make/chevrolet
For mileage and throttle response this would likely be even better but would run out of breath by 4,500.
http://www.summitracing.com/parts/cc...make/chevrolet
Last edited by Fast355; 11-06-2013 at 06:03 PM.
Xenon,
If you do the math on your tire size you will find that you are not truly running a 3.73 gear ratio, If you go to a tire/gear calculator program on the net, you will find your final drive ratio. If you add a overdrive trans, which reduces the final drive approx 30% your driving rpm is actually lugging the engine. That is why you do not have throttle response, acceleration, and the result fuel economy.
The 3705 Edelbrock manifold is for TBI heads. It will not fit your 454 throttle body. The throttle plate size is for the 1 11/16" throttle blades. The manifold will have to me machined, to accept the 454 w/o an adapter, the machine of this is fairly expensive, because beside machining, tig welding is also involved for the water ports in the plenum area. This mod is not for the faint at heart or wallet. If you have the standard bolt pattern heads/non tbi heads, you can modify the center bolt holes to accept the older bolt pattern. If you are using a non high velocity head on a TBI (the old carb heads) you will not be able to get the throttle response needed to move 6500# efficiently. I have used a 170cc twisted wedge on a tbi and worked very well. I have also ported 093 tbi heads and worked very well also. Dart 180 cc iron eagles work well.
The 700R4 wasn't designed to haul 6500# from a dead start. GM thought the same as you are in the 80's in their 4wd's. The tranny just would not hold up. Too much heat, even with auxiliary coolers. 2nd gear usually goes out first, and with that OD.
I don't know what heads you have, however if you are using 454 injectors you are correct fuel isn't a troubled area, in fact it has too much fuel. Have you watched the map sensor on a scanner, and the O2 readings. How many crosscounts do you have?
Hope I have given you info to investigate
Street Perf
Last edited by streetperf; 11-06-2013 at 07:31 PM.
Really appreciate all the information... I do have it tuned for the 454 injectors... Eagle Mark and others here helped me out with that. Runs as well as it can given the current setup.
If you were building a 400 small block for a suburban what would you do? I'm not opposed to changing heads, intake, cam, whatever.
-Frank
1987 GMC Suburban K2500 400SBC, TH400 Trans, 3.73 Gears
1995 GMC Suburban K2500 454BBC, 4L80E Trans, 3.73 Gears
Depending on the pistons in the engine, I would use one of the two cams I linked, swap over to some vortec heads, run a water heated performer rpm dual plane intake with a TBI to carb adapter. Concentrate on low-midrange torque as that is what will propel that 3 ton monster.
Not sure on the pistons, but it measures to 8.6:1 compression with 76cc heads, so they're not too special.
Don't remember what the heads are exactly, but I remember looking up the casting number and being rather disappointed. They were just some heads off a 350... And there was some failure they were prone to... Cracking or something.
it has a Holley spreadbore intake, but not really a performance one... It was an older one that was designed to be basically a stock replacement but in aluminum.
Last edited by Xenon; 11-07-2013 at 03:47 AM.
-Frank
1987 GMC Suburban K2500 400SBC, TH400 Trans, 3.73 Gears
1995 GMC Suburban K2500 454BBC, 4L80E Trans, 3.73 Gears
well I've been looking around more and I really like this one you suggested.
How do I know if I need to have it ground on a small circle? And do I need different springs, pushrods or anything? Or will stock be ok?
thanks.
-Frank
1987 GMC Suburban K2500 400SBC, TH400 Trans, 3.73 Gears
1995 GMC Suburban K2500 454BBC, 4L80E Trans, 3.73 Gears
Xenon,
With all the info you have received on your 400 TBI engine, You should be able to make an somewhat decision. I don't know how many dollars you have to spend on this project but to get gas mileage out of a 6500# vehicle that has the areo package of a brick, is going to be very difficult. Being a 400 is a good start in that vehicle, most chev camshafts are ground for a 350 application in the catalogs, unless otherwise stated, so in a 400 the cam will seem to be smaller due to the larger displacement of the engine and torque output. Therefore you can use a Slightly larger cam duration to achieve the desired results. For instance, a 204 duration camshaft works very well in a 350 application, in a 400 you can use a 209-212 and get better results and approx same power band increased toque, hence the increase in CID, and Stroke of the engine.
You have stated what heads you have, example- casting number. If you want to change them or not, again goes back to dollars. Newer heads work better than 80's open chamber emission heads by far. As was stated earlier install a set of vortecs and go. However that will involve a new intake manifold. Again dollars.
If I were you, and I'm shooting in the dark here. If you don't have allot of money to spend and you don't know how the expected results will turn out for you, I would be conservative on my changes. A camshaft that has been previously recommended be purchased with lifters, installed, tuned and test driven for results over a period of time.
I have posted some links to a DIY type modification for the stock TBI intake that will help improve airflow. It will still fall short of what a 400 wants but it can help. The same would apply if using the TBI Vortec intake. Along with opening up the bores, this will help improve flow as engine rpm increases.
Ultimately, the rear gear and trans ratios should be in line with the cam's powerband. Trying to change intake, exhaust, etc when the cam is not appropriate is just an attempt to bandaid the problem.
Last edited by 1project2many; 12-03-2013 at 09:36 PM.
Stage 8 locking header bolts help keep gaskets in good shape, just make sure to get six point heads instead of 12 point heads. That way you can get a wrench on them to tighten em up if tubing clearance becomes an issue. That is if you decide to run headers.
Last edited by loadedi812; 12-04-2013 at 02:08 PM.
Being a 400 it will require a bit more cam then you'd use in an equivalent 350. I'd think it would do well with around 215* @ 0.050" on the duration and as much lift as you can get in that duration, which will likely end up in the 0.425" to 0.450" range for a flat tappet hydraulic.
As for the cam size -check the existing push rods. You might find longer push rods that would indicate a smaller base circle cam. You could look at the lifters too to make sure there aren't longer lifters in it. Otherwise, you may need to pull the cam and see if it has a part number on it.
As for springs - You could keep the same springs if you know the old cam was more aggressive. Since it seems you don't know what the old cam was it would be a good idea to just use the recommended matching springs.
thanks. That's what I needed to know
-Frank
1987 GMC Suburban K2500 400SBC, TH400 Trans, 3.73 Gears
1995 GMC Suburban K2500 454BBC, 4L80E Trans, 3.73 Gears
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