[kcscott11]

I am in the process of rebuilding my 1978 Pontiac Trans Am. I have a 400 block and a 455 block. I want to put the 400 block in the machine shop and build my true race motor out of it. But Thats a long term project... and I want to get something going a little sooner.... The 455 block has the crank and pistons installed already, there is very little wear in the cylinders, the guy i bought it from said that it was recently rebuilt, and I do believe him, although I know its not always good to take someones word for things, I figure since this will be my temporary motor Id go with it. Im not sure what all has been done to the lower end, but I am pretty sure its fairly new though not much more than stock. I want to get some power out of this thing...

I was thinking of using a COMP Cams SK51-245-4 - http://www.summitracing.com/parts/CCA-SK51-245-4/

and possibly this intake
Edelbrock 7156 - http://www.summitracing.com/parts/EDL-7156/

although I notice the power ranges are not quite in sync... would they work well together?

I have the stock Dport heads, although they have been completely reworked, have screw in studs and springs for a high lift cam... they unfortunately are not ported.

I have a Holley 650 Double Pumper im thinking of getting rebuilt and souped up a bit... any suggestions??

I was thinking of putting roller rockers in the car, although i dont know much about them or anything about compatibility... i thought i might buy this set
http://www.summitracing.com/parts/CCA-1451-16/
what gains and advantages would they give me? Would they be compatible with my setup?

I want to put new hardened push rods in it, but I don't know the best brand, and was curious what length I needed...

Let mw know any modifications I need to make to this setup, tips, etc.

The car has a 3.43 rear end. I have a TH-350 which i realize normally isnt recommended for the torque, but I have a hell of a transmission guy and he guarantees me he can build it to hold up, it will be full slap shift, and he is going to put it in a bop housing. I was curious what type torque converter/stall convertor i should use with this setup... originally I was thinking 2500 stall, but with this being a torque based engine I was thinking thats probably a little High considering I really dont want to push it past 5500 rpm.... i was thinking something that locks up at around 2000.... any suggestions....?

I think im going to do away with the powersteering, put an underdrive pulley for the alternator, and an electric waterpump. Also im going to have hooker comp headers, crossover xpipe, have chosen my mufflers yet, I am open to suggestions, although I do think im going to buy cutouts and electric cutout valves... Im also going to have a a high volume oil pump, that doesnt really fit in place here, but I thought I would mention it ;-)

Please any and all suggestions.... Any idea approximately what HP this would be? I know its a lot of stuff for a "temporary" motor, but I figure alot of it can be used on the new motor I build. Thank you.

 

[LATECH]

The 455 has plenty of torque for a street build.
The 400 would be a great strip motor, unless it is the 557 casting number.
The 400 can be stroked to 462 and can make a nasty strip motor,and will actually be stronger than the 455 , due to the smaller main journals which allow more metal to be retained at the main bosses...making it a stronger choice for a strip motor.
A cam as large as you propose for the 455 will need 9.5 compression or above, making it a not as good choice, as your block probably isnt zero decked.The heads are number ?? Have you CC ed them ?Does it have those stupid 8 valve relief pistons in it?
The 7156 edelbrock would work better with a quadrajet. Great carbs.
Also the redline is 5250 for a stock 455 bottom end. The cam you chose shows to make power higher up to start (2000) and goes to 6000.
With stock heads on the 455 and a stock bottom end, low compression...the XE 262 would be a good choice for the street.You wont need a 2000 stall converter, which will help your trans live longer, and make it more pump gas friendly a whole lot easier and cheaper than any alternative.
High volume or high pressure pumps are not a good idea.Stock pumps are quite adequate. Stock pumps are 60 PSI. Ram air 4 pumps are 80 psi,but require a "looser" tolerance on the bearings.
The only thing I would say is to get as much tire on the back as you can fit in the wheel well.You will need it for the 455.
Tires with a low treadwear number, wear out faster as the compound is softer, a higher treadwear number is harder and lasts longer. A low number is softer and gives better traction, just sayin.

 

[cobalt327]

You will hear a 4777 is too small for a 455. But I can tell you from experience that w/an all steel '80 Camaro you can run 12.6 (1.7 60") in the quarter w/a 455 Pontiac w/3.31 rear gears, McCreary L60-15 tires, TH400 and a 2200 RPM torque converter, shifting at <5000 rpm , using self-ported 6X heads (stock valves) and a Performer intake (not the RPM- it wasn't out yet) and 4-tube Hedman headers and 3" Flowmasters. Leaving it in Drive it would run quicker than 13 seconds ET shifting at about 4000 rpm. Cam was a no-name from Columbus Performance, they're now out of business. It had about 234 degrees @ 0.050", 0.480" lift and a tight LSA. I ran Rhodes lifters on the intakes only.

Would it have ET'ed better w/a larger carb? I do not know- mine was supposed to get either a reworked Q-jet or an 800 Holley. But it ran so good I never bothered to swap the 650 DP out, so I cannot say one way or the other. I suspect I might have picked up a little, but it was just so responsive and just a freakin' JOY to drive (I drove it daily, everywhere, ran 89 octane gas), so why f w/it, I said.

You can do a search on this forum for 455 pontiac build or similar terms for a bunch more threads on the subject. Also there are a few links here.

 

[Mr. P-Body]

I give, what's a "4777"? Is that a Holley list number? At 5,500 RPM, a 460 CID engine needs about 825 CFM to "peak" (varies with volumetric efficiency, of course).

First and foremost, DO NOT rely on Summitt, Jeg's or any other "mail order" parts people for accurate advice on building the Pontiac. They have no clue (except Eric at Competition Products, he knows, because he has a 10 second Pontiac of his own). Jim Hand's "How to Build Max-performance Pontiac V8s" published by SA Designs, is currently the best study of the ol' *****. Highly recommend you get a copy. There's a "re-write" in the works, but most of the original contributors aren't involved. The Pontiac "world" has become polarized between "old school" and "modern" approaches to building the engine. We (CVMS) are firmly in the "modern" camp, and have fallen "out of favor" as a result. It's okay. Our customers (and others using the modern approach) generally enjoy a significant advantage over the old-school guys regarding performance and longevity. We've learned! You really CAN "rev" a Pontiac and it will live. Pretty tough to "tune out" the low-end torque, though, resulting in a VERY "broad" power band. Many of our street engines "peak" power at 6,200-6,400 RPM, an area not long ago considered improbable for the Pontiac (and "live" anyway). Dirty Bird's 4" stroke 475 went 9,200 every pass. We wore the rods and pistons OUT (40 passes), never "blew it up". The point here is, it's okay to think "outside the box".

That cam is a perfect example of WHY you need to research among Pontiac builders. Magnum grinds were developed by Comp MANY years ago, and were basically "aimed" at the small block Chevy. Pontiacs don't "like" single-pattern cam grinds unless there's been a WHOLE bunch of exhaust port work. ALL factory grinds (including the mid-'50s "2-bbl." cams) were dual-pattern. Usually, 6-8 degrees more duration on the exhaust "side". If you MUST have a hydraulic "flat tappet" cam (least expensive type), use a Comp Xtreme Energy (for the one in the same parametric "range" of the Magnum, XE274H) or Lunati "VooDoo" grind in compressoin ratios under 9.5:1.

Also, beware "kits". While there are many good components in a "K" kit, there are also a couple of "white elephants". The valve stem seals and timing set are completely unacceptable for the Pontiac as a street engine. The seals are "Teflon" ('60s technology) instead of Viton. The "roller chain" is not a "true" roller, more of a glorified bicycle chain (2112 is the Comp part number, 3112 is the set "of choice"). We also use a different approach to valve springs.

What LATECH says is 100% correct about the 400 block versus the 455 block. The 3" main journal is certainly not a liability, as it's still 1/4" bigger than those in a Hemi or BBC.

Be happy to help you with this AND the "race" engine waiting in the "wings". Be aware, it's no problem AT ALL, to make 700 HP and 650 lb. ft. using a 400 block as a basis. Good cranks and rods are readily available, as are several different brands of cyliner heads. The days of the Pontiac being the "red-headed stepchild" of GM performance are over.

Jim

 

[cobalt327]

I give, what's a "4777"?

You're kidding, right? On the off chance that the OP doesn't know (but I bet he does), yeah- it's a carb number. I'd expect most guys to know the 47- series (4776- 600 cfm, 4777- 650 cfm, ... 4780- 800 cfm) DP carbs (DP = "double pumper"), and I think most guys know what a 3310 is, also I imagine most guys know what a 1850 is. Being as how they're the most common Holley carbs in existence. Maybe I give 'most guys' too much credit, but I don't think so.

 

[Mr. P-Body]

Nope, not "kidding". I haven't kept "track" of list numbers for many years. Being a small carb, I suppose that's why I'm not too familiar with it. I just call AED and tell them what I'm doing, and they send me a carb. The vast majority of carbs we use are 800 CFM and larger (engines are usually 450 CID-plus). Mostly "HO", but a lot of Q-Jets, too. And yes, I know about 3310s, propbably rebuilt a hundred of them in the '70s.

I use the 650HO on 350s... Never knew the list numbers... The only time we use an "out of the box" Holley is when the customer provides it.

Jim

 

[kcscott11]

Hmmm my holley is a double pumper the list number is 6210-3... i was thinking a good carb man could get me a little more out of it? I really dont know, just thought it may make a good carb for it... which quadrajet would I use? I was told by a guy that "knows pontiacs" that i should get a 240-250+ duration @50 cam. These cams start in the 2500rpm power range, which is why i chose the 236 duration.... its in the 2000rmp power range. I at least want as much cam as I can have with the stock lower end. Any recommendations? What intake should I use with the cam of choice?

 

[cobalt327]

Hmmm my holley is a double pumper the list number is 6210-3... i was thinking a good carb man could get me a little more out of it? I really dont know, just thought it may make a good carb for it

You have a spreadbore Holley. I use Q-jet carbs when a spreadbore is needed. Here's a link to the baseline specs.

 

[cobalt327]

I was told by a guy that "knows pontiacs" that i should get a 240-250+ duration @50 cam. These cams start in the 2500rpm power range, which is why i chose the 236 duration.... its in the 2000rmp power range. I at least want as much cam as I can have with the stock lower end. Any recommendations? What intake should I use with the cam of choice?

The cam specs are going to depend in large part on how and how much you use the engine. The big cams like 250 degrees + duration @ 0.050" lift can get to be a bit much for some guys on a daily basis, some don't mind it at all. I think a cam in the area of 236 degrees @ 0.050" lift would be the limit of what I would use on a daily basis w/a 455 using D-port production heads unless they were heavily ported professionally.

But either way, the cam has to be matched to the head flow, induction, compression, torque converter stall and/or rear gear. If you are going to use aftermarket heads, someone else can do a better job than me to recommend a cam, etc. If you are going to use stock or light to moderately ported production cast iron D-port heads (the vast majority of stock Pontiac heads, in other words), I would not use that much cam because the heads are all done way before the rpm where those cams should be peaking.

The engine I mentioned earlier is a good daily driver w/adequate performance. Makes maybe 450 hp and 550 ft/lbs torque, give or take. If you want to turn your Pontiac into a BBC, again- I'm not your guy. I'm just not so "brand blind" that I can justify turning a Pontiac into a BBC when I can just do a BBC and be done w/it instead of re engineering a Pontiac into something it wasn't originally intended to be (which was a low rpm torque-producer, also called a 'tractor motor' by some guys

). But then again I do not make my living selling Pontiac parts and engines. If I did, my opinion might have to change.

If you want to build a strong street engine that will put a 3500 lb. vehicle soundly into the 12's, you do not need any aftermarket parts except a set of headers and some valve train components. If you want to build it into a BBC you can, but you will have more aftermarket parts in it- by a large margin- than you will stock-type parts, and the cost will reflect this fact. At least now those parts are available. Not that long ago it was a different story altogether.

I like the RPM intake, personally.

 

[WDCreech]

billonwheels, I think it is hightly unethical for you to highjack someone else's thread with your question. You should start your own thread if you are not posting on the origional subject of the thread!

 

[68NovaSS]

billonwheels, I think it is hightly unethical for you to highjack someone else's thread with your question. You should start your own thread if you are not posting on the origional subject of the thread!

billionwheels' post and related replies have been moved to Basic into it's own thread.

 

[WDCreech]

billionwheels' post and related replies have been moved to Basic into it's own thread.

Thank you!

 

[billonwheels]

ooop's

Sorry! Didnt mean to HiJack! :spank: I was excited to see someone else building a Pontiac 455!

 

[Thumpin455]

These guys have given great advice, the only thing about the engine I would add is a dual pattern cam like Pbody said, and with unported heads staying under 230 on the intake will run better. Port the heads and you can go bigger, but with stock rods in the bottom end, stay under 240 or thereabouts. Just my preference, and I am still a fan of UltraDyne cams. The 280/288 is the one I would go with if Bullet will still make one. Have it in a 455 that was in the GTO, great cam with lots of power. I would get the heads ported by one of the gurus.

The RPM intake wont fit with the stock shaker scoop. Its too tall for a 2nd gen bird. There is a drop base that will allow it to work with the top half of the shaker, if you want to run the RPM. MrPbody might have one, but Butler carries it if he doesnt. The Torker II tends to load up while driving around on the street, at least mine did. The Performer is somewhat small, but will work. The stock intake is a good piece too, and all three of those will fit under the shaker.

I prefer a Qjet or 850 Holley on my 455s. A well built Qjet is more than capable of hanging with a street/strip 455.

Jim is spot on about building a 700hp engine with a 400 block. It takes some big heads, good rods, and light slugs but not a ton of compression if you want to run pump gas. I wouldnt try it with a 557 block, but the early blocks work fine. Mine is a 73 vintage 400, and it will turn 7500 if I want it to, usually shift it around 6500 though. With the stock bottom end on the 455 you dont want to do that, keep it under 5500 and it will live a long time. You'll want to build a tractor engine with the 455 shortblock.

The biggest problem with a 455 on the street is getting moving. Its very easy to spin the tires so hard they dont squeal, just smoke. 12s are so easy its silly, provided you can hook it. Just dont put more than a 3.73 gear under it, they like 3.50 or lower best. We got an 80 Formula into the mid 12s with unported 6X heads, 280/288 cam, 2200 stall, stock intake and 2.56 gears pulling 3600lbs. Just dont over gear it and it will run.

 

[Mr. P-Body]

Now, the 6210 IS a list number I know. It's a 650 CFM "spread bore" (as 327cobalt said). It has "side pivot" bowls (unless "converted") and was intended as a Q-Jet "replacement" on smaller engines, circa 1973. A 400 Pontiac with ANY "salt"" falls on its nose at 5,100 RPM with that carb, regardless of jetting. It's nowhere NEAR "big enough" for a 455. The 6212 is the "Competition Series" version (center pivot bowls). The "good" one is the 6213. That's the 800 CFM w/center pivot bowls, and when properly set up, it was a "must have" (thirty years ago). My 421 GTO went 12.60s all week with one of those, circa 1979. I know these things because these carbs are OLD, just like me! On that 'note", I highly recommend you ditch the old spread bore, and go for a well-done Q-Jet (mid-'73 and newer are 800s). If you "like" Holleys, get an AED 850HO, a "no brainer".

Thumpin's problem with the T-2 was probably too much fuel at lower speed. I've seen it before. It's difficult to get them jetted "just right" to where they can "run" at low speed (in traffic, etc.) AND make power on the "big end". The open plenum Pontiacs are HUNGRY for fuel at higher revs. The AED carbs seem to work better than most in these applications.

I fail to understand the "BBC" reference. The ONLY BBC parts we "use" are the rod bearings. BTW, they're less expensive and more available than the "good" bearings for a Pontiac. The Eagle (6.8) rod has changed EVERYTHING. The stock Pontiac rods were inadequate when "new", and certainly should be replaced in a 40 year old engine. When the crank is properly ground (enough radii), it's actually stronger than "stock", even though is .050" smaller in diameter. Attempts at making a "good" canted valve head for the Pontiac have been less than "successful", to say the least. In fact, the quickest two Pontiacs in the history of the world use the standard valve "layout", the Butler car using E-heads (extra "wide" and extra "tall") and ours using Tigers, both based on Ram Air IV. The only time a BBC-powered F/C showed up at a track when we were there, he refused to unload the car because he saw our 1/8 mile times. And he had "Big Chief" heads, NOT "standard layout". BTW, we're 6 for 8 against cars with "Brad" motors... Our "slogan": We're on safari! (hunting elephants...)

We've heard for many years, how "you can't make a Pontiac "run"." Yet, GTO didn't earn a reputation for LOSING to SS396... After a 25 year "blight" of performance parts and serious developement, the ol' ***** is back, with a vengence! I'm anxious to see if some of those RA V heads will fall into the "right" hands of a modern port guy. Gaby Labosa, Dave Wilcox, Johnny (Cirelli Engines) are the only ones I know in the "Pontiac world" that could really extract "the most" from them. All three of those guys don't care WHAT color the engine is, they can port it...

Please, this is not a "contest". I really am among the better (not "bigger") Pontiac builders, and I give my time and experience here at no charge, nor any requirement in the future. I DO NOT try to steer people "my way". We (CVMS) have a much different "approach" to building engines than many "old-school" crowds. I have no problem with them. I do, however, say, just because YOU may not know what we're doing, doesn't mean WE don't. To lend credibility to our skills, I site the previously mentioned car "Dirty Bird", the first Pontiac EVER in the 6.50s AND the first one in the 6.40s. The Butler ProMod is now in the 6.20s. DB is sitting beside Dave's dad's house, doing "nothing" as Dave has found something he finds "more interesting" for his future, having nothing to do with cars or racing. As for other engine "families", we have track champs with small block Chevys (current Modfied champ at VMP is one). We also had, a while back, a track champ in circle track with a small block ("Charger Division"), and a 2.4 lr. Mitsubishi in a '83 Dodge "Challenger" in "mini-stock". One of our customers held, for a brief period, an NHRA "record" in Q/SA with a Mitsi "Conquest".

Results of "racing" aren't a "tell all", either. But they DO offer insight into the overall skills and commitment of the builders.

I know, it must have been laughable, that I didn't know the list number 4777. Oh well. Not my "department". But I KNOW engines, machines and "how to get there from here". The local "billy-bob" crowd thinks I'm an idiot because I don't keep lots of Chevy parts "in stock", or that I tell them "double hump" heads are obsolete (not "worthless", just there are better heads "out there" for the same or less money). Of course, those same folks have a hard time getting three consecutive passes down the track without breaking something, or brag about 12s when others are going 10s. "My guys" usually go a couple seasons before they refresh, including Bill King, the reigning champ at VMP.

PAX

Jim

 

[kcscott11]

Ok, so from what ive gathered from yall
Xtreme Energy 274H Cam
Edelbrock 7156 Intake
Quadrajet

This would be suitable for a street build? What type torque convertor? how about this
http://www.ebay.com/itm/ACC-1600-22...Parts_Accessories&hash=item4cf68af2f1&vxp=mtr

also im having a little confusion with the fly wheel.... i dont have the stock flywheel.... it was lost before I got to the car.... I there are a couple different ones.... and I just dont know which one I need. I do know I need one with the 2 3/4" hole... how do i know about the balance and such?
http://www.ebay.com/itm/67-75-326-4...fits=Make:Pontiac&hash=item1c2782c036&vxp=mtr would that be what i needed? what bolt pattern would i need to be able to bolt up a th350 torque convertor?

also, this quadrajet should do the trick? http://www.autozone.com/autozone/pa...arburetor/_/N-8vd1l?itemIdentifier=52642_0_0_
the part number matches a 78 ta with the 6.6l and a 1970 gto with a 455.... the autozone part number is ND4631 or reference number c9477

 

[Mr. P-Body]

That converter is for a TH350. I must have missed that. TH350 is not well suited to 455 Pontiacs. The low-end torque the engine makes is very "hard" on them. While there ARE success stories, there are also failures. TH400 is a much better choice. Would you use a TH350 behind a 500 HP 454? That's about the same level of raw power we're talking here, at a lower RPM.

But the rev range of that converter is okay for the cam. Understand, too, most converters "off the shelf" are rated based on 350 Chevy as a "base line". Bigger (higher torque) engines raise the stall speed proportionally.

An AutoZone reman carb is probably a decent basis, but remans can be problematic. They aren't necessarily kept "together" during the process. You COULD get the same base, body and top that Rochester orginally shipped, but you COULD get a mish-mash. It's a bit of a "crap shoot". Even if a "good one", it will need to have the upgrades outlined in Cliff's book to really perform well. Later (post '72) carbs are "emmissions" carbs and the idle circuits won't properly support a "big" cam. If you were lucky enough to find a '73 or '74 455SD carb, THEN you'd have something! Very rare and very expensive today.

The best option may be to find a good "core" locally, and send it to one of the Q-Jet builders. Many Pontiac guys are very proud of their Q-Jets. It's easy enough to make an Olds or Buick carb work on the Pontiac, too. Chevy and Caddy versions are a little more difficult, but not insurmountable.

Jim

 

[kcscott11]

Hmmm got a th400 tranny today from my uncle. Its a good transmission, and he gave it to me for 100 bucks, just lucked out on him having that! anyhow I came across a guy local who may have some other parts, I should be getting my flex plate and possibly an intake from him, although I may hold off on that because he doesnt know if he has any intakes worth a crap. He said at one point he had 12 455's, knew quite a bit about these motors, so He is going to call me and tell me what all he has tomorrrow. I think this thing might come along a little bit. I need to order my cam soon, thats the next step to getting this going! just having so many problems deciding what to get.... I know my heads are supposedly set up for a "big cam" they are 6x heads.... i dunno. I just know i want as much cam as i can use. Then I will choose my intake accordingly..

 

[cobalt327]

Heads/cam

I know my heads are supposedly set up for a "big cam" they are 6x heads.... i dunno. I just know i want as much cam as i can use. Then I will choose my intake accordingly..

Check the spring installed height to be sure it is equal between the valves. The spring's seat and open pressure is also important but all but impossible to measure unless the springs are checked w/a spring gauge. There are spring gauges that can be used on an assembled head. You might ask for a receipt for the parts including the springs so you can verify they are appropriate for the cam you want to use.

Often, modified Pontiac "X" heads have 1.77" exhaust valves installed in place if the stock 1.66" and this is obviously going to be very easy to determine. As far as the rest of the work that may have been done to the heads, you can visually look to see if they both have at least 3-angle seats (that won't tell you if the seats are concentric, though), the valves can be inspected to see that they have adequate margins, seat widths, and if they've been back cut or have undercut stems. I would suggest you measure the valve guide clearances, too.

One of the most important things that you need to know about these heads is the exact chamber volumes. I'm guessing you have looked to see the secondary identifiers are the same. Even if they are, both heads need to be checked- although doing the end chambers of each head (four chambers total) will be enough to tell that the chambers are equal. This is necessary because there's no way to be sure the heads were always a pair from day one, onward. Even if they were paired from birth, one head might have had a bad head gasket that required it to be resurfaced. If both heads weren't cut an equal amount that can cause the chambers to vary. If the heads were from different engines originally, obviously they can vary due to all the above reasons plus manufacturing and casting differences from the factory.

Then there's the port volumes. Those heads have relatively small intake ports; the 6X-4 heads I used on my last 455 were 158cc "stock" (I don't know the history on them; they came on a friend's T/A he bought used), and they did not in any way look to have been ported. After porting they measured 173cc. These heads stock would be like a ~ 125cc head on a 350 SBC. The comparison isn't as bad as it sounds because of the design of the Pontiac head/ports and the 30 degree intake valve angle, but the fact remains- they ARE small.

In my opinion a stock or mildly reworked D-port doesn't need lift in excess of 0.480". That is a little past where maximum flow is reached but before any port stall occurs, given the rpm range of a 455. Combining that w/a duration @ 0.050" of around 234-236 or so will be about right. I used Rhodes on the intake side of a single pattern cam; Comp hadn't yet come out w/the XE series at the time. I'm not suggesting you do what I did, instead look into a Voodoo or XE.

With the D-port heads unless they've been heavily ported I will always recommend an RPM intake. It will hit harder off idle and gives up nothing to a single plane at the modest peak rpm the 455 is going to be turning (5000 rpm), built as described here; I preferred to harness the torque by using sticky McCreary tires (tread wear "0"). I suppose there might be an argument made for a single plane to "tame the torque". But that's for someone else to expand on, I don't do it or personally recommend anyone else do it unless all other avenues have been exhausted.

 

[Thumpin455]

I like the RPM too, but it wont fit under the stock Shaker, or under a flat hood on a 70-81 Firebird. Fits A body cars great, but on a Bird the carb vent ends up being between one and two inches above the hood line. Even worse is a Victor, the bottom of the carb is higher than the fenders.

Tomahawk intakes will fit under the shaker too, and any stock iron Qjet intake will work as good as a Performer. There are other options, but I would suggest a dual plane rather than the single plane. I never found the Torker II to make it any easier to hook up, but it did like to load up driving around at low speeds. Probably the 850 double pumper I had on it, but still a dual plane works better.